1) Molecular junctions
The presence of a strong inter-molecular interaction, in particular hydrogen bond, can introduce a negative differential resistance behavior in a charge-transfer molecular device. The underlying mechanism is found to be related to the geometry distortion and the dephasing of coherent electron transport processes.
2) Inelastic electron tunneling spectroscopy
A generalized Green's function theory is developed to simulate the inelastic electron tunneling spectroscopy (IETS) of molecular junctions. It has been applied to a realistic molecular junction with an octanedithiolate embedded between two gold contacts in combination with the hybrid density functional theory calculations. The calculated spectra are in excellent agreement with recent experimental results. Strong temperature dependence of the experimental IETS spectra is also reproduced. It is shown that the IETS is extremely sensitive to the intra-molecular conformation and to the molecule-metal contact geometry.
3) Nano-electronics
A) polymer
The room temperature IVs of the self-assembled TA-PPE molecular junction exhibit highly periodic and identical stepwise features, which correspond to the opening of different conducting channels of the polymer molecule for the coherent electron transport through the junction. The calculated and experimental results agreed well. It is shown that an 18 nm long polymer is of quantized electronic structures and behaviors like a ballistic transport device.
B) Nanotubes
A CIS based on ab initio quantum chemistry approaches is presented. It allows to study electronic structures and coherent electron transportation properties of single-walled carbon nanotubes (SWCNTs) up to 22nm in length using the hybrid density functional theory. The 22nm long SWCNT, consisting of more than ten thousands electrons, is the largest carbon nanotube that has ever been studied at such a sophisticated all-electron level. Interesting oscillating behaviour of the energy gap with respect to the length of the nanotube is revealed. The calculated current-voltage characteristics of SWCNTs are in excellent agreement with recent experimental results. It confirms the experimental observation that a 15nm long SWCNT is still largely a ballistic transport device. The proposed CIS method opens up a new door for the first principle study of nano- and bio-electronics.
4) Bio-electronics
The electronic structures and coherent electron transportation properties of short DNA molecules have been studied using a newly developed CIS method based on the hybrid density fuctional theory. The excellent agreement between calculated and experimental current-voltage characteristics for poly(G)-poly(C) DNA up to 60 pairs has been obtained which leads to an unambiguous conclusion that the elastic scattering process is the dominant electron migration mechanism in short DNA molecules. We have also derived the length dependence of coherent electron transport in the poly(G)-poly(C) DNA molecules.
