Scanning Tunneling Spectroscopy Of Surface Supported Graphene Nanoribbons And Multilayer Organic Films

Graphene,first successfully prepared in 2004,has attracted growing interest in view of their potential applications in next-generation carbon-based electronics.While the band structures of Graphene exhibit semimetallic behavior,impedes their applications as real semiconductor devices.To open the band gap,quasi one dimensional graphene nanoribbons(GNR)was put forward according to edge effect and quantum confinement effect.On the basis of tight binding theory,local density approximation(LDA)and GW approximation with first principle,theoretical researchers reckon that band gap can be realized by GNR,especially GNR with armchair edge structure.For armchair graphene nanoribbon(AGNR),it can be divided into three families according to their widths,and band gap is inverse proportional to the width in same family.Following the theoretical forecast,scientists utilized ultrahigh vacuum technique to fabricate atomically precise GNR in a bottom-up method,which makes it possible to investigate the electronic structure of GNR with scanning tunneling spectroscopy and photoemission electron microscopy.However,all the GNRs mentioned before were fabricated on a certain metal surface,thus interaction can't be avoided between GRN and metal substrate.Apparently the electronic structure obtained from experiments is not the intrinsic property of GNR.So far,some theories and models have been used to calibrate the effect of substrate,while they are not perfect and versatile in different families.Hence it is of great significance to complete the test of band gap of armchair GNR in different families and try to explain the effect of metal substrate on surface material from diverse point of view:1.Utilize scanning tunneling spectroscopy to get band gaps of 3P family AGNRIt's a developed technique that graphene nanoribbons can be fabricated on catalytic metal surface with organic molecule as precursor.This method is based on dehalogenation processes,the final products will be formed after cyclodehydrogenation in a higher temperature.We took example by this method and fabricated 3P family GNR with diverse widths simultaneously on Au(111)surface with 4,4"-dibromo-p-terphenyl(DBTP)as precursor.Following we took advantage of scanning tunneling spectroscopy(STS)to obtain the electronic structure of ribbons.As a result,we can get the relationship between geometric structure and electronic structure.Combining the results of the other two series and theoretical calculation,we hold the view that the theory which was tried to explain the effect of substrate is not versatile.2.Use scanning tunneling spectroscopy to investigate the effect of metal substrate on the electronic structure of multilayer organic thin filmOn Ag(111)surface,two kinds of derivative molecule of pentacene,6,13-pentacenequinone(P2O)and 5,7,12,14-pentacenetetrone(P4O)were used to investigate the interaction between self-assembled multilayer film.Through STM images,we can conclude that when CuPc is absorbed as second layer,the property of first layer will make effect on the approach of CuPc absorption.On Ag(111)surface which is already absorbed by P4O,CuPc will be absorbed only as second layer,while on Ag(111)surface which is already absorbed by P2O,CuP c will directly absorbed on Ag(111)with replacement of the first layer molecules.This discrepancy is caused by the interaction between first layer material and silver substrate,which implies the interaction between silver and P4O is stronger than P2O,which is in accord with results of other experiments.For deeply understanding the electronic structure of P4O and P2O,STS was used to investigate their electronic properties on Au(111),Ag(111)and Cu(111)surfaces respectively.