Synthesis And Characterization Of Two-dimensional Nanosheets And Van Der Waals Heterostructures From Non-layered ?-CuI

Two-dimensional?2D?materials have attracted significant attention as a new generation of atomically thin material for next-generation electronic and optoelectronic devices due to their ultrathin geometry and unique thickness-dependent physical properties.Amonst,some 2D materials can be further combined,producing new van der Waals heterostructures with tunable chemical composition and electronic structure.Without the requirement of lattice matching,van der Waals heterostructures allow the integration of more abundant 2D materials than the traditional semiconductor heterostructures,offering a much more flexible approach for heterogeneous material integration.However,the current 2D nanosheets available are generally limited to intrinsically layered materials,in which the covalently bonded atomic layers are held together by weak van der Waals forces and can be readily exfoliated or grown into single or few-atom thick nanosheets.Apparently,preparing2D nanosheets from non-layered materials can greatly expand the 2D material library.However,it still remains as a great challenge because in non-layered materials,the atoms are convelently bonded and are not readily exfoliated.Therefore,the research interest of this thesis focuses on non-layered?-CuI,with the aim to synthesize 2D nanosheets and van der Waals heterostructures from non-layered?-CuI using a facile physical vapor deposition method and systematically study their chemical composition,structure and electrical performance.The main research contents and results are outlined as follows:?1?Synthesis of 2D nanosheets from non-layered?-CuI.This thesis synthesized 2D nanosheets using a simple physical vapor deposition method and systematicaly investigated the influence of growth temperature,argon flow rate,growth time,and the distance between the substrate and source on the size,thickness,and quality of?-CuI nanosheets.The studies of optical microscopy?OM?,scan electron microscopy?SEM?,Raman spectroscopy,X-ray diffraction?XRD?,transmission electron microscopy?TEM?and selective area electron diffraction?SAED?reveal that the resultant 2D nanosheets exhibits triangular and hexagonal shapes with different sizes?1-10?m?and thicknesses?1-300 nm?.Moreover,the nanosheets are single crystals,with identical cubic phase to the bulk?-CuI.?2?Synthesis of?-CuI/WSe₂ and?-CuI/WS₂ van der Waals heterostructures.Using WSe₂ and WS₂ as template for the following growth of?-CuI nanosheets,this thesis synthesized?-CuI/WSe₂ and?-CuI/WS₂ van der Waals heterostructures using a two-step growth method.OM,atomic force microscopy?AFM?,and Raman spectroscopy studies reveal that the as-obtained WSe₂ and WS₂ are high quality monolayer nanoseets and on them,perfect?-CuI/WSe₂ and?-CuI/WS₂ van der Waals heterostructures can be formed.?3?Electric properties of the 2D?-CuI nanosheets and?-CuI/WSe₂ and?-CuI/WS₂ van der Waals heterostructures.Using e-beam lithography and thermal evaporation techniques,this thesis defined 150 nm Au contact electrodes on the?-CuI nanosheets and?-CuI/WS₂ van der Waals heterostructures to form nanodevices.Electrical transport studies show that?-CuI nanosheets exhibit a low resistivity of⁰.3?·cm,while?-CuI/WS₂ van der Waals heterostructures display a p-n diode behavior with distinct current rectification.