| For nanoscale material,the size of the material has an important impact on its physical and chemical properties,and their electronic structure highly depends on their sizes.However,the understanding of the structure-electronic property correlation remained challenging due to the experiemtnal dififculties to investigate the charge transport through nanoscale materials,which also offers a new chance for revealing the novel physicochemical properties of nanocluster materials.Electronic transport properties of nanoscale material structure can reflect to a large extent the inherent characteristics of the component,geometry structure,electronic structure and surroundings of the detected sample.Besides,development of single-molecule electronics measurement techniques provide the possibility of investigating the electronic property of nanostructure under single molecular scale.Thus,investigating the charge transport properties through single nanocluster junctions can offer us the access to recognize the fundamental nature of these important transition state material structures,and to develop the applications of single cluster in electronics field.The focus of this thesis is to study the charge transport through atomically defined single silver nanoclusters by mechanically controllable break junction(MCBJ)technique,and to explore the unique electronic structure and bandgap properties from the view of charge transport through single cluster with the ultimate aim to provide experimental or theoretical support for developing single cluster catalysis or electronics.In this work,we investigate the charge transport properties of spherical silver nanocluster,non-spherical silver nanocluster and gold-silver alloy nanoclusters.It is found that the conductance corresponding to the spherical silver clusters increases with the size of the nanocluster.For the non-spherical silver nanoclusters Ag63(cube),Ag43(tetrahedron),Ag,36(oblate spheroid),and Ag78(chiral twisted triangular prism),the statistical results exhibit different conductance values corresponding to different characteristic length.It is also found that the high conductance of the single cluster junctions is corresponding to the long junction configuration and the low conductance is corresponding to the short junction configuration formed between the two electrodes.Furthermore,for the same cluster,its conductance also increases with the stretching distance between the two gold electrodes till the rupture of the cluster junction.Especially for the biggest silver nanocluster Ag374,with the diameter of 3 nm,it’s detected that the conductance increases from 10-4.08 G0 to 10"3 20 Go during the stretching process.The control expeirment demonstrated that gold electrode-cluster metal core-gold electrode junctions are formed and ruptured repeatedly during the conductance measurment of single-cluster junctions,suggestingthat electrons might transport from one electrode through the metal core to the other side without passing through the surface ligands of the cluster.The increase of the conductance with the nanocluster size is due to the decrease of the HOMO-LUMO gap of the cluster with the size.As perspective,the investigations of atomically well-defined single cluster junctions may offer an unqiue chance to monitor the catalytical reaction on the cluster surfaces. |
