Redox-assisted Electron Transport in Rotational State-based Molecular Electronics

Mei Xue
Advisor: Kang L. Wang

Wednesday, September 9, 2009 at 2:00pm-4:00pm
Engr IV Room 67-124

Abstract:
A new electrically driven molecular rotor device was studied. This device is comprised of a monolayer of redox-active ligated copper compounds sandwiched between a gold electrode and a highly-doped P+ Si substrate was fabricated. A self-assembly method to fabricate the molecular rotor layer was developed based on a "surface outward sequential synthesis" strategy that ensures the formation of Si-immobilized heteroleptic copper compounds. Indirect experimental evidence of the rotation of a rotor on a solid support was observed for the first time, and a theory was proposed to explain various experimental observations.

We conducted current-voltage spectroscopy (I-V) measurement on the afore-mentioned devices at different temperatures and observed a temperature-dependent negative differential resistance (NDR). A theoretical model based on the Time-dependent density functional theory was constructed, which suggests that the source of the observed NDR is the redox-dependent ligand rotation around the copper metal axel center, an explanation consistent with the results from an independent optical absorption spectroscopy experiment. Based upon the observed NDR, an electronic switