A Study Of On-surface Fusion Of Graphene Nanoribbons Catalyzed By Ni Atoms By Using Scanning Tunneling Microscopy

The heterojunction of graphene nanoribbons has good electrical contact between the interfaces and the band gap facilitates the precise control of the graphene nanoribbons.It has good application prospect in electronic,optoelectronic and spintronic devices.In this paper,a new method of synthesizing graphene nanoribbons with heterogeneity and increasing their yield is proposed: the catalyst Ni is incorporated into the reaction.We experimentally grew samples by molecular beam epitaxy(MBE)and measured and characterized the samples using a low temperature,intense magnetic field scanning tunneling microscope(STM).The thesis is divided into the following three parts:The second chapter introduces the principle and the acquisition of ultra-high vacuum system,including all levels of vacuum pump and vacuum gauge.On this basis,we introduce the principle of scanning tunneling microscope,structure and imaging and detection technology.For the sample growth,a brief introduction of molecular beam epitaxy.Also introduced are the cryogenic and magnetic field technologies integrated in our Unisoku MBE-STM system.In the third chapter,we study the catalytic effect of Ni in the DBBA Ullmann coupling reaction by STM measurement,and catalyze the fusion of the edges of the graphene nanoribbons to form the nanoribbon heterojunction with adjustable width.At room temperature,we have obtained organometallic intermediates linked by a C-Ni-C bridge,which has never been seen in previous reports.It was found that Ni plays a catalytic role in the dehydrocyclization stage after debromination of DBBA molecules.Finally,we demonstrate that these convergent AGNRs are metal-semiconductor contact heterojunctions through the distribution of different electronic states in real space.Our research provides a catalyst that has made a breakthrough in improving the yield of edge-fused all-carbon AGNRs heterojunctions.The first half of the fourth chapter introduces Kondo resonance physical image,principle and STM detection.In the experimental part,we measured the long keying data of Fe-C bond by using STM topography to determine the formation of Fe-TCNQ organic metal self-assembly structure.By fitting the STS spectrum of this self-assembled structure,the formant of q = 0 near the Fermi surface under zero magnetic field was obtained,which confirmed the existence of Kondo effect,that is,Fe was magnetic in the molecular coordination field.