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Title: High-frequency study of two-dimensional materials
Author: Meng, Kun
ISNI:       0000 0004 8504 6998
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2019
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Two-dimensional (2D) materials show different properties from threedimensional materials owing to the quantum confinement they have in the vertical direction (perpendicular to their plane). Graphene, as the first established one-atom-thick 2D material, has received widespread attention owing to its versatile and rather extraordinary properties. Metasurfaces, as an artificial 2D material, have shown potential for new functional electromagnetic (EM) devices since they possess EM properties not found in natural materials. On top of that, the graphene-metasurface hybrid devices are receiving progressing attention. This thesis investigates the two 2D materials' interactions with highfrequency signals, aiming to develop some exemplar applications, including a high-sensitive dielectric sensor, a THz-pulse detector, a broadband tunable THz polarizer, and tunable (MHz-GHz) acoustoelectric (AE) current source. The interaction of 2D materials with THz waves was first investigated. The resonant frequency of a THz split-ring resonator (SRR) was found to be altered by the introduction of etched trenches into the LC gap area, owing to a reduction in the effective permittivity, which allowed a significant enhancement in its sensitivity to overlaid dielectric material. Carriers in graphene can be accelerated by the electrical field of freespace THz pulse, which enabled a free-space THz detector, whose performances were also tested. Combining the technologies developed in these two projects, the interaction between graphene-metasurface hybrid devices and THz waves was next explored. Our graphene-metal hybrid stripe arrays showed both a significant direction-dependent transmission, and a strong modulation effect for the transmitted THz waves across a wide frequency range, so demonstrating a broadband tunable THz polarizer. 2D materials interacting with surface acoustic waves (SAWs) were then investigated. The SAW induced carriers transport in graphene was examined with SAW frequencies from 10s of MHz to GHz and at cryogenic to room temperature. Experiments were made on bars of graphene, graphene ribbons and gate-modulated graphene strips. The combination of these works suggests strong future possibilities for the study of quantized AE currents in graphene.
Supervisor: Cunningham, John ; Linfield, Edmund Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available