Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Department

Electrical Engineering

First Advisor's Name

Grover Larkins

First Advisor's Committee Title

Committee Chair

Second Advisor's Name

Armando Barreto

Third Advisor's Name

Kinzy Jones

Fourth Advisor's Name

Chunlei Wang

Fifth Advisor's Name

Jeffrey Fan

Keywords

Superconductivity, Graphene, Doping, HOPG

Date of Defense

7-6-2016

Abstract

The possibility of creating superconductivity in Highly Oriented Pyrolytic Graphite (HOPG) by means of doping was investigated. Bulk HOPG samples were doped with phosphorous using either ion-implantation or by Chemical Vapor Deposition growth with phosphine in the gas mixture. The methods for testing the graphene samples, once doped, were done by performing R vs. T measurements, and determining via observation suppressed superconductive characteristics signaling the presence of the Meissner Effect in a strong applied magnetic field. Before doping, the resistance vs. temperature (R vs. T) characteristic of the HOPG was measured. The R vs. T characteristic was again measured after doping, and for surface multilayers of graphene exfoliated from the post doped bulk sample. A 100 to 350 mT magnetic field was supplied, and the R vs. T characteristic was re-measured on a number of samples.

Phosphorous-implanted HOPG samples exhibit deviations from the expected rise in resistance as the temperature is reduced to some point above 100 K. The application of a modest magnetic field reverses this trend. A step in resistance at a temperature of approximately 50-60 K in all of the samples is clearly observed, as well as a second step at 100-120 K, a third at a temperature range of 150-180 K and a fourth from about 200-240 K. A response consistent with the presence of magnetic field flux pancake vortices in phosphorous implanted HOPG and in phosphorous-doped exfoliated multilayer graphene has been observed. The lack of zero resistance at low temperatures is also consistent with pancake vortex behaviour in the flux-flow regime. The presence of magnetic vortices requires, and is direct evidence of superconductivity.

Identifier

FIDC000772

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