Impact Of High Pressure On The Physical Properties Of Platinum Disulfide

Among low dimensional systems,two-dimensional?2D?materials have attracted the interest of researchers because of their unique layered structure,excellent physical and chemical properties,wide potential applications,and etc.In recent years,many new 2D materials have been discovered.Among them,the 2D layered transition metal chalcogenides?MXn,where M is the transition metal,X= S,Se,Te?exhibit unique physical and chemical properties,have potential applications in optoelectronic devices,energy conversion and so on,and have become a new hotspot in the research field of photoelectric.The transition metal dichalcogenides have quasi two-dimensional characteristics.Studies showed that by adjusting the lattice structure and changing the elementary composition,the energy band structure can be controlled effectively,thereby the physical and chemical properties getting improved for transition metal chalcogenides.Common methods to tune band structure include changing the number of layers,embedding different alkali metal atoms or transition metal atoms between layers,applying pressure,external electric field or magnetic field and so on.Especially,applying pressure is a clean and effective way to manipulate the lattice of a material.In contrast to element doping,it can effectively avoid lattice defect interference,such as vacancies and interstitial atoms,so it is an ideal material performance research method.Among transition metal chalcogenides,PtS₂ has high carrier mobility and tunable band gap structure.Moreover,theoretical calculation shows that the band gap can be changed from an indirect nature to a direct one under pressure.In this dissertation,PtS₂ is chosen as the research object.Based on the preparation of high quality PtS₂ single crystals,we systematically studied the impact of high pressure on the structure and photoelectric properties of PtS₂.Our work carried out a research work as below:?.High quality PtS₂ single crystal was successfully prepared by chemical vapor transport method with phosphorus as a transport agent.?.We studied the effect of pressure on the structure of PtS₂ by synchrotron radiation X ray diffraction?XRD?.As the pressure increases,the lattice constant of PtS₂ decreases.However,there is no peak splitting or new diffraction peak generated in X ray diffraction spectrum.It indicates that pressure causes material compression,but no structural transformation occurs.?.We investigated the effect of pressure on the vibration mode of PtS₂ by Raman spectroscopy.No matter whether the pressure is applied or not,the main vibration modes of PtS₂ are shown as the in-plane vibration mode of the S atom Eg and the out of plane vibration mode A1 g.As the pressure increases,the peak position shows monotonous blue shift,which proves that the pressure leads to the hardening of the lattice,but there is no structural phase transition.?.We explored the effect of pressure on the photoelectric properties of PtS₂ by electrical transport measurements.As the pressure increases,the resistance decreases,and the band structure of PtS₂ undergoes a transition from an indirect to a direct band gap and a semiconductor-to-metal transition.When the applied pressure is in the range of 1-3 GPa,there is no obvious change in the photocurrent with pressure.When the applied pressure varies in the range of 3-4 GPa,photocurrent increases rapidly up to 6 times higher than that of at ambient pressure.The fast increase of carrier photoexcitation efficiency indicates that the band gap of PtS₂ changes from an indirect nature to a direct one.When the applied pressure increases in the range of 4-6.4 GPa,the photocurrent gradually decreases down to zero,indicating a metallization of the system.In summary,our results show that the structure of PtS₂ is stable under high pressure,and pressure in an appropriate range can increase the photocurrent and photoelectric properties of PtS₂.The findings provides a new method for improving the performance of optoelectronic devices.