2024-03-29T14:52:46Z
http://docs.lib.purdue.edu/do/oai/
oai:docs.lib.purdue.edu:nanodocs-1000
2007-11-13T14:40:07Z
publication:nanodocs
publication:dp
publication:nano
Detection of bacterial cells and antibodies using surface micromachined thin silicon cantilever resonators
Akin, Demir
Gupta, Amit
Bashir, Rashid
Article
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures -- November 2004 -- Volume 22, Issue 6, pp. 2785-2791
This article describes a surface micromachined cantilever beam-based resonator for biological sensing applications. The study used a novel microfabrication technique of merged epitaxial lateral overgrowth (MELO) and chemical mechanical polishing (CMP) to fabricate thin, low stress, single-crystal silicon cantilever beams. The vibration spectra of the cantilever beams, excited by thermal and ambient noise, was measured in air using a Dimension 3100 Series scanning probe microscope (SPM), and in certain cases, a Polytec MSV300 laser Doppler vibrometer. The sensors were used to detect the mass of Listeria innocua bacteria by applying increasing concentration of bacteria suspension on the same cantilever beams and measuring the resonant frequency changes in air. Cantilever beams were also used to detect the mass of proteins such as Bovine Serum Albumin (BSA) and antibodies for Listeria that were attached to the cantilever's surfaces by physical adsorption; following which they were used to capture and detect the mass of the bacterial cells on the functionalized cantilever beam surfaces'. The effects of critical point drying of the proteins were evaluated and the results indicate that the functionality of the antibodies was not reduced once rehydrated after critical point drying. The developed biosensor is capable of rapid and ultrasensitive detection of bacteria and promises significant potential for the enhancement of microbiological research and diagnostics. ©2004 American Vacuum Society
doi:10.1116/1.1824047
PACS: 87.80.-y, 87.17.-d, 07.10.Cm
2004-11-17T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/1
oai:docs.lib.purdue.edu:nanodocs-1008
2007-11-26T20:23:23Z
publication:nanodocs
publication:dp
publication:nano
Frequency kesponse of top-gated carbon nanotube field-effect transistors
Singh, Dinkar V.
Jenkins, Keith A.
Appenzeller, Joerg
Neumayer, D.
Grill, Alfred
Wong, H.S. Philip
Article
The ac performance of carbon nanotube field-effect transistors (CNFETs) has been characterized using two approaches involving: 1) time- and 2) frequency-domain measurements. A high input impedance measurement system was used to demonstrate time-domain switching of CNFETs at frequencies up to 100 kHz. The low level of signal crosstalk in CNFETs fabricated on quartz substrates enabled frequency-domain measurements of the ac response of CNFETs in the megahertz range, over five orders of magnitude higher in frequency than previously reported ac measurements of CNFET devices.
AC measurement; carbon nanotube (CN); high frequency
2004-09-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/9
oai:docs.lib.purdue.edu:nanodocs-1009
2007-11-26T20:32:55Z
publication:nanodocs
publication:dp
publication:nano
Downstream oxygen etching characteristics of polymers from the parylene family
Callahan, Russell R. A.
Pruden, Kristin G.
Raupp, Gregory B.
Beaudoin, Stephen P.
Article
As dictated by the International Technology Roadmap for Semiconductors, there is an immediate need to develop low dielectric materials for use in metalization and packaging schemes in integrated circuits. The etching characteristics of a family of low dielectric polymers, the parylenes, are discussed. These are good models for polymer dielectrics, and are attractive for packaging applications. Three types of parylene are studied: parylene-N, parylene-C, and parylene AF-4. Parylene films on silicon substrates were etched in a downstream microwave oxygen plasma system. The goal was to characterize the chemical reactions that occurred on the parylene in the afterglow of the microwave oxygen plasma. The effect of temperature on the etch rate of each polymer was studied and an apparent activation energy was determined. The apparent activation energy for the etch process is approximately 7.0 kcal/mol for each polymer. Infrared analysis showed carbonyl formation during etching in the parylene-N and -C. Based on these analyses and the calculated activation energies, it was determined that a likely rate-limiting step in the etching was the ring opening.
2003-07-24T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/10
oai:docs.lib.purdue.edu:nanodocs-1007
2007-11-26T20:17:41Z
publication:nanodocs
publication:dp
publication:nano
High-performance carbon nanotube field-effect transistor with tunable Polarities
Lin, Yu-Ming
Appenzeller, Joerg
Knoch, Joachim
Avouris, Phaedon
Article
State-of-the-art carbon nanotube field-effect transistors (CNFETs) behave as Schottky-barrier-modulated transistors. It is known that vertical scaling of the gate oxide significantly improves the performance of these devices. However, decreasing the oxide thickness also results in pronounced ambipolar transistor characteristics and increased drain leakage currents. Using a novel device concept, we have fabricated high-performance enhancement-mode CNFETs exhibiting n- or p-type unipolar behavior, tunable by electrostatic and/or chemical doping, with excellent OFF-State performance and a steep subthreshold swing (S = 63 mV/dec). The device design allows for aggressive oxide thickness and gate-length scaling while maintaining the desired device characteristics.
carbon nanotube
doping
field-effect transistor
Schottky barrier (SB)
2005-09-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/8
oai:docs.lib.purdue.edu:nanodocs-1005
2007-11-26T19:58:51Z
publication:nanodocs
publication:dp
publication:nano
Computational Model for Transport in Nanotube-Based Composites with Applications to Flexible Electronics
Kumar, Satish
Alam, Muhammad A.
Murthy, Jayathi Y
Article
Thermal and electrical transport in a new class of nanocomposites composed of random
isotropic two-dimensional ensembles of nanotubes or nanowires in a substrate (host
matrix) is considered for use in the channel region of thin-film transistors (TFTs). The
random ensemble of nanotubes is generated numerically and each nanotube is discretized
using a finite volume scheme. To simulate transport in composites, the network is embedded
in a background substrate mesh, which is also discretized using a finite volume
scheme. Energy and charge exchange between nanotubes at the points of contact and
between the network and the substrate are accounted for. A variety of test problems are
computed for both network transport in the absence of a substrate, as well as for determination
of lateral thermal and electrical conductivity in composites. For nanotube networks
in the absence of a substrate, the conductance exponent relating the network
conductance to the channel length is computed and found to match experimental electrical
measurements. The effective thermal conductivity of a nanotube network embedded in
a thin substrate is computed for a range of substrate-to-tube conductivity ratios. It is
observed that the effective thermal conductivity of the composite saturates to a sizeindependent
value for large enough samples, establishing the limits beyond which bulk
behavior obtains. The effective electrical conductivity of carbon nanotube-organic thin
films used in organic TFTs is computed and is observed to be in good agreement with the
experimental results.
DOI: 10.1115/1.2709969
nanotube
thin film transistor
nanocomposite
percolation
2007-04-30T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/6
oai:docs.lib.purdue.edu:nanodocs-1003
2007-11-26T19:41:11Z
publication:nanodocs
publication:dp
publication:nano
High Performance Electronics Based on Dense, Perfectly Aligned Arrays of Single Walled Carbon Nanotubes
Kang, Seong Jun
Kocabas, Coskun
Ozel, Taner
Shim, Moonsub
Pimparkar, Ninad
Alam, Muhammad A.
Rotkin, Slava
Rogers, John A
Article
Single-walled carbon nanotubes (SWNTs) have many exceptional electronic properties. Realizing the full potential of SWNTs in
realistic electronic systems requires a scalable approach to device and circuit integration. We report the use of dense, perfectly
aligned arrays of long, perfectly linear SWNTs as an effective thin-film semiconductor suitable for integration into transistors
and other classes of electronic devices. The large number of SWNTs enable excellent device-level performance characteristics
and good device-to-device uniformity, even with SWNTs that are electronically heterogeneous. Measurements on p- and
n-channel transistors that involve as many as 2,100 SWNTs reveal device-level mobilities and scaled transconductances
approaching 1,000 cm2 V21 s21 and 3,000 Sm21, respectively, and with current outputs of up to 1 A in devices that use
interdigitated electrodes. PMOS and CMOS logic gates and mechanically flexible transistors on plastic provide examples of
devices that can be formed with this approach. Collectively, these results may represent a route to large-scale integrated
nanotube electronics.
2007-03-25T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/4
oai:docs.lib.purdue.edu:nanodocs-1001
2007-11-26T19:12:24Z
publication:nanodocs
publication:dp
publication:nano
Bacteria-mediated delivery of nanoparticles and cargo into cells
Akin, Demir
Ragheb, Kathy
Sturgis, Jennifer
Sherman, Debby
Burkholder, Kristen
Robinson, J. Paul
Bhunia, Arun K
Mohammed, Sulma
Bashir, Rashid
Article
Published online: 10 June 2007; doi:10.1038/nnano.2007.149
Nanoparticles and bacteria can be used, independently, to deliver genes and proteins into mammalian cells for monitoring or altering
gene expression and protein production. Here, we show the simultaneous use of nanoparticles and bacteria to deliver DNA-based
model drug molecules in vivo and in vitro. In our approach, cargo (in this case, a fluorescent or a bioluminescent gene) is loaded
onto the nanoparticles, which are carried on the bacteria surface. When incubated with cells, the cargo-carrying bacteria
(‘microbots’) were internalized by the cells, and the genes released from the nanoparticles were expressed in the cells. Mice
injected with microbots also successfully expressed the genes as seen by the luminescence in different organs. This new approach
may be used to deliver different types of cargo into live animals and a variety of cells in culture without the need for complicated
genetic manipulations.
nanoparticles
2007-06-10T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/2
oai:docs.lib.purdue.edu:nanodocs-1004
2007-11-26T19:50:46Z
publication:nanodocs
publication:dp
publication:nano
The catalytic reduction of NO by H-2 on Ru(0001): Observation of NHads species
Hornung, A.
Zemlyanov, Dmitry
Muhler, M.
Ertl, G.
Article
Adsorption of NO and the reaction between NO and H-2 were investigated on the Ru(0001) surface by X-ray photoelectron spectroscopy (XPS). Surface composition was measured after NO adsorption and after the selective catalytic reduction of nitric oxide with hydrogen in steady-state conditions at 320 K and 390 K in a 30:1 mixture of H-2 and NO (total pressure = 10(-4) mbar). After steady-state NO reduction, molecularly adsorbed NO in both the linear on-top and threefold coordinations, NHads and N-ads species were identified by XPS. The coverage of the NHads and N-ads species was higher after the reaction at 390 K than the corresponding values at 320 K Strong destabilisation of N-ads by O-ads was detected. A possible reaction mechanism is discussed. (c) 2005 Elsevier B.V. All rights reserved.
2005-10-22T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/5
oai:docs.lib.purdue.edu:nanodocs-1002
2007-11-26T19:22:17Z
publication:nanodocs
publication:dp
publication:nano
Capture of airborne nanoparticles in swirling flows using non-uniform electrostatic fields for bio-sensor applications
Jang, Jaesung
Akin, Demir
Lim, Kwan Seop
Broyles, Steve
Ladisch, Michael R.
Bashir, Rashid
Article
Sensors and Actuators B 121 (2007) 560–566
Collection of biological particles is the first and critical step for any biological agent detection system. Towards our goal of capturing and detecting airborne biological entities in real time, here we investigate on the design of an electrostatic particle capture system. We report on the capture of airborne 100 nm diameter polystyrene nanoparticles as a model system, in swirling flows under non-uniform electrostatic fields with an electrospray aerosol generator and a homemade particle collector. The particle collector has five positive electrodes on the bottom and one large grounded electrode on the top. The nanoparticles coming into the collector were slowed down during their swirling and stayed in the collector long before leaving the collector. Silicon chips were placed on the bottom electrodes and the electrostatically captured particles were counted as a function of flow rates, electrode positions, bias voltages, and capture times by epifluorescent images and scanning electron micrographs (SEMs). Particles captured in the electrode at the center of the collector were much less than those on the surrounding four electrodes and 10–25% of the particles with negative charges entering the collector were captured on the bottom electrodes at a flow rate of 1.1 l/min and an applied potential of 2 kV. Particle capture increased with decreasing flow rates. We also simulated flow and electrical fields separately, and found the positional trends to be in good agreement with the measurements. This collector is well adaptable to integration with micro resonator devices and can be used for real-time monitoring of bioaerosols.
Airborne nanoparticles
Electrostatic capture
Swirling flows
2006-06-02T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/3
oai:docs.lib.purdue.edu:nanodocs-1013
2007-11-26T21:29:06Z
publication:nanodocs
publication:dp
publication:nano
Electrostatics of nanowire transistors
Guo, Jing
Wang, Jing
Polizzi, E.
Datta, Supriyo
Lundstrom, Mark S.
Article
The electrostatics of nanowire transistors are studied by solving the Poisson equation self-consistently with the equilibrium carrier statistics of the nanowire. For a one-dimensional, intrinsic nanowire channel, charge transfer from the metal contacts is important. We examine how the charge transfer depends on the insulator and the metal/semiconductor Schottky barrier height. We also show that charge density on the nanowire is a sensitive function of the contact geometry. For a nanowire transistor with large gate underlaps, charge transferred from bulk electrodes can effectively "dope" the intrinsic, ungated region and allow the transistor to operate. Reducing the gate oxide thickness and the source/drain contact size decreases the length by which the source/drain electric field penetrates into the channel, thereby, improving the transistor characteristics.
2003-12-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/14
oai:docs.lib.purdue.edu:nanodocs-1016
2015-04-07T15:30:42Z
publication:nanodocs
publication:dp
publication:nano
A comparative analysis of studies on heat transfer and fluid flow in microchannels
Sobhan, Choondal B.
Garimella, Suresh
Article
<p>The extremely high rates of heat transfer obtained by employing microchannels makes them an attractive alternative to conventional methods of heat dissipation, especially in applications related to the cooling of microelectronics. A compilation and analysis of the results from investigations on fluid flow and heat transfer in micro- and mini-channels and microtubes in the literature is presented in this review, with a special emphasis on quantitative experimental results and theoretical predictions. Anomalies and deviations from the behavior expected for conventional channels, both in terms of the frictional and heat transfer characteristics, are discussed.</p>
2001-12-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/17
oai:docs.lib.purdue.edu:nanodocs-1014
2015-04-07T15:29:41Z
publication:nanodocs
publication:dp
publication:nano
Advances in mesoscale thermal management technologies for microelectronics
Garimella, Suresh
Article
<p>This paper presents recent advances in a number of novel, high-performance cooling techniques for emerging electronics applications Critical enabling thermal management technologies covered include microchannel transport and micropumps, jet impingement, miniatur flat heat pipes, transient phase change energy storage systems, piezoelectric fans, and prediction of interface contact conductance. (c) 2005 Elsevier Ltd. All rights reserved.</p>
2006-11-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/15
oai:docs.lib.purdue.edu:nanodocs-1010
2007-11-26T21:09:30Z
publication:nanodocs
publication:dp
publication:nano
Heterogeneous wafer-scale circuit architectures
Katehi, Linda
Chappell, William J.
Mohammadi, Saeed
Margomenos, Alexandros
Steer, Michael
Article
Future military and commercial communication systems require a new generation of circuits with
cognitive, deployable, agile, versatile, survivable, and sustainable capabilities. For these future
system concepts to materialize, there is a need to substantially reduce size and cost and increase
functionality and density, thus leading to high operating frequencies and wide bandwidths.
However, at high frequencies and with wide analog and digital bandwidths, conventional chip-substrate
integration techniques (e.g., solder bumps and wire-bonds) and filtering technologies limit system capability
and compromise efficiency.
The super-heterodyne radio architecture, most prevalent in present technologies, necessitates multiple passive offchip
components including intermediate frequency (IF) filters adapted to the channel filtering requirements for various
standards. Direct conversion (including low IF) architectures have evolved as they lend themselves to single- or few-chip
mixed signal implementation, although performance may be compromised primarily,
due to the direct current (dc) offset shift and the loss (finite Q) of on-chip passives
leading to low radio frequency (RF) efficiency and high phase noise. In this
circuit architecture, digital noise coupled into the RF circuitry further
limits detectability. For future military communication systems, the
above attributes must be obtained with performance superior to
that available commercially and delivered with volumes relatively
small in comparison to that in the commercial world.
These performance requirements put a premium on heterogeneous
wafer-scale integration whereby various optimized
chip and component technologies can be combined
to obtain improved overall performance.
2007-02-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/11
oai:docs.lib.purdue.edu:nanodocs-1011
2007-11-26T21:20:22Z
publication:nanodocs
publication:dp
publication:nano
Theory of high bias coulomb blockade in ultrashort molecules
Muralidharan, Bhaskaran
Ghosh, Avik W.
Pati, Swapan K.
