Investigation On The Preparation And Photoelectrical Properties Of MoO₂ And MoS₂ Nanomaterials

Owing to the unique physical and chemical properties,two dimensional MoO₂ and MoS₂nanomaterials have exhibited promising applications in catalysis,sensor,electrochemistry and transistor devices as well as other fields.Therefore,the preparation of two-dimensional MoO₂and MoS₂ nanomaterials,exploring their growth patterns,controlling the size and shape,and studying the relationship between growth and properties are important to the synthsis and application.I n this paper,optimization of the synthesis methods and properties of MoO₂ and MoS₂ nanostructures are investigated.The main results are as follows:?1?CVD was used to prepare two-dimensional MoO₂ nanosheets.With S powder and MoO₂ powder as the raw material in the Ar atmosphere,the triangle,pentagon and rhombus nanosheets with thicknesses of more than ten nanometers and lengths up to 20-30?m are obtained on the surface of SiO₂/Si substrate.The thickness,uniformity,composition and crystallinity of MoO₂ were characterized by AFM,XPS,Raman spectroscopy and TEM.It is discover that the different shape of products on SiO₂/Si substrate is mainly due to the difference of gaseous reactant proportion and growth temperature.The rhombus nanosheets are monocrystal MoO₂,while triangular and pentagonal nanosheets contain a small amount of MoS₂.The proportion of the gas phase reactants is the main influence factor of the shape and purity of the nanosheets.UV-Vis absorption spectra showed that three kinds of nanosheets had strong absorption band in the ultraviolet range of 200-300 nm.The band gap widths of triangular,pentagonal and rhombic nanosheets were 3.75 e V,3.97 eV and 4.25 e V,respectively.The PL shows that each nanosheets has three luminous peaks,and the stronge st peaks are located at 328.57 nm?triangles?,312.2 nm?pentagonal?and 294.3 nm?rhombus?.The band gap is measured by UV-Vis absorption spectrum,which is similar to the energy level of the photoluminescence peak of the corresponding photoluminescence spectrum.The strongest peak of each shape is determined by the transition of electrons between conduction band and valence band.The peak position of the three main peaks is different because the composition of the three kinds of nanosheets is different,a nd the two accompanying peaks of the main peak are caused by oxygen vacancies and other defects.?2?The single layer MoS₂ with large size and high quality was prepared by CVD method.The effects of the use and distribution density of accelerator PTCDA and the type of substrate?SiO₂/Si and sapphire substrate?on the size and crystalline quality of MoS₂ are mainly studied.A high quality single layer MoS₂ with large size?60-80?m?was synthesized on sapphire substrate.The single layer MoS₂ prepared on the SiO₂/Si substrate directively and spined with promoter is 5?m and 30-40?m respectively.The influence of the substrate and the accelerator is studied by the calculation of the lattice matching degree.It is discovered that the larger the size of the nanosheets film is,the higher the lattice matching degree is.AFM,XPS,Raman spectroscopy and TEM have proved that we have prepared a high quality single layer MoS₂.According to Raman spectra and PL spectrum,we found that the MoS₂ was n type doped on the SiO₂/Si substrate.However,the sapphire substrate does not introduce doping to MoS₂ nanosheet.After annealing in Ar and Ar+S atmosphere,it is discovered that when S is added,partial vacancy defects of S are eliminated after annealing,and the qualit y of MoS₂ is increased,so the luminous intensity of MoS₂ is enhanced.After annealing in the mixed atmosphere of Ar and S,Hall test showed that the MoS₂ grown on SiO₂/Si substrate was n type semiconductor with mobility of 72.9 cm²·V^-1S^-1.The MoS₂ growth of sapphire substrate is also n type semiconductor,with a mobility of 16.2 cm²·V^-1S^-1.Compared to the mobility of MoS₂ annealed in Ar gas only,it increased annealed in the mixed atmosphere of Ar and S.