Controlled Interfacial Adsorption of Aunw Along 1-NM Wide Dipole Arrays on Layered Materials and the Catalysis of Sulfide Oxygenation

Ashlin G Porter, Purdue University

Abstract

Controlling the surface chemistry of 2D materials is critical for the development of next generation applications including nanoelectronics and organic photovoltaics (OPVs). Further, next generation nanoelectronics devices require very specific 2D patterns of conductors and insulators with prescribed connectivity and repeating patterns less than 10 nm. However, both top-down and bottom-up approaches currently used lack the ability to pattern materials with sub 10-nm precision over large scales. Nevertheless, a class of monolayer chemistry offers a way to solve this problem through controlled long-range ordering with superior sub-10 nm patterning resolution. Graphene is most often functionalized noncovalently, which preserves most of its intrinsic properties (i.e., electronic conductivity) and allows spatial modulation of the surface.1–5 Phospholipids such as 1,2- bis(10,12-tricsadiynoyl)-sn-glycero-3-phosphoethanolamine (diyne PE) form lying down lamellar phases on graphene where both the hydrophilic head and hydrophobic tail are exposed to the interface and resemble a repeating cross section of the cell membrane.6,7 Phospholipid is made up of a complex headgroup structure and strong headgroup dipole which allows for a diverse range of chemistry and docking of objects to occur at the nonpolar membrane, these principals are equally as important at the nonpolar interface of 2D materials.8–10 A key component in the development of nanoelectronics is the integration of inorganic nanocrystals such as nanowires into materials at the wafer scale.11Nanocrystals can be integrated into materials through templated growth on to surface of interest as well as through assembly processes (i.e. interfacial adsorption). In this work, I have demonstrated that gold nanowires (AuNWs) can be templated on striped phospholipid monolayers, which have an orientable headgroup dipoles that can order and straighten flexible 2-nm diameter AuNWs with wire lengths of ~1 µm. While AuNWs in solution experience bundling effects due to depletion attraction interactions, wires adsorb to the surface in a well separated fashion with wire-wire distances (e.g. 14 or 21 nm) matching multiples of the PE template pitch. This suggests repulsive interactions between wires upon interaction with dipole arrays on the surface. Although the reaction and templating of AuNWs is completed in a nonpolar environment (cyclohexane), the ordering of wires varies based on the hydration of the PE template in the presence of excess oleylamine, which forms hemicylindrical micelles around the hydrated headgroups protecting the polar environment. Results suggest that PE template experience membrane-mimetic dipole orientation behaviors, which in turn influences the orientation and ordering of objects in a nonpolar environment. Another promising material for bottom-up device applications is MoS2 substrates due to their useful electronic properties.12 However, being able to control the surface chemistry of different materials, like MoS2, is relatively understudied, resulting in very limited examples of MoS2 substrates used in bottom-up approaches for nanoelectronics devices. Diyne PE templates adsorb on to MoS2 in an edge-on conformation in which the alkyl tails stack on top of each other increasing the overall stability of the monolayer.13A decrease in lateral spacing results in high local concentrations of orientable headgroups dipoles along with stacked tails which could affect the interactions and adsorption of inorganic materials (i.e. AuNW) at the interface.

Degree

Ph.D.

Advisors

Claridge, Purdue University.

Subject Area

Chemistry|Electromagnetics|Nanotechnology|Physics|Polymer chemistry

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