Zachary Swart

Date of Award

Spring 5-2020

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Molecular Science and Nanotechnology

First Advisor

Adarsh Radadia

Abstract

In this thesis, the physical and electrical alterations caused by local oxidation nanolithography (LON) on highly oriented pyrolytic graphite (HOPG) are characterized. The LON is an atomic force microscopy (AFM) based technique that applies a positive bias to the sample relative to the AFM tip, leading to an electrochemical oxidation of the sample surface. If these physical and electrical alterations due to LON are well understood, this could yield a higher degree of control over tailoring the surface to become conductive, semiconductive or insulative in nature. The advantages of LON include room temperature operation in a non-vacuum environment, less steps to fabricate nanoscale devices, reduced photoresist residues, and an ability to perform metrology in situ.

First, we characterized patterns obtained through LON on HOPG as the write bias, write speed, and write force were varied. We organized patterns formed as either– bumps, cracked bumps, or trenches–which were characterized using four shape descriptors–pattern width, pattern height, cut width, and cut depth. This was the first reported attempt to characterize LON patterns on HOPG with shape descriptors. These findings help solve the mystery of why bumps were not reported at threshold voltages before 2008.

Subsequently, the electrical nature of the LON patterns were characterized using Kelvin probe force microscopy (KPFM); only write force was varied during this study. The in situ KPFM after LON allowed mapping LON-induced changes in work function and capacitance gradient (dC/dz) of the surface, the latter being an indicator of a change in dielectric permittivity of the surface. This was the first attempt to characterize LON patterns using KPFM in-situ.

The findings of this thesis hold potential to make LON a more repeatable process. For future work on LON, it was also shown that the tip conditions need to be checked consistently using cantilever resonance frequency and scanning electron microscopy, and an environmental cell should be used to control the relative humidity around the tip.

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