Copyright (c) 2009 Purdue Libraries All rights reserved. http://docs.lib.purdue.edu/nanopub Recent documents in Birck and NCN Publications en-us Fri, 23 Oct 2009 23:18:18 PDT 3600 http://docs.lib.purdue.edu/nanopub/460 http://docs.lib.purdue.edu/nanopub/460 Thu, 22 Oct 2009 10:00:33 PDT We report on the efficient generation, propagation, and reemission of squeezed long-range surface-plasmon polaritons in a gold waveguide. Squeezed light is used to excite the nonclassical surface-plasmon polaritons, and the reemitted quantum state is fully characterized by complete quantum tomographic reconstruction of the density matrix. We find that the plasmon-assisted transmission of nonclassical light in metallic waveguides can be described by a beam splitter relation. This result is explained theoretically. Alexander Huck http://docs.lib.purdue.edu/nanopub/459 http://docs.lib.purdue.edu/nanopub/459 Thu, 22 Oct 2009 10:00:30 PDT Neuronal growth cones are motile structures located at the end of axons that translate extracellular guidance information into directional movements. Despite the important role of growth cones in neuronal development and regeneration, relatively little is known about the topography and mechanical properties of distinct subcellular growth cone regions under live conditions. In this study, we used the AFM to study the P domain, T zone, and C domain of live Aplysia growth cones. The average height of these regions was calculated from contact mode AFM images to be 183 +/- 33, 690 +/- 274, and 1322 +/- 164 nm, respectively. These findings are consistent with data derived from dynamic mode images of live and contact mode images of fixed growth cones. Nano-indentation measurements indicate that the elastic moduli of the C domain and T zone ruffling region ranged between 3-7 and 7-23 kPa, respectively. The range of the measured elastic modulus of the P domain was 10-40 kPa. High resolution images of the P domain suggest its relatively high elastic modulus results from a dense meshwork of actin filaments in lamellipodia and from actin bundles in the filopodia. The increased mechanical stiffness of the P and T domains is likely important to support and transduce tension that develops during growth cone steering. Xiong Ying http://docs.lib.purdue.edu/nanopub/458 http://docs.lib.purdue.edu/nanopub/458 Thu, 22 Oct 2009 10:00:28 PDT A mask programmable technology to implement RF and microwave integrated circuits using an array of standard 90-nm CMOS transistors is presented. Using this technology, three wideband amplifiers with more than 15-dB forward transmission gain operating in different frequency bands inside a 4-22-GHz range are implemented. The amplifiers achieve high gain-bandwidth products (79-96 GHz) despite their standard multistage designs. These amplifiers are based on an identical transistor array interconnected with application specific coplanar waveguide (CPW) transmission lines and on-chip capacitors and resistors. CPW lines are implemented using a one-metal-layer post-processing technology over a thick Parylene-N (15 mu m) dielectric layer that enables very low loss lines (similar to 0.6 dB/mm at 20 GHz) and high-performance CMOS amplifiers. The proposed integration approach has the potential for implementing cost-efficient and high-performance RF and microwave circuits with a short turnaround time. Laleh Rabieirad http://docs.lib.purdue.edu/nanopub/457 http://docs.lib.purdue.edu/nanopub/457 Wed, 21 Oct 2009 13:36:05 PDT This study examines the heat transfer enhancement attributes of carbon nanotubes (CNTs) applied to the bottom wall of a shallow rectangular micro-channel. Using deionized water as working fluid, experiments were performed with both a bare copper bottom wall and a CNT-coated copper wall. Boiling curves were generated for both walls, aided by high-speed video analysis of interfacial features. CNT arrays promoted earlier, abundant and intense bubble nucleation at low mass velocities, consistent with findings from previous pool boiling studies. However, high mass velocities compromised or eliminated altogether any enhancement in the nucleate boiling region. The enhancement achieved at low mass velocities appears to be the result of deep, near-zero-angle cavities formed by the mesh of CNT arrays. On the other hand, high mass velocities tend to fold the CNTs upon the wall, greatly reducing the depth of the CNT-mesh-induced cavities, and compromising the effectiveness of CNTs at capturing embryos and sustaining the bubble nucleation process. CHF enhancement was also achieved mostly at low mass velocities. It is postulated CNT arrays enhance CHF by increasing the heat transfer area as well as by serving as very high conductivity fins that penetrate into the cooler, bulk liquid flow and take advantage of the liquid subcooling away from the wall. While these mechanisms are prevalent at low velocities, they are both weakened, especially the fin effect, at high mass velocities because of the folding of CNT arrays upon the wall. Vikash Khanikar http://docs.lib.purdue.edu/nanopub/456 http://docs.lib.purdue.edu/nanopub/456 Wed, 21 Oct 2009 13:36:03 PDT The interplay between local mechanical strain energy and lateral frictional forces determines the shape of carbon nanotubes on substrates. In turn, because of its nanometer-size diameter, the shape of a carbon nanotube strongly influences its local electronic, chemical, and mechanical properties. Few, if any, methods exist for resolving the strain energy and static frictional forces along the length of a deformed nanotube supported on a substrate. We present a method using nonlinear elastic rod theory in which we compute the flexural strain energy and static frictional forces along the length of single walled carbon nanotubes (SWCNTs) manipulated into various shapes on a clean SiO2 substrate. Using only high resolution atomic force microscopy images of curved single walled nanotubes, we estimate flexural strain energy distributions on the order of attojoules per nanometer and the static frictional forces between a SWCNT and SiO2 surface to be a minimum of 230 pN nm(-1). Mark Strus http://docs.lib.purdue.edu/nanopub/455 http://docs.lib.purdue.edu/nanopub/455 Wed, 21 Oct 2009 13:36:02 PDT We present a cleanroom-free, simple and low-cost fabrication approach utilizing a laser-cut tape for rapidly patterning slurry-like elastomer composites. A conductive polydimethylsiloxane (PDMS) composite was chosen for demonstration in this paper due to its wide use of sensing and heating in many applications. Two fabrication schemes were developed: embedding in a PDMS matrix and relieving on a PDMS substrate. In both schemes, the patterns were