Date on Master's Thesis/Doctoral Dissertation

5-2018

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Electrical and Computer Engineering

Degree Program

Electrical Engineering, PhD

Committee Chair

Alphenaar, Bruce

Committee Member

Mendes, Sergio

Committee Member

Walsh, Kevin

Committee Member

Harnett, Cindy

Author's Keywords

microscopy; super-resolution; electrical engineering; optics; STED; imaging

Abstract

This dissertation discusses the development and refinement of a new two-dimensional imaging technique, funded in part through a NSF MRI equipment development grant. Capacitive-Photocurrent (CPC) spectroscopy allows for the probing of samples without the requirement of free-carrier collection. The CPC technique allows for the studying of various states within a material. With this electronic measurement technique, we developed a scanning technique, scanning-CPC, that provides two-dimensional material property images without requiring environments that must be high-vacuum, humidity-controlled, or temperature-controlled. This new technique also provides two-dimensional, electronic mapping without damaging samples. With this successful result, we then modified an existing resolution improving technique, Stimulated Emission Depletion (STED), to create a similar technique to improve the scanning-CPC resolution. The result was a new scanning technique, CPC-STED. With the CPC-STED technique we could achieve super-resolution of electronic response based images while maintaining the environmental flexibility of scanning-CPC. This dissertation is divided into six chapters, covering motivations and background, early work using the CPC technique, the development of the scanning-CPC system, testing and showcase of the scanning-CPC technique, testing and showcase of the CPC-STED technique, and finally, discussion of the results and proposals for future work. Chapter One discusses the motivations for this dissertation as well as the background of multiple one-dimensional and two-dimensional techniques. Chapter Two reviews the systems used for CPC spectroscopy, the previous work done in with the CPC technique, and the CPC work completed with my direct involvement. Chapter Three details the specifics of the scanning-CPC and CPC-STED system’s optical layout, sample holder design, and the custom LabView design for the scanning system. Chapter Four details the results of the scanning-CPC system, focusing on the physical mechanisms leading to successful scanning-CPC images. Chapter Five details the results of the CPC-STED system. Chapter Five also discusses the specific outcomes of how the depletion technique functions in the context of electronic imaging, rather than fluorescence imaging. Finally, Chapter Six concludes the results and provides recommendations for future work.

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