INSTRUMENTATION AND APPLICATION OF SCANNING PROBE MICROSCOPY IN NOVEL 2D SYSTEMS
Restricted (Penn State Only)
- Author:
- Pabbi, Lavish
- Graduate Program:
- Physics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 28, 2019
- Committee Members:
- Eric W Hudson, Dissertation Advisor/Co-Advisor
Eric W Hudson, Committee Chair/Co-Chair
Mauricio Terrones, Committee Member
Jainendra Jain, Committee Member
Joan Marie Redwing, Outside Member
Richard Wallace Robinett, Program Head/Chair - Keywords:
- Scanning Tunneling Microscopy
Atomic Force Microscopy
Active noise cancellation
Doped Graphene
2 dimensional materials
Transition metal dichalcogenides
Spinodal decomposition - Abstract:
- Scanning Probe Microscopy (SPM) has proven to be a powerful and sensitive tool for the study of exotic materials by measuring, with atomic resolution, topographic and electronic properties. In this dissertation, I describe my contributions to both SPM instrumentation and scientific developments as a graduate student. On the instrumentation side, I implemented a dry refrigeration cooling system for both a home-built scanning tunneling microscope (STM) and a modified commercial SPM. The vibrational challenges I faced during this work led me to invent ANITA, an active noise cancellation technique that reduces vibrational effects on SPM measurements. Over the time that I was developing these instrumental advances, we witnessed the growth and emergence of novel physics in two-dimensional (2D) materials like graphene and 2D transition metal dichalcogenides (TMDs), making them prominent candidates to take advantage of our new SPM capabilities. I have been particularly interested in investigating variations in local topographic and electronic structure arising from rain, doping and defects; with the goal of discovering new physics in reduced dimensions. All of my research has been done in collaboration with local synthesis research groups, both assisting their efforts to develop new techniques and materials, and seeking out new physics in the systems they grow. Here I describe my work in two different material systems: graphene and MoS2. In graphene, for example, I studied the effects of substitutional doping achieved by liquid-precursor based growth, and vacancy defects created by He-ion plasma etching of epitaxial graphene. These studies led to the discovery of non-classical mechanical properties and surprising electronic features in strained graphene draped over copper step edges. Similarly, in investigating the surface structure of MoS2/Mo2C heterojunctions, I used a special set of consecutive local STM and AFM measurements, as well as a new invention for locally peeling away surface layers to perform local depth profiling, to resolve outstanding questions about the nature of complex island structures caused by spinodal decomposition, and the local doping changes and electron confinement effects they create.