first inscribed on adhesive tape using a CO2 laser. The patterned tape then served as a positive mask when spreading the conductive PDMS over it. The patterns were eventually transferred to a substrate after scraping the excessive composite with a razor blade and then removing the tape. The feature resolution of the technique was about 90-100 mu m primarily determined by the laser beam diameter, the translational speed and the power. The height of the patterned structures was associated with the thickness of the tape, which ranged from 76.1 +/- 4.3 mu m to 168.9 +/- 8.2 mu m in this study. A thicker structure can be achieved by stacking more adhesive tapes. For a practical demonstration, the conductive PDMS was patterned on a PDMS substrate serving as a heating element. The elastomeric microheater was successfully heated to 92 degrees C with a power of 210 +/- 12 mW applied. Han-Sheng Chuang http://docs.lib.purdue.edu/nanopub/454 http://docs.lib.purdue.edu/nanopub/454 Wed, 21 Oct 2009 13:36:00 PDT Templated synthesis of thermoelectric nanowires in porous anodic alumina (PAA) have potential for enhanced performance relative to bulk materials. A significant challenge is the template material, which can serve as a thermal shunt. In this work, an approach for creating a branched PAA template is described. The process utilizes localized self-heating to destabilize the planar anodization front, yielding branched and interconnected pores growing at a rate of 300 mu m/h. The template is selectively etched after electrodeposition of desired materials, yielding self-supporting nanowire arrays with thicknesses up to about 300 mu m, thereby eliminating the thermal shunt through the template. Kalapi G. Biswas http://docs.lib.purdue.edu/nanopub/453 http://docs.lib.purdue.edu/nanopub/453 Wed, 21 Oct 2009 13:35:58 PDT We study the physical origins of phase contrast in dynamic atomic force microscopy (dAFM) in liquids where low-stiffness microcantilever probes are often used for nanoscale imaging of soft biological samples with gentle forces. Under these conditions, we show that the phase contrast derives primarily from a unique energy flow channel that opens up in liquids due to the momentary excitation of higher eigenmodes. Contrary to the common assumption, phase-contrast images in liquids using soft microcantilevers are often maps of short-range conservative interactions, such as local elastic response, rather than tip-sample dissipation. The theory is used to demonstrate variations in local elasticity of purple membrane and bacteriophage phi 29 virions in buffer solutions using the phase- contrast images. John Melcher http://docs.lib.purdue.edu/nanopub/452 http://docs.lib.purdue.edu/nanopub/452 Wed, 21 Oct 2009 13:35:55 PDT One of the most rapidly growing areas of physics and nanotechnology focuses on plasmonic effects on the nanometre scale, with possible applications ranging from sensing and biomedicine to imaging and information technology(1,2). However, the full development of nanoplasmonics is hindered by the lack of devices that can generate coherent plasmonic fields. It has been proposed(3) that in the same way as a laser generates stimulated emission of coherent photons, a 'spaser' could generate stimulated emission of surface plasmons (oscillations of free electrons in metallic nanostructures) in resonating metallic nanostructures adjacent to a gain medium. But attempts to realize a spaser face the challenge of absorption loss in metal, which is particularly strong at optical frequencies. The suggestion(4-6) to compensate loss by optical gain in localized and propagating surface plasmons has been implemented recently(7-10) and even allowed the amplification of propagating surface plasmons in open paths(11). Still, these experiments and the reported enhancement of the stimulated emission of dye molecules in the presence of metallic nanoparticles(12-14) lack the feedback mechanism present in a spaser. Here we show that 44-nm-diameter nanoparticles with a gold core and dye-doped silica shell allow us to completely overcome the loss of localized surface plasmons by gain and realize a spaser. And in accord with the notion that only surface plasmon resonances are capable of squeezing optical frequency oscillations into a nanoscopic cavity to enable a true nanolaser(15-18), we show that outcoupling of surface plasmon oscillations to photonic modes at a wavelength of 531 nm makes our system the smallest nanolaser reported to date-and to our knowledge the first operating at visible wavelengths. We anticipate that now it has been realized experimentally, the spaser will advance our fundamental understanding of nanoplasmonics and the development of practical applications. M A. Noginov http://docs.lib.purdue.edu/nanopub/451 http://docs.lib.purdue.edu/nanopub/451 Wed, 21 Oct 2009 13:35:53 PDT We use molecular dynamics (MD) with the reactive interatomic potential ReaxFF to characterize the local strains of epitaxial Si/Ge/Si nanoscale bars as a function of their width and height. While the longitudinal strain (along the bars length) is independent of geometry, surface relaxation leads to transverse strain relaxation in the Ge section. This strain relaxation increases with increasing height of the Ge section and reduction in its width and is complete (i.e., zero transverse strain) for roughly square cross sections of Ge leading to a uniaxial strain state. Such strain state is desirable in some microelectronics applications. From the MD results, which are in excellent agreement with experiments, we derive a simple model to predict lateral strain as a function of geometry for this class of nanobars. Yumi Park http://docs.lib.purdue.edu/nanopub/450 http://docs.lib.purdue.edu/nanopub/450 Wed, 21 Oct 2009 13:35:51 PDT This paper presents the first complete water-based waveguide absorptive switch from 25-40 GHz integrated with commercially available micropumps. The design exploits the absorptive properties of water in the microwave and millimeter-wave bands along with innovative techniques to achieve an optimized performance in both switching states. Besides its static RF performance, the hot-switching response is also experimentally characterized. Successful hot-switching measurements are presented for power levels of up to 32 and 0.16 W for circulating and noncirculating water, respectively. This is achieved with a circulation rate of only similar to 20 mL min. We also show that this power handling can readily reach 125 and 1250 W if the circulation rate is increased to 30 and 300 mL/min, respectively. In addition, the dynamic scattering matrix under hot-switching conditions is also measured and compared to the cold-switching