Datta, Supriyo
Article
We point out that single electron charging effects such as coulomb blockade (CB) and high-bias staircases play a crucial role in transport through single ultrashort molecules. A treatment of CB through a prototypical molecule, benzene, is developed using a master-equation in its complete many-electron Fock space, evaluated through exact diagonalization or full configuration interaction (CI). This approach can explain a whole class of nontrivial experimental features including vanishing zero bias conductances, sharp current onsets followed by ohmic current rises, and gateable current levels and conductance structures, most of which cannot be captured even qualitatively within the traditional self-consistent field (SCF) approach coupled with perturbative transport theories. By comparing the two approaches, namely SCF and CB, in the limit of weak coupling to the electrode, we establish that the inclusion of strong correlations within the molecule becomes critical in addressing the above experiments. Our approach includes on-bridge correlations fully, and is therefore well-suited for describing transport through short molecules in the limit of weak coupling to electrodes.
2007-09-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/12
oai:docs.lib.purdue.edu:nanodocs-1015
2015-04-07T15:30:06Z
publication:nanodocs
publication:dp
publication:nano
An energy-based model for electrowetting-induced droplet actuation
Bahadur, Vaibhav A.
Garimella, Suresh
Article
<p>Electrowetting (EW) induced droplet motion has been explored in the past decade in view of its promising applications in the field of microfluidics. This paper demonstrates the potential of energy-based analyses for modeling the performance of EW-based fluid actuation systems. Analyses based on system energy minimization offer simplified modeling tools to predict the overall performance of EW systems while circumventing the need to model the numerous complexities in the system. An analytical model is developed to estimate the actuation force on a droplet moving between two electrodes. The origins and contributions of various components of the actuation force are analyzed. The effects of dielectric parameters, electrode layout, droplet geometry and shape are discussed with the objective of maximizing the actuation force. The actuation force model is combined with semi-analytical models for predicting the forces opposing droplet motion to develop a model that predicts transient EW-induced droplet motion. Parametric results are obtained to evaluate the importance of operating voltage, fluid properties and droplet geometry on droplet motion.</p>
2006-08-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/16
oai:docs.lib.purdue.edu:nanodocs-1012
2007-11-26T21:22:52Z
publication:nanodocs
publication:dp
publication:nano
Electrical resistance: an atomistic view
Datta, Supriyo
Article
This tutorial article presents a 'bottom-up' view of electrical resistance starting from something really small, like a molecule, and then discussing the issues that arise as we move to bigger conductors. Remarkably, no serious quantum mechanics is needed to understand electrical conduction through something really small, except for unusual things like the Kondo effect that are seen only for a special range of parameters. This article starts with energy level diagrams (section 2), shows that the broadening that accompanies coupling limits the conductance to a maximum of q(2) / h per level (sections 3, 4), describes how a change in the shape of the self-consistent potential profile can turn a symmetric current-voltage characteristic into a rectifying one (sections 5, 6), shows that many interesting effects in molecular electronics can be understood in terms of a simple model (section 7), introduces the non-equilibrium Green function (NEGF) formalism as a sophisticated version of this simple model with ordinary numbers replaced by appropriate matrices (section 8) and ends with a personal view of unsolved problems in the field of nanoscale electron transport (section 9). Appendix A discusses the Coulomb blockade regime of transport, while appendix B presents a formal derivation of the NEGF equations. MATLAB codes for numerical examples are listed in appendix C.
2004-07-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/13
oai:docs.lib.purdue.edu:nanodocs-1017
2007-11-27T13:54:03Z
publication:nanodocs
publication:dp
publication:nano
A special issue on bionanotechnology - Preface
Guo, Peixuan
Article
Nanotechnology is concerned with the creation and manipulation
of functional structures having dimensions ranging
from a few to hundreds of nanometers. This size
range encompasses a scientific and technological gap.
The most effective strategy for the development of viable
new technology is, therefore, to close this gap at both
ends through the use of the “top-down” or “bottom-up”
approaches. A top-down approach refers to the production
of nanoscale structures by breaking, cutting, or etching
techniques, whereas a bottom-up approach refers to
the assembly of structures atom-by-atom or molecule-bymolecule.
A general and simple bottom-up approach
used in bionanotechnology relies upon the cooperative
interaction of individual macromolecules which spontaneously
assemble in a predefined manner to form a larger
two- or three-dimensional structure.Self-assembly can be
viewed as either template or nontemplate in nature.
Template assembly involves the interaction of biomacromolecules
under the influence of a specific sequence,
pattern, structure, external force, or spatial constraint.In
contrast, nontemplate assembly involves the formation of a
larger structure by individual components without external
influence.
2005-12-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/18
oai:docs.lib.purdue.edu:nanodocs-1019
2007-11-27T14:19:03Z
publication:nanodocs
publication:dp
publication:nano
Fabrication of fully transparent nanowire transistors for transparent and flexible electronics
Ju, Sanghyun
Facchetti, Antonio
Xuan, Yi
Liu, Jun
Ishikawa, Fumaiki
Ye, P. D.
Zhou, Chongwu
Marks, Tobin J.
Janes, David B
Article
The development of optically transparent and mechanically flexible electronic circuitry is an essential step in the effort to develop next-generation display technologies, including 'see-through' and conformable products. Nanowire transistors (NWTs) are of particular interest for future display devices because of their high carrier mobilities compared with bulk or thin-film transistors made from the same materials, the prospect of processing at low temperatures compatible with plastic substrates, as well as their optical transparency and inherent mechanical flexibility. Here we report fully transparent In2O3 and ZnO NWTs fabricated on both glass and flexible plastic substrates, exhibiting high-performance n-type transistor characteristics with similar to 82% optical transparency. These NWTs should be attractive as pixel-switching and driving transistors in active-matrix organic light-emitting diode (AMOLED) displays. The transparency of the entire pixel area should significantly enhance aperture ratio efficiency in active-matrix arrays and thus substantially decrease power consumption.
THIN-FILM TRANSISTORS
FIELD-EFFECT TRANSISTORS
CRYSTALLINE IN2O3 NANOWIRES
ZINC-OXIDE
ELECTRICAL-PROPERTIES
ZNO NANOSTRUCTURES
TIN-OXIDE
SEMICONDUCTOR
SILICON
GROWTH
2007-06-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/89
oai:docs.lib.purdue.edu:nanodocs-1028
2007-11-27T15:49:09Z
publication:nanodocs
publication:dp
publication:nano
Nanoelectronic device applications of a chemically stable GaAs structure
Janes, David B
Kolagunta, V. R
Batistuta, M.
Walsh, B. L
Andres, Ronald P
Liu, Jia
Dicke, J.
Lauterbach, J.
Pletcher, T.
Chen, E. H
Melloch, Michael R
Peckham, E. L
Ueng, H. J
Woodall, Jerry M
Lee, Takhee
Reifenberger, R.
Kubiak, C. P
Kasibhatla, B.
Article
We report on nanoelectronic device applications of a nonalloyed contact structure which utilizes a surface layer of low-temperature grown GaAs as a chemically stable surface. In contrast to typical ex situ ohmic contacts formed on n-type semiconductors such as GaAs, this approach can provide uniform contact interfaces which are essentially planar injectors, making them suitable as contacts to shallow devices with overall dimensions below 50 nm. Characterization of the native layers and surfaces coated with self-assembled monolayers of organic molecules provides a picture of the chemical and electronic stability of the layer structures. We have recently developed controlled nanostructures which incorporate metallic nanoclusters, a conjugated organic interface layer, and the chemically stable semiconductor surface layers. These studies indicate that stable nanocontacts (4 nmX4 nm) can be realized with specific contact resistances less than 1 X 10(-6) Ohm cm(2) and maximum current densities (1 X 10(6) A/cm(2)) comparable to those observed in high quality large area contacts. The ability to form stable, low resistance interfaces between metallic nanoclusters and semiconductor device layers using ex situ processing allows chemical self-assembly techniques to be utilized to form interesting nanoscale semiconductor devices. This article will describe the surface and nanocontact characterization results, and will discuss device applications and novel techniques for patterning close-packed arrays of nanocontacts and for imaging the resulting structures. (C) 1999 American Vacuum Society. [S0734-211X(99)05504-3].
1999-08-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/28
oai:docs.lib.purdue.edu:nanodocs-1024
2007-11-27T15:02:40Z
publication:nanodocs
publication:dp
publication:nano
Negative resist behavior of neutral sodium atoms deposited on self-assembled monolayers
Ju, Sanghyun
Mills, A.K.
Hang, Qingling
Elliott, Daniel S
Janes, David B
Article
The authors report their initial studies of the negative resist behavior of neutral sodium atoms deposited on alkanethiol molecules during neutral atom lithographic processing. Their results show that neutral sodium atoms incident upon octadecanethiol, the longest molecule of the various alkanethiols among alkanethiol self-assembled monolayers (SAMs), formed the most robust negative resist during the patterning process and made high quality patterning profile. In order to interpret the nature of the surface interaction between neutral sodium atoms and SAMs, they examine the surface components using x-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and rinse tests. Their results indicate that sodium neutral atoms do not chemically react with or physically damage the SAMs but rather accumulate on and possibly diffuse into the SAMs. (c) 2007 American Vacuum Society.
2007-02-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/24
oai:docs.lib.purdue.edu:nanodocs-1023
2007-11-27T14:51:13Z
publication:nanodocs
publication:dp
publication:nano
High performance ZnO nanowire field effect transistors with organic gate nanodielectrics: effects of metal contacts and ozone treatment
Ju, Sanghyun
Lee, Kangho
Yoon, Myung-Han
Facchetti, Antonio
Marks, Tobin J
Janes, David B
Article
High performance ZnO nanowire field effect transistors (NW-FETs) were fabricated using a nanoscopic self-assembled organic gate insulator and characterized in terms of conventional device performance metrics. To optimize device performance and understand the effects of interface properties, devices were fabricated with both Al and Au/Ti source/drain contacts, and device electrical properties were characterized following annealing and ozone treatment. Ozone-treated single ZnO NW-FETs with Al contacts exhibited an on-current (I-on) of similar to 4 mu A at 0.9 V-gs and 1.0 V-ds, a threshold voltage (V-th) of 0.2 V, a subthreshold slope (S) of similar to 130 mV/ decade, an on - off current ratio (I-on: I-off) of similar to 10(7), and a field effect mobility (mu(eff)) of similar to 1175 cm(2) V-1 s(-1). In addition, ozone-treated ZnO NW-FETs consistently retained the enhanced device performance metrics after SiO2 passivation. A 2D device simulation was performed to explain the enhanced device performance in terms of changes in interfacial trap and fixed charge densities.
2007-04-18T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/23
oai:docs.lib.purdue.edu:nanodocs-1022
2007-11-27T14:45:41Z
publication:nanodocs
publication:dp
publication:nano
Electrical readouts of single and few molecule systems in metal-molecule-metal device structures
Mahapatro, Ajit K
Janes, David B
Article
Electrical conduction through molecular junctions are measured in different local environments through two test beds that are ideal for single/few molecule and molecular monolayer systems. A technique has been developed to realize Au films with similar to 1.5 angstrom surface roughness comparable to the best available techniques and suitable for formation of patterned device structures. The technique utilizes room temperature e-beam evaporated Au films over oxidized Si substrates silanized with (3-mercaptopropyl)trimethoxysilane (MPTMS). The lateral (single/few molecule) and vertical (many molecules) device structures are both enabled by the process for realizing ultraflat Au layer. Lateral metal-molecule-metal (M-M-M) device structures are fabricated by forming pairs of Au electrodes with nanometer separation (nano-gap) through an electromigration-induced break-junction (EIBJ) technique at room temperature and conductivity measurements are carried out for dithiol functionalized single molecules. We have used the flat Au layer (using the current technique) as the bottom contact in vertical M-M-M device structures. Here, molecular self-assembly are formed on the Au surface, and patterned (20 x 20 mu m(2)) top Au contacts were successfully transferred on to the device using a stamping technique (where the Au is deposited on a polydimethylsiloxane (PDMS) pad and following a physical contact on the thiolated Au layer). The single molecular property of XYL, a highly conductive molecule and many molecular property of HS-C9-SH, an insulating molecule in its molecular monolayer form are measured. Observation of enhanced conduction following molecular deposition, and comparison of conductance-voltage characteristics to those predicted theoretically, confirms the success of trapping single/few molecules in the nano-gap. The observed similar to 10(2) less conductance through the molecular monolayer of HS-C9-SH compared to the estimation of a linear sum of single molecule conductances over large area indicate that either all the molecules are not in physical contact with the top stamping electrode or electrode-molecule coupling has a less broadening in presence of it own environment or both.
2007-06-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/22
oai:docs.lib.purdue.edu:nanodocs-1018
2007-11-27T14:03:51Z
publication:nanodocs
publication:dp
publication:nano
RNA nanotechnology: Engineering, assembly and applications in detection, gene delivery and therapy
Guo, Peixuan
Article
Biological macromolecules including DNA, RNA, and proteins, have intrinsic features that make W them potential building blocks for the bottom-up fabrication of nanodevices. RNA is unique in nanoscale fabrication due to its amazing diversity of function and structure. RNA molecules can be designed and manipulated with a level of simplicity characteristic of DNA while possessing versatility in structure and function similar to that of proteins. RNA molecules typically contain a large variety of single stranded loops suitable for inter- and intra-molecular interaction. These loops can serve as mounting dovetails obviating the need for external linking dowels in fabrication and assembly.
The self-assembly of nanoparticles from RNA involves cooperative interaction of individual RNA molecules that spontaneously assemble in a predefined manner to form a larger two- or three-dimensional structure. Within the realm of self-assembly there are two main categories, namely template and non-template. Template assembly involves interaction of RNA molecules under the influence of specific external sequence, forces, or spatial constraints such as RNA transcription, hybridization, replication, annealing, molding, or replicas. In contrast, non-template assembly involves formation of a larger structure by individual components without the influence of external forces. Examples of non-template assembly are ligation, chemical conjugation, covalent linkage, and loop/loop interaction of RNA, especially the formation of RNA multimeric complexes. The best characterized RNA multiplier and the first to be described in RNA nanotechnological application is the motor pRNA of bacteriophage phi29 which form dimers, trimers, and hexamers, via hand-in-hand interaction. phi29 pRNA can be redesigned to form a variety of structures and shapes including twins, tetramers, rods, triangles, and 3D arrays several microns in size via interaction of programmed helical regions and loops. 3D RNA array formation requires a defined nucleotide number for twisting and a palindromic sequence. Such arrays are unusually stable and resistant to a wide range of temperatures, salt concentrations, and pH. Both the therapeutic siRNA or ribozyme and a receptor-binding RNA aptamer or other ligands have been engineered into individual pRNAs. Individual chimeric RNA building blocks harboring siRNA or other therapeutic molecules have been fabricated subsequently into a trimer through hand-in-hand interaction of the engineered right and left interlocking RNA loops. The incubation of these particles containing the receptor-binding aptamer or other ligands results in the binding and co-entry of trivalent therapeutic particles into cells. Such particles were subsequently shown to modulate the apoptosis of cancer cells in both cell cultures and animal trials. The use of such antigen-free 20-40 nm particles holds promise for the repeated long-term treatment of chronic diseases. Other potentially useful RNA molecules that form multimers include HIV RNA that contain kissing loop to form dimers, tecto-RNA that forms a "jigsaw puzzle," and the Drosophila bicoid mRNA that forms multimers; via "hand-by-arm" interactions.
Applications of RNA molecules involving replication, molding, embossing, and other related techniques, have recently been described that allow the utilization of a variety of materials to enhance diversity and resolution of nanomaterials. It should eventually be possible to adapt RNA to facilitate construction of ordered, patterned, or pre-programmed arrays or superstructures. Given the potential for 3D fabrication, the chance to produce reversible self-assembly, and the ability of self-repair, editing and replication, RNA self-assembly will play an increasingly significant role in integrated biological nanofabrication. A random 100-nucleotide RNA library may exist in 1.6 x 10(60) varieties with multifarious structure to serve as a vital system for efficient fabrication, with a complexity and diversity far exceeding that of any current nanoscale system.
This review covers the basic concepts of RNA structure and function, certain methods for the study of RNA structure, the approaches for engineering or fabricating RNA into nanoparticles or arrays, and special features of RNA molecules that form multimers. The most recent development in exploration of RNA nanoparticles for pathogen detection, drug/gene delivery, and therapeutic application is also introduced in this review.
2005-12-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/19
oai:docs.lib.purdue.edu:nanodocs-1020
2007-11-27T14:31:49Z
publication:nanodocs
publication:dp
publication:nano
N-type field-effect transistors using multiple Mg-doped ZnO nanorods
Ju, Sanghyun
Li, Jianye
Pimparkar, Ninad
Alam, Muhammad A.
