Structure Modification And Properties Of Two-Dimensional Materials:PtSe₂ And Antimonene

The outstanding physical and chemical properties with its promising potential applications make graphene to be a“superstar”material,attracting increasing attention and intensive research rapidly after its first isolation in 2014.Meanwhile,the rise of graphene has opened up a new world of two-dimensional?2D?materials beyond graphene,inspiring people to show increasing enthusiasm for other 2D materials.Till now,among the huge family of 2D materials,2D transition metal dichalcogenides?TMDs?and graphene-like 2D materials?X-ene?have attracted continuous attention beyond graphene mostly due to their diverse and excellent properties,modifications in structures and properties,along with their versatility of applications.This thesis mainly focused on three novel 2D materials,named PtSe₂,NiSe₂ and antimonene,fabricating these materials in large area and high quality by the method of molecular beam epitaxy?MBE?in ultra-high vacuum?UHV?system,modificating their structures and properties by choosing proper substrates and experimental parameters,characterizing their structures and properties by combining low energy electron diffraction?LEED?,scanning tunneling microscopy?STM?,X-ray photoelectron spectroscopy?XPS?and first-principle calculations,finally investigating their potential applications in future application fields.?1?Monolayer PtSe₂,a novel 2D TMDs material with many superior properties and applications,has been fabricated in experiment recently.Based on this,this thesis focused on structure modification and functionalization of PtSe₂,transforming partial PtSe₂ with octahedral?1T?conformation into trigonal prismatic?1H?conformation and obtaining a novel PtSe₂ structure—intrinsically patterned 1H/1T-PtSe₂ triangular patterns by high-temperature annealing.Its atomic structure and formation mechanism were verified by combining LEED,STM,XPS and first-principle calculations.This structure can be modified by choosing different parameters,realizing the reversible transformation between 1H/1T-PtSe₂ and 1T-PtSe₂,obtaining 1H/1T-PtSe₂ with different domain size and density.In the end,this structure can be used as an intrinsically patterned template to be functionalized through selective adsorption,indicating the great potential of this new type 2D material structure in future applications.?2?Monolayer antimonene,a novel graphene-like material consists of antimony atoms,has attracted increasing attention since it was predicted to have excellent intrinsic optoelectronic properties and spin-electronic properties under strain modulations.However,studies on the preparation of monolayer antimonene and the modification of its structure and properties experimentally are still lacking.This thesis focused on structure and properties modification of antimonene.A novel flat antimonene monolayer on Ag?111?was firstly fabricated by MBE method.The atomic structure of antimonene with non-buckled honeycomb structure and stretched lattice was verified by LEED,STM and first-principle calculations,which is different from the buckled honeycomb structure in freestanding antimonene.The interaction states within the antimony-antimony and antimony-silver atoms are investigated by XPS and ELF calculations,indicating a continuous antimonene film with weak interaction to the substrate.The modification of its electronic structure was studied by calculations,demonstrating the semiconductor to semimetal transition and non-trivial topological states at the edge occurred in the flat antimonene monolayer.Combined with its good stability in O₂ atmosphere,flat antimonene monolayer has great potential in future topological electronic applications.?3?2D TMDs materials have attracted people's enthusiasm continuously with their versatile and novel physical properties and diverse application fields.However,there are still a large number of 2D TMDs not be obtained experimentally up to date.This thesis focused on the fabrication of a novel 2D material-layered NiSe₂.Here,large-area high-quality 2D NiSe₂ material was firstly fabricatied on Ni?111?substrate by“directly selenization”method.The successful formation and atomic structure of NiSe₂films were veryfied by combining LEED,STM and first-principle calculations,demonstrating a layered octahedral structure instead of the pyrite-type structure in its bulk form.The successful fabrication of novel 2D NiSe₂ film is a significant step forward in expanding the family of 2D TMDs materials,paving the way to the modification of structure and properties in 2D NiSe₂ film along with investigating its applications in the future.