scattering matrix. Furthermore, critical temperature effects are also studied. In particular, contrary to common wisdom, we show that increased water temperature can result in improved RF isolation with the appropriate waveguide-switching design. Chung-Hao Chen http://docs.lib.purdue.edu/nanopub/449 http://docs.lib.purdue.edu/nanopub/449 Wed, 21 Oct 2009 13:35:49 PDT The topology and geometry of microstructures play a crucial role in determining their heat transfer performance in passive cooling devices such as heat pipes. It is therefore important to characterize microstructures based on their wicking performance, the thermal conduction resistance of the liquid filling the microstructure, and the thin-film characteristics of the liquid meniscus. In the present study, the free-surface shapes of the static liquid meniscus in common microstructures are modeled using SURFACE EVOLVER for zero Bond number. Four well-defined topologies, viz., surfaces with parallel rectangular ribs, horizontal parallel cylinders, vertically aligned cylinders, and spheres (the latter two in both square and hexagonal packing arrangements), are considered. Nondimensional capillary pressure, average distance of the liquid free-surface from solid walls (a measure of the conduction resistance of the liquid), total exposed area, and thin-film area are computed. These performance parameters are presented as functions of the nondimensional geometrical parameters characterizing the microstructures, the volume of the liquid filling the structure, and the contact angle between the liquid and solid. Based on these performance parameters, hexagonally-packed spheres on a surface are identified to be the most efficient microstructure geometry for wicking and thin-film evaporation. The solid-liquid contact angle and the nondimensional liquid volume that yield the best performance are also identified. The optimum liquid level in the wick pore that yields the highest capillary pressure and heat transfer is obtained by analyzing the variation in capillary pressure and heat transfer with liquid level and using an effective thermal resistance model for the wick. Ram Ranjan http://docs.lib.purdue.edu/nanopub/448 http://docs.lib.purdue.edu/nanopub/448 Wed, 21 Oct 2009 13:35:47 PDT The future development of polymer composite materials with nanotubes or nanoscale fibers requires the ability to understand and improve the interfacial bonding at the nanotube-polymer matrix interface. In recent work [Strus MC, Zalamea L, Raman A, Pipes RB, Nguyen CV, Stach EA. Peeling force spectroscopy: exposing the adhesive nanomechanics of one-dimensional nanostructures. Nano Lett 2008;8(2):544-50], it has been shown that a new mode in the Atomic Force Microscope (AFM), peeling force spectroscopy, can be used to understand the adhesive mechanics of carbon nanotubes peeled from a surface. In the present work, we demonstrate how AFM peeling force spectroscopy can be used to distinguish between elastic and interfacial components during a nanoscale peel test, thus enabling the direct measurement of interfacial energy between an individual nanotube or nanofiber and a given material surface. The proposed method provides a convenient experimental framework to quickly screen different combinations of polymers and functionalized nanotubes for optimal interfacial strength. Mark C. Strus http://docs.lib.purdue.edu/nanopub/447 http://docs.lib.purdue.edu/nanopub/447 Wed, 21 Oct 2009 13:35:46 PDT Gallium nitride (GaN) in its stable wurtzite phase has proven its utility in light-emitting diodes and diode lasers as well as high-temperature and high-power electronic devices. In addition to its equilibrium wurtzite phase, GaN exhibits two cubic polymorphs, a zinc-blende phase and a high-pressure rocksalt phase. Here, we report the pseudomorphic stabilization of the high-pressure rocksalt phase of GaN within TiN/GaN multilayers as verified using x-ray diffraction and high-resolution transmission electron microscopy. High-resolution lattice imaging confirmed that the lattice parameter of the rocksalt GaN phase is 0.41 nm. The critical thickness of the GaN film that can be pseudomophically stabilized in rocksalt phase within TiN/GaN superlattices is determined to be less than 2 nm. Vijay Rawat http://docs.lib.purdue.edu/nanopub/446 http://docs.lib.purdue.edu/nanopub/446 Wed, 21 Oct 2009 13:35:44 PDT We employ numerical simulations to show that highly localized, enhanced electromagnetic fields, also known as "hot spots," produced by a periodic array of silver nanoantennas can be spatially translated to the other side of a metal-dielectric composite superlens. The proposed translation of the hot spots enables surface-enhanced optical spectroscopy without the undesirable contact of molecules with metal, and thus it broadens and reinforces the potential applications of sensing based on field-enhanced fluorescence and surface-enhanced Raman scattering. Zhengtong Liu http://docs.lib.purdue.edu/nanopub/445 http://docs.lib.purdue.edu/nanopub/445 Wed, 21 Oct 2009 13:35:42 PDT We demonstrate a thermally tunable optical metamaterial with negative permeability working in the visible range. By covering coupled metallic nanostrips with aligned nematic liquid crystals (NLCs), the magnetic response wavelength of the metamaterial is effectively tuned through control of the ambient temperature, changing the refractive index of LC via phase transitions. By increasing the ambient temperature from 20 to 50 degrees C, the magnetic response wavelength shifts from 650 to 632 nm. Numerical simulations confirm our tests and match the experimental observations well. Shumin Xiao http://docs.lib.purdue.edu/nanopub/444 http://docs.lib.purdue.edu/nanopub/444 Wed, 21 Oct 2009 13:35:40 PDT An efficient technique using hydrazine (N2H4) vapor as an agent for the rapid reduction of high-density layers of catalytic nanoparticles is demonstrated. With as little as 10 mTorr hydrazine bled into a thermal chemical vapor deposition (CVD) apparatus, efficient reduction of metal-oxide catalyst particles is achieved more rapidly than when using atomic hydrogen as the reducing agent. Postreduction catalyst imaging emphasizes the differences in nanoparticle formation under different reduction environments, with the most uniform and compact catalyst size distribution observed following hydrazine exposure. Low-temperature reduction studies suggest that as little as 15 s N2H4 exposure at temperatures of 350 degrees C can yield a reduced catalyst layer preceding the synthesis of dense, aligned arrays of single-walled carbon nanotubes (SWNT) with uniform height. This work demonstrates a simple route toward scalable, vapor