The Conductance Of Single-Molecule Junction With Phenyl-Based Derivatives And Crown-Ether

The development of electronic devices can promote great progress in science and technology. In order to continuously pursue the higher integration, molecular electronic device have been paid much attention, and brings a new field of science- molecular electronics. Molecular electronic devices include molecular switch, molecular wire, molecular rectifier, field effect transistor and so on. Those devices can only realized through the exploration of electronic transport properties of molecules, which can be obtained by measuring the conductance of metal-molecule-metal junctions. Many Factors can affect conductance of molecular junction, including molecular structure, metal material, anchoring group, contact configuration between the molecule and metal electrode, the surroundings, and so on. Usually, the construction and measurement of molecular junction with Au electrode can be realized by using the scanning tunneling microscope-break junction method (STM-BJ). But for non-Au electrode (such as Cu and Ag), we utilize an electrochemical jump-to-contact scanning tunneling microscope-break junction approach (ECSTM-BJ) to systematically measure the molecular junction conductance to over come the limitation of the traditional STM-BJ. The main researches of the thesis are as follows:1. The conductance of single-molecule junctions with terephthalic acid, 1,4-naphthalenedicarboxylic acid and 9,10-anthracenedicarboxylic acid binding to Au, Ag and Cu electrodes are systematically studied by using STM-BJ and ECSTM-BJ. The result shows that all three molecules contacting to Au electrode have three sets of conductance values and both show the order of terephthalic acid > 1,4-naphthalenedicarboxylic acid> 9,10-anthracenedicarboxylic acid, which may attributed to the different contact geometries between the molecules and electrodes. The single molecular conductance of terephthalic acid contacting to Cu and Ag electrodes was measured by ECSTM-BJ, and the conductance histograms showed a well-defined shape without any data selection. Two sets of conductance values were found for both Cu and Ag electrodes, and the high conductance were typically approximately three times larger than that of low conductance. For all three molecules, the conductance order follows the G(Cu)>G(Ag), which indicates the different electronic coupling efficiency between the molecules and electrodes. These results demonstrated the influence of electrode and molecular structure on the molecular junction conductance.2. The single molecular conductance of 2,6-naphthalenedicarboxylic acid, 2,2’-dicarboxylic acid and 4,4’-dicarboxylic acid binding to Ag and Cu electrodes were studied by using ECSTM-BJ. The conductance values follow the order of G(Ag)<G(Cu) for all three molecules, it may be due to the strong electronic coupling between the molecules and Cu electrode; And the conductance values follow the order of G(2,6-naphthalenedicarboxylic acid)<G(1,4-naphthalenedicarboxylic acid), because of the longer electron transport distance in 2,6-naphthalenedicarboxylic acid; Then, the conductance follow the order of G(4,4’-dicarboxylic acid)<G(2,2’-dicarboxylic acid), since there is also longer distance for electron transport of 4,4’-dicarboxylic acid.3. We desinged complexes of the crown-ether molecules and measured the conductance of complexes with metal ions binding to Au electrode by using STM-BJ. For the C42H44O9S4, the coordination of metal ions does not have much effect on the molecular junction conductance, it is possibly owing to the crown-ether in the molecular side chain, which make the coordination of metal ions has no impact on the structure of the main chain.. However, the coordination of metal ions can increase the molecular junction conductance of C48H48O9S4, and the order is K+>Li+>Ca2+>Ba2+>Mg2+>Na+, it may be because the torsion angle among the two benzenes changed in the main chain, and the coordination of metal ions could have caused the shifting of the molecular energy levers, and the ring size of crown-ether could also have effect on the electron transport.