| Summary: | 碩士 === 國立臺灣科技大學 === 應用科技研究所 === 106 === In recent years, transition metal di chalcogenides (TMDCs) has received more attentions as potential materials for application as optoelectronic devices, green catalyst, hydrogen energy and also in solar cells. We have synthesized and grown the layered single crystals of chromium doped molybdenum di selenides Mo1-xCrxSe2 (0≤ x ≤0.2) series and also Cr2Se3 crystal using chemical vapor transport (CVT) method using Iodine as transport agent. Crystal structures of Mo1-xCrxSe2 series and Cr2Se3 are well identified by XRD measurement. An enhanced crystal quality and enlarged lattice constant of Mo1-xCrxSe2 series as a result of gradual increase of chromium amount were characterized by high resolution transmission electron microscope (HRTEM).
The first order E1g and A1g modes of these sample crystals were clearly detected by Raman spectroscopy which allowed shift to lower wavenumber as the chromium concentration increased in the series. Investigation on the various optical and photochemical properties such as photo-transmission, photoconductivity on both samples were carried out. The results showed good optical responsivity due to incorporation of chromium in the Mo1-xCrxSe2. The free excitonic features EA1, EA2 and EB of the chromium doped Mo1-xCrxSe2 were observed by thermoreflectance (TR) spectroscopy.
Metallic behavior of Cr2Se3 crystal was confirmed by four-point resistivity measurement, where the resistivity increases with temperature increased between 20 and 300K. Mo1-xCrxSe2 series displayed n-type semiconductor behavior by hot probe method owing to Cr6+. Thus, Mo1-xCrxSe2 explicated photo-catalyst nature of these sample crystals showed better degradation of methylene blue (MB) because of redox property of Cr3+/Cr6+ and reduced band gap of Mo1-xCrxSe2. Therefore, the tunable photo-catalyst nature of Mo1-xCrxSe2 series renders the material a suitable candidate for green energy application.
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