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Preparation of atomic-layer transition metal chalcogenides with application in opto-electronic devices
thesisposted on 27.02.2017, 00:13 by Xu, Zaiquan
Graphene like two-dimensional materials are important elements of potential optoelectronics applications due to their exceptional electronic and optical properties. The preparation and processing of these materials towards the realization of opto-electronic devices has been one of the main motivations for the recent development of photonics and optoelectronics. My Ph.D projects involves with three aspects: 1. Preparations of atomic-layer transition metal dichalcogenides (TMDs), e.g. MoS₂ , WS₂ and WSe₂ with chemical vapour depositions. In this part, we present the synthesis of large size (>100 μm) single crystals of atomically thin tungsten disulfide (WS₂ ), a member of TMDs family, on sapphire substrate. More importantly, we demonstrate a polystyrene (PS) mediated delamination process via capillary force in water which allows recyclable use of the growth substrates; 2. Fabrication of TMDs based photodetectors and study the performance and mechanisms with spatial photocurrent mapping. We developed an efficient photodetector with extremely large photo-responsive active area based on a lateral p-n junction of monolayer-bilayer WSe₂ . The junction is produced by partially peeling off the upper layer of a bilayer WSe₂ crystal grown by atmospheric pressure chemical vapour deposition. Kelvin probe force microscope and photocurrent mapping were used to understand the performance and the mechanism; 3. Atomic layered thin TMDs based flat lenses: fabrication and imaging. An ultrathin flat lens with a thickness of 7 Å, which corresponds to the fundamental physical limit of material thickness, is fabricated on a large monolayer WSe2 single crystals with direct femtosecond laser writing. We apply the material with ultra-high refractive index to achieve three-dimensional (3D) focusing with almost diffraction-limited resolution by effective modulation of the amplitude of the incident light.