Quantum Interference Effect And Electrical Transport Properties Of Rare Earth-Transition Metal Clusters Based On Scanning Tunneling Microscope Break Junction Technique

The purpose of molecular electronics is to construct nanoscale devices with different electrical functions by single or several atoms,molecules and clusters,so as to achieve or even exceed the performance of silicon-based electronic devices.At present,a large number of electrical measuring techniques at molecular scale have been developed in single-molecule electronics,such as scanning tunneling microscope break junction technique,mechanically controlled break junction technique and carbon-based molecular junction technique.These electrical measuring methods have been widely used to study the charge transport abilities of organic molecules at single-molecule scale,and have also realized the construction and characterization functions of singlemolecule devices,including molecular switches,molecular rectifier and molecular transistors,which are significant for molecular electronics.At present,the development of molecular electronics mainly has two aspects.One is the depth of research contents,which is to study novel physical phenomena and special effects in the charge transport process,including quantum interference effect and thermal effect,etc.These studies can improve the electrical properties of molecular devices.The second one is the scope of research contents,which is to explore new systems of molecular electronics,such as nanocluster and biomolecular systems,to expand the molecular materials with different functions and properties.In view of the above research perspectives,this paper conducted a detailed study on the quantum interference effect and the charge transport properties of rare earth-transition metal cluster molecules at single-molecule scale by means of scanning tunneling microscope technique.The main investigation process and contents are as follows:(1)Quantum interference effects based on configuration and position controlThe quantum interference phenomenon has become an important factor that can affect the molecular charge transport process,so it is urgent to establish a simple and effective molecular design strategy to understand and regulate quantum interference effect in molecular electronics.In this paper,we take the oligophenyl-acetylene molecular system as the main research system.Through the conformation and position change of the methoxy substituents around the central benzene ring,we realize the regulation of the quantum interference effect of the molecular system.These methoxy groups can be regarded as "molecular taps",and the transformation of conformation states can achieve effective switch control of molecular current.In addition,the results of the "magic ratio" theory and DFT can also support our experimental results.This study provides a new chemical design strategy for the regulation of single-molecule quantum interference effects and provides experimental and theoretical support for the construction of novel electronic functional single-molecular devices.(2)Study on charge transport properties of rare earth-transition metal clustersDue to the special size and structure features,rare earth-transition metal clusters have promising applications in the fields of magnetism and catalysis.To make full use of functional properties of cluster molecules,it is significant to investigate the relationship between their structures and properties.Starting from the single cluster,we investigate the charge transport properties of lanthanum rare earth-transition metal clusters Eu12Fe14,Gdi2Fe14,Tb12Fe14,Dy12Fe14.Through the analysis of the flicker noise and DFT calculations,we find that the charge transport process of these clusters are dominated by through-space state.In addition,different rare earth atoms have different coupling interactions with iron atoms,and the on-site energy of different rare earth atoms are also different,so these factors can cause the different HOMO-LUMO gap for different clusters in transmission spectrum,which can also affect the charge transport performance.This study is of great significance to understand the electrical transport performance of clusters and the corresponding relationship between the structure of the clusters and the electrical transport process.