Exploring nanoscale characterization of low dimensional electronic materials

by Eric M Seabron

Institution: University of Illinois – Urbana-Champaign
Year: 2015
Keywords: Atomic Force Microscopy (AFM); Nanotubes; Nanowires
Posted: 02/05/2017
Record ID: 2134215
Full text PDF: http://hdl.handle.net/2142/88126


The advent of Atomic Force Microscopy (AFM) has allowed researchers to probe materials on the atomic scale with relative simplicity. For the study of nanoscale materials, structure is very important and often has a large impact on the materials intrinsic properties. The conventional form of Atomic Force Microscopy was developed to study material structure in the form of surface topography measurements. Since then there has been many advances which have taken advantage of the ability to detect small forces using an AFM tip along with surface topology. A driving motivation in the scan probe microscopy field is the ability to spatially correlate properties of electronic materials such as charge density, conductivity, and doping distribution with nanoscale structure. Nanoscale characterization has become increasingly relevant as device features continue to shrink according to Moore’s Law leading to the advent of next generation electronic materials such as semiconducting nanowires and Carbon nanotubes. The primary issue with measuring nanoscale materials properties is that the tip-sample coulomb forces and quantum effects that provide insight into the material’s properties are very difficult to detect. A semiconducting Nanowire (NW) typically less than 500nm in diameter, is a quasi 1-dimensional structure with feature sizes approaching the diffraction limit of light rendering conventional optical spectroscopy ineffective; hence scan probe techniques are the most promising for characterization. Carbon Nanotubes, typically 1.0nm – 3.0nm in diameter, are 1-dimensional structures that are particularly difficult to characterize due to their infinitesimal sample volume. So far there has been very limited success electrically characterizing CNTs at the individual nanotube scale. Despite the challenges associated with nanomaterial characterization there have been successes at characterizing the electrical and chemical composition in parallel with morphology using capacitance sensitive AFM techniques. In this study I will describe and present data from AFM techniques with the ability to characterize semiconducting nanowires and carbon nanotubes. In chapter 1, there is a review of several variations of capacitive AFM used to measure electrical properties and chemical properties of nanomaterials, some of which require specific sample preparation making them incompatible with nanotube and nanowire characterization. Next, in chapter 2, is an introduction to Microwave Impedance Microscopy (MIM), a novel nondestructive scan probe technique we offer as a viable alternative for low dimensional electronic material characterization. The goal of Chapter 3 is to demonstrate the ability to measure the quantum capacitance of individual CNTs using MIM illustrating it’s capability to measure nanoscale electrical phenomena. In chapter 4, MIM-AFM is used to provide insight into the structurally correlated doping dynamics of laterally grown GaAs nanowires. Finally, in chapter 5, a new scan probe technique called Near Field Infrared Microscopy… Advisors/Committee Members: Wilson, William (advisor), Rogers, John A. (committee member).