Preparation Of Two-dimensional Phosphorene And Its Surface Structure Modulation By Scanning Tunneling Microscopy

Since the discovery and successful exfoliation of graphene,two-dimensional(2D)materials have attracted significant attention for their unique mechanical,electronic and optical properties.Among them,the synthesis of monoelemental two-dimensional materials(ME2DMs)are especially concerned,because they represent the simplest state of physical and chemical structures and properties,providing ideal models for exploring growth mechanism of 2D materials and investigation of surface physical and chemical properties.Blue phosphorene(Blue P)is an allotrope of black phosphorene(Black P).Theoretical calculations show that Blue P has suitable band gaps(1.2?2.0 e V)and carrier mobility(?10⁴cm²/V s),thus having great potential in the field of electronic devices.In this dissertation,a research has been made on the growth mechanism,structure and properties of Blue P and its related 2D materials based on molecular beam epitaxy(MBE),scanning tunneling microscopy/spectroscopy(STM/S)and density functional theory(DFT).The main contents of this dissertation are as follows:(1)Preparation of 2D inorganic binary-elements alloy based on Blue P:Large-area regular Au-Blue P honeycomb structures were successfully prepared on Au(111)substrate by MBE.A Blue P segment is composed of nine P atoms,which are connected by Au atoms.The self-limiting single-layer growth of 2D inorganic binary-elements alloy based on Blue P is realized.Combined with DFT calculations,the atomic structures and electrical properties of 2D Au-P alloy are studied.(2)Surface modification of 2D Au-P alloy by C₆₀:Different from ordered aggregation on conventional surfaces,C₆₀molecules prefer adsorbing on the domain boundaries of Au-P honeycomb structures.STS spectra prove the interfacial charge transfer between 2D Au-P alloy and C₆₀molecules.In addition,2D Au-P alloy surfaces with a large number of defects are obtained by coadsorption of C₆₀with phosphorous precursors followed by annealing on Au(111).The defective surface structures are composed of larger triangles and dislocation lines with higher density,and are favorable for anchoring bulky C₆₀balls.This new reconstruction of 2D Au-P alloy monolayer has controllable defects and more catalytic active sites,having great potential applications in the field of adsorption and catalysis.Depositing bismuth on the surface of 2D Au-P alloy,it is found that with increasing the coverage of bismuth,the 2D Au-P alloy on Au(111)is covered by bismuth with periodic stripes,indicating the instability of 2D Au-P alloy.(3)Nanoconfinement assembly and dynamics of H₂O molecules on 2D Au-P alloy monolayer:Due to the six unbonded Au atoms from the substrate in the honeycomb structure,water hexamers confined within the nanopores of epitaxial Au-P alloy on Au(111).We found a localized interfacial charge rearrangement between the water hexamers and P atoms underneath that is responsible for the reversible desorption and adsorption of water molecules by changing the sample bias polarity from positive to negative,which is meaningful to tune the local electrostatic fields of 2D Au-P alloy,expanding its applications in nanoelectronic and optoelectronic devices.(4)Construction of the organic-Au-Blue P lateral heterostructure based on molecular self-assembly:We fabricated a lateral heterostructure comprising semiconducting F₄TCNQ-Au and metallic Blue P-Au networks with structurally and electronically abrupt interfaces by depositing F₄TCNQ molecules on the surface of Au-P honeycomb structure.The structural and electronic properties of the heterostructure have been investigated by means of STM/S,complemented by DFT calculations,demonstrating a structurally and electrically abrupt interface.Our approach offers the possibility of high flexibility and control that can be extended to other metal-organic species and 2D materials,establishing a foundation for the development of atomically thin in-plane superlattice and devices.