Study On The Epitaxial Growth And Physical Properties Of Transition Metal Sulfide Thin Films

Transition metal sulfides have good properties in electricity,magnetism,optics,etc.,and have shown good application prospects in fields such as field effect transistors,magnetic devices,and optoelectronic devices.However,compared with the transition metal oxides that have been widely studied,there are relatively few studies on transition metal sulfides,and the research mainly focuses on the electrochemical properties of polycrystalline,bulk,nanoparticles and other morphologies.The understanding of the basic physical properties of such materials is still relatively lacking.From the perspective of basic physics and applications,high-quality thin films have the unique advantages of being able to explain the intrinsic properties of substances,thereby enabling the regulation of physical properties,and being easy to integrate on devices.Therefore,it is of great scientific significance to prepare high-quality single-crystal epitaxial thin films.Based on this,this paper proposes to prepare single crystal epitaxial thin films of Co₉S₈and Ni Co₂S₄ on Yttria-Stabilized Zirconia（YSZ）substrates by pulsed laser deposition,and test the structure and physical properties of the thin films.The main research contents are as follows:（1）Single crystal epitaxial films of Co₉S₈ were prepared by pulsed laser deposition technique.Through the reciprocal space mapping（RSM）and Phi-scan tests of the samples under the optimal growth conditions,it is found that the film has a good epitaxy relationship with the substrate and is a non-relaxation growth.The films with variable temperature and thickness were characterized by X-ray Diffraction（XRD）,Atomic Force Microscope（AFM）and Raman Spectra.Scanning Electron Microscope（SEM）surface and cross-section tests were carried out on single crystal epitaxial films.The single-crystal epitaxial films were tested by X-ray Photoelectron Spectroscopy（XPS）,and the results showed that the samples contained Co and S elements.The temperature-variable resistance test of the single-crystal epitaxial thin film was carried out using the four-wire method.The test results show that the electrical transport of the sample exhibits metallic characteristics.Optical tests show that the transmittance of the thin film in the range of400 nm-800 nm is about 60%.The increase in optical absorption of the film occurs in the range of 3.41 e V-3.96 e V.（2）Single crystal epitaxial films of Ni Co₂S₄ were prepared by pulsed laser deposition technique.RSM and Phi-scan tests indicate that the films are epitaxial and non-relaxation grown.SEM test shows that the Ni Co₂S₄ film is not so flat compared to Co₉S₈,and it can be seen from the cross section that the boundary between the Ni Co₂S₄ film and the substrate is very obvious.The ratio of Ni,Co and S elements obtained by EDX energy spectrum test is 1:1.66:3.33,which is close to the stoichiometry of Ni Co₂S₄.XPS test results show that the sample contains Ni,Co,S elements.The resistance of the films measured by the four-wire method shows that Ni Co₂S₄ also exhibits metallic properties.Optical tests show that the transmittance of the film in the range of 400 nm-800 nm is about 38%.The increase in optical absorption of the film occurs in the range of 3.46 e V-4.01 e V.