transport reduction of metal-oxide catalyst relevant to a number of catalytic applications, including the synthesis and selective synthesis of aligned SWNT arrays. Cary Pint http://docs.lib.purdue.edu/nanopub/443 http://docs.lib.purdue.edu/nanopub/443 Wed, 21 Oct 2009 13:35:38 PDT We have used molecular dynamics to calculate the thermal conductivity of symmetric and asymmetric graphene nanoribbons (GNRs) of several nanometers in size (up to similar to 4 nm wide and similar to 10 nm long). For symmetric nanoribbons, the calculated thermal conductivity (e.g., similar to 2000 W/m-K at 400 K for a 1.5 nm x 5.7 nm zigzag GNR) is on the similar order of magnitude of the experimentally measured value for graphene. We have investigated the effects of edge chirality and found that nanoribbons with zigzag edges have appreciably larger thermal conductivity than nanoribbons with armchair edges. For asymmetric nanoribbons, we have found significant thermal rectification. Among various triangularly shaped GNRs we investigated, the GNR with armchair bottom edge and a vertex angle of 300 gives the maximal thermal rectification. We also studied the effect of defects and found that vacancies and edge roughness in the nanoribbons can significantly decrease the thermal conductivity. However, substantial thermal rectification is observed even in the presence of edge roughness. Jiuning Hu http://docs.lib.purdue.edu/nanopub/442 http://docs.lib.purdue.edu/nanopub/442 Wed, 21 Oct 2009 13:35:36 PDT Vertical single-walled carbon nanotubes (vSWCNTs) are synthesized within highly ordered porous anodic alumina (PAA) templates supported on Si substrates. A process for obtaining thin-film PAA with long-range ordered nanopores is presented in this paper. Each nanopore contains at most one v-SWCNT that is supported by a dielectric and addressed by electrochemically formed Pd nanowire source contacts and evaporated Pd drain contacts. Characteristics of these completely vertical, two-terminal nanotube devices are presented. Control of the v-SWCNT length is demonstrated using a straightforward etching process with lengths of less than 100 nm achieved without the need for complex/expensive lithography. This effective nanoscale length control of highly ordered v-SWCNTs provides a practical basis for the realization of CNT-based nanoelectronics. Aaron D. Franklin http://docs.lib.purdue.edu/nanopub/441 http://docs.lib.purdue.edu/nanopub/441 Wed, 21 Oct 2009 12:38:17 PDT Triple junctions (TJs) are the lines where three grains or grain boundaries meet and become increasingly important in nanocrystalline materials where they have a high areal number density and occupy a significant fraction of the total volume of the material. Surface pits are associated with TJs, just as surface grooves are associated with grain boundaries, and these pits may have particularly deleterious effects on the behaviors of thin films. We evaluate the surface topography associated with TJs in nanocrystalline ZrO2 thin films using thickness mapping images produced by energy-filtered transmission electron microscopy (EFTEM), and compare our results with theoretical predictions. While many of the pits conform to the standard theoretical treatment, some of them exhibit considerably increased depth, possibly indicating that the junctions have line energy. No pits were observed with less than the theoretically predicted depth. Hakkwan Kim http://docs.lib.purdue.edu/nanopub/440 http://docs.lib.purdue.edu/nanopub/440 Wed, 21 Oct 2009 11:28:29 PDT 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 DNAsensors are discussed. Clemens Heitzinger http://docs.lib.purdue.edu/nanopub/439 http://docs.lib.purdue.edu/nanopub/439 Wed, 21 Oct 2009 11:28:27 PDT 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 freelyavailable 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. Shaikh Ahmed http://docs.lib.purdue.edu/nanopub/438 http://docs.lib.purdue.edu/nanopub/438 Wed, 21 Oct 2009 11:28:25 PDT We ana/lyze the performance of a recently reported Ge/Si core/shell nanowire transistor using a semiclassical, ballistic transport model and an sp3d5s* tight-binding treatment of the electronic structure. Comparison of the measured performance of the device with the effects of series resistance removed to the simulated result assuming ballistic transport shows that the experimental device operates between 60 and 85% of the ballistic limit. For this !15 nm diameter Ge nanowire, we also find that 14−18 modes are occupied at room temperature under ON-current conditions with ION/IOFF ) 100. To observe true one-dimensional transport in a 〈110〉Ge nanowire transistor, the nanowire diameter would have to be less than about 5 nm. The methodology described here should prove useful for analyzing and comparing on a common basis nanowire transistors of various materials and structures. Gengchiau Liang http://docs.lib.purdue.edu/nanopub/437 http://docs.lib.purdue.edu/nanopub/437 Wed, 21 Oct 2009 11:28:23 PDT 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 primitivecell 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. Timothy B. Boykin http://docs.lib.purdue.edu/nanopub/436 http://docs.lib.purdue.edu/nanopub/436 Wed, 21 Oct 2009 11:28:21 PDT Bandstructure effects in the electronic transport of strongly quantized silicon nanowire field-effect-transistors (FET) in various transport orientations are examined. A 10-band sp3d5s∗ semiempirical atomistic tight-binding model coupled to a self-consistent Poisson solver is used for the dispersion calculation. A semi-classical, ballistic FET model is used to evaluate the current-voltage characteristics. It is found that the total gate capacitance is degraded from the oxide capacitance value by 30% for wires in all the considered transport orientations ([100], [110], [111]). Different wire directions primarily influence the carrier velocities, which mainly determine the relative performance differences, while the total charge difference is weakly affected. The velocities depend on the effective mass and degeneracy of the dispersions. The [110] and secondly the [100] oriented 3 nm thick nanowires examined, indicate the best ON-current performance compared to [111] wires. The dispersion features are strong functions of quantization. Effects such as valley splitting can lift the degeneracies particularly for wires with cross section sides below 3 nm. The effective masses also change significantly with quantization, and change differently for different transport orientations. For the cases of [100] and [111] wires the masses increase with quantization, however, in the [110] case, the mass decreases. The mass variations can be explained from the non-parabolicities