On-Surface Preparation And Scanning Probe Microscopy Study Of Low Dimensional Structures

Dimensional effect is one of the intrinsic properties of condensed system.The symmetry of condensed system can be switched by the regulation of local dimensions,which can deeply influence the physics of the condensed matter.Scanning probe microscopy(SPM)can detect and manipulate low dimensional materials in real space,thus it becomes a extremely important method for scientific research.In this thesis,we will utilize this technology to the study of the synthesis of ordered low dimensional materials,localized intermolecular interactions and the interference of low dimensional quantum states.In Chapter ?,we introduced the basic theory of scanning tunneling microscopy(STM)and atomic force microscopy(AFM)as parts of SPM.Furthermore,we discussed the operating principles for STM and non-contact AFM working in low temperature and ultra-high vacuum(UHV).In the end we introduced the research progress of both STM and AFM in recent years.In Chapter ?,we summarized the strategies and the recent progress of on-surface synthesis.Using UHV on-surface reactions,we synthesized one-dimensional graphene nanoribbons and graphdiyne wires.Comparing with the results of STM and AFM images,we discovered the new mechanism of protection of alkynyl from on-surface gold adatom.Based on this discovery,we optimized the reaction process and obtained much more ordered low dimension material.We detected the interactions between the gold adatom and the alkynyl as the theory predicted and mapped them in real space.Moreover,we measured the scanning tunneling spectroscopies in different positions of a graphdiyne wire which met the result of theoretical calculation of its band structure.We also designed and synthesized an on-surface chiral precursor molecule,and synthesized zigzag type graphene nanoribbon via on-surface reactions.In Chapter ?,we introduced the halogen-halogen interactions between the halogen organics called halogen bonds,and discussed the current progress of the imaging of intermolecular interactions by AFM.Using different tip decorating molecules,we imaged the interactions between the bromine atoms in HBT molecules in real space.The following calculations showed that the interactions were far stronger than normal halogen bonds.In next step,we doped alkali atoms to the HBT self-assembly,and imaged it by AFM.We noticed that the co-assemblies of different alkali ions were strongly influenced by the radii of these alkali ions,and the significant difference of lithium ions from other alkali ions which indicated the existence of dilithium ions.In Chapter ?,we introduced the background and the newest progress of 2D transition metal dichalcogenides(TMDCs),with the introduction of charge density wave(CDW)phenomenon in several TMDCs.We detected the influences of defects and doping to the TiSe2 and SnSe2,then we prepared an in-plain heterojunction consisted by NbSe2 and TiSe2 with different CDWs by molecular beam epitaxy method.We observed the interference of both CDWs and found an explanation for this phenomenon.