Experimental Approaches and Device Fabrication Methods Toward Investigation of Properties of Two-dimensional Transition Metal Dichalcogenides (TMDCs)

Dong, Siyan

doi:https://doi.org/10.21985/n2-rxzg-0x73

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Experimental Approaches and Device Fabrication Methods Toward Investigation of Properties of Two-dimensional Transition Metal Dichalcogenides (TMDCs)

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Transition Metal Dichalcogenides (TDMCs) are one of many families of two-dimensional (2D) beyond graphene, that started to gain more attention due to the need for miniaturization and their unique electrical, mechanical, and optical properties. Some members of TMDCs, such as MoS2, has direct band gap in its monolayer form, making it a great candidate for electronics and nano devices of the future. Other properties such as piezoelectricity and mechanical resonance give promise to TMDCs in applications such as sensing and self-powered devices. Progress in this field calls for more experimental techniques to enable more exotic studies of TMDCs such as measurement of resonance and piezoelectricity. One of the priorities toward this goal is fabrication that allows devices with suspended 2D TMDCs isolated from the bottom substrate. This dissertation explored multiple fabrication options available to researchers and summarized 3 different approaches to achieve suspended TMDC devices through the use of e-beam lithography, laser writer lithography and etc. In order to be versatile with device creation, A novel 2D material transfer method was developed, which requires only water to facilitate the transfer. With the device fabrication capacity achieved, we further developed an in-vacuum cavity-interferometry system based on a Raman spectroscope platform that allowed detection of resonance of 2D TMDCs. We measured resonance of monolayer and few-layer WS2 resonators. On monolayer WS2, piezoelectricity was experimentally extracted for the first time in a contactless manner. We also found unique internal resonance in monolayer WS2. In addition, we prepared large arrays of MoS2 and MoSe2 resonators from Chemical Vapor Deposition (CVD) grown samples and studied their resonance properties. Furthermore, we recently expanded to investigation of thermal transport in MoS2 junctions to study its interlayer thermal coupling. These development and findings can aid the understanding and applications of TMDCs.

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