Electrical Transport and Current-driven Dynamics in Molecular Junctions

Chao-Cheng Kaun (關肇正 )

Research Center for Applied SciencesAcademia Sinica

July 3, 2010

Collaborators:D. A. Luzhbin (RCAS)N. L. Yoder, R. Jorn, T. Seideman and M. C. Hersam (Northwestern Univ., USA)

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)

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. C 111, 11450 (2010)

Is the HC and LC due to atop-hollow and atop-atop contact geometries?

Nature 395, 780 (1998)

Faraday Discuss. 131, 145 (2006)

Experimental results

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)

N. L. Yoder et al., PRL 97, 187601 (2006)

-2V, 0.1 nA

-2V, 0.1 nA

Elevated sample bias (threshold voltage: -2.5 and 3.5)

Experimental results

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

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

Our model:

Cyclopentene -2.49 6.90Cyclopentene+Si -2.00 2.95

HOMO LUMO

Hybridization introduces new states into the gap

PDOS peaks and the localized orbitals:

The negative ion lifetime 257 fs

The positive ionlifetime 94 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.