and anisotropies that reside in the first Brillouin zone of silicon. Neophytos Neophytou http://docs.lib.purdue.edu/nanopub/435 http://docs.lib.purdue.edu/nanopub/435 Wed, 21 Oct 2009 11:28:19 PDT The rapid progress in nanofabrication technologies has led to the development of novel devices and structures which could revolutionize many high technology industries. These devices demonstrate new capabilities and functionalities where the quantum nature of charge carriers plays an important role in determining the overall device properties and performance. For device sizes in the range of tens of nanometers, the atomistic granularity of constituent materials cannot be neglected: effects of atomistic strain, surface roughness, unintentional doping, the underlying crystal symmetries, or distortions of the crystal lattice can have a dramatic impact on the device operation and performance. Shaikh Ahmed http://docs.lib.purdue.edu/nanopub/434 http://docs.lib.purdue.edu/nanopub/434 Wed, 21 Oct 2009 11:28:17 PDT The Science Gateways program seeks to provide researchers with easy access to TeraGrid's high-performance computing resources. A look at four successful gateways illustrates the program's goals, challenges, and opportunities. Nancy Wilkins-Diehr http://docs.lib.purdue.edu/nanopub/433 http://docs.lib.purdue.edu/nanopub/433 Wed, 21 Oct 2009 11:28:15 PDT THE NETWORK FOR COMPUTATIONAL NANOTECHNOLOGY (NCN) is a six-university initiative that was established in 2002 to connect those who develop simulation tools with those who use them. The NCN currently addresses three science themes, nanoelectronics, nano-electrical-mechanical systems (NEMS) and nanofluidics, and nanomedicine, but is expanding its coverage into other areas of nanotechnology. The NCN's strategy to serve and engage the nanotechnology community centers on a unique, science gateway, www.nanoHUB.org, offering online simulation services for research, education, and collaboration and a new way to publish research and instructional materials. The NCN's primary goal is to lower barriers for the use of simulations in emerging fields of study. Mark Lundstrom http://docs.lib.purdue.edu/nanopub/432 http://docs.lib.purdue.edu/nanopub/432 Wed, 21 Oct 2009 11:28:13 PDT Low-loss optical communication requires light sources at 1.5μmwavelengths.Experiments showed,without much theoretical guidance, that InAs/GaAs quantum dots (QDs) may be tuned to such wavelengths by adjusting the In fraction in an InxGa1−xAs strain-reducing capping layer. In this paper, systematic multimillion-atom electronic structure calculations explain, qualitatively and quantitatively, for the first time, available experimental data. The nanoelectronic modeling NEMO 3-D simulations treat strain in a 15-million-atom system and electronic structure in a subset of ∼9 million atoms using the experimentally given nominal geometries, and without any further parameter adjustments, the simulations match the nonlinear behavior of experimental data very closely. With the match to experimental data and the availability of internal model quantities, significant insight can be gained through mapping to reduced-order models and their relative importance. We can also demonstrate that starting from simple models has, in the past, led to the wrong conclusions. The critical new insight presented here is that the QD changes its shape. The quantitative simulation agreement with experiment, without any material or geometry parameter adjustment in a general atomistic tool, leads us to believe that the era of nanotechnology computer-aided design is approaching. NEMO3-D will be released on nanoHUB.org, where the community can duplicate and expand on the results presented here through interactive simulations. Muhammad Usman http://docs.lib.purdue.edu/nanopub/431 http://docs.lib.purdue.edu/nanopub/431 Wed, 21 Oct 2009 11:28:11 PDT A 20-band sp3d5s* spin-orbit-coupled, semiempirical, atomistic tight-binding model is used with a semiclassical, ballistic, field effect transistor (FET) model, to examine the ON-current variations to size variations of [110]-oriented PMOS nanowire devices. Infinitely long, uniform, rectangular nanowires of side dimensions from 3 to 12 nm are examined and significantly different behavior in width versus height variations are identified and explained. Design regions are identified, which show minor ON-current variations to significant width variations that might occur due to lack of line width control. Regions which show large ON-current variations to small height variations are also identified. The considerations of the full band model here show that ON-current doubling can be observed in the ON-state at the onset of volume inversion to surface inversion transport caused by structural side size variations. Strain engineering can smooth out or tune such sensitivities to size variations. The cause of variations described is the structural quantization behavior of the nanowires, which provide an additional variation mechanism to any other ON-current variations such as surface roughness, phonon scattering, etc. Neophytos Neophytou http://docs.lib.purdue.edu/nanopub/430 http://docs.lib.purdue.edu/nanopub/430 Wed, 21 Oct 2009 11:28:09 PDT The experimental characterization of gate capacitance in nanoscale devices is challenging. We report an application of the charge-based capacitance measurement (CBCM) technique to measure the gate capacitance of a single-channel nanowire transistor. The measurement results are validated by 3-D electrostatic computations for parasitic estimation and 2-D self-consistent sp3s∗d5 tight-binding computations for intrinsic gate capacitance calculations. The device simulation domains were constructed based on SEM and TEM images of the experimental device. The carefully designed CBCM technique thus emerges as a useful technique formeasuring the capacitance and characterizing the transport in nanoscale devices. Hui Zhao http://docs.lib.purdue.edu/nanopub/429 http://docs.lib.purdue.edu/nanopub/429 Wed, 21 Oct 2009 11:28:07 PDT A solid-state analog of stimulated Raman adiabatic passage can be implemented in a triple-well solid-state system to coherently transport an electron across the wells with exponentially suppressed occupation in the central well at any point of time. Termed coherent-tunneling adiabatic passage CTAP, this method provides a robust way to transfer quantum information encoded in the electronic spin across a chain of quantum dots or donors. Using large-scale atomistic tight-binding simulations involving over 3.5106 atoms, we verify the existence of a CTAP pathway in a realistic solid-state system: gated triple donors in silicon. Realistic gate