Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.618530
Title: Terahertz spectroscopy of graphene and other two-dimensional materials
Author: Docherty, Callum James
ISNI:       0000 0004 5354 591X
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2014
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Abstract:
In this thesis, two-dimensional materials such as graphene are tested for their suitability for opto-electronic applications using terahertz time domain spectroscopy (THz-TDS). This ultrafast all-optical technique can probe the response of novel materials to photoexcitation, and yield information about the dynamics of the material systems. Graphene grown by chemical vapour deposition (CVD) is studied using optical-pump THz-probe time domain spectroscopy in a variety of gaseous environments in Chapter 4. The photoconductivity response of graphene grown by CVD is found to vary dramatically depending on which atmospheric gases are present. Adsorption of these gases can open a local bandgap in the material, allowing stimulated emission of THz radiation across the gap. Semiconducting equivalents to graphene, molybdenum disulphide (MoS2) and tungsten diselenide (WSe2), grown by CVD, are investigated in Chapter 5. These members of the transition metal dichalcogenide family show sub-picosecond responses to photoexcitation, suggesting promise for use in high-speed THz devices. In Chapter 6, an alternative production route to CVD is studied. Liquid-phase exfoliation offers fast, easy production of few-layer materials. THz spectroscopy reveals that the dynamics of these materials after photoexcitation are remarkably similar to those in CVD-grown materials, offering the potential of cheaper materials for future devices. Finally in Chapter 7, it is shown that carbon nanotubes can be used to make ultrafast THz devices. Unaligned, semiconducting single walled carbon nanotubes can be photoexcited to produce an ultrafast, dynamic THz polariser. The work in this thesis demonstrates the potential for these novel materials in future opto-electronic applications. THz spectroscopy is shown to be an important tool for the characterisation of new materials, providing information that can be used to understand the dynamics of materials, and improve production methods.
Supervisor: Johnston, Michael B. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.618530  DOI: Not available
Keywords: Semiconductor devices ; Condensed Matter Physics ; Nanostructures ; Graphene ; Terahertz Spectroscopy ; Transition Metal Dichalcogenides
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