1. Electrical Transport and Current-driven Dynamics in Molecular Junctions Chao-Cheng Kaun ( 關肇正 ) Research Center for Applied Sciences Academia Sinica July 3, 2010 Collaborators: D. A. Luzhbin (RCAS) N. L. Yoder, R. Jorn, T. Seideman and M. C. Hersam (Northwestern Univ., USA)

2. Outline: 1.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)

3. 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.

4. 1. High- and low-conductance in alkanediisothiocyanate single-molecule junctions: Experimental results J. Phys. Chem. C 111, 11450 (2010) Is the HC and LC due to atop-hollow and atop- atop contact geometries?

5. Nature 395, 780 (1998) Faraday Discuss. 131, 145 (2006) Experimental results

6. Our model: The HC and LC may comes from the geometric configurations of electrodes

7. Sumary: Our first-principles calculated results are agree with measured data The HC and LC may comes from the geometric configurations of electrodes

8. 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).

9. Desorption of cyclopentene from Si(100) N. L. Yoder et al., PRL 97, 187601 (2006) -2V, 0.1 nA Elevated sample bias (threshold voltage: -2.5 and 3.5) Experimental results

10. Previous studies: benzene bound to Si(100) with π- orbital character S. Alavi, et al., PRL 85, 5372 (2000). Low-lying ionic resonances Why threshold voltages is so small (-2.5 V and 3.5 V)? Cyclopentene on Si(100): A saturated molecule

11. The yield is a factor of 500-1000 lower than for benzene/Si(100) or chlorobenzene/Si(111). A new avenue for desorption dynamics! Yield = N*e/(I*t) Experimental results

12. Our model: Cyclopentene -2.49 6.90 Cyclopentene+Si -2.00 2.95 HOMO LUMO Hybridization introduces new states into the gap

13. PDOS peaks and the localized orbitals: The negative ion lifetime 257 fs The positive ion lifetime 94 fs

14. Geometries of cyclopentene on a Si 9 H 12 cluster: Neutral molecule Positive molecule Negative molecule

15. Sumary: Hybridization introduces new states into the gap leading to lower threshold voltages New desorption pathways are found in a cyclopentene/silicon system.