The Effects Of Solvent Environment On The Electronic Properties Of Molecular Devices

Within the last decade, there is an increasing interest in molecular electronics that is one of the important branches of the nanoelectronics. With molecules as a drive of information processing, lots of electronic characters in the molecular devices are researched in the molecular electronics. Nowadays, many theoretical and experimental groups have devoted to study of electronic properties of single molecule and obtained exciting results. One has noted that small conjugated molecules, single- and multiple-wall carbon nanotubes and macromolecules such as DNA possess many useful device characteristics, for instance, molecular switch, molecular memory, negative differential resistance and single-molecule transistors. While experimental techniques and theories in molecular electronics need to be developed, because not only do theoretical results not give a well explanation for experimental measurement, but also the experimental results of the same molecule with different techniques show great difference among each other.The main reason for the questions mentioned above is that, compared with the electrode, the molecule is a small system in the size. Therefore the geometric and the electronic structures of the molecule are likely influenced by the change of the external factors. The electronic structure of molecules dominates their electronic properties directly. In this thesis, based on the quantum chemistry calculation, different gold-molecule-gold systems are investigated by using elastic scattering Green's function method. The relationship of molecular structure and properties, as well as the environment effect on the electronic properties of molecular junctions, is investigated. Firstly, we study the molecular device that situates in the vacuum and compare our result with experimental measurement. We find that our result has a relative agreement with experimental results within voltage range from 0.8 V to 2 V. In our work, the currents at 0.8 V and 2 V are respective 0.39 nA and 45 nA, while the corresponding experimental values are 2.2 nA and 14 nA. We thus could say that our model and method together with computational basis vectors are reliable. Then, we study electronic properties of molecular devices with different number of waters. With the distance of two electrode fixed, we discuss the change of electronic properties of molecular devices with different number of waters. When the molecular junction absorb two waters, the molecular junction's conductivity is reduced. When more waters are adsorbed, the molecular junction's conductivity gets large. We draw out currents of molecular devices with different numbers of waters at 0.5 V and compare with experimental measurement. The theoretic calculations show a good simulation of the experiment.This thesis consists of five chapters. In the first chapter, background and recent development of molecular electronics in the view of experimental and theoretical works are introduced. The questions need to be solved in this area in the future are also mentioned in this chapter. The theory of self-consistent field (SCF) for many-particle system is presented in the second chapter which includes Born-Oppenheimer approximation, Hartree-Fock method and density functional theory. The elastic scattering Green's function method, the electronic transition spectra and current-voltage formula for the molecular junctions are introduced in the third chapter. In the fourth chapter, the computational work and the main theoretical results are presented. The electronic properties of conjugated oligomeric phenylene ethynylene (OPE) molecular junctions with different numbers of waters are analyzed. The fifth chapter draws a conclusion and views the future development of the molecular electronics.