Construction And Properties Of Several Novel Two-Dimensional Materials

As the size of electronic devices approaching its theoretical limit nowdays,two-dimensional(2D)materials,as the most promising candidate for the developing of next-generation electronic,optoelectronic and spintronic devices,are drawing great attention from researchers all over the world.In order to maximize the application potential of 2D materials,it is necessary to further explore the novel properties in the2D systems.Based on the principle that structure determines properties,exploration of novel properties requires more means to control the structure of 2D materials.Therefore,how to construct new structures in 2D system has become an issue worthy of study.This thesis mainly focuses on two kinds of 2D material systems:Monolayer vanadium diselenide(ML VSe₂)on graphite surface and selenium(Se)intercalation to graphene-Pt(111)interface,including their fabrication,structural engineering and properties.(1)Research on the fabrication and properties of ML VSe₂.The growth of ML VSe₂ on highly oriented pyrolytic graphite(HOPG)was realized by molecular beam epitaxy(MBE)method.And the atomic structure of the ML VSe₂ was characterized by scanning tunneling microscope(STM)and other measurements.Further scanning tunneling spectroscopy(STS)measurements revealed that the monolayer VSe₂ has the predicted magnetic characteristic peaks in its electronic density of states and a lower work-function at its edges.In addition,air exposure experiments show good air-stability of the monolayer VSe₂.Such high-quality monolayer VSe₂,an air-stable2D material with magnetism and low edge work function,is promising for applications in developing next-generation low power-consumption,high efficiency spintronic devices and new electrocatalysts.(2)Research on the 1D-patterned ML VSe₂ and its dispersive deposition of Pt atoms.Se-deficient defects was induced to ML VSe₂ by annealing,leading to the spontaneous formation of a well-ordered 1D pattern in it.Such 1D pattern can be reversibly transformed to homogenous VSe₂ monolayer by restoring Se atoms.STM measurements combined with theoretical calculations revealed the atomic structure of the 1D-patterned VSe₂ and the mechanism of the reversible structural transformation.Moreover,the dispersive deposition of Pt atoms on the 1D structures of patterned VSe₂ was achieved.Theoretical calculations found that their catalytic activity for hydrogen evolution reaction(HER)is as good as that of Pt surfaces.The formation of such 1D pattern not only demonstrates an effective way of structural modulation in2D materials,but also enriches the potential of intrinsically patterned 2D materials for promising catalytic activities.(3)Research on the Se monolayer intercalation to graphene-Pt(111)interface.By inducing confined conditions of graphene-Pt(111)(Gr/Pt(111))interface,the selenization of Pt(111)was suppressed to form a Se intercalated layer,instead of a Pt Se₂ monolayer.Experiments with selenized graphene-island samples demonstrated that the monolayer Pt Se₂ was controllably fabricated only on the bare Pt surface,while the Se intercalated layer was formed underneath Gr,as verified by scanning transmission electron microscopy(STEM)and STM.In addition,low energy electron diffraction(LEED)and STM measurements show that the orientation of the Gr island exhibits a negligible influence on the Se intercalated layer induced by the Gr coating.This work provides a new method to control the fabrication and pattern 2D materials during the fabrication process using the 2D confined technique.(4)Research on the Se nanowire intercalation to graphene-Pt(111)interface.By limiting the amount of Se to a very low level,a sort of Se nanowire intercalation structure was fabricated.And the atomic structure of such intercalated nanowires was revealed by STM.It was also found that the nanowires have great structual flexibility,which can be precisely shaped by STM tip.Further STS measurements showed that such nanowire structures have significant influence on the electronic structure of graphene on it.In other words,with such nanowire intercalation,the electronic structure of graphene can be modulated without breaking the structure of it.Such results are of great significance to construct novel physical systems for search and to extend the application of graphene.