profiles from commercial tools were combined with tight-binding methods to simulate gate control of the donor to donor tunnel barriers in the presence of crosstalk. As CTAP is an adiabatic protocol, it can be analyzed by solving the time-independent problem at various stages of the pulse justifying the use of time-independent tight-binding methods to this problem. This work also involves the first atomistic treatment to translate the three-state-based quantum-optics type of modeling into a solid-state description beyond the ideal localization assumption. Our results show that a three-donor CTAP transfer, with interdonor spacing of 15 nm can occur on time scales greater than 23 ps, well within experimentally accessible regimes. The method not only provides a tool to guide future CTAP experiments but also illuminates the possibility of system engineering to enhance control and transfer times. Rajib Rahman http://docs.lib.purdue.edu/nanopub/428 http://docs.lib.purdue.edu/nanopub/428 Wed, 21 Oct 2009 11:28:05 PDT Quantum wave function engineering of dopant-based Si nano-structures reveals new physics in the solid-state, and is expected to play a vital role in future nanoelectronics. Central to any fundamental understanding or application is the ability to accurately characterize the deformation of the electron wave functions in these atom-based structures through electromagnetic field control. We present a method for mapping the subtle changes that occur in the electron wave function through the measurement of the hyperfine tensor probed by 29Si impurities. Our results show that detecting the donor electron wave function deformation is possible with resolution at the sub-Bohr radius level. Seung H. Park http://docs.lib.purdue.edu/nanopub/427 http://docs.lib.purdue.edu/nanopub/427 Wed, 21 Oct 2009 11:28:03 PDT The dependence of the g-factors of semiconductor donors on applied electric and magnetic fields is of immense importance in spin based quantum computation and in semiconductor spintronics. The donor g-factor Stark shift is sensitive to the orientation of the electric and magnetic fields and strongly influenced by the band-structure and spin-orbit interactions of the host. Using a multimillion atom tight-binding framework the spin-orbit Stark parameters are computed for donors in multi-valley semiconductors, silicon and germanium. Comparison with limited experimental data shows good agreement for a donor in silicon. Results for gate induced transition from 3D to 2D wave function confinement show that the corresponding g-factor shift in Si is experimentally observable. Rajib Rahman http://docs.lib.purdue.edu/nanopub/426 http://docs.lib.purdue.edu/nanopub/426 Wed, 21 Oct 2009 11:28:01 PDT This work focuses on the determination of the valid device domain for the use of the Top of the barrier (ToB) model to simulate quantum transport in nanowire MOSFETs in the ballistic regime. The presence of a proper Source/Drain barrier in the device is an important criterion for the applicability of the model. Long channel devices can be accurately modeled under low and high drain bias with DIBL adjustment. Abhijeet Paul http://docs.lib.purdue.edu/nanopub/425 http://docs.lib.purdue.edu/nanopub/425 Wed, 21 Oct 2009 11:27:59 PDT The atomistic tight binding simulator NEMO 3-D has previously been validated against the experimental data for quantum dots, wells, and wires in the InGaAlAs and SiGe material systems. Here, we demonstrate our new capability to compute optical matrix elements and transition strengths in tight binding. Systematic multi-million atom electronic structure calculations explore the quantum confined stark shift and the ground state optical transition rate for an electric field in the lateral [100] direction. The simulations treat the strain in a ~15 million atom system and the electronic structure in a subset of ~9 million atoms. The effects of the long range strain, the optical polarization anisotropy, the interface roughness, and the nondegeneracy of the p-states which are missing in continuum methods like effective mass approximation or kp are included. A significant red shift in the emission spectra due to an applied inplane electric field indicating a strong quantum confined stark effect (QSCE) is observed. The ground state optical transition rate rapidly decreases with the increasing electric field magnitude due to reduced spatial overlap of ground electron and hole states. Muhammad Usman http://docs.lib.purdue.edu/nanopub/424 http://docs.lib.purdue.edu/nanopub/424 Wed, 21 Oct 2009 11:27:57 PDT A highly phosphorus δ-doped Si device is modeled with a quantum well with periodic boundary conditions and the semi-empirical spds* tight-binding band model. Its temperaturedependent electronic properties are studied. To account for high doping density with many electrons, a highly parallelized selfconsistent Schrödinger-Poisson solver is used with atomistic representations of multiple impurity ions. The band-structure in equilibrium and the corresponding Fermi-level position are computed for a selective set of temperatures. The result at room temperature is compared with previous studies and the temperature-dependent electronic properties are discussed further in detail with the calculated 3-D self-consistent potential profile. Hoon Ryu http://docs.lib.purdue.edu/nanopub/423 http://docs.lib.purdue.edu/nanopub/423 Wed, 21 Oct 2009 11:27:55 PDT Semiconductor devices are scaled down to the level which constituent materials are no longer considered continuous. To account for atomistic randomness, surface effects and quantum mechanical effects, an atomistic modeling approach needs to be pursued. The Nanoelectronic Modeling Tool (NEMO 3-D) has satisfied the requirement by including emprical sp3s∗ and sp3d5s∗ tight binding models and considering strain to successfully simulate various semiconductor material systems. Computationally, however, NEMO 3-D needs significant improvements to utilize increasing supply of processors. This paper introduces the new modeling tool, OMEN 3-D, and discusses the major computational improvements, the 3-D domain decomposition and the multi-level parallelism. As a featured application, a full 3- D parallelized Schr¨odinger-Poisson solver and its application to calculate the bandstructure of δ doped phosphorus(P) layer in silicon is demonstrated. Impurity bands due to the donor ion potentials are computed. Sunhee Lee http://docs.lib.purdue.edu/nanopub/422 http://docs.lib.purdue.edu/nanopub/422 Wed, 21 Oct 2009 11:27:52 PDT The ABACUS and AQME on-line tools and their associated wiki pages form one-stop shops for educators and students of existing university courses. They are