Semester

Spring

Date of Graduation

2021

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Physics and Astronomy

Committee Chair

Mikel Holcomb

Committee Member

Wathiq Abdul -Razzaq

Committee Member

Lian Li

Committee Member

Fabien Goulay

Abstract

Results obtained from experimental investigations of contact friction in monolayer and bilayers graphene and the related effects on their transport properties are presented here along with their discussion and interpretation. For this purpose, chemical vapor deposited (CVD) graphene samples on SiO2/Si were prepared. The samples were characterized by atomic force microscopy (AFM), Raman and X-ray photoelectron spectroscopy (XPS). Summaries of the results are given below.

Defects-controlled friction in graphene is of technological importance but the underlying mechanism remains a subject of debate. The new results obtained from the analysis of lateral force microscopy images revealed that the contact friction in chemical vapor deposition (CVD) grown graphene is dominated by the vacancies formed instead of the bonding with add-atoms. This effect is attributed to the vacancy-enhanced out-of-plane deformation flexibility in graphene, which tends to produce large puckering of graphene sheet near the contact edge and thus increases the effective contact area. Modified graphene with large contact friction has a large density of defects. However, it remains a good electrical conductor, in which the carrier transport is strongly affected by quantum localization effects even at room temperature. Negative magnetoresistance observed in high defect density monolayer graphene samples revealed that scattering event is dominated by the short-range scattering (intervalley). It is also found that the oxidation process in mono-layer graphene is substrate sensitive since the oxidation process progresses much faster when the substrate is Strontium Titanate (SrTiO3) compared to SiO2 substrate. However, bilayer graphene exhibits great oxidation resistance on both substrates. These observations provide important information for tailoring the mechanical, electrical, and chemical properties of graphene through selected defects and substrates.

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