| Summary: | 碩士 === 國立臺灣大學 === 化學研究所 === 107 === This thesis presents the molecular structures and the single-molecular conductivity of a long-chain-shaped polynuclear metal string complex [Ni11(bnatpya)4(NCS)2]4+ (Ni11) on the single crystal surface of Au(111) by ultrahigh-vacuum scanning tunneling microscopy (UHV-STM). The Au(111) surface was prepared by annealing to generate the reconstruction. Ni11 was dissolved in methanol and deposited on Au(111). At 78 K UHV-STM, the STM images showed oblate-shaped structures of Ni11 on Au(111). From the height profiles, single-molecular size of Ni11 could be obtained from the images of topography. Scanning tunneling spectroscopy (STS) indicated density of states (DOS) of Ni11 by dI/dV spectra exhibiting the distributions of peaks at -1.20 eV and +0.82 eV, excluding the shifting peak of gold surface state. Compared with ultraviolet-visible spectroscopy, the energy difference acquired from dI/dV spectra could be identified with aligned energy of HOMO-LUMO gap. The STM probe was able to contact the ending thiocyanate group of Ni11, which would contribute to the single-molecular circuit while the Ni11 molecules were lifted from the surface. Conductance-to-distance graph was measured in the process of lifting to calculate the single-molecular conductance. The measured conductance at 78 K was slightly higher than the previous results at room temperature. Despite the discrepancy from heat-dependent mechanism of electron tunneling, this is an important reference to further discuss on molecular conductance if considering the effects of setpoint bias as well as coupling interactions between ending thiocyanate group and the electrodes.
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