Chang, R. P. H.
Janes, David B
Article
Nanorod field-effect transistors (FETs) that use multiple Mg-doped ZnO nanorods and a SiO2 gate insulator were fabricated and characterized. The use of multiple nanorods provides higher on-currents without significant degradation in threshold voltage shift and subthreshold slopes. It has been observed that the on-currents of the multiple ZnO nanorod FETs increase approximately linearly with the number of nanorods, with on-currents of similar to 1 mu A per nanorod and little change in off-current (similar to 4 x 10(-12)). The subthreshold slopes and on-off ratios typically improve as the number of nanorods within the device channel is increased, reflecting good uniformity of properties from nanorod to nanorod. It is expected that Mg dopants contribute to high n-type semiconductor characteristics during ZnO nanorod growth. For comparison, nonintentionally doped ZnO nanorod FETs are fabricated, and show low conductivity to compare with Mg-doped ZnO nanorods. In addition, temperature-dependent current-voltage characteristics of single ZnO nanorod FETs indicate that the activation energy of the drain current is very low (0.05-0.16 eV) at gate voltages both above and below threshold.
2007-05-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/20
oai:docs.lib.purdue.edu:nanodocs-1021
2007-11-27T14:37:30Z
publication:nanodocs
publication:dp
publication:nano
Sequence specific electronic conduction through polyion-stabilized double-stranded DNA in nanoscale break junctions
Mahapatro, Ajit K
Jeong, Kyung J
Lee, Gil U
Janes, David B
Article
This paper presents a study of sequence specific electronic conduction through short (15-base- pair) double-stranded (ds) DNA molecules, measured by immobilizing 3'-thiol-derivatized DNAs in nanometre scale gaps between gold electrodes. The polycation spermidine was used to stabilize the ds-DNA structure, allowing electrical measurements to be performed in a dry state. For specific sequences, the conductivity was observed to scale with the surface density of immobilized DNA, which can be controlled by the buffer concentration. A series of 15-base DNA oligonucleotide pairs, in which the centre sequence of five base pairs was changed from G: C to A: T pairs, has been studied. The conductivity per molecule is observed to decrease exponentially with the number of adjacent A: T pairs replacing G: C pairs, consistent with a barrier at the A: T sites. Conductance-based devices for short DNA sequences could provide sensing approaches with direct electrical readout, as well as label-free detection.
2007-05-16T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/21
oai:docs.lib.purdue.edu:nanodocs-1025
2007-11-27T15:08:22Z
publication:nanodocs
publication:dp
publication:nano
A nanocapacitor with giant dielectric permittivity
Saha, S. K.
DaSilva, Manuel
Hang, qhang@purdue.edu
Sands, Timothy D
Janes, David B
Article
A nanocapacitor with ultra high capacitance (718 +/- 0.2 pF) has been fabricated using electro-deposited Au nanowires manipulated between two Au microelectrodes by the dielectrophoresis technique. A high dc resistance value (similar to 100 M Omega) and nonlinear current-voltage characteristics indicate the formation of a dielectric interface between the nanowires. From frequency dependent conductivity, it is seen that the interface exhibits a giant dielectric permittivity (epsilon similar to 1.8x107), which shows no frequency dispersion over the range from 30 Hz to 1 MHz. The enhancement of this permittivity value is attributed to the formation of a disordered interface containing gold atoms disrupted from the surface of the Au nanowires.
2006-05-14T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/25
oai:docs.lib.purdue.edu:nanodocs-1026
2007-11-27T15:11:54Z
publication:nanodocs
publication:dp
publication:nano
Nanometer scale electrode separation (nanogap) using electromigration at room temperature
Mahapatro, Ajit K
Ghosh, Subhasis
Janes, David B
Article
Pairs of electrodes with nanometer separation (nanogap) are achieved through an electromigration-induced break-junction (EIBJ) technique at room temperature. Lithographically defined gold (An) wires are formed by e-beam evaporation over oxide-coated silicon substrates silanized with (3-Mercaptopropyl)trimethoxysilane (MPTMS) and then subjected to, electromigration at room temperature to create a nanometer scale gap between the two newly formed An electrodes. The MPTMS is an efficient adhesive monolayer between SiO2 and An. Although the An wires are initially 2 pm wide, gaps with length similar to 1 nm and width similar to 5 nm are observed after breaking and imaging through a field effect scanning electron microscope. This technique eliminates the presence of any residual metal interlink in the adhesion layer (chromium or titanium for An deposition over SiO2) after breaking the gold wire, and it is much easier to implement than the commonly used low-temperature EIBJ technique which needs to be executed at 4.2 K. Metal-molecule-metal structures with symmetrical metal-molecule contacts at both ends of the molecule are fabricated by forming a self-assembled monolayer of -dithiol molecules between the EIBJ-created An electrodes with nanometer separation. Electrical conduction through single molecules of 1,4-Benzenedimethanethiol (XYL) is tested using the Au/XYL/Au structure with chemisorbed gold-sulfur coupling at both contacts.
2006-05-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/26
oai:docs.lib.purdue.edu:nanodocs-1027
2007-11-27T15:35:12Z
publication:nanodocs
publication:dp
publication:nano
Deposition of platinum clusters on surface-modified tobacco mosaic virus
Lee, Sang-Yup
Choi, Jaewon
Royston, Elizabeth
Janes, David B
Culver, James N
Harris, Michael T
Article
Nanoscaled Pt conductors were prepared from genetically engineered Tobacco mosaic virus (TMV) templates through Pt cluster deposition on the outer surface of the TMV. Pt clusters were synthesized and deposited on the engineered TMV with surface-exposed cysteine via the in situ mineralization of hexachloroplatinate anions. This deposition was driven by the specific binding between thiols and the solid metal clusters. In addition, Pt-thiolate adducts are suggested to form on the engineered TMV in aqueous solutions that work as nucleation sites for the formation of the Pt clusters. The specific binding between Pt clusters and the engineered TMV template was investigated using UV/vis spectrophotometry and quartz crystal microbalance (QCM) analysis. The electric conductance of Pt-deposited TMV was greater than that of the uncoated TMV virion particles. This result suggests the application of metal cluster-deposited engineered TMV in future electrical devices such as rapid response sensors.
2006-04-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/27
oai:docs.lib.purdue.edu:nanodocs-1029
2007-11-27T15:57:04Z
publication:nanodocs
publication:dp
publication:nano
Dimensional scaling treatment of stability of atomic anions induced by superintense, high-frequency laser fields
Wei, Qi
Kais, Sabre
Herschbach, Dudley
Article
We show that dimensional scaling, combined with the high-frequency Floquet theory, provides useful means to evaluate the stability of gas phase atomic anions in a superintense laser field. At the large-dimension limit (D ->infinity), in a suitably scaled space, electrons become localized along the polarization direction of the laser field. We find that calculations at large D are much simpler than D=3, yet yield similar results for the field strengths needed to bind an "extra" one or two electrons to H and He atoms. For both linearly and circularly polarized laser fields, the amplitude of quiver motion of the electrons correlates with the detachment energy. Despite large differences in scale, this correlation is qualitatively like that found between internuclear distances and dissociation energies of chemical bonds. (C) 2007 American Institute of Physics.
2007-09-07T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/29
oai:docs.lib.purdue.edu:nanodocs-1030
2007-11-27T16:01:44Z
publication:nanodocs
publication:dp
publication:nano
Internal entanglement amplification by external interactions
Peskin, Uri
Huang, Zhen
Kais, Sabre
Article
We propose a scheme to control the level of entanglement between two fixed spin-1/2 systems by interaction with a third particle. For specific designs, entanglement is shown to be "pumped" into the system from the surroundings even when the spin-spin interaction within the system is small or nonexistent. The effect of the external particle on the system is introduced by including a dynamic spinor in the Hamiltonian. Controlled amplification of the internal entanglement to its maximum value is demonstrated. The possibility of entangling noninteracting spins in a stationary state is also demonstrated by coupling each one of them to a flying qubit in a quantum wire.
2007-07-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/30
oai:docs.lib.purdue.edu:nanodocs-1031
2007-11-27T16:06:00Z
publication:nanodocs
publication:dp
publication:nano
New stable multiply charged negative atomic ions in linearly polarized superintense laser fields
Wei, Qi
Kais, Sabre
Moiseyev, Nimrod
Article
Singly charged negative atomic ions exist in the gas phase and are of fundamental importance in atomic and molecular physics. However, theoretical calculations and experimental results clearly exclude the existence of any stable doubly-negatively-charged atomic ion in the gas phase, only one electron can be added to a free atom in the gas phase. In this report, using the high-frequency Floquet theory, we predict that in a linear superintense laser field one can stabilize multiply charged negative atomic ions in the gas phase. We present self-consistent field calculations for the linear superintense laser fields needed to bind extra one and two electrons to form He-, He2-, and Li2-, with detachment energies dependent on the laser intensity and maximal values of 1.2, 0.12, and 0.13 eV, respectively. The fields and frequencies needed for binding extra electrons are within experimental reach. This method of stabilization is general and can be used to predict stability of larger multiply charged negative atomic ions. (c) 2006 American Institute of Physics.
2006-05-28T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/31
oai:docs.lib.purdue.edu:nanodocs-1032
2007-11-27T16:13:14Z
publication:nanodocs
publication:dp
publication:nano
Coupled mode space approach for the simulation of realistic carbon nanotube field-effect transistors
Fiori, Gianluca
Iannaccone, Giuseppe
Klimeck, Gerhard
Article
A coupled mode space approach within the nonequiibriurn Green's function formalism is presented, which allows to perform simulations of realistic carbon nanotube field-effect transistors (CNT-FETs) with no spatial symmetry. Computing :time is significantly reduced with respect to the real space ap)roach, since only few modes are needed in order to obtain accurate results. The advantage of the method increases with increasing nanotube diameter, and is a factor of 20 in computing time for a (25,0) nanotube. As a consequence, comoutationally demanding simulations like those required by a statistical investigation, or by a device performance study based on the exploration of the design space, become more affordable. As a further test of he method, we have applied the coupled mode space approach to double-gate CNT-FETs devices and devices with discrete distribution of doping atoms. In the latter case, nonballistic transport due to elastic scattering with ionized impurities in doped source ind drain extensions occurs. We show that even in the case of very rough potential, the coupled mode space approach is accurate vith very few modes, enabling atomistic simulations of statistical properties with reduced computational resources.
2007-07-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/32
oai:docs.lib.purdue.edu:nanodocs-1035
2007-11-27T16:41:23Z
publication:nanodocs
publication:dp
publication:nano
Templated synthesis of gold-iron alloy nanoparticles using pulsed laser deposition
Chang, Won-Suk
Park, Jin-Won
Rawat, Vijay
Sands, Timothy D
Lee, Gil U
Article
A means for synthesizing paramagnetic nanoparticles composed of an Au-Fe alloy is described using pulsed laser deposition (PLD) of the alloy into a mesoporous alumina membrane template. Nanoparticles 46 +/- 13 nm in diameter and composed of a 17% Fe alloy have been created by depositing a 35% Fe alloy into a template with 65 nm diameter pores. These paramagnetic nanoparticles had a saturation magnetization of 11.5 emu g(-1) at 2000 G, and their UV-visible extinction spectrum was dominated by strong absorption similar to that of Fe3O4 nanoparticles. The surfaces of these nanoparticles were readily functionalized with a dense monolayer of DNA oligonucleotides that had a 5' thiol group. The Au-Fe nanoparticles appear to be well suited for biotechnological applications and single molecule measurements as they can be synthesized in a specific size range, are strongly paramagnetic, and may be easily functionalized with biological macromolecules.
2006-10-28T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/35
oai:docs.lib.purdue.edu:nanodocs-1033
2007-11-27T16:18:52Z
publication:nanodocs
publication:dp
publication:nano
The electronic structure and transmission characteristics of disordered AlGaAs nanowires
Boykin, Timothy B.
Luisier, Mathieu
Schenk, Andreas
Kharche, Neerav
Klimeck, Gerhard
Article
Perfect nanowires may be studied from both the bandstructure and transmission perspectives, and relating features in one set of curves to those in another often yields much insight into their behavior. For random-alloy nanowires, however, only transmission characteristics and virtual-crystal approximation (VCA) bands have been available. This is a serious shortcoming since the VCA cannot properly capture disorder at the primitive cell level: those bulk properties which it can satisfactorily reproduce arise from spatially extended states and measurements which average out primitive cell-level fluctuations. Here we address this deficiency by projecting approximate bands out of supercell states for Al0.15Ga0.85 As random alloy nanowires. The resulting bands correspond to the transmission characteristics very closely, unlike the VCA bands, which cannot explain important transmission features. Using both bandstructure and transmission results, we are better able to explain the operation of these nanowires.
2007-01-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/33
oai:docs.lib.purdue.edu:nanodocs-1036
2007-11-27T16:45:42Z
publication:nanodocs
publication:dp
publication:nano
Transport and functional behaviour of poly(ethylene glycol)-modified nanoporous alumina membranes
Lee, Sang Won
Shang, Hao
Haasch, Richard T
Petrova, Vania
Lee, Gil U
Article
The development of hybrid organic-inorganic membranes with a low propensity for protein adsorption and highly uniform nanometre size pores is described. Poly(ethylene glycol) (PEG) monolayers were grafted to nanoporous alumina membranes using covalent silane and physical adsorption poly(ethyleneimine) (PEI) immobilization chemistries. X-ray photoelectron spectroscopy (XPS) and electron microscopy were used to investigate the chemical and physical surface properties of the membranes. The adsorption behaviour of a serum albumin on the membranes was characterized with fluorescence spectroscopy and it was determined that the PEG coating reduced nonspecific protein adsorption to a level too small to be measured. The gas and liquid permeabilities of membranes were measured to determine if the surface chemistries changed the functional behaviour of the membranes. Surprisingly, the silane chemistry produced little change in the permeabilities while polymer adsorption resulted in a total loss of water permeability. The diffusion of ovalbumin through the membranes was also measured and compared with a theoretical value. Diffusion of ovalbumin through the silane-PEG-modified membranes was found to be 50% slower than the unmodified membranes, which suggests that the pores are coated with a dense film of PEG. These results suggest that hybrid organic-inorganic membranes can provide significantly improved functional behaviour over existing organic or inorganic membranes.
2005-08-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/36
oai:docs.lib.purdue.edu:nanodocs-1034
2007-11-27T16:25:44Z
publication:nanodocs
publication:dp
publication:nano
Ultra high-speed sorting
Leary, James F
Article
Background: Cell sorting has a history dating back approximately 40 years. The main limitation has been that, although flow cytometry is a science, cell sorting has been an art during most of this time. Recent advances in assisting technologies have helped to decrease the amount of expertise necessary to perform sorting.
Methods: Droplet-based sorting is based on a controlled disturbance of a jet stream dependent on surface tension. Sorting yield and purity are highly dependent on stable jet break-off position. System pressures and orifice diameters dictate the number of droplets per second, which is the sort rate limiting step because modern electronics can more than handle the higher cell signal processing rates.
Results: Cell sorting still requires considerable expertise. Complex multicolor sorting also requires new and more sophisticated sort decisions, especially when cell subpopulations are rare and need to be extracted from back- High-speed sorting continues to pose major problems in terms of biosafcty due to the aerosols generated.
Conclusions: Cell sorting has become more stable and predictable and requires less expertise to operate. However, the problems of aerosol containment continue to make droplet-based cell sorting problematical. Fluid physics and cell viability restraints pose practical limits for high-speed sorting that have almost been reached. Over the next 5 years there may be advances in fluidic switching sorting in lab-on-a-chip microfluidic systems that could not only solve the aerosol and viability problems but also make ultra high-speed sorting possible and practical through massively parallel and exponential staging microfluidic architectures. (c) 2005 International Society for Analytical Cytology.
2005-10-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/34
oai:docs.lib.purdue.edu:nanodocs-1037
2007-11-27T20:39:54Z
publication:nanodocs
publication:dp
publication:nano
Dependence of DC characteristics of CNT MOSFETs on bandstructure models
Koswatta, Siyuranga O
Neophytou, Neophytos
Kienle, Diego
Fiori, Gianluca
Lundstrom, Mark S.
Article
Since their discovery in the early 1990s, the interest in carbon nanotube (CNT) electronics has exploded. One main factor that controls the device performance of CNT field-effect transistors (CNT MOSFETs) is the electronic structure of the nanotube. In this paper we use three different bandstructure models. 1) extended Huckel theory (EHT); 2) orthogonal p(z) tight-binding (OTB); and 3) parabolic effective mass model (EFM) to investigate the bandstructure effects on the device characteristics of a CNT MOSFET using semiclassical and quantum treatments of transport. We find that, after proper calibration, the OTB model is essentially identical to the EHT over the energy range of interest. We also find that an even simpler parabolic EFM facilitates CNT MOSFET simulations within practically applied bias ranges.
