Manipulation Of Electron States Of Low Dimensional Carbon Nanostrutures On Transition Metal/semiconductor Substrates

The interface between materials has a decisive influence on the performance of devices.The performance of photovoltaic cells,transistors and other devices are closely related to the interface of materials.Therefore,it is important to study the interface properties of materials.In addition,small organic molecules have attracted much attention in recent years due to their modular assembly and flexibility.However,due to the differences between the interface behavior of organic molecules and metal(semiconductor)and that of traditional semiconductor,it is necessary to further study their interface behavior.In this thesis,the interfacial properties of organic small molecule-metal interface and organic small molecule-semiconductor interface are discussed firstly.Secondly,the main factors affecting these properties are summarized and the conclusion that these properties affect the electronic state of the interface is drawn.Finally,according to these factors,representative small molecule cobalt phthalocyanine(CoPc)and 2,7-dibromopyrene(2,7-Dibromopyre)are selected.With Ag(111),Cu(111),Si(111)and SiC(0001)as substrates,the electronic states of organic molecules on metals and semiconductors were studied,and their electronic states were controlled.In general,the experimental part of the article can be divided into three parts.Chapter 3 is the experiment of electronic state regulation of small organic molecules on metals.Chapter 4 and Chapter 5 compare the structure of small organic molecules on metals and semiconductors,and regulate small organic molecules on semiconductors.Chapter 6 discusses how to regulate single-layer graphene on SiC substrates.CoPc atom substitution reaction occurs at the interface of Cu(111).Substrate Cu atom substitutes for Co atom in the center of phthalocyanine ring to form CuPc,and product Co atom forms alloy with Cu substrate.This process starts at room temperature,and thermal annealing promotes the reaction.The trend of electronic states can be obtained through XPS and UPS.DFT calculations verify our hypothesis.In this chapter,we can make small organic molecules react with substrates by in situ annealing,and control the changes of electronic states.Self-assembled C16H8Br2 island structures can be prepared on room-temperature substrates.The intermediate(Ag-C16H8-Ag)and chain structure([C16H8]n)formed by the reaction of C16H8Br2 with Ag atoms can be obtained by preparing samples on hot substrates.The Br atoms produced during the process affect the orientation of the intermediate and chain on Ag(111)surface.Different from the previous methods,C16H8Br2 on Si(111)7×7 was heated by direct current heating to obtain samples,and its electronic state changes were studied.It was concluded that dibromopyrene could dehydrogenation and debromination to form radical-C16-structure(Radical 2,7-Dibromopyrene,RDP).These activated molecules were self-assembled on Si(111)7×7 surface by electrostatic repulsion,and the number of direct current heating(Flash)could be controlled.Stable chain carbon nanostructures were formed on semiconductor Si.By comparison,the distance and orientation of organic molecular monomers and chains on Ag metal are controlled by hydrogen bond interaction,while the orientation of RDP and organic molecular chains on Si semiconductor is affected by electrostatic repulsion.Quasi-freestanding graphene was obtained by intercalating Fe atoms on SiC(0001).Firstly,a single layer of graphene was obtained by Flash SiC(0001),on which the Fe atoms were vaporized,and then the quasi-freestanding graphene structure was obtained by multi-step thermal annealing.In this process,the change of core energy level can be clearly seen through XPS,and the increase of graphene content can be found.The change of valence band was observed by ARPES,and the transition from single-layer graphene to double-layer graphene was observed.In this process,Raman spectroscopy can be used to determine that the quality of graphene has been improved.In this thesis,we mainly discuss the behavior of organic molecules on metal and semiconductor substrates and control their electronic state change process,mainly through thermal annealing(radiation heating,direct current heating)and intercalation of atoms.It is hoped that this thesis can broaden the preparation methods of carbon nanostructures on metal/semiconductor substrates and provide reference for electronic state regulation of low-dimensional carbon nanostructures.