geared towards courses like "introduction to Semiconductor Devices" and "Quantum Mechanics for Engineers". The service is free to anyone and no software installation is required on the user's computer. All simulations, including advanced visualization are performed at a remote computer. The tools have been deployed on nanoHUB.org in August 2008 and haven already been used by over 700 users. This paper describes nanoHUB educational tool user requirements and the motivation for and some details about these new tools. Usage patterns and future planned assessment are discussed. The concepts of "NCN supported" and "Community Supported" tools are discussed. Gerhard Klimeck http://docs.lib.purdue.edu/nanopub/421 http://docs.lib.purdue.edu/nanopub/421 Wed, 21 Oct 2009 11:27:50 PDT Single-walled carbon nanotubes can be classified as either metallic or semiconducting, depending on their conductivity, which is determined by their chirality. Existing synthesis methods cannot controllably grow nanotubes with a specific type of conductivity. By varying the noble gas ambient during thermal annealing of the catalyst, and in combination with oxidative and reductive species, we altered the fraction of tubes with metallic conductivity from one-third of the population to a maximum of 91%. In situ transmission electron microscopy studies reveal that this variation leads to differences in both morphology and coarsening behavior of the nanoparticles that we used to nucleate nanotubes. These catalyst rearrangements demonstrate that there are correlations between catalyst morphology and resulting nanotube electronic structure and indicate that chiral-selective growth may be possible. Avetik R. Harutyunyan http://docs.lib.purdue.edu/nanopub/420 http://docs.lib.purdue.edu/nanopub/420 Wed, 21 Oct 2009 11:27:48 PDT The ability to easily and dynamically control fluid mo- tion as well as manipulate particles in suspension is impor- tant for the development and characterization of a variety of lab-on-a-chip processes. Recently, we have introduced an op- tically induced electrokinetic technique termed rapid electro- kinetic patterning (REP) that can rapidly concentrate, trans- late, and pattern colloids of many different sizes and compositions. We have tested polystyrene, latex, and silica beads in sizes ranging from 49 nm to 3.0 um.1,2 Stuart J. Williams http://docs.lib.purdue.edu/nanopub/419 http://docs.lib.purdue.edu/nanopub/419 Wed, 21 Oct 2009 11:27:46 PDT Graphene is created through thermal decomposition of the Si face of 4H-SiC in high-vacuum. Growth temperature and time are varied independently to gain a better understanding of how surface features and morphology affect graphene formation. Growth mechanisms of graphene are studied by ex situ atomic force microscopy (AFM) and scanning tunneling microscopy (STM). On the route toward a continuous graphene film, various growth features, such as macroscale step bunching, terrace pits, and fingers, are found and analyzed. Topographic and phase AFM analysis demonstrates how surface morphology changes with experimental conditions. Step-bunched terraces and terrace pits show a strong preference for eroding along the {11 (2) over bar0} planes. Data from AFM are corroborated with STM to determine the surface structure of the growth features. It is shown that elevated finger structures are SiC while the depressed interdigitated areas between the fingers are comprised of at least a monolayer of graphene. Graphene formation at the bottom of terrace pits shows a dependence on pit depth. These features lend support for a stoichiometric view of graphene formation based on the number of decomposing SiC bilayers. Michael Bolen http://docs.lib.purdue.edu/nanopub/418 http://docs.lib.purdue.edu/nanopub/418 Wed, 21 Oct 2009 11:27:44 PDT Modified volume Fresnel zone plates (MVFZPs) fabricated with laser direct writing were optimized for higher diffraction efficiencies. The Fresnel radii in each layer of a volume zone plate were iteratively adjusted by a simulation-based direct search optimization. The results show that optimization is effective but depends strongly on the starting diffraction efficiencies determined by the MVFZP parameters. The simulations indicate that the optimized MVFZP can achieve 93% diffraction efficiency. Pornsak Srisungsitthisunti http://docs.lib.purdue.edu/nanopub/417 http://docs.lib.purdue.edu/nanopub/417 Wed, 21 Oct 2009 11:27:42 PDT The current state of information technology accentuates the dichotomy between processing and storage of information, with logical operations carried out by charge-based devices and non-volatile memory based on magnetic materials. The main obstacle for a wider use of magnetic materials for information processing is the lack of efficient control of magnetization. Reorientation of magnetic domains is conventionally carried out by non-local external magnetic fields or by externally polarized currents(1-3). The efficiency of the latter approach is enhanced in materials where ferromagnetism is carrier-mediated(4), because in such materials the control of carrier polarization provides an alternative means for manipulating the orientation of magnetic domains. In some crystalline conductors, the charge current couples to the spins by means of intrinsic spin-orbit interactions, thus generating non-equilibrium electron spin polarization(5-11) tunable by local electric fields. Here, we show that magnetization can be reversibly manipulated by the spin-orbit-induced polarization of carrier spins generated by the injection of unpolarized currents. Specifically, we demonstrate domain rotation and hysteretic switching of magnetization between two orthogonal easy axes in a model ferromagnetic semiconductor. Alexander Chernyshov http://docs.lib.purdue.edu/nanopub/416 http://docs.lib.purdue.edu/nanopub/416 Wed, 21 Oct 2009 11:27:40 PDT Finding the optimal solution to a complex optimisation problem is of great importance in practically all fields of science, technology, technical design and econometrics. We demonstrate that a modified Grover's quantum algorithm can be applied to real problems of finding a global minimum using modest numbers of quantum bits. Calculations of the global minimum of simple test functions and Lennard-Jones clusters have been carried out on a quantum computer simulator using a modified Grover's algorithm. The number of function evaluations N reduced from O(N) in classical simulation to O(N1/2) in quantum simulation. We also show how the Grover's quantum algorithm can be combined with the classical Pivot method for global optimisation to treat larger systems. Jing Zhu http://docs.lib.purdue.edu/nanopub/415 http://docs.lib.purdue.edu/nanopub/415 Wed, 21 Oct 2009 11:27:38 PDT An improved theoretical approach is proposed to predict the dynamic behavior of long, slender and flexible microcantilevers affected by squeeze-film damping at low ambient pressures. Our approach extends recent continuum gas damping models (Veijola 2004 J. Micromech. Microeng. 