2006-07-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/37
oai:docs.lib.purdue.edu:nanodocs-1040
2007-11-27T20:55:17Z
publication:nanodocs
publication:dp
publication:nano
Simulating quantum transport in nanoscale MOSFETs: Ballistic hole transport, subband engineering and boundary conditions
Venugopal, Ramesh
Ren, Zhibin
Lundstrom, Mark S.
Article
We present a modeling scheme for simulating ballistic hole transport in thin-body fully depleted silicon-on-insulator pMOSFETs. The scheme includes all of the quantum effects associated with hole confinement and also accounts for valence band nonparabolicity approximately. This simulator is used to examine the effects of hole quantization on device performance by simulating a thin (1.5-nm) and thick (5-nm) body double-gated pMOSFET in the ballistic limit. Two-dimensional electrostatic effects such as drain-induced barrier lowering (DIBL) and off-equilibrium transport are emphasized as part of this study. The effect of channel orientation on the device performance is examined by simulating pMOSFETs with channels directed along (100) and (110). Simulated device characteristics for identical nMOSFETs and pMOSFETs are compared in order to explore the effects of subband engineering on CMOS technology. Novel floating boundary conditions used in simulating ballistic transport are highlighted and discussed.
2003-09-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/40
oai:docs.lib.purdue.edu:nanodocs-1039
2007-11-27T20:48:33Z
publication:nanodocs
publication:dp
publication:nano
Assessment of high-frequency performance potential of carbon nanotube transistors
Guo, Jing
Hasan, Sayed
Javey, Ali
Bosman, Gijs
Lundstrom, Mark S.
Article
Self-consistent quantum simulations are used to explore the high-frequency performance potential of carbon nantube field-effect transistors (CNTFETs). The cutoff frequency expected for a recently reported CNT Schottky-barrier FET is well below the performance limit, due to the large parasitic capacitance between electrodes. We show that using an array of parallel nanotubes as the transistor channel reduces parasitic capacitance per tube. Increasing tube density gives a large improvement of high-frequency performance when tubes are widely spaced and parasitic capacitance, dominates but only a small improvement when the tube spacing is small and intrinsic gate capacitance dominates. Alternatively, using quasi-one-dimensional nanowires as source and drain contacts should significantly reduce parasitic capacitance and improve high-frequency performance. Ballistic CNTFETs should outperform ballistic Si MOSFETs in terms of the high-frequency performance limit because of their larger band-structure-limited velocity.
2005-11-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/39
oai:docs.lib.purdue.edu:nanodocs-1041
2007-11-27T21:20:26Z
publication:nanodocs
publication:dp
publication:nano
Enhancement-mode quantum transistors for single electron spin
Jones, G. M.
Hu, B. H
Yang, C. H
Yang, M. J
Lyanda-Geller, Yuli
Article
Using an InAs/GaSb composite quantum well, we demonstrate an enhancement mode single electron transistor. With a Hall bar geometry, we show that the device undergoes a transition from accumulation of two-dimensional (2D) holes in GaSb to a complete depletion and finally to an inversion layer of 2D electrons in InAs. When the top-gate area is reduced to nanometer scale, the inversion electrons are confined to a quantum dot, and the transistor displays single electron characteristics: a series of conductance peaks resulting from electrons tunnelling through the quantum dot. The occurrence of the first peak is the signature of one electron occupying InAs quantum dot. The unique configuration of enhancement quantum dots makes it possible to upscale to 2D arrays for manipulation and transporting of single spins.
2006-08-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/41
oai:docs.lib.purdue.edu:nanodocs-1038
2007-11-27T20:43:24Z
publication:nanodocs
publication:dp
publication:nano
Three-dimensional electrostatic effects of carbon nanotube transistors
Neophytou, Neophytos
Guo, Jing
Lundstrom, Mark S.
Article
We explore the three-dimensional (3-D) electrostatics of planar-gate carbon nanotube field-effect transistors (CNTFETs) using a self-consistent solution to the Poisson equation with equilibrium carrier statistics. We examine the effects of the gate insulator thickness and dielectric constant and the source/drain contact geometry on the electrostatics of bottom-gated (BG) and top-gated (TG) devices. We find that the electrostatic scaling length is mostly -determined by the gate oxide thickness, not by the oxide dielectric constant. We also find that a high-k gate insulator does not necessarily improve short-channel immunity because it increases the coupling of both the gate and the source/drain contact to the channel. It also increases the parasitic coupling of the source/drain to the gate. Although both the width and the height of the source and drain contacts are important, we find that for the BG device, reducing the width of the 3-D contacts is more effective for improving short channel immunity than reducing the height. The TG device, however, is sensitive to both the width and height of the contact. We find that one-dimensional source and drain contacts promise the best short channel immunity. We also show that an optimized TG device with a thin gate oxide can provide near ideal subthreshold behavior. The results of this paper should provide useful guidance for designing high-performance CNTFETs.
2006-07-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/38
oai:docs.lib.purdue.edu:nanodocs-1043
2007-11-27T21:38:47Z
publication:nanodocs
publication:dp
publication:nano
Three-dimensional imaging of living and dying neurons with atomic force microscopy
McNally, Helen
Borgens, Richard B.
Article
Atomic Force Microscopy (AFM) has been used to image the morphology of developing neurons and their processes. Additionally, AFM can physically interact with the cell under investigation in numerous ways. Here we use the AFM to both three-dimensionally image the neuron and to inflict a nano/micro-puncture to its membrane. Thus, the same instrument used as a tool to precisely penetrate/cut the membrane at the nanoscale level is employed to image the morphological responses to damage. These first high resolution AFM images of living chick dorsal root ganglion cells and cells of sympathetic ganglion and their growing processes provide confirmation of familiar morphologies. The increased resolution of the AFM revealed these structures to be significantly more complex and variable than anticipated. Moreover we describe novel, dynamic, and unreported architectures, particularly large dorsally projecting ridges, spines, and ribbons of cytoplasm that appear and disappear on the order of minutes. In addition, minute (ca. 100 nm) hair-like extensions of membrane along the walls of nerve processes that also shift in shape and density, appearing and disappearing over periods of minutes were seen. We also provide "real time'' images of the death of the neuron cell body after nano/micro scale damage to its membrane. These somas excreted their degraded cytoplasm, revealed as an enlarging pool beneath and around the cell. Conversely, identical injury, even repeated perforations and nanoslices, to the neurite's membrane do not lead to demise of the process. This experimental study not only provides unreported neurobiology and neurotrauma, but also emphasizes the unique versatility of AFM as an instrument that can ( 1) physically manipulate cells, ( 2) provide precise quantitative measurements of distance, surface area and volume at the nanoscale if required, ( 3) derive physiologically significant data such as membrane pressure and compliance, and ( 4) during the same period of study-provide unexcelled imaging of living samples.
2004-03-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/43
oai:docs.lib.purdue.edu:nanodocs-1044
2007-11-27T21:42:47Z
publication:nanodocs
publication:dp
publication:nano
Self-assembly of micro- and nano-scale particles using bio-inspired events
McNally, Helen
Pingle, M.
Lee, S. W.
Guo, D.
Bergstrom, Donald E
Bashir, Rashid
Article
High sensitivity chemical and biological detection techniques and the development of future electronic systems can greatly benefit from self-assembly processes and techniques. We have approached this challenge using biologically inspired events such as the hybridization of single (ss)- to double-stranded (ds) DNA and the strong affinity between the protein avidin and its associated Vitamin, biotin. Using these molecules, micro-scale polystyrene beads and nano-scale gold particles were assembled with high efficiency on gold patterns and the procedures used for these processes were optimized. The DNA and avidin-biotin complex was also used to demonstrate the attachment of micro-scale silicon islands to each other in a fluid. This work also provides insight into the techniques for the self-assembly of heterogeneous materials. (C) 2003 Elsevier Science B.V. All rights reserved.
2003-05-31T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/44
oai:docs.lib.purdue.edu:nanodocs-1047
2007-11-28T15:23:12Z
publication:nanodocs
publication:dp
publication:nano
Resonant light interaction with plasmonic nanowire systems
Podolskiy, Viktor
Sarychev, Andrey
Narimanov, Evgenii
Shalaev, Vladimir
Article
We compare the optical response of isolated nanowires, double-wire systems, and Pi-structures, and show that their radiation is well described in terms of their electric and magnetic dipole moments. We also show that both dielectric permittivity and magnetic permeability can be negative at optical and near infrared frequencies, and demonstrate the connection between the geometry of the system and its resonance characteristics. We conclude that plasmonic nanowires can be employed for novel negative-index materials. Finally, we demonstrate that it is possible to construct a nanowire-based,transparent nanoresonator' with dramatically enhanced intensity and metal concentration below 5%.
2005-02-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/47
oai:docs.lib.purdue.edu:nanodocs-1045
2007-11-28T14:01:11Z
publication:nanodocs
publication:dp
publication:nano
Conductance quantization and zero bias peak in a gated quantum wire
Giannetta, R. W.
Olheiser, T. A.
Hannan, M.
Adesida, I.
Melloch, Michael R
Article
Conductance measurements are reported for an 0.4 mu m wide GaAs/AlGaAs quantum wire with 7 cross-channel gates. The device exhibited integral conductance steps, magnetoconductance plateaus in agreement with the multi probe formula and a conductance feature at 0.65 (2e(2)/h). Differential conductance measurements down to 50 mK revealed a zero bias conductance peak that vanished with an in-plane field of I T. The width of this peak was comparable to that reported in high mobility quantum point contacts (Phys. Rev. Lett. 88 (2002) 2268051). At low conductances this device also exhibited single electron charging characteristic of a multiple quantum dot. (c) 2004 Elsevier B.V. All rights reserved.
2005-03-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/45
oai:docs.lib.purdue.edu:nanodocs-1046
2007-11-28T14:20:56Z
publication:nanodocs
publication:dp
publication:nano
High-Q micromachined three-dimensional integrated inductors for high-frequency applications
Weon, Dae-Hee
Jeong, Jong-Hyeok
Mohammadi, Saeed
Article
Three-dimensional micromachined inductors are fabricated on high-resistivity (10 k Omega cm) and low-resistivity (10 Omega cm) Si substrates using a stressed metal technology. On high-resistivity Si substrate with low-k dielectric material (SU-8 (TM)), this technology achieves a quality factor Q of 75 for a I nH inductor at frequencies around 4 GHz and a self-resonant frequency f(sr), above 20 GHz. Using Si bulk micromachining to etch away the low-resistivity Si substrate with a combination of deep reactive ion etching and tetramethyl ammonium hydroxide etching methods, a 1.2 nH inductor achieves a peak quality factor Q of 140 at a frequency of 12 GHz with a self-resonant frequency f(ST) above 40 GHz. The dependence of high-frequency performance on the inductor's variables, such as the number of turns, turn-to-turn gap, and substrate type, has been investigated. Excellent performance is achieved by removing the substrate due to the complete elimination of substrate losses and the reduction of the parasitic capacitance. This technology is simple and provides high performance integrated inductors on Si or compound-semiconductor platforms. (c) 2007 American Vacuum Society.
2007-02-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/46
oai:docs.lib.purdue.edu:nanodocs-1050
2007-11-29T14:21:00Z
publication:nanodocs
publication:dp
publication:nano
Nonlinear tapping dynamics of multi-walled carbon nanotube tipped atomic force microcantilevers
Lee, S. I
Howell, S. W.
Raman, Arvind
Reifenberger, R.
Nguyen, C. V
Meyyappan, M.
Article
The nonlinear dynamics of an atomic force microcantilever (AFM) with an attached multi-walled carbon nanotube (MWCNT) tip is investigated experimentally and theoretically. We present the experimental nonlinear frequency response of a MWCNT tipped microcantilever in the tapping mode. Several unusual features in the response distinguish it from those traditionally observed for conventional tips. The MWCNT tipped AFM probe is apparently immune to conventional imaging instabilities related to the coexistence of attractive and repulsive tapping regimes. A theoretical interaction model for the system using an Euler elastica MWCNT model is developed and found to predict several unusual features of the measured nonlinear response.
2004-05-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/49
oai:docs.lib.purdue.edu:nanodocs-1051
2007-11-29T14:39:09Z
publication:nanodocs
publication:dp
publication:nano
Synthesis and patterning of gold nanostructures on InP and GaAs via galvanic displacement
Hormozi Nezhad, Mohammad R
Aizawa, Masato
Porter, Lon A., Jr.
Ribbe, Alexander E
Buriak, Jillian M
Article
Author Keywords: galvanic displacement; gold; nanolithography; nanoparticles; semiconductors
KeyWords Plus: OPEN-CIRCUIT DEPOSITION; HIGH-YIELD SYNTHESIS; ELECTROLESS DEPOSITION; FLUORIDE SOLUTIONS; CHEMICAL-SYNTHESIS; AQUEOUS-SOLUTION; SILICON; NANOPARTICLES; SURFACES; NANOCRYSTALS
2005-11-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/50
oai:docs.lib.purdue.edu:nanodocs-1057
2007-11-29T16:20:40Z
publication:nanodocs
publication:dp
publication:nano
Integration of hydrogels with hard and soft microstructures
Li, Ming
Ziaie, Babak
Nuxoll, Eric
Iván, Kristóf
Siegel, Ronald A
Article
Hydrogels, i.e., water-swollen polymer networks, have been studied and utilized for decades. These materials can either passively support mass transport, or can actively respond in their swelling properties, enabling modulation of mass and fluid transport, and chemomechanical actuation. Response rates increase with decreasing hydrogel dimension. In this paper, we present three examples where incorporation of hydrogels into solid microstructures permits acceleration of their response, and also provides novel functional capabilities. In the first example, a hydrogel is immobilized inside microfabricated pores within a thin silicon membrane. This hydrogel does not have a swelling response under the conditions investigated, but under proper conditions it can be utilized as a part of an electrolytic diode. In the second example, hydrogels are polymerized under microcantilever beams, and their swelling response to pH or glucose concentration causes variable deflection of the beam, observable under a microscope. In the third example, swelling and shrinking of a hydrogel embedded in a microfabricated valve structure leads to chemical gating of fluid motion through that valve. In all cases, the small size of the system enhances its response rate.
2007-03-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/56
oai:docs.lib.purdue.edu:nanodocs-1052
2007-11-29T14:59:09Z
publication:nanodocs
publication:dp
publication:nano
Gaseous slip flow analysis of a micromachined flow sensor for ultra small flow applications
Jang, Jaesung
Wereley, Steven
Article
The velocity slip of a fluid at a wall is one of the most typical phenomena in microscale gas flows. This paper presents a flow analysis considering the velocity slip in a capacitive micro gas flow sensor based on pressure difference measurements along a microchannel. The tangential momentum accommodation coefficient (TMAC) measurements of a particular channel wall in planar microchannels will be presented while the previous micro gas flow studies have been based on the same TMACs on both walls. The sensors consist of a pair of capacitive pressure sensors, inlet/outlet and a microchannel. The main microchannel is 128.0 mu m wide, 4.64 mu m deep and 5680 mu m long, and operated under nearly atmospheric conditions where the outlet Knudsen number is 0.0137. The sensor was fabricated using silicon wet etching, ultrasonic drilling, deep reactive ion etching (DRIE) and anodic bonding. The capacitance change of the sensor and the mass flow rate of nitrogen were measured as the inlet-to-outlet pressure ratio was varied from 1.00 to 1.24. The measured maximum mass flow rate was 3.86 x 10(-10) kg s(-1) (0.019 sccm) at the highest pressure ratio tested. As the pressure difference increased, both the capacitance of the differential pressure sensor and the flow rate through the main microchannel increased. The laminar friction constant f.Re, an important consideration in sensor design, varied from the incompressible no-slip case and the mass sensitivity and resolution of this sensor were discussed. Using the current slip flow formulae, a microchannel with much smaller mass flow rates can be designed at the same pressure ratios.
2007-02-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/51
oai:docs.lib.purdue.edu:nanodocs-1055
2007-11-29T15:58:10Z
publication:nanodocs
publication:dp
publication:nano
Fabrication of fully transparent nanowire transistors for transparent and flexible electronics
Ju, Sanghyun
Facchetti, Antonio
XUAN, Xi
Liu, Jun
Ishikawa, Fumaiki
Ye, P. D.
Zhou, Chongwu
Marks, Tobin J.
