Fabrication And Physical Properties Of Several New Type Of Two-dimensioanl Materials And FeTPP Molecular Nanostructures

In recent years,two-dimensional materials and organic molecules have been regarded as ideal material carriers for constructing nanoscale electronic devices in the future.For two-dimensional materials,graphene has been successfully exfoliated since2004,its excellent properties,such as:ultra-high carrier mobility,good light transmittance,ultra-high Young’s modulus,room temperature quantum Hall effects,superconducting transitions,etc.,inspire researchers to explore the world of two-dimensional materials.After the advent of graphene,carbon-based one-component two-dimensional materials（silicene,germanene,tinene,etc.）,transition metal sulphides Two-dimensional materials of family compounds（molybdenum disulfide,etc.）have been introduced one after another,and they have exhibited a series of excellent properties,which make everyone look forward to two-dimensional materials.In terms of organic molecules,OLEDs and solar cells that have been industrialized have been greatly affected by human life because of their unique optical and electrical properties and high chemical stability.The development of surface molecular science provides a good research planel for the study of nanostructure construction and physical properties of organic molecules.This paper will introduce the use of bottom-up methods to successfully grow several new two-dimensional materials on the surface of graphene,using surface analysis methods(such as:scanning tunneling microscopy（STM）,angular resolved photoelectron spectroscopy（ARPES）X-ray photoelectron spectroscopy（XPS）,low energy electron diffraction（LEED）,etc.,combined with density functional theory（DFT）,to study the structure and physical properties of the new two-dimensional materials.At the same time,this thesis uses STM,combined with DFT,to introduce the nanostructure of iron porphyrin molecules on the metal surface and the chemical activation of C-F bonds on the metal surface.This paper has four main parts:Research on the thermal drive phase transition of single layer Cu₂Se.Two-dimensional materials,especially TMDCs,have great interest in the properties before and after the phase transition,and the rich physics contained in them.The researchers have generated great interest.Based on this,a single-layer Cu₂Se film has been grown.For the first time,the phase transition under the two-dimensional limit induced by the heat drive method was reported,and the phase transition behavior（such as liquid water ice）which is ubiquitous in the three-dimensional world was studied at the two-dimensional limit.In this paper,the structural transitions of the single-layer Cu₂Se before and after the phase transformation were determined by STM and STEM.Combined with the DFT theoretical calculation,two structural models before and after the single-layer Cu₂Se phase transition are given.Then,using the continuous temperature-changing LEED experiment,the structural change of single-layer Cu₂Se in K space with temperature was observed, and the phase transition temperature was about 147 K.Using the variable temperature ARPES,we found that the energy band structure of the single-layer Cu₂Se changed before and after the phase transition,and the degenerate energy band of the Fermi surface attachment was poorly cleft.The theory also gives a mechanism explanation for the phase transition of single-layer Cu₂Se.From the perspective of phonon vibration,the phonon spectrum at low temperature and room temperature is given.Further,from the perspective of molecular dynamics simulation,a single layer of Cu₂Se is also given.Vibration at different temperatures.After successfully growing a single layer of Cu₂Se,we also successfully developed the same type of two-dimensional material Cu₂Te,and characterized it by STM and LEED.XPS measured its stoichiometry,and the structure DFT theoretical calculation,a structural model of a single layer of Cu₂Te is given.Afterwards,the electronic structure of single-layer Cu₂Te was also characterized by ARPES,which is in good agreement with the theoretical results.It proves that the structural analysis of single-layer Cu₂Te is correct.We also studied the chemical stability of the single-layer Cu₂Te.The single-layer Cu₂Te,after half an hour of exposure to the atmosphere,did not deteriorate.A sandwich film structure was constructed using the synergistic assembly of porphyrin iron molecules and DABCO molecules on the Au（111）surface.The formation mechanism of the sandwich structure of porphyrin iron and DABCO molecules was analyzed by STM,XPS and thermal desorption mass spectrometry. First,a single layer of porphyrin iron film was formed on the surface of Au（111）. The excess molecules and the porphyrin iron suspended Cl atoms were removed by heating,and then the DABCO molecules were deposited because the activity of the porphyrin iron center was large.The DABCO molecule regularly adsorbs the molecular center of the porphyrin iron.Then a third layer of molecules is deposited and a regular mirror-symmetrical sandwich structure is formed.In this process,we used XPS to observe the chemical information of the central iron atom and the N atom of the coordination field,and also analyzed the formation mechanism of the molecular sandwich structure by temperature.Using different chemical catalytic activities exhibited by different metal surfaces, we investigated the activation of C-F bonds of Fe TPPF20 on Au（111）and Cu（111）. Using STM characterization,it was found that on the surface of Au（111）,the Fe TPPF20 molecule undergoes an intramolecular reaction,because all the F in the ortho position C-F on the Fe TPPF20 molecule is defluorination,and intramolecular cyclization occurs,and four kinds of cyclization reactions are generated.We found that around 80%of the products are two chiral molecules,and the two molecules self-assemble into islands.On the surface of Cu（111）,we found an intermolecular reaction of Fe TPPF20 molecule,defluorination between meta-C-F of Fe TPPF20, and a C-C bond with a nearby Fe TPPF20.