14 1109-18, Gallis and Torczynski 2004 J. Microelectromech. Syst. 13 653-9), which were originally derived for a rigid oscillating plate near a wall, to flexible microcantilevers for calculating and predicting squeeze-film damping ratios of higher order bending modes at reduced ambient pressures. Theoretical frequency response functions are derived for a flexible microcantilever beam excited both inertially and via external forcing. Experiments performed carefully at controlled gas pressures are used to validate our theoretical approach over five orders of the Knudsen number. In addition, we investigate the relative importance of theoretical assumptions made in the Reynolds-equation-based approach for flexible microelectromechanical systems. Jin Woo Lee http://docs.lib.purdue.edu/nanopub/414 http://docs.lib.purdue.edu/nanopub/414 Wed, 21 Oct 2009 11:27:36 PDT Slender sharp-edged flexible beams such as flapping wings of micro air vehicles (MAVs), piezoelectric fans and insect wings typically oscillate at moderate-to-high values of non-dimensional frequency parameter beta with amplitude as large as their widths resulting in Keulegan-Carpenter (KC) numbers or order one. Their oscillations give rise to aerodynamic damping forces which vary nonlinearly with the oscillation amplitude and frequency; in contrast, at infinitesimal KC numbers the fluid damping coefficient is independent of the oscillation amplitude. In this article, we present experimental results to demonstrate the phenomenon of nonlinear aerodynamic damping in slender sharp-edged beams oscillating in surrounding fluid with amplitudes comparable to their widths. Furthermore, we develop a general theory to predict the amplitude and frequency dependence of aerodynamic damping of these beams by coupling the structural motions to an inviscid incompressible fluid. The fluid-structure interaction model developed here accounts for separation of flow and vortex shedding at sharp edges of the beam, and studies vortex-shedding-induced aerodynamic damping in slender sharp-edged beams for different values of the KC number and the frequency parameter beta. The predictions of the theoretical model agree well with the experimental results obtained after performing experiments with piezoelectric fans under vacuum and ambient conditions. Rahul Bidkar http://docs.lib.purdue.edu/nanopub/413 http://docs.lib.purdue.edu/nanopub/413 Wed, 21 Oct 2009 11:27:34 PDT By adding controlled thicknesses of nickel and gold plating to the conductors of a coaxial transmission line, the magnitude of passive intermodulation produced by the transmission line can be controlled with precision. Theoretical predictions of distortion magnitude as a function of plating thicknesses are presented, along with an experimental validation. These adjustable-magnitude passive intermodulation sources are used to give a fourfold improvement in the bandwidth of techniques presented previously, demonstrating that cancellation can for the first time be achieved in bandwidths needed for cellular systems. Justin Henrie http://docs.lib.purdue.edu/nanopub/412 http://docs.lib.purdue.edu/nanopub/412 Wed, 21 Oct 2009 11:27:32 PDT Multifunctional nanoparticles hold great promise for drug/gene delivery and simultaneous diagnostics and therapeutics ("theragnostics") including use of core materials that provide in vivo imaging and opportunities for externally modulated therapeutic interventions. Multilayered nanoparticles can act as nanomedical systems with on-board molecular programming done through the chemistry of highly specialized layers to accomplish complex and potentially decision-making tasks. The targeting process itself is a multi-step process consisting of initial cell recognition through cell surface receptors, cell entry through the membrane in a manner to prevent undesired alterations of the nanomedical system, re-targeting to the appropriate sub-region of the cell where the therapeutic package can be localized, and potentially control of that therapeutic process through feedback systems using molecular biosensors. This paper describes a bionanoengineering design process in which sophisticated nanomedical platform systems can be designed for diagnosis and treatment of disease. The feasibility of most of these subsystems has been demonstrated, but the full integration of these interacting sub-components remains a challenge for the field. Specific examples of sub-components developed for specific applications are described. Emily Haglund http://docs.lib.purdue.edu/nanopub/411 http://docs.lib.purdue.edu/nanopub/411 Wed, 21 Oct 2009 11:27:30 PDT We demonstrate electrically addressable localized heating in fluid at the dielectric surface of silicon-on-insulator field-effect transistors via radio-frequency Joule heating of mobile ions in the Debye layer. Measurement of fluid temperatures in close vicinity to surfaces poses a challenge due to the localized nature of the temperature profile. To address this, we developed a localized thermometry technique based on the fluorescence decay rate of covalently attached fluorophores to extract the temperature within 2 nm of any oxide surface. We demonstrate precise spatial control of voltage dependent temperature profiles on the transistor surfaces. Our results introduce a new dimension to present sensing systems by enabling dual purpose silicon transistor-heaters that serve both as field effect sensors as well as temperature controllers that could perform localized bio-chemical reactions in Lab on Chip applications. Oguz H. Elibol http://docs.lib.purdue.edu/nanopub/410 http://docs.lib.purdue.edu/nanopub/410 Wed, 21 Oct 2009 11:22:45 PDT This letter presents the observation of stable and reproducible electronic conduction through double stranded (ds) DNA molecules in a nominally dry state. Stable conduction was realized by immobilizing 15 base-pair guanine:cytosine rich dsDNA within gold nanogap junctions, stabilizing the dsDNA with a polycation, and characterizing in nitrogen. In air, the current levels decrease with successive voltage scans likely due to oxidation of the guanine bases under bias. In nitrogen, reproducible current-voltage traces are observed and the current levels at specific bias points are stable with time. The stability allows comprehensive electrical studies and could enable conductance-based DNA sensors. Ajit K. Mahapatro