Janes, David B
Article
The development of optically transparent and mechanically flexible electronic circuitry is an essential step in the effort to develop next-generation display technologies, including 'see-through' and conformable products. Nanowire transistors (NWTs) are of particular interest for future display devices because of their high carrier mobilities compared with bulk or thin-film transistors made from the same materials, the prospect of processing at low temperatures compatible with plastic substrates, as well as their optical transparency and inherent mechanical flexibility. Here we report fully transparent In2O3 and ZnO NWTs fabricated on both glass and flexible plastic substrates, exhibiting high-performance n-type transistor characteristics with similar to 82% optical transparency. These NWTs should be attractive as pixel-switching and driving transistors in active-matrix organic light-emitting diode (AMOLED) displays. The transparency of the entire pixel area should significantly enhance aperture ratio efficiency in active-matrix arrays and thus substantially decrease power consumption.
2007-06-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/54
oai:docs.lib.purdue.edu:nanodocs-1049
2007-11-29T14:15:30Z
publication:nanodocs
publication:dp
publication:nano
Imaging artefacts in atomic force microscopy with carbon nanotube tips
Strus, Mark C
Raman, Arvind
Nguyen, C. V
Article
Dynamic atomic force microscopy (dynamic AFM) with carbon nanotube tips has been suggested as an enabling tool for high precision nanometrology of critical dimension features of semiconductor surfaces. We investigate the performance of oscillating AFM microcantilevers with multi-walled carbon nanotube (multi-walled CNT) tips interacting with high aspect ratio structures while in the attractive regime of dynamic AM We present experimental results on SiO2 gratings and tungsten nanorods, which show two distinct imaging artefacts, namely the fort-nation of divots and large ringing artefacts that are inherent to CNT AFM probe operation. Through meticulous adjustment of operating parameters, the connection of these artefacts to CNT bending, adhesion, and stiction is described qualitatively and explained.
2005-11-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/48
oai:docs.lib.purdue.edu:nanodocs-1053
2007-11-29T15:01:27Z
publication:nanodocs
publication:dp
publication:nano
Effective heights and tangential momentum accommodation coefficients of gaseous slip flows in deep reactive ion etching rectangular microchannels
Jang, Jaesung
Wereley, Steven
Article
he behavior of a rarefied, compressible flow in long, constant cross section channels provides an opportunity to study complex gas dynamics in a simple geometry that allows analytical solutions. The problem of a rarefied, compressible flow in near unity aspect ratio rectangular cross section channels has been all but ignored despite it being a common flow geometry. We present analytical expressions for the mass flow rate in long, straight and uniform rectangular cross section microchannels in the slip flow regime. Using these analytical expressions, we extract the tangential momentum accommodation coefficient (TMAC) as well as the effective channel dimensions to account for a slight curvature of one of the walls of the rectangle. These expressions are effective in near unity aspect ratio rectangular microchannels made by deep reactive ion etching. The dependence of the flow behavior on the channel height to width aspect ratio is discussed as is the effect of the slight deviation from a rectangular cross section. The obtained TMAC results are consistent with values found by previous researchers using similar materials. Finally, a method of determining TMACs in channels consisting of non-homogenous materials or processing methods is presented.
2006-03-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/52
oai:docs.lib.purdue.edu:nanodocs-1054
2007-11-29T15:12:07Z
publication:nanodocs
publication:dp
publication:nano
Laser bending for adjusting curvatures of hard disk suspensions
Zhang, Xi R
Xu, Xianfan
Article
The purpose of this work is to use 3D finite element analyses to compute bending of a hard disk suspension using a laser. The pitch and roll of the suspension can be precisely adjusted by producing a controlled amount of residual strain using the laser as a heat source. In the computational model, an uncoupled thermo-mechanical analysis is applied to calculate the laser induced thermal loading and mechanical deformation. The relation between suspension bending and laser parameters is studied based on extensive simulations. Bending resolution as high as 0.01 degrees can be achieved. In addition, a data table is established where laser parameters, such as laser power and laser scan length can be found to correct a given pitch and roll of a hard disk suspension. Effects of uncertainties, such as sample thickness and material yield strength are also studied.
2005-10-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/53
oai:docs.lib.purdue.edu:nanodocs-1056
2007-11-29T16:05:44Z
publication:nanodocs
publication:dp
publication:nano
Remotely adjustable check-valves with an electrochemical release mechanism for implantable biomedical microsystems
Pan, Tingrui
Baldi, Antonio
Ziaie, Babak
Article
In this paper, we present two remotely adjustable check-valves with an electrochemical release mechanism for implantable biomedical microsystems. These valves allow one to vary the opening pressure set-point and flow resistance over a period of time. The first design consists of a micromachined check-valve array using a SU-8 polymer structural layer deposited on the top of a gold sacrificial layer. The second design is based on a variable length cantilever beam structure with a gold sacrificial layer. The adjustable cantilever-beam structure is fabricated by gold thermo-compression bond of a thin silicon wafer over a glass substrate. In both designs, the evaporated gold can be electrochemically dissolved using a constant DC current via a telemetry link. In the first design the dissolution simply opens up individual outlets, while in the second design, gold anchors are sequentially dissolved hence increasing the effective length of the cantilever beam (reducing the opening pressure). A current density of 35 mA/cm(2) is used to dissolve the gold sacrificial layers. Both gravity and syringe-pump driven flow are used to characterize the valve performance. A multi-stage fluidic performance (e.g. flow resistance and opening pressure) is clearly demonstrated.
2007-06-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/55
oai:docs.lib.purdue.edu:nanodocs-1058
2007-11-29T16:31:25Z
publication:nanodocs
publication:dp
publication:nano
A wideband PVDF-on-silicon ultrasonic transducer array with microspheres embedded low melting temperature alloy backing
Kim, Hyun-Joong
Lee, Hanwoo
Ziaie, Babak
Article
A PVDF-based 8-element ultrasound transducer array (1 mm x 1 mm element size with an inter-element spacing of 1 mm) on a silicon carrier substrate is fabricated and characterized. To improve the performance of the transducer, new CMOS-compatible fabrication technologies are introduced. These include: (1) adhesive micro-contact printing on non-radiating areas, and (2) glass microspheres (7-20 mu m in diameter) embedded low melting temperature alloy (LMA) for backside electrical connection. The first improvement removes the adverse effects of adhesive layer (e.g., lower sensitivity) between the PVDF and backside contact while the second one improves the pulse-echo signal quality by eliminating reflections at the backing/water interface. The fabricated array elements are tested in a water tank and their pulse-echo response are recorded. The central frequency of each element is 25 MHz with a 100% measured 6-dB bandwidth (60% 3-dB bandwidth).
2007-02-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/57
oai:docs.lib.purdue.edu:nanodocs-1059
2007-11-29T16:54:26Z
publication:nanodocs
publication:dp
publication:nano
A magnetically driven PDMS micropump with ball check-valves
Pan, Tingrui
McDonald, Scott J
Kai, Eleanor M
Ziaie, Babak
Article
In this paper, we present a low-cost, PDMS-membrane micropump with two one-way ball check-valves for lab-on-a-chip and microfluidic applications. The micropump consists of two functional PDMS layers, one holding the ball check-valves and an actuating chamber, and the other covering the chamber and holding a miniature permanent magnet on top for actuation. An additional PDMS layer is used to cover the top magnet, and thereby encapsulate the entire device. A simple approach was used to assemble a high-performance ball check-valve using a micropipette and heat shrink tubing. The micropump can be driven by an external magnetic force provided by another permanent magnet or an integrated coil. In the first driving scheme, a small do motor (6 mm in diameter and 15 mm in length) with a neodymium-iron-boron permanent magnet embedded in its shaft was used to actuate the membrane-mounted magnet. This driving method yielded a large pumping rate with very low power consumption. A maximum pumping rate of 774 μ L min(-1) for deionized water was achieved at the input power of 13 mW, the highest pumping rate reported in the literature for micropumps at such power consumptions. Alternatively, we actuated the micropump with a 10-turn planar coil fabricated on a PC board. This method resulted in a higher pumping rate of 1 mL min(-1) for deionized water. Although more integratable and compact, the planar microcoil driving technique has a much higher power consumption.
2005-05-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/58
oai:docs.lib.purdue.edu:nanodocs-1060
2008-01-04T14:38:09Z
publication:nanodocs
publication:dp
publication:nano
Comparative three-dimensional imaging of living neurons with confocal and atomic force microscopy
McNally, Helen
Rajwa, Bartek
Sturgis, Jennifer
Robinson, J. Paul
Article
Atomic force microscopy applications extend across a number of fields; however, limitations have reduced its effectiveness in live cell
analysis. This report discusses the use of AFM to evaluate the three-dimensional (3-D) architecture of living chick dorsal root ganglia and
sympathetic ganglia. These data sets were compared to similar images acquired with confocal laser scanning microscopy of identical cells.
For this comparison we made use of visualization techniques which were applicable to both sets of data and identified several issues when
coupling these technologies. These direct comparisons offer quantitative validation and confirmation of the character of novel images acquired
by AFM. This paper is one in a series emphasizing various new applications of AFM in neurobiology.
confocal
atomic force microscopy
neurons
2005-01-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/59
oai:docs.lib.purdue.edu:nanodocs-1061
2008-01-04T16:47:31Z
publication:nanodocs
publication:dp
publication:nano
Chemical kinetic considerations for postflame synthesis of carbon nanotubes in premixed flames using a support catalyst
Gopinath, Prarthana
Gore, Jay P.
Article
Multiwalled carbon nanotubes (MWCNTs) on a grid supported cobalt nanocatalyst were grown, by exposing it
to combustion gases from ethylene/air rich premixed flames. Ten equivalence ratios (φ) were investigated, as follows:
1.37, 1.44, 1.47, 1.50, 1.55, 1.57, 1.62, 1.75, 1.82, and 1.91. MWCNT growth could be observed for the range
of equivalence ratios between 1.45 and 1.75, with the best yield restricted to the range 1.5–1.6. A one-dimensional
premixed flame code with a postflame heat loss model, including detailed chemistry, was used to estimate the gas
phase chemical composition that favorsMWCNT growth. The results of the calculations show that the mixture, including
the water gas shift reaction, is not even in partial chemical equilibrium. Therefore, past discussions of compositional
parameters that relate to optimum carbon nanotube (CNT) growth are revised to include chemical kinetic
effects. Specifically, rapid departures of the water gas shift reaction from partial equilibrium and changes in mole
fraction ratios of unburned C2 hydrocarbons to hydrogen correlate well with experimentally observed CNT yields.
2007-08-31T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/60
oai:docs.lib.purdue.edu:nanodocs-1062
2008-01-11T14:34:40Z
publication:nanodocs
publication:dp
publication:nano
Nanofabrication of double-gyroid thin films
Urade, Vikrant
Wei, Ta-Chen
Tate, Michael P
Kowalski, Jonathan
Hillhouse, Hugh
Article
http://pubs.acs.org/cgi-bin/article.cgi/cmatex/2007/19/i04/pdf/cm062136n.pdf
Nanoporous silica films with the double-gyroid structure offer tremendous technological potential for sensors and separations because of their high surface area and potentially facile transport properties. Further, metals and semiconductors with similar structure open up new opportunities for high-surface-area electrodes, photoelectrochemical devices, photovoltaics, and thermoelectrics. Here, we report a new robust synthesis of highly ordered nanoporous silica films with the double-gyroid structure by evaporation-induced self-assembly (EISA) at room temperature and laboratory humidity using a commercially available EO17-PO12-C-14 surfactant. The continuous nanoporous films are synthesized on conducting electrodes. Electrochemical impedance spectroscopy is then used to quantitatively measure the accessible surface area of the underlying electrode via transport through the pore system. It is found that the double-gyroid-structure silica films expose a much higher fraction of the electrode than other commonly synthesized nanostructures such as 2D centered rectangular or 3D rhombohedral nanostructures. The double-gyroid nanoporous-film-coated electrodes are then used to fabricate inverse double-gyroid platinum nanostructures by electrodeposition, followed by etching to remove the silica. The structure of both the nanoporous silica films and the nanoporous platinum films (after etching) have been elucidated using high-resolution field-emission scanning electron microscopy (FESEM), comparing measured and simulated 2D grazing angle-of-incidence small-angle X-ray scattering (GISAXS) patterns, and comparing observed and simulated transmission electron microscopy (TEM) images. Both films are highly (211) oriented and described by a cubic Ia (3) over bard space group that has undergone uniaxial contraction perpendicular to the substrate. Upon this contraction, Ia (3) over bard symmetry is broken, but the films retain the double-gyroid topology. The nanoporous silica and the platinum nanowires have a characteristic wall or wire thicknesses of approximately 3 nm. This nanofabrication process opens up a facile general route for fabrication of ordered structures on the sub-5 nm length scale.
2007-02-20T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/61
oai:docs.lib.purdue.edu:nanodocs-1064
2008-01-11T14:55:41Z
publication:nanodocs
publication:dp
publication:nano
Rhombohedral structure of highly ordered and oriented self-assembled nanoporous silica thin films
Eggiman, Brian W
Tate, Michael P
Hillhouse, Hugh
Article
http://pubs.acs.org/cgi-bin/article.cgi/cmatex/2006/18/i03/pdf/cm0520766.pdf
Nanoporous silica films have been synthesized by self-assembly on substrates by dip-coating from a combined solution of aged silica oligomers and poly(ethylene oxide)(20)-poly(propylene oxide)(70)-poly(ethylene oxides)(20) triblock copolymer (Pluronic P123) in ethanol and water. The films are indexed with the rhombohedral space group R3m and are oriented through the thickness of the film with the (111) axis perpendicular to the substrate. Sixfold symmetry perpendicular to the substrate is directly observed by high-resolution top-view field emission scanning electron microscopy over the entire substrate. The films have domains that sample many orientations in the plane of the substrate resulting in a reciprocal space composed of rings. These rings are directly observed by collecting small-angle X-ray scattering data at many angles of incidence from transmission (beam perpendicular to the substrate) all the way down to the grazing angle of incidence. At each rotation, the Bragg spot location in the two-dimensional pattern is quantitatively predicted by an Rim unit cell with lattice constants a = 112 angstrom and alpha = 86 degrees. On the basis of these lattice constants, it is conjectured that the rhombohedral structure results from a uniaxial contraction of a (111) oriented film of self-assembled aggregates ordered on a face-centered cubic lattice. The film structure and orientation reported here differ from previous reports of cubic, or distorted cubic, nanoporous films synthesized with P123 and F127 and are expected to be important steps in controlling structure and accessibility in nanoporous films.
2006-02-07T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/63
oai:docs.lib.purdue.edu:nanodocs-1065
2008-01-11T15:01:46Z
publication:nanodocs
publication:dp
publication:nano
Simulation and interpretation of 2D diffraction patterns from self-assembled nanostructured films at arbitrary angles of incidence: From grazing incidence (above the critical angle) to transmission perpendicular to the substrate
Tate, Michael P
Urade, Vikrant
Kowalski, Jonathan
Wei, Ta-Chen
Hamilton, Benjamin D
Eggiman, Brian
Hillhouse, Hugh
Article
http://pubs.acs.org/cgi-bin/article.cgi/jpcbfk/2006/110/i20/pdf/jp0566008.pdf
A method to calculate the location of all Bragg diffraction peaks from nanostructured thin films for arbitrary angles of incidence from just above the critical angle to transmission perpendicular to the film is reported. At grazing angles, the positions are calculated using the distorted wave Born approximation (DWBA), whereas for larger angles where the diffracted beams are transmitted though the substrate, the Born approximation ( BA) is used. This method has been incorporated into simulation code ( called NANOCELL) and may be used to overlay simulated spot patterns directly onto two-dimensional (2D) grazing angle of incidence small-angle X-ray scattering (GISAXS) patterns and 2D SAXS patterns. The GISAXS simulations are limited to the case where the angle of incidence is greater than the critical angle (alpha(i) > alpha(c)) and the diffraction occurs above the critical angle (alpha(f) > alpha(c)). For cases of surfactant self-assembled films, the limitations are not restrictive because, typically, the critical angle is around 0.2 degrees but the largest d spacings occur around 0.8 degrees 2 theta. For these materials, one finds that the DWBA predicts that the spot positions from the transmitted main beam deviate only slightly from the BA and only for diffraction peaks close the critical angle. Additional diffraction peaks from the reflected main beam are observed in GISAXS geometry but are much less intense. Using these simulations, 2D spot patterns may be used to identify space group, identify the orientation, and quantitatively fit the lattice constants for SAXS data from any angle of incidence. Characteristic patterns for 2D GISAXS and 2D low-angle transmission SAXS patterns are generated for the most common thin film structures, and as a result, GISAXS and SAXS patterns that were previously difficult to interpret are now relatively straightforward. The simulation code (NANOCELL) is written in Mathematica and is available from the author upon request.
