In Situ Construction And Physical Properties Of Two-Dimensional Lead Selenium(Tellurium) Thin Films

Graphene-like two-dimensional materials have attracted great attention from researchers.Compared with three-dimensional crystalline materials,due to the reduced dimensionality,two-dimensional materials exhibit many excellent properties in optics,electronics and mechanics,such as ultra-high carrier mobility,ultra-high light transmission,quantum Hall effect at room temperature,etc.,which make them great potential for future applications in optoelectronic devices.In this thesis,two-dimensional lead selenide（telluride）was epitaxially grown on metallic crystal substrates using molecular beam epitaxy（MBE）technique,and its microstructures and electronic properties were investigated by combining ultra-high vacuum room temperature scanning tunneling microscopy（UHV-RTSTM）and scanning tunneling spectroscopy（STS）.The main contents are as follows:1.Lead selenide（PbSe）is prepared on Au（111）substrate,and it’s found that the epitaxial deposition sequence critically affected the formation of PbSe.Upon depositing lead on Au（111）substrate,Pb directly reacts with Au substrate.Further deposition of Se and subsequent annealing result the formation of the selenide,instead of the formation of lead selenide.Exchanging the deposition sequence,Se was first deposited on Au（111）and formed the Se₈ molecular structure.Further deposition of Pb element results in successful preparation of a phosphorene-type monolayer lead selenide with a 5?×9?reconstruction lattice.Corresponding DFT calculations reveal that the strong coupling between PbSe and Au（111）substrate leas to the formation of phosphorene-type lead selenide.Differential conductivity spectroscopy shows the characteristic metallic properties,verifying the strong coupling.2.PbSe is prepared on Ag（111）substrate and its growth mechanism was investigated.Se is first deposited on Ag（111）substrate,and then the concomitant phase of Ag Se and Ag₅Se₂ is obtained after annealing.Further deposition of Pb element results in successful preparation of ultrathin bilayer PbSe。It’s also found that the morphology of PbSe films varies with the quantity of deposited Pb,and the accumulation of Pb lead to the improved quality of PbSe with larger and more uniform flatness.The local differential conductance spectroscopy reveals the metallic feature,indicating strong interaction between PbSe and Ag（111）.In addition,the moirépattern originating from the lattice mismatch between PbSe and Ag（111）is observed,which provides the opportunity for studying physical properties of periodic modulation and for potential device applications.3.Lead telluride（PbTe）is tried to be prepared on Au（111）and Ag（111）substrates,respectively.Te is deposited on Ag（111）substrate and subsequent annealing results in the formation of the silver telluride structure.It’s found that Pb selectively adsorbes on the silver telluride surface,forming Pb nanowires with three orientations.On the other hand,upon depositing Pb on Au（111）substrate,Pb directly reacts with Au substrate.Further deposition of Te results in the formation of PbTe.Alternately,Te and Pb are successively deposited on the Au（111）substrate,and it’s found that the Pb is inclined to adsorb on the edges or holes of the tellurium film.Subsequent annealing process facilitates the successful formation of PbTe.Corresponding local differential conductance spectroscopy reveals the metallic feature of the PbTe film,indicating the strong interaction between PbSe and the underlying Au（111）.