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Electrical Transport and Current-drivenDynamics in Molecular Junctions Chao-Cheng Kaun (關肇正) Research Center for Applied Sciences Academia Sinica Collaborators: D. A. Luzhbin (RCAS) N. L. Yoder, R. Jorn, T. Seideman and M. C. Hersam (Northwestern Univ., USA) July 3, 2010
Outline: • High- and low-conductance in alkanediisothiocyanate single-molecule junctions • Phys. Rev. B 81, 035424 (2010) • 2. Current-Driven Desorption at the Organic Molecule–Semiconductor Interface: Cyclopentene on Si(100) Current-Driven Phenomena in Nanoelectronics, in press (Pan Stanford, Singapore, 2010)
1. High- and low-conductance in alkanediisothiocyanate single-molecule junctions: Bridging up the theory and experiment is one of the key issues involving the progress of molecular electronics.
1. High- and low-conductance in alkanediisothiocyanate single-molecule junctions: Experimental results J. Phys. Chem. C111, 11450 (2010) Is the HC and LC due to atop-hollow and atop-atop contact geometries?
Experimental results Nature 395, 780 (1998) Faraday Discuss. 131, 145 (2006)
Our model: The HC and LC may comes from the geometric configurations of electrodes
Sumary: • Our first-principles calculated results are agree with measured data • The HC and LC may comes from the geometric configurations of electrodes
2. Current-Driven Desorption at the Organic Molecule–Semiconductor Interface: Cyclopentene on Si(100) Molecular electronic devices + silicon microelectronic technology The stability of organic molecules on semiconductors must be established. Saturated organic/silicon systems offer stability with respect to current-induced failure of silicon-based molecular electronics. S. N. Patitsas et al., Surf. Sci. 457, L425 (2000).
Desorption of cyclopentene from Si(100) Experimental results -2V, 0.1 nA Elevated sample bias (threshold voltage: -2.5 and 3.5) -2V, 0.1 nA N. L. Yoder et al., PRL 97, 187601 (2006)
Previous studies: benzene bound to Si(100) with π-orbitalcharacter Low-lying ionic resonances S. Alavi, et al., PRL 85, 5372 (2000). Cyclopentene on Si(100): A saturated molecule Why threshold voltages is so small (-2.5 V and 3.5 V)?
Experimental results Yield= N*e/(I*t) The yield is a factor of 500-1000 lower than for benzene/Si(100) or chlorobenzene/Si(111). A new avenue for desorption dynamics!
Our model: HOMO LUMO Cyclopentene -2.49 6.90Cyclopentene+Si -2.00 2.95 Hybridization introduces new states into the gap
PDOS peaks and the localized orbitals: The positive ion lifetime 94 fs The negative ion lifetime 257 fs
Geometries of cyclopentene on a Si9H12 cluster: Neutral molecule Positive molecule Negative molecule
Sumary: • Hybridization introduces new states into the gap leading to lower threshold voltages • New desorption pathways are found in a cyclopentene/silicon system.