2006-05-25T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/64
oai:docs.lib.purdue.edu:nanodocs-1066
2008-01-11T15:04:28Z
publication:nanodocs
publication:dp
publication:nano
Ion transport in the microporous titanosilicate ETS-10
Wei, Ta-Chen
Hillhouse, Hugh
Article
http://pubs.acs.org/cgi-bin/article.cgi/jpcbfk/2006/110/i28/pdf/jp061037u.pdf
Impedance spectroscopy was used to investigate ion transport in the microporous crystalline framework titanosilicate ETS-10 in the frequency range from 1 Hz to 10 MHz. These data were compared to measured data from the microporous aluminosilicate zeolite X. Na-ETS-10 was found to have a lower activation energy for ion conduction than that of NaX, 58.5 kJ/mol compared to 66.8 kJ/mol. However, the dc conductivity and ion hopping rate for Na-ETS-10 were also lower than NaX. This was found to be due to the smaller entropy contribution in Na-ETS-10 because of its high cation site occupancy. This was verified by ion exchanging Na+ with Cu2+ in both microporous frameworks. This exchange decreases the cation site occupancy and reduces correlation effects. The exchanged Cu-ETS-10 was found to have both lower activation energy and higher ionic conductivity than CuX. Zeolite X has the highest ion conductivity among the zeolites, and thus the data shown here indicate that ETS-10 has more facile transport of higher valence cations which may be important for ion-exchange, environmental remediation of radionucleotides, and nanofabrication.
2006-07-20T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/65
oai:docs.lib.purdue.edu:nanodocs-1069
2008-01-11T15:10:52Z
publication:nanodocs
publication:dp
publication:nano
Synthesis of thermally stable highly ordered nanoporous tin oxide thin films with a 3D face-centered orthorhombic nanostructure
Urade, Vikrant
Hillhouse, Hugh
Article
http://pubs.acs.org/cgi-bin/article.cgi/jpcbfk/2005/109/i21/pdf/jp051229+.pdf
Thin films of nanoporous tin oxide with a 3D face-centered orthorhombic nanostructure have been synthesized by self-assembly that is controlled by post-coating thermal treatment under controlled humidity. In contrast to the conventional evaporation-induced self-assembly (EISA), the films here have no ordered nanostructure after dip-coating. However, the initial coatings are formed under conditions that inhibit significant hydrolysis and condensation for extended periods. This allows the use of postsynthesis thermal vapor treatments to completely control the formation of the nanostructure. With EO106-PO70-EO106 (Pluronic F127) triblock copolymer as the template, highly ordered nanostructures were generated by exposing the disordered films to a stream of water vapor at elevated temperature, which rehydrates the films and allows the formation of the thermodynamically favored phase. Further exposure to water vapor drives the condensation reaction through the elimination of HCl. The X-ray diffraction pattern from the nanostructure was indexed in the space group Fmmm as determined by analysis of 2D small-angle X-ray scattering patterns at various angles of incidence. The nanostructure is then stabilized and made nanoporous by extended controlled thermal treatments. After self-assembly and template removal, the films are thermally stable up to 600 degrees C and retain an ordered, face-centered orthorhombic nanostructure.
2005-06-02T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/68
oai:docs.lib.purdue.edu:nanodocs-1063
2008-01-11T14:49:14Z
publication:nanodocs
publication:dp
publication:nano
Order and orientation control of mesoporous silica films on conducting gold substrates formed by dip-coating and self-assembly: A grazing angle of incidence small-angle X-ray scattering and field emission scanning electron microscopy study
Tate, Michael P
Eggiman, Brian W.
Kowalski, Jonathan
Hillhouse, Hugh
Article
http://pubs.acs.org/cgi-bin/article.cgi/langd5/2005/21/i22/pdf/la050595h.pdf
Grazing-angle of incidence small-angle X-ray scattering (GISAXS) and high-resolution field emission scanning electron microscopy have been used to characterize the mesophase symmetry, orientation, and long-range order in PEO20-PPO70-PEO20 (Pluronic P123) templated mesoporous silica thin films on conducting gold substrates as a function of silica-to-ethylene oxide (Si/EO) block ratio and relative humidity (RH). The films are formed by dip-coating followed by evaporation-induced self-assembly under tightly controlled RH. The general evolution of the mesophase follows the trends that are expected based on shape factors due to swelling of the PEO block. However, changes in orientation of the nanostructure relative to the substrate and the degree of long-range order are found to depend on Si/EO ratio. These effects are likely due to the dynamics of evaporation and self-assembly. Generally, at Si/EO ratios lower than 3.29, the films contained regions where the nanostructure was not oriented relative to the plane of the substrate. However, for Si/EO ratios greater than 3.62, conditions were found where the nanostructure of the film was highly oriented relative to the plane of the substrate. This is true over the range of RH studied, independent of the nanostructure symmetry. For low Si/EO ratios at the highest RH levels, the films were composed of a mixture of spherical and cylindrical pores. At high Si/EO ratios and high RH levels, the films had a highly oriented R-3m nanostructure but displayed streaking perpendicular to the substrate in the Bragg spots on GISAXS patterns. This streaking is interpreted as faulting along planes parallel to the substrate.
2005-10-25T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/62
oai:docs.lib.purdue.edu:nanodocs-1067
2008-01-11T15:06:15Z
publication:nanodocs
publication:dp
publication:nano
General method for simulation of 2D GISAXS intensities for any nanostructured film using discrete Fourier transforms
Tate, Michael P
Hillhouse, Hugh
Article
http://pubs.acs.org/cgi-bin/article.cgi/jpccck/2007/111/i21/pdf/jp066111n.pdf
A fast, flexible 2D GISAXS simulation method based on the distorted-wave Born approximation (DWBA) has been developed for nanostructured thin films using discrete Fourier transforms of a N x N x N matrix that represents the electron density. By expressing the electron density in matrix form, various models of electron density distributions can be easily simulated and compared to experimental data. In addition to modeling the effects of overall symmetry and orientation on the relative intensities of the Bragg peaks, this approach can be used to evaluate specific details of the nanostructure such as pore connectivity, domain size, domain shape, positional disorder, orientation disorder, and polydispersity. These effects are included in a natural way without making a decoupling approximation between structure factor and form factor. The range of reciprocal space simulated is set by the size of the matrix N and the scale factor beta that sets the real-space length of each matrix element, given by 1/(2N beta) < vertical bar s vertical bar < 1/(2 beta). However, the computation time of the 3D transform scales with N as N(3)log(N-3). A matrix with N = 200 and a real-space resolution of beta = 1 nm was sufficient to model the relevant features of self-assembled nanomaterials while remaining computationally inexpensive. Here, we describe the methodology, show simulations for several examples, and compare simulation to experimental 2D GISAXS patterns. Specific examples include simulated 2D GISAXS patterns for 2D hexagonal nanostructures (p6mm) where the pores are perpendicular to the substrate and for (110)-oriented body-centered cubic nanostructures (Im(3) over bar m) based on the level surface approximation of the I-WP surface. For the latter, results show that systematic suppression of Bragg peaks occurs for specific values of the contour level and may be used to identify accessible phases. In addition, we compare simulated patterns to experimental 2D GISAXS synchrotron data for (111)-oriented rhombohedral (R(3) over bar m) nanostructured films. Curved arcs in the experimental data are identified by simulations to result from domain shape effects. Simulations show that the domains in the film are rhombus shaped, where the edges of the domain are co-aligned with the (100) faces of the R(3) over bar m unit cell. The simulation code, entitled NANODIFT, is written in Mathematica and is available upon request.
2007-05-31T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/66
oai:docs.lib.purdue.edu:nanodocs-1068
2008-01-11T15:08:44Z
publication:nanodocs
publication:dp
publication:nano
Controlling interfacial curvature in nanoporous silica films formed by evaporation-induced self-assembly from nonionic surfactants. I. Evolution of nanoscale structures in coating solutions
Bollmann, Luis
Urade, Vikrant
Hillhouse, Hugh
Article
http://pubs.acs.org/cgi-bin/article.cgi/langd5/2007/23/i08/pdf/la0626407.pdf
The double-gyroid phase of nanoporous silica films formed by evaporation-induced self-assembly (EISA) has been shown to possess facile mass-transport properties and may be used as a robust template for the nanofabrication of metal and semiconductor nanostructures. Recently, we developed a new synthesis of double-gyroid nanoporous silica films where the aging time of the coating solution prior to EISA was the key parameter required to control the interfacial curvature that results upon self-assembly of the film. Here, we use Si-29 nuclear magnetic resonance (NMR) and small-angle X-ray scattering (SAXS) to investigate the nanoscale structure of the coating solutions used to obtain double-gyroid nanoporous silica films. NMR and SAXS were carried out on the water, ethanol, silica, and poly(ethylene oxide)-b-poly(propylene oxide)-b-alkyl (EO17-PO12-C-14) surfactant coating solutions as well as similar solutions that excluded either the silica or the surfactant. NMR data reveal that the silica monomers in the coating solution condense very rapidly to form rings and connected ring species. After 1 day of aging, all monomers and dimers have disappeared, and the distribution is dominated by Q(2) and Q(3) species, where the superscript in Q(n) describes the number of silicon atoms in the second coordination shell of the central silicon. Over the course of the next 9 days, the Q(3) population slowly rises at the expense of the Q(2) and Q(3t) populations. Absolute intensity SAXS measurements reveal that the size of the silica clusters increases steadily during this aging period, reaching an average radius of gyration of 9.0 A after 9 days of aging. Longer aging results in the continued growth of clusters with a mass fractal dimension of 1.8. Absolute intensity SAXS data also reveals that micelles are not present in the coating solution. At 9% volume fraction of surfactant, the coating solution is far above the aqueous critical micellar concentration. However, even a small amount of ethanol inhibits micellization. SAXS data also shows that when surfactant is present the radius of gyration is larger but increases more slowly. This indicates that there are weak associative interactions between the silica clusters and surfactant in solution that reduce the cluster-cluster growth rate. In part II of this work, we use the results discovered here to interpret the effects of aging on interfacial curvature in the nanostructured films that self-assemble from these solutions.
2007-04-10T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/67
oai:docs.lib.purdue.edu:nanodocs-1070
2008-01-11T15:12:10Z
publication:nanodocs
publication:dp
publication:nano
Mass transport and electrode accessibility through periodic self-assembled nanoporous silica thin films
Wei, Ta-Chen
Hillhouse, Hugh
Article
http://pubs.acs.org/cgi-bin/article.cgi/langd5/2007/23/i10/pdf/la062699d.pdf
Ordered nanoporous silica films have attracted great interest for their potential use to template nanowires for photovoltaics and thermoelectrics. However, it is crucial to develop films such that an electrode under the nanoporous film is accessible to solution species via facile mass transport through well-defined pores. Here, we quantitatively measure the electrode accessibility and the effective species diffusivity for nearly all the known nanoporous silica film structures formed by evaporation-induced self-assembly upon dip-coating or spin-coating. Grazing-angle of incidence small-angle X-ray scattering was used to verify the nanoscale structure of the films and to ensure that all films were highly ordered and oriented. Electrochemical impedance spectroscopy (EIS) was then used to assess the transport properties. A model has been developed that separates the electrode/film kinetics and the film transport properties from the film/solution interface and bulk solution effects. Accounting for this, the accessible area of the nanoporous film coated FTO electrode (1 - theta) is obtained from the high-frequency data, while the effective diffusivity of the ferrocene dimethanol (D-FDM) redox couple is obtained from intermediate frequencies. It was found that the degree of order and orientation in the film, in addition to the symmetry/topology, is a dominant factor that determines these two key parameters. The EIS data show that the (211) oriented double gyroid, (110) oriented distorted body center cubic, and (211) distorted primitive cubic silica films have significant accessibility (larger than 26% of geometric area). However, the double-gyroid films showed the highest diffusivity by over an order of magnitude. Both the (10) oriented 2D hexagonal and (111) oriented rhombohedral films were found to be highly blocking with only small accessibility due to microporosity. The impedance data were also collected to study the stability of the nanoporous silica films in aqueous solutions as a function of pH. The distorted primitive silica film showed much faster degradation in pH 7 solution when compared to a blocking film such as the 2D hexagonal. However, silica films maintained their structure at pH 2 for at least 12 h.
2007-05-08T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/69
oai:docs.lib.purdue.edu:nanodocs-1071
2008-01-11T15:16:33Z
publication:nanodocs
publication:dp
publication:nano
Controlling interfacial curvature in nanoporous silica films formed by evaporation-induced self-assembly from nonionic surfactants. II. Effect of processing parameters on film structure
Urade, Vikrant
Bollmann, Luis
Kowalski, Jonathan
Tate, Michael P
Hillhouse, Hugh
Article
http://pubs.acs.org/cgi-bin/article.cgi/langd5/2007/23/i08/pdf/la062641z.pdf
The double-gyroid phase of nanoporous silica films has been shown to possess facile mass-transport properties and may be used as a mold to fabricate a variety of highly ordered inverse double-gyroid metal and semiconductor films. This phase exists only over a very small region of the binary phase diagram for most surfactants, and it has been very difficult to synthesize metal oxide films with this structure by evaporation-induced self-assembly (EISA). Here, we show the interplay of the key parameters needed to synthesize these structures reproducibly and show that the interfacial curvature may be systematically controlled. Grazing angle of incidence small-angle X-ray scattering (GISAXS) is used to determine the structure and orientation of nanostructured silica films formed by EISA from dilute silica/(poly(ethylene oxide)-b-poly(propylene oxide)-b-alkyl) surfactant solutions. Four different highly ordered film structures are observed by changing only the concentration of the surfactant, the relative humidity during dip-coating, and the aging time of the solution prior to coating. The highly ordered films progress from rhombohedral (R (3) over barm) to 2D rectangular (c2m) to double-gyroid (distorted Ia (3) over bard) to lamellar systematically as interfacial curvature decreases. Under all experimental conditions investigated, increasing the aging time of the coating solution was found to decrease the interfacial curvature. In particular, this parameter was critical to being able to synthesize highly ordered, pure-phase double-gyroid films. The key role of the aging time is shown via processing diagrams that map out the interplay between the aging time, composition, and relative humidity. Si-29 nuclear magnetic resonance (NMR) spectroscopy and solution-phase small-angle X-ray scattering (SAXS) of the aged coating solutions presented in part I of this series are then used to interpret the effects of aging prior to dip-coating. Specifically, it was found that a predictive model based on volume fractions and the silica cluster stoichiometry obtained from Si-29 NMR qualitatively explains the trends observed with composition and aging. However, apart from the effects of relative humidity, a quantitative comparison of the predicted phase with the experimental processing diagram suggests that less-condensed silica clusters are more effective at swelling the EO blocks at early aging times. This enhanced swelling decreases with aging time and results in lower-curvature nanostructures such as the double-gyroid. The decrease in swelling is attributed to the decreased thermodynamic driving force for the more-condensed silica clusters to mix with the EO block of the surfactant.
2007-04-10T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/70
oai:docs.lib.purdue.edu:nanodocs-1073
2008-04-11T22:26:46Z
publication:nanodocs
publication:dp
publication:nano
Recent Issues in Negative-Bias Temperature Instability: Initial Degradation, Field Dependence of Interface Trap Generation, Hole Trapping Effects, and Relaxation
Islam, Ahmad Ehteshamul
Kufluoglu, Haldun
Varghese, Dhanoop
Mahapatra, Souvik
Alam, Muhammad A.
Article
Recent advances in experimental techniques (on-the-fly and ultrafast techniques) allow measurement of threshold voltage degradation due to negative-bias temperature instability (NBTI) over many decades in timescale. Such measurements over wider temperature range (−25 ◦C to 145 ◦C), film thicknesses (1.2–2.2 nm of effective oxide thickness), and processing conditions (variation of nitrogen within gate dielectric) provide an excellent framework for a theoretical analysis of NBTI degradation. In this paper, we analyze these experiments to refine the existing theory of NBTI to 1) explore the mechanics of time transients of NBTI over many orders of magnitude in time; 2) establish field dependence of interface trap generation to resolve questions regarding the appropriateness of power law versus exponential projection of lifetimes; 3) ascertain the relative contributions to NBTI from interface traps versus hole trapping as a function of processing conditions; and 4) briefly discuss relaxation dynamics for fast-transient NBTI recovery that involves interface traps and trapped holes.
Fast transient recovery
hole–trapping
interface traps
negative-bias temperature instability
reaction–diffusion (R-D) model
2007-09-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/86
oai:docs.lib.purdue.edu:nanodocs-1075
2008-04-11T22:37:59Z
publication:nanodocs
publication:dp
publication:nano
Optimization of Gate Leakage and NBTI for Plasma-Nitrided Gate Oxides by Numerical and Analytical Models
Islam, Ahmad Ehteshamul
Mahapatra, Souvik
Alam, Muhammad A.
Article
Reduction in static-power dissipation (gate leakage) by using nitrided oxides comes at the expense of enhanced negative-bias temperature instability (NBTI). Therefore, determining the nitrogen content in gate oxides that can simultaneously optimize gate-leakage and NBTI degradation is a problem of significant technological relevance. In this paper, we experimentally and theoretically analyze wide range of gate-leakage and NBTI stress data from a variety of plasma-oxynitride gate dielectric devices to establish an optimization scheme for gate-leakage and NBTI degradation. Calculating electric fields and leakage current both numerically and using simple analytical expressions, we demonstrate a design diagram for arbitrary nitrogen concentration
and effective oxide thickness that may be used for process and IC design.
Gate leakage
negative-bias temperature instability
(NBTI)
optimization
plasma-oxynitride dielectric
quantum–mechanical (QM) effects
reaction–diffusion (R-D) model
2008-04-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/84
oai:docs.lib.purdue.edu:nanodocs-1074
2008-04-11T22:32:42Z
publication:nanodocs
publication:dp
publication:nano
Critical analysis of short-term negative bias temperature instability measurements: Explaining the effect of time-zero delay for on-the-fly measurements
Islam, Ahmad Ehteshamul
Kufluoglu, Haldun
Varghese, Dhanoop
Alam, Muhammad A.
Article
Recently several groups have used the reaction-diffusion (R-D) model with H2 diffusion in interpreting negative bias temperature Instability (NBTI) degradation. While the classical “H2 R-D” model can interpret long-term NBTI behavior, it is inconsistent with short-term stress data obtained by recently developed ultrafast measurements and widely used on-the-fly measurements. Moreover, experimental data from various techniques are not consistent with each other. Here, the authors show that the H2 R-D model must be generalized to consistently interpret NBTI at all time scales. The generalized model highlights the previously unappreciated role of time-zero delay in reconciling differences among the so-called delay-free on-the-fly measurements.
Negative Bias Temperature Instability
time exponent
Reaction-Diffusion (R-D) Model
time-zero delay
2007-02-21T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/85
oai:docs.lib.purdue.edu:nanodocs-1077
2008-06-06T22:33:03Z
publication:nanodocs
publication:dp
publication:nano
Influence of Phonon Scattering on the Performance of p-i-n Band-to-Band-Tunneling Transistors
Koswatta, Siyuranga O
Article
APPLIED PHYSICS LETTERS, v. 92, 043125, 2008
Power dissipation has become a major obstacle in performance scaling of modern integrated circuits, and has spurred the search for devices operating at lower voltage swing. In this letter, we study p-i-n band-to-band tunneling field effect transistors (TFET) taking semiconducting carbon nanotubes as the channel material. The on-current of these devices is mainly limited by the tunneling barrier properties, and phonon scattering has only a moderate effect. We show, however, that the off-current is limited by phonon absorption assisted tunneling, and thus is strongly temperature-dependent. Subthreshold swings below the 60mV/decade conventional limit can be readily achieved even at room temperature. Interestingly, although subthreshold swing degrades due to the effects of phonon scattering, it remains low under practical biasing conditions.
2008-06-06T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/82
oai:docs.lib.purdue.edu:nanodocs-1076
2008-06-06T22:26:41Z
publication:nanodocs
publication:dp
publication:nano
Nonequilibrium Green's function treatment of phonon scattering in carbon nanotube transistors
Koswatta, Siyuranga O
Article
IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 54, NO. 9, SEPTEMBER 2007
We present the detailed treatment of dissipative quantum transport in carbon nanotube field-effect transistors (CNTFETs) using the non-equilibrium Green's function formalism. The effect of phonon scattering on the device characteristics of CNTFETs is explored using extensive numerical simulation. Both intra-valley and inter-valley scattering mediated by acoustic (AP), optical (OP), and radial breathing mode (RBM) phonons are treated. Realistic phonon dispersion calculations are performed using force-constant methods, and electron-phonon coupling is determined through microscopic theory. Specific simulation results are presented for (16,0), (19,0), and (22,0) zigzag CNTFETs that are in the experimentally useful diameter range. We find that the effect of phonon scattering on device performance has a distinct bias dependence. Up to moderate gate biases the influence of high-energy OP scattering is suppressed, and the device current is reduced due to elastic back-scattering by AP and low-energy RBM phonons. At large gate biases the current degradation is mainly due to high-energy OP scattering. The influence of both AP and high-energy OP scattering is reduced for larger diameter tubes. The effect of RBM mode, however, is nearly independent of the diameter for the tubes studied here.
Nonequilibrium Green's function
NEGF
carbon nanotube
transistor
phonon scattering
dissipative transport
quantum transport
2008-06-06T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/83
oai:docs.lib.purdue.edu:nanodocs-1078
2008-11-17T16:22:22Z
publication:nanodocs
publication:dp
publication:nano
Field-Effect Transistors with Doped Reservoirs and Realistic Geometry
Fiori, Gianluca
Iannaccone, Giuseppe
Klimeck, Gerhard
Article
The authors would like to make corrections to some results presented in IEEE Trans. Electron Devices, Vol. 53, No. 8, pp. 1782-1733, Aug. 2006.
2008-04-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/81
oai:docs.lib.purdue.edu:nanodocs-1081
2012-07-06T17:39:59Z
publication:nanodocs
publication:dp
publication:nano
Eigenvalue solvers for atomistic simulations of electronic structures with NEMO-3D
Naumov, Maxim
Lee, Sunhee
Haley, Ben
Bae, H.
Clark, Steve
Rahman, Rajib
Ryu, Hoon
Saied, Faisal
Klimeck, Gerhard
Article
<p>The atomistic simulations of electronic structures, using a tight binding model with millions of atoms, require solution of very large sparse Hermitian eigenvalue problems. To obtain the eigenpairs of interest in the interior of the spectrum, we must take advantage of the most efficient parallel numerical algorithms. Several methods have been developed and implemented in Nanoelectronic Modeling software package NEMO-3D, including (P)ARPACK, (Block) Lanczos and Tracemin. In this paper, the performance and tradeoffs of these algorithms for realistic models are discussed. The effectiveness of code optimization techniques such as SSE2 vectorization is also presented.</p>
Lanczos
PARPACK
Tracemin
Eigenvalues
Atomistic
Tight Binding
Quantum dot
NEMO-3D
2008-07-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/78
oai:docs.lib.purdue.edu:nanodocs-1082
2008-11-17T18:50:05Z
publication:nanodocs
publication:dp
publication:nano
Atomistic non-equilibrium Green's function simulations of Graphene nano-ribbons in the quantum hall regime
Golizadeh-Mojarad, Roksana
Zainuddin, Abu Naser M.
Klimeck, Gerhard
Datta, Supriyo
Article
The quantum Hall effect in Graphene nanoribbons (GNR) is investigated with the non-equilibrium Green's function (NEGF) based quantum transport model in the ballistic regime. The nearest neighbor tight-binding model based on pz orbital constructs the device Hamiltonian. GNRs of different edge geometries (Zigzag and Armchair) are considered. The magnetic field is included in both the channels and contact through Peierls substitution. Efficient algorithms for calculating the surface Green function are used to reduce computation time to enable simulating realistically large dimensions comparable to those used in experiments. Hall resistance calculations exactly reproduce the quantum Hall plateaus observed in the experiments. Use of large dimensions in the simulation is crucial in order to capture the quantum Hall effect within experimentally magnetic fields relevant 10-20 T.
Graphene nano-ribbon
Quantum Hall effect
Surface Green function
NEGF
2008-07-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/77
oai:docs.lib.purdue.edu:nanodocs-1080
2008-11-17T17:01:18Z
publication:nanodocs
publication:dp
publication:nano
Multiband transmission calculations for nanowires using an optimized renormalization method
Boykin, Timothy B.
Luisier, Mathieu
Klimeck, Gerhard
Article
The discovery of an interesting nanostructure behavior or the design of useful nanodevices requires state-of-the-art physical models. Realistic, multiband nanowire calculations especially tend to be computationally intensive and slow. Here, we develop optimizations to the renormalization method of Grosso et al. [Phys. Rev. B 40, 12328 (1989)] specifically for nanowires with [100]- or [111]-oriented axes. For no-spin-orbit models, our optimizations give far superior performance to other available methods, while for spin-orbit models on a single processor, our results are at least as good as the best alternative. More importantly, th parallel scalability of our optimizations is superior to that of other available methods, making optimized renormalization very attractive for multiple-processor computers. We demonstrate the method with calculations for Si nanowires.
2008-11-16T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/79
oai:docs.lib.purdue.edu:nanodocs-1079
2008-11-17T16:47:27Z
publication:nanodocs
publication:dp
publication:nano
nanoHUB.org: Advancing Education and Research in Nanotechnology
Klimeck, Gerhard
McLennan, Michael
Brophy, Sean B.
Adams, George B., III
Lundstrom, Mark S.
Article
Through he Network for Computational Nanotechnology Web site, nanoHUB.org, tens of thousands of users from 172 countries collaborate, share resources, and solve real nanotechnology problems. The authors share their experiences in developing and using the site's unique cyberinfrastructure.
2008-10-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/80
oai:docs.lib.purdue.edu:nanodocs-1083
2008-11-17T19:09:09Z
publication:nanodocs
publication:dp
publication:nano
Electronic structure and transmission characteristics of SiGe nanowires
Kharche, Neerav
Luisier, Mathieu
Boykin, Timothy B.
Klimeck, Gerhard
Article
Atomistic disorder such as alloy disorder, surface roughness and inhomogeneous strain are known to influence electronic structure and charge transport. Scaling of device dimensions to the nanometer regime enhances the effects of disorder on device characteristics and the need for atomistic modeling arises. In this work SiGe alloy nanowires are studied from two different points of view: (1) Electronic structure where the bandstructure of a nanowire is obtained by projecting out small cell bands from a supercell eigen-spectrum and (2) Transport where the transmission coefficient thrugh the nanowire is computed using an atomistic wave function approach. The nearest neighbor sp3d5s* semi-empirical tight-binding model is employed for both electronic structure and transport. The connection between dispersions and transmission coefficients of SiGe random alloy nanowires of different sizes is highlighted. Localization is observed in thin disordered wires and a transition to bulk-like behavior is observed with increasing wire diameter.
Nanowires
SiGe
Brillouin zone-unfolding
Open boundary conditions
NEGF
2008-11-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/76
oai:docs.lib.purdue.edu:nanodocs-1085
2008-11-17T19:43:11Z
publication:nanodocs
publication:dp
publication:nano
NEMO-3D based atomistic simulation of a double quantum dot structure for spin-blockaded transport
Muralidharan, Bhaskaran
Ryu, Hoon
Huang, Zhen
Klimeck, Gerhard
Article
This work combines an atomistic electronic structure calculation with many-body rate equations to simulate the current-voltage (I–V) characteristics of a weakly coupled Double Quantum Dot (DQD) system in the spin-blockade regime. Here we performed a NEMO-3D based, atomistic simulation of the geometry of the DQD to obtain its single electron eigen-states, hopping parameters, and
Coulomb integrals followed by the evaluation of I–V characteristics with the many-electron spectrum of the DQD
system, derived from this single-electron parameter set.
The many-electron spectra and wave-functions are evaluated by exact-diagonalization of the many-electron system. The Hamiltonian is constructed from single electron eigenstates,
hopping parameters and Coulomb integrals derived from atomistic NEMO 3-D simulations. Calculated I–V characteristics exhibit multiple regions of prominent Negative Differential Resistances (NDRs) that resemble the experimental trends. Unlike resonant tunnelling devices, however, level crossings in DQDs are negligible, and the NDRs result from a delicate interplay of delocalization, orbital offset and Coulomb interaction.
Double quantum dots
NEMO-3D
Spin blockade
2008-07-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/74
oai:docs.lib.purdue.edu:nanodocs-1084
2008-11-17T19:17:42Z
publication:nanodocs
publication:dp
publication:nano
Simulations of nanowire transistors: atomistic vs. effective mass models
Neophytou, Neophytos
Paul, Abhijeet
Lundstrom, Mark S.
Klimeck, Gerhard
Article
The ballistic performance of electron transport in
nanowire transistors is examined using a 10 orbital sp3d5s*
atomistic tight-binding model for the description of the
electronic structure, and the top-of-the-barrier semiclassical
ballistic model for calculation of the transport properties
of the transistors. The dispersion is self consistently computed
with a 2D Poisson solution for the electrostatic potential
in the cross section of the wire. The effective mass
of the nanowire changes significantly from the bulk value
under strong quantization, and effects such as valley splitting
strongly lift the degeneracies of the valleys. These effects
are pronounced even further under filling of the lattice
with charge. The effective mass approximation is in good
agreement with the tight binding model in terms of current–
voltage characteristics only in certain cases. In general, for
small diameter wires, the effective mass approximation fails.
MOSFET
Nanowire
Dispersion
Tight binding
Ballistic transport
Self-consistency
sp3d5s*
2008-07-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/75
oai:docs.lib.purdue.edu:nanodocs-1086
2008-11-17T19:57:45Z
publication:nanodocs
publication:dp
publication:nano
A Tight-Binding Study of the Ballistic Injection Velocity for Ultrathin-Body SOI MOSFETs
Liu, Yang
Neophytou, Neophytos
Low, Tony
Klimeck, Gerhard
Lundstrom, Mark
Article
This paper examines the validity of the widely used parabolic effective mass approximation by computing the ballistic
injection velocity of a double-gate, ultrathin-body (UTB)
n-MOSFET. The energy dispersion relations for a Si UTB are first
computed by using a 20-band sp3d5 s∗-SO semiempirical atomistic
tight-binding (TB) model coupled with a self-consistent Poisson
solver. A semiclassical ballistic FET model is then used to evaluate the ballistic injection velocity of the n-type UTB MOSFET based on both an TB dispersion relation and parabolic energy bands. In comparison with the TB approach, the parabolic band model with bulk effective masses is found to be reasonably accurate as a first order approximation until down to about 3 nm, where the ballistic injection velocity is significantly over- estimated. Such significant nonparabolicity effects on ballistic injection velocity are observed for various surface/transport orientations. Meanwhile, the injection velocity shows strong dependence on the device structure as the thickness of the UTB changes. Finally, the injection velocity is found to have the same trend as mobility for different surface/transport orientations, indicating a correlation between them.
Band structure
effective mass
injection velocity
MOSFETs
nonparabolicity
pseudopotential (PP)
quantum confinement
tight-binding (TB)
ultrathin-body (UTB)
2008-03-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/73
oai:docs.lib.purdue.edu:nanodocs-1087
2008-11-17T20:43:19Z
publication:nanodocs
publication:dp
publication:nano
High Precision Quantum Control of Single Donor Spins in Silicon
Rahman, Rajib
Wellard, Cameron J.
Bradbury, Forrest R.
Prada, Marta
Cole, Jared H.
Klimeck, Gerhard
Hollenberg, Lloyd C. L.
Article
The Stark shift of the hyperfine coupling constant is investigated for a P donor in Si far below the ionization regime in the presence of interfaces using tight-binding and band minima basis approaches and compared to the recent precision measurements. In contrast with previous effective mass-based results, the quadratic Stark coefficient obtained from both theories agrees closely with the experiments. It is also shown that there is a significant linear Stark effect for an impurity near the interface, whereas, far from the interface, the quadratic Stark effect dominates. This work represents the most sensitive and precise comparison between theory and experiment for single donor spin control. Such precise control of single donor spin states is required particularly in quantum computing applications of single donor electronics, which forms the driving motivation of this work.
2008-07-20T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/72
oai:docs.lib.purdue.edu:nanodocs-1088
2008-11-17T20:51:28Z
publication:nanodocs
publication:dp
publication:nano
Brillouin-zone unfolding of perfect supercells having nonequivalent primitie cells illustrated with a Si/Ge tight-binding parameterization
Boykin, Timothy B.
Kharche, Neerav
Klimeck, Gerhard
Article
Numerical calculations of nanostructure electronic properties are often based on a nonprimitive rectangular unit cell, because the rectangular geometry allows for both highly efficient algorithms and ease of debugging while having no drawback in calculating quantum dot energy levels or the one-dimensional energy bands of
nanowires. Since general nanostructure programs can also handle superlattices, it is natural to apply them to these structures as well, but here problems arise due to the fact that the rectangular unit cell is generally not the primitive cell of the superlattice, so that the resulting E!k" relations must be unfolded to obtain the primitive cell E!k" curves. If all of the primitive cells in the rectangular unit cell are identical, then the unfolding is reasonably straightforward; if not, the problem becomes more difficult. Here, we provide a method for zone
unfolding when the primitive cells in a rectangular cell are not all identical. The method is applied to a Si!4"Ge!4" superlattice using a set of optimized Si and Ge tight-binding strain parameters.
2007-03-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/71
oai:docs.lib.purdue.edu:nanodocs-1091
2008-11-18T15:02:47Z
publication:nanodocs
publication:dp
publication:nano
Band-Structure Effects on the Performance of III-V Ultrathin-Body SOI MOSFETs
Liu, Yang
Neophytou, Neophytos
Klimeck, Gerhard
Lundstrom, Mark S.
Article
This paper examines the impact of band structure on deeply scaled III–V devices by using a self-consistent 20-band sp3d5s∗-SO semiempirical atomistic tight-binding model. The density of states and the ballistic transport for both GaAs and InAs
ultrathin-body n-MOSFETs are calculated and compared with the
commonly used bulk effective mass approximation, including all
the valleys (Γ, X, and L). Our results show that for III–V semiconductors under strong quantum confinement, the conduction
band nonparabolicity affects the confinement effectivemasses and,
therefore, changes the relative importance of different valleys. A parabolic effective mass model with bulk effective masses fails to capture these effects and leads to significant errors, and therefore, a rigorous treatment of the full band structure is required.
Band structure
effective mass
injection velocity
MOSFETs
nonparabolicity
pseudopotential (PP)
quantum confinement
tight-binding (TB)
ultrathin-body (UTB)
2008-05-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/107
oai:docs.lib.purdue.edu:nanodocs-1092
2008-11-18T15:46:10Z
publication:nanodocs
publication:dp
publication:nano
Quantum Transport with Spin Dephasing: A Nonequilibrium Green's Function Approach
Yanik, Ahmet Ali
Klimeck, Gerhard
Datta, Supriyo
Article
A quantum transport model incorporating spin scattering processes is presented using the nonequilibrium Green’s function (NEGF) formalism within the self-consistent Born approximation.
This model offers a unified approach by capturing the spin-flip scattering and the quantum effects simultaneously. A numerical implementation of the model is illustrated for magnetic tunnel junction devices with embedded magnetic impurity layers. The results are compared with experimental data, revealing the underlying physics of the coherent and incoherent transport regimes. It is shown that spin scattering processes are suppressed with increasing barrier heights while small
variations in magnetic impurity spin-states/concentrations could cause large deviations in junction magnetoresistances.
2006-11-22T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/106
oai:docs.lib.purdue.edu:nanodocs-1096
2008-11-18T17:29:51Z
publication:nanodocs
publication:dp
publication:nano
Influence of vacancies on metallic nanotube transport properties
Neophytou, Neophytos
Ahmed, Shaikh
Klimeck, Gerhard
Article
The electronic behavior of metallic carbon nanotubes under the influence of atomistic vacancy defects present in the channel is theoretically investigated using non-equilibrium Green’s function
method self-consistently coupled with three-dimensional electrostatics. A nearest neighbor tight binding model based on a single pz orbital is used for the device Hamiltonian. A single vacancy defect in the channel of a small diameter metallic carbon nanotube can decrease its conductance by a factor of 2. More than one vacancy in the channel can further drastically decrease the conductance. Larger diameter nanotubes suffer less from the presence of vacancy defects.
2007-05-04T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/104
oai:docs.lib.purdue.edu:nanodocs-1095
2008-11-18T17:20:59Z
publication:nanodocs
publication:dp
publication:nano
Evolution time and energy uncertainty
Boykin, Timothy B.
Kharche, Neerav
Klimeck, Gerhard
Article
Often one needs to calculate the evolution time of a state under a Hamiltonian with no explicit time dependence when only numerical methods are available. In cases such as this, the usual application of Fermi’s golden rule and firstorder
perturbation theory is inadequate as well as being computationally inconvenient. Instead, what one needs are conditions under which the evolution time may be obtained from the easily calculated energy uncertainty. This work derives some general conditions for obtaining the evolution time from the energy uncertainty.
2008-11-18T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/105
oai:docs.lib.purdue.edu:nanodocs-1097
2008-11-18T20:38:22Z
publication:nanodocs
publication:dp
publication:nano
Accumulation Gate Capacitance of MOS Devices With Ultrathin High-κ Gate Dielectrics: Modeling and Characterization
Islam, Ahmad Ehteshamul
Haque, Anisul
Article
A quantum–mechanical (QM) model is presented for
accumulation gate capacitance of MOS structures with high-κ
gate dielectrics. The model incorporates effects due to penetration of wave functions of accumulation carriers into the gate dielectric. Excellent agreement is obtained between simulation and experimental C–V data. It is found that the slope of the C–V curves in weak and moderate accumulation as well as gate capacitance in strong accumulation varies from one dielectric material to another. Inclusion of penetration effect is essential to accurately describe this behavior. The physically based calculation shows that the relationship between the accumulation semiconductor capacitance and Si surface potential may be approximated by a linear function in moderate accumulation. Using this relationship, a simple technique to extract dielectric capacitance for high-κ gate dielectrics is proposed. The accuracy of the technique is verified by successfully applying the method to a number of different
simulated and experimental C–V characteristics. The proposed
technique is also compared with another method available in the
literature. The improvements made in the proposed technique by
properly incorporating QM and other physical effects are clearly
demonstrated.
High-? dielectric
MOS capacitors
parameter extraction
quantum–mechanical (QM) modeling
2006-06-06T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/103
oai:docs.lib.purdue.edu:nanodocs-1098
2008-11-21T16:23:31Z
publication:nanodocs
publication:dp
publication:nano
Quantum Simulations of Dual Gate MOSFET Devices: Building and Deploying Community Nanotechnology Software Tools on nanoHUB.org
Ahmed, Shaikh
Klimeck, Gerhard
Kearney, Derrick
McLennan, Michael
Anantram, M. P.
Article
Undesirable short-channel effects associated with the relentless downscaling of conventional CMOS devices have led to the emergence of new classes of MOSFETs. This has led to new and unprecedented challenges in computational nanoelectronics. The device sizes have already reached the level of tens of nanometers where quantum nature of charge-carriers dominates the device operation and performance. The goal of this paper is to describe an on-going initiative on nanoHUB.org to provide new models, algorithms, approaches, and a comprehensive suite of freely-available web-based simulation tools for nanoscale devices with capabilities not yet available commercially. Three software packages nanoFET, nanoMOS and QuaMC are benchmarked in the simulation of a widely-studied high-performance novel MOSFET device. The impact of quantum mechanical effects on the device properties is elucidated and key design issues are suggested.
NanoHUB
MOSFETs
Quantum effects
Online simulation
NEGF
2007-03-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/102
oai:docs.lib.purdue.edu:nanodocs-1099
2008-11-21T18:14:20Z
publication:nanodocs
publication:dp
publication:nano
Valley splitting in strained silicon quantum wells modeled with 2 deg miscuts, step disordere, and alloy disorder
Kharche, Neerav
Prada, Marta
Boykin, Timothy B.
Klimeck, Gerhard
Article
Valley splitting !VS" in strained SiGe/Si/SiGe quantum wells grown on !001" and 2° miscut substrates is computed in a magnetic field. Calculations of flat structures significantly overestimate, while calculations of perfectly ordered structures underestimate experimentally observed VS. Step disorder and confinement alloy disorder raise the VS to the experimentally observed levels. Atomistic alloy disorder is identified as the critical physics, which cannot be modeled with analytical effective mass theory. NEMO-3D is used to simulate up to 106 atoms, where strain is
computed in the valence-force field and electronic structure in the sp3d5s* model.
2008-11-21T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/101
oai:docs.lib.purdue.edu:nanodocs-1101
2008-11-21T19:05:23Z
publication:nanodocs
publication:dp
publication:nano
Transport calculation of semiconductor nanowires coupled to quantum well reservoirs
Luisier, Mathieu
Schenk, Andreas
Fichtner, Wolfgang
Klimeck, Gerhard
Article
Semiconductor nanowires are possible candidates to replace the metal-oxide-semiconductor field-effect transistors (MOSFET) since they can act both as active devices or as device connectors. In this article, the transmission coefficients
of Si and GaAs nanowires with arbitrary transport directions and cross sections are simulated in the nearestneighbor sp3d5s" semi-empirical tight-binding method. The open boundary conditions (OBC) are calculated with a new scattering boundary method where a normal eigenvalue problem of reduced size is solved. Two different types of contacts are studied. In the ideal case, semi-infinite reservoirs (the
source and the drain) that are the prolongation of the device are assumed. In a more realistic configuration, the active nanowire is embedded between two quantum well (QW) reservoirs. The electrical properties of the device are obtained
by a non-equilibrium Green’s function (NEGF) calculation.
Nanowires
Tight-binding method
NEGF
Open boundary conditions
2007-06-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/99
oai:docs.lib.purdue.edu:nanodocs-1100
2008-11-21T18:58:41Z
publication:nanodocs
publication:dp
publication:nano
Computational aspects of the three-dimensional feature-scale simulation of silicon-nanowire field-effect sensors for DNA detection
Heitzinger, Clemens
Klimeck, Gerhard
Article
In recent years DNA-sensors, and generally biosensors, with semiconducting transducers were fabricated and characterized. Although the concept of so-called BioFETs was proposed already two decades ago, its realization has become feasible only recently due to advances in process technology. In this paper a comprehensive and rigorous approach to the simulation of silicon-nanowire DNAFETs at the feature-scale is presented. It allows to investigate the feasibility of single-molecule detectors and is used to elucidate the performance that can be expected from sensors with nanowire diameters in the deca-nanometer range. Finally the computational challenges for the simulation of silicon-nanowire DNA-sensors are discussed.
DNAFET
BioFET
Simulation
Silicon nanowire
2007-06-21T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/100
oai:docs.lib.purdue.edu:nanodocs-1102
2008-11-21T19:27:25Z
publication:nanodocs
publication:dp
publication:nano
Non-equilibrium Green's function (NEGF) simulation of metallic carbon nanotubes including vacancy defects
Neophytou, Neophytos
Ahmed, Shaikh
Klimeck, Gerhard
Article
The electronic behavior of metallic carbon nanotubes under the influence of externally applied electric fields is investigated using the Non-Equilibrium Green’s function method self consistently coupled with three-dimensional (3D) electrostatics. A nearest neighbor tight binding model based on a single pz orbital for constructing the device Hamiltonian is used. The 3D Poisson equation is solved using the Finite Element Method. Carbon nanotubes exhibit a very weak metallic behavior, and external electric fields can alter the electrostatic potential of the tubes significantly. A single vacancy defect in the channel of a metallic carbon nanotube can decrease its conductance by a factor of two. More than one vacancy can further decrease the conductance.
Carbon nanotubes
defects
vacancies
Non-Equilibrium Green's Function
Finite Element Method
2007-06-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/98
oai:docs.lib.purdue.edu:nanodocs-1106
2008-11-21T20:00:45Z
publication:nanodocs
publication:dp
publication:nano
Hub-based Simulation and Graphics Hardware Accelerated Visualization for Nanotechnology Applications
Qiao, Wei
McLennan, Michael
Kennell, Rick
Ebert, David S.
Klimeck, Gerhard
Article
The Network for Computational Nanotechnology (NCN) has developed a science gateway at nanoHUB.org for nanotechnology education and research. Remote users can browse through online seminars and courses, and launch sophisticated nanotechnology simulation tools, all within their web browser. Simulations are supported by a middleware that can route complex jobs to grid supercomputing resources. But what is truly unique about the middleware is the way that it uses hardware accelerated graphics to support both problem setup and result visualization. This paper describes the design and integration of a remote visualization framework into the nanoHUB for interactive visual analytics of nanotechnology simulations. Our services flexibly handle a variety of nanoscience simulations, render them utilizing graphics hardware acceleration in a scalable manner, and deliver them seamlessly through the middleware to the user. Rendering is done only on-demand, as needed, so each graphics hardware unit can simultaneously support many user sessions. Additionally, a novel node distribution scheme further improves our system’s scalability. Our approach is not only efficient but also cost-effective. Only a half-dozen render nodes are anticipated to support hundreds of active tool sessions on the nanoHUB. Moreover, this architecture and visual analytics environment provides capabilities that can serve many areas of
scientific simulation and analysis beyond nanotechnology with its ability to interactively analyze and visualize multivariate scalar and vector fields.
remote visualization
volume visualization
flow visualization
graphics hardware
nanotechnolgy simulation
2006-09-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/94
oai:docs.lib.purdue.edu:nanodocs-1105
2008-11-21T19:49:27Z
publication:nanodocs
publication:dp
publication:nano
The Electronic Structure and Transmission Characteristics of Disordered AlGaAs Nanowires
Boykin, Timothy B.
Luisier, Mathieu
Schenk, Andreas
Kharche, Neerav
Klimeck, Gerhard
Article
Perfect nanowires may be studied from both the bandstructure and transmission perspectives, and relating features in one set of curves to those in another often yields much insight into their behavior. For random-alloy nanowires, however, only
transmission characteristics and virtual-crystal approximation (VCA) bands have been available. This is a serious shortcoming since the VCA cannot properly capture disorder at the primitive cell level: those bulk properties which it can satisfactorily reproduce arise from spatially extended states and measurements which verage out primitive cell-level fluctuations. Here we address this deficiency by projecting approximate bands out of supercell states for Al Ga As random alloy nanowires. The resulting bands correspond to the transmission characteristics very closely, unlike the VCA bands, which cannot explain important transmission features. Using both bandstructure and transmission results, we are better able to explain the operation of these nanowires.
Nanotechnology
quantum effect semiconductor devices
quantum wires
2007-01-01T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/95
oai:docs.lib.purdue.edu:nanodocs-1104
2008-11-21T19:41:28Z
publication:nanodocs
publication:dp
publication:nano
Approximate bandstructures of semiconductor alloys from tight-binding supercell calculations
Boykin, Timothy B.
Kharche, Neerav
Klimeck, Gerhard
Korkusinski, Marek
Article
Alloys such as AlGaAs, InGaAs, and SiGe find widespread usage in nanoelectronic devices such as quantum dots and nanowires. For these devices, in which the carriers probe nanometre-scale local disorder, the commonly employed virtual crystal approximation (VCA) is inadequate. Although the VCA produces small-cell E(k) relations it fails to include local disorder. In contrast, random-alloy supercell calculations do include local disorder but only deliver band extrema and supercell (not small cell) E(k) relations. Small-cell E(k) relations are, however, needed to interpret transport parameters such as effective masses. This work presents a method to extract the necessary approximate small-cell E(k) relations from the disordered supercell states. The method is applied to AlGaAs and gives significantly improved energy gaps versus the VCA, as well as approximate effective masses. The results illuminate the bowing of the !-valley gap and the good agreement with bulk experimental
data shows that this method is well suited for nanodevices.
2007-01-05T08:00:00Z
https://docs.lib.purdue.edu/nanodocs/96
oai:docs.lib.purdue.edu:nanodocs-1103
2008-11-21T19:34:39Z
publication:nanodocs
publication:dp
publication:nano
Energy dispersion relations for holes inn silicon quantum wells and quantum wires
Mitin, Vladimir
Vagidov, Nizami
Luisier, Mathieu
Klimeck, Gerhard
Article
We calculate the energy dispersion relations in Si quantum wells (QW), E(k2D), and quantum wires (QWR), E(k1D), focusing on the regions with negative effective mass
(NEM) in the valence band. The existence of such NEM regions is a necessary condition for the current oscillations in ballistic quasineutral plasma in semiconductor structures. The frequency range of such oscillations can be extended to the terahertz region by scaling down the length of structures. Our analysis shows that silicon is a promising material for prospective NEM-based terahertz wave generators. We also found that comparing to Si QWRs, Si QWs are preferable structures for NEM-based generation in the terahertz range.
Energy dispersion relations
Tight-binding model
Negative effective mass
Quantum well
Quantum wire
2007-06-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/97
oai:docs.lib.purdue.edu:nanodocs-1107
2008-11-25T15:14:42Z
publication:nanodocs
publication:dp
publication:nano
Phonon runaway in carbon nanotube quantum dots
Siddiqui, L
Ghosh, A W
Datta, Supriyo
Article
We explore electronic transport in a nanotube quantum dot strongly coupled with vibrations and weakly with leads and the thermal environment. We show that the recent observation of anomalous conductance signatures in single-walled carbon nanotube quantum dots [B. J. LeRoy , Nature (London) 395, 371 (2004) and B. J. LeRoy , Phys. Rev. B 72, 075413 (2005)] can be understood quantitatively in terms of current driven "hot phonons" that are strongly correlated with electrons. Using rate equations in the many-body configuration space for the joint electron-phonon distribution, we argue that the variations are indicative of strong electron-phonon coupling requiring an analysis beyond the traditional uncorrelated phonon-assisted transport (Tien-Gordon) approach.
2008-08-01T07:00:00Z
https://docs.lib.purdue.edu/nanodocs/93
389231/simple-dublin-core/100//