Preparation And Physical Properties Of Copper Selenide(Indium) And Copper Telluride By Molecular Beam Epitaxy

Since graphene was successfully prepared in 2004,two-dimensional materials have attracted great attention,and corresponding research has also been carried out..Silicene,germanene,and stanene of the same main group have also been prepared successively,and have some novel physical properties,such as quantum Hall spin effect.The excellent properties of these materials have also inspired a series of studies on other graphene-like two-dimensional atomic crystal materials,such as transition metal chalcogenides.This thesis mainly uses ultra-high vacuum molecular beam epitaxy to grow new graphene-like two-dimensional atomic crystals,and uses ultra-high vacuum room temperature scanning tunneling microscope（UHV-RTSTM）combined with scanning tunneling spectroscopy（STS）to analyze its structure and electronic properties.The main content is as follows:1.Using molecular beam epitaxy,by controlling the amount of selenium deposition,copper selenide（Cu Se）and cuprous selenide（Cu₂Se）are epitaxially grown on a Cu（111）substrate.When a small amount of selenium is deposited,a hole-like Cu Se can be obtained;when a large amount of selenium is used,Cu₂Se can be obtained.The STS spectrum shows that the hole-shaped Cu Se is metallic,while Cu₂Se shows obvious semiconductivity,and its band gap is about 0.78 e V.Further DFT calculations show that Cu₂Se is a semiconductor with an indirect band gap of about 0.8 e V,which is in good agreement with the experimental results.2.Indium selenide is epitaxially grown on Cu（111）substrate by molecular beam epitaxy.Two methods of two-step method and one-step method are used respectively.The two-step method is to deposit one element in the selenium-indium compound first,and then deposit another element after annealing.The experimental results obtained by this growth method show that single elements are easy to combine on the Cu（111）surface or alloying,it is difficult to carry out the next step of growth synthesis.Another growth strategy adopts a one-step method,that is,simultaneously depositing selenium and indium by molecular beam epitaxy,and annealing treatment to synthesize selenium-indium compound in one step.This growth method can effectively avoid alloying of Cu（111）surface,indium and selenium can directly chemically react on the Cu（111）surface to obtain a two-dimensional single-layer selenide-indium compound,and the scanning tunnel spectrum shows that the single-layer selenide-indium compound has significantly different semiconductor characteristics from the substrate,and its band gap is 1.4 e V.3.Copper telluride is epitaxially grown on the Cu（111）surface by molecular beam epitaxy,and copper telluride with different metering ratios can be obtained by controlling the amount of tellurium deposited.Tellurium is deposited on a Cu（111）substrate and annealed to obtain Cu₂Te;while tellurium is deposited with a greater coverage and annealed to obtain a copper-tellurium compound with an indeterminate stoichiometric ratio.Combined with the STS spectrum study,it is found that these two copper tellurium compounds are semiconducting,and the corresponding band gaps are about 0.9e V and 0.8e V.