Date of Award

Fall 2007

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Micro and Nanoscale Systems

First Advisor

James Palmer

Abstract

A primary goal of semiconductor industry is to improve device performance and capability by downscaling feature size and upscaling packaging density. As optical-lithography, the mainstream technology for microfabrication, is being stretched to its limit, new unconventional fabrication techniques are being explored as alternatives. A "Bottom-up" approach for manufacturing is emerging as an answer to limitations posed by the traditional "Top-down" approach. Nanowires, bearing the potential of being the basic building blocks for such an approach, are gaining tremendous attention in nanoelectronics. Metal nanowires fabricated using DNA as templates have potential for precise control of length, diameter and positioning. However, wires formed by assembly of metal nanostructures were found to have considerably high electrical resistivity. Oxide formation, irregular structure and formation of grain boundaries in metal nanostructure can be attributed to this problem.

This dissertation is an investigation into factors that affect the formation of DNA templated indium nanowires. They could be treated thermally to increase overall electrical conductivity by utilizing the low melting point of the metal. We have used indium(0), (I) and (III) species as precursors to DNA metallization. Indium(0) in the form of nanoparticles was prepared by reducing indium(I) complex to indium(0). A organic complex {[HB(3-phpz)3]In} was synthesized to stabilize otherwise highly air-sensitive indium(I) species derived from cyclopentadine. Indium(III) species in the form of aqueous indium trichloride was also used.

During the interaction studies of indium species with DNA, we found that indium(III) binds to DNA in aqueous medium inducing conformal changes and considerable coiling and condensation of DNA molecules, making it unsuitable for nanowire preparation. Indium nanoparticles did not selectively deposit on DNA, indicating that indium(0) has no specific affinity towards DNA molecules. However, reduction of {[HB(3-phpz)3]In} using sodium in the presence of DNA shows successful metallization of DNA. Even though laterally stretched wires with uniform diameter were not formed, selective deposition of indium metal on DNA, forming random network of metallized DNA bundles with diameters between 20-100 nm was accomplished. Preliminary investigation on electrical resistivity indicates that heat treatment of the nanowires reduces the resistivity of these wires by a factor of five.

In the future, it will be possible to assemble nanowires with better orientation, higher uniformity and lower diameters by applying the knowledge gained during this study to already existing techniques of DNA templated nanowire assembly. Indium nanowires thus assembled can be feasibly heat-treated to achieve highly uniform structure with low resistively making it compatible as a component for futuristic nanocircuits.

Download

Share

COinS