| Summary: | 碩士 === 國立臺灣大學 === 化學研究所 === 97 === My thesis is composed of three chapters which address several different but related aspects of the quantum transport in single molecular electronic devices.
In the first chapter, we investigate the relative importance of electron-electron and electron-phonon interactions on conductive behaviors of a mixed-valence molecule by using the two-site Peierls-Hubbard model. Transport behaviors depend on the interplay among these two interactions due to the structural instability that exhibits in this model Hamiltonian. We also demonstrate that the transport spectrum of this system can be qualitatively classified according to different types of adiabatic potential profiles. Moreover, we show that the distortion of the adiabatic potential surface may result in the missing of Coulomb diamonds and the negative differential conductance arises from the inelastic tunneling or the spin flip encountered between singlet and triplet states.
In the second chapter, we study the characteristics of thermopower of a molecular transistor consists of a single mixed-valence dimer in the weak coupling limit. The molecule is modeled by the two-site Peierls-Hubbard model, and its adiabatic potential profiles can exhibit different broken symmetries due to the competition of molecular parameters. In this chapter, we focus on the Coulomb-blockade oscillation regime and show how the thermopower reflects the symmetry of the first excited state which directly corresponds to different electron-phonon coupling.
Finally, in the final chapter, we argue that an ideal electrical wire needs not only good conductivity for its central conductor but also a surrounding insulating layer in order to protect its current from leaking. We show that compounds consisted of the extended metal-atom chains are promising candidates to be the smallest molecular electrical wire for future practical applications. The electron can tunnel across core metals easily, while the internal current is insulated from outside by the surrounding $pi$-conjugated functional groups. Moreover, we also show the existence of unavoidable hidden pathways at each site to the electrodes in a nanoscaled quantum circuit. Nevertheless, the Kirchhoff''s junction rule still holds when the current inflow and outflow arising from the additional terms of the self energies of contacts are included.
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