Principle And Mechanism Of On-surface Synthesis On Semimetal And Noble Metal Surfaces

With the rapid development of semiconductor industry,interface enigeering have been seriously taken into account gradually.Meanwhile,the mature technology of scanning tunneling microscope triggered the widely application of on-surface synthesis into precisely fabrication of nanostructure.Apart from the solution-chemistry synthesis,on-surface synthesis under ultrahigh vacuum environment shows its superiority in predesign of nanostructure and control of reaction process,which have been a great success in producing new functional nanomaterials.However,a big challenge of irregular growth of polymers on substrate appears and need to be overcome for potential application in the future.Recently,several groups have tried to understand the mechanism of on-surface synthesis so that precisely fabrication of nanostructure with long-range order could be fully managed.In this thesis,exploring the assemble behavior of precursor on substrate,reaction pathway at elevated annealing temperature and origin of catalyst have been studied to find the important factors related to the growth quality of nanomaterials.Firstly,the assemble pattern of 2,7-dibromopyrene?Br₂Py?absorbed on the Au???surface has been investigated by scanning tunneling microscope?STM?under different coverages and annealing temperature.It has been found that assemble precursor and extended supramolecular structures are balanced by intermolecular halogen bonding.Further,the reaction pathway of thin layer of Br₂Py on Au???heated step by step up to 300?has been explored.Organometallic intermediates with the gold-carbon bonding has been observed after first heating to 150?.Combined with XPS results and DFT calculation,we found Au adatoms play an important role in catalyzing dehalogenation process of Br₂Py absorbed on Au???,and the energy acquired by Au???surface to activate C-Br bond is higher than Au adatoms.Compared to the widely reported catalysts from noble metal surfaces,my PhD work creatively addressed the importance of adatoms in on-surface synthesis.Inspired by previous work about the Au adatom produced through heating Au???substrate,group V semimetals antimony and bismuth have been chosen to activate N-H bond via heating to produce enough semimetal adatoms.Photoelectron spectroscopy results indicate that semimetal adatoms diffuse to the bottom of metal-free phthalocyanine?H₂Pc?to activate N-H bond,ending in covalent coupling to four adjacent nitrogen,and how easily the semimetal adatoms produced by heating is a key factor to the metalation process.Apart from surface adatoms originating from the substrate,extra cobalt atoms have been introduced through additional deposition to check if they exchanged with copper atoms as the new coordinated central.Ultimately,the exchange process was found to occurr at room temperature,however,copper atoms can't be exchanged back even after annealing to 500?.Thus,this work has also addressed the catalysis discrepancy between different metal atoms.In my PhD thesis,the self-assemble behavior of molecular layers and the manipulation of surface adatoms have been thoroughly explored in order to obtain covalently bound nanoarchitecutures.It is demonstrated in the end that surface adatoms play an important role in on-surface reactions,not only in surface Ullmann coupling but also in metalation on semimetal surface,which could serve as an appealing guide to on-surface synthesis.