Theoretical Studies On Inelastic Electron Transport Of Molecular Junctions

Molecule juctions have attracted much attention with the minimization of electronicdevices in recent years，and great progress has been achieved. However, there are stillmany problems urgent to be solved. As it is known to all, molecular devicesconstructed from different methods show diverse properties and even if the moleculardevices constructed from the same method also display different properties, which ingreat degree depend on plenty of factors such as the configuration of the junction, theorientation of the molecule and the intermolecular effects.The inelastic electron tunneling spectra is an effective tool to probe the propertiesof molecular devices because of its sensitivity. It can reflect the vibration of molecule,the composition of molecular junction as well as the internal information of moleculardevice. Unfortunately we can’t attain those goals as above merely by experiments, sothe theoretical work begins to play its role.The main content of our study is asfollows:1. Theoretical investigation of Inelastic Electron Tunneling Spectroscopy ofbimolecular junctionsFirst-principles investigation on the inelastic electron tunneling spectra ofbi-oligophenyleneethynylenes (OPEs)- monothiol molecular junctions is performed. Itis demonstrated that the inelastic electron tunneling spectras are very sensitive to thedeviation, stagger or separation of the two molecules in the bimolecular junctions.When the overlap between the two molecules is relatively strong, the out of planevibration modes are active in the spectra and provide more intermolecular tunnelingpaths for electrons.Our theoretical investigations provide the direct configuration-spectra relationshipof bimolecular junctions, which will help experimental workers to understand their results better and perform more precise measurement of the molecular junctions.2. Theoretical investigation of Inelastic Electronic Tunnling Spectroscopy ofmethyl isocyanide：First-principles investigation on the inelastic electron tunneling spectra of MethylIsocyanide molecule is performed，the results indicate that the inelastic electrontunneling spectra are very sensitive to the contact configuration and the orientation ofmolecule，which could be benefit for determining the geometric structure of device inthe experiment. Our results verify the preferred orientation property of inelasticelectron tunneling spectra.This thesis consists of six chapters as follows：In the first chapter, the investigationbackground, the preparation and measurement methods of molecular junctions and thebasic information of the inelastic electron tunneling spectroscopy are introduced. TheHartree-Fock method and the Density Function Theory have been presented in chaptertwo. The basis sets usually used in our calculations have been introduced simply.Following, the basic concepts to perform the calculation of the frequencies have beenexplained and the vibration modes of two kinds of model systems have been presentedat the last part of this chapter. In chapter three, transport mechanisms and thecorresponding theoretical methods as well as the basic information of the inelasticelectron tunneling spectroscopy have been briefly introduced. From chapter four tochapter six, the applications of the inelastic electron tunneling is presented. In chapterfour, we investigate the inelastic electron tunneling spectroscopy of bimolecularjunctions. In chapter five, we investigate the inelastic electron tunneling spectroscopyof methyl isocyanide. In chapter six, we draw a conclusion for the whole work of thisthesis and give the prospect of the IETS of molecular electronic devices.