Date of Award

Spring 2011

Project Type

Thesis

Program or Major

Mechanical Engineering

Degree Name

Master of Science

First Advisor

Todd S Gross

Abstract

The fabrication of nanostructures is of great importance for the continued development of nanodevices and molecular electronics. While field assisted tip based techniques are proposed to be versatile nanofabrication techniques that can be used for atomic-scale surface modification of wide variety of materials, the mechanism of material transport is not well understood. This research was performed to better understand the mechanisms of surface modification when the voltage bias is applied in ambient conditions; in particular, the conditions that Liu et al.1,2 proposed will cause material transport.

We studied the evolution of the current voltage behavior of a doped silicon AFM tip on gold film on mica and highly ordered pyrolytic graphite (HOPG) to understand the impact of current on material modification for negative tip biases up to 10V. The SEM images of tips before and after use were compared to examine the physical changes caused to the tip and x-ray energy dispersive spectroscopy analysis was performed to study the chemical composition of used tips. We monitored modification on substrates and proposed possible mechanisms of material transport. We performed heat transfer analysis of the tip-substrate interface to show that the measured powers for negative tip biases in the range of 6--10 V are sufficient to raise the temperature at the interface to as high as 100--1100 °C which in combination with very high electric field (> 108 Vm-1) is sufficient to cause tip oxidation of bare silicon tip in an ambient environment and can cause diffusion, evaporation or melting of thin coatings from coated silicon tips used by Liu and Miller.1,2.

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