SPECIFICS OF THE FORMATION OF THIN LAYERS OF MOLYBDENUM DISULFIDE MoS2 ON METAL MOLYBDENUM AT DIFFERENT TEMPERATURES
Abstract
MoS2 is classified as a transition metal dichalcogenide. They crystallize as layered structures of various modifications. The strong anisotropy of the crystal structure of these compounds leads to the easy splitting of the layers along the cleavage planes perpendicular to the parameter c of the crystal. Therefore, the physical properties of these compounds are very anisotropic.
The aim of the paper is to show the influence of temperature on the phase composition and crystal structure of thin layers formed on metal molybdenum plates during gas transfer of sulphur vapours to the hot zone of the reactor. Molybdenum disulphides were produced in a sealed quartz tube, the middle part of which was heated to the necessary temperatures in the range of 300-1000 °С. In this high-temperature part of the quartz tube, molybdenum foil was placed, which was purified of oxides in advance. In the quartz tube, from the side of the entrance of the argon gas, in the temperature zone of 150 °C, there was a ceramic boat with sulphur. The resulting sulphur vapours were transferred by a flow of argon to the high-temperature region of the tube and there interacted with the surface of the molybdenum plate. As a result of this interaction, a layer of molybdenum disulphides was formed on the molybdenum surface, the density morphology and the structure of which depended on the synthesis temperature.
The results of the X-ray diffraction and scanning electron microscopy samples investigations of molybdenum disulphides MоS2 obtained on metal Mo plates at different temperatures show that at high temperatures of gas transport synthesis in the range 800-1000 °C, molybdenum disulphides of various modifications/polytypes are formed: the polytype of 2H hexagonal syngony P63/ mmc at 800 °C and the polytype 3R of rhombohedral (trigonal) syngony R3m at 1000 °C.
At the temperature of 1000 °C, MoS2 microcrystals with a facet corresponding to the rhombohedral phase of R3m are formed.
ACKNOWLEDGMENTS
The work was supported by the Ministry of Education and Science of the Russian Federation in the framework of the state order to higher education institutions in the sphere of scientific research for years 2017 - -2019. Projects № 3.6263.2017/VU and № 16.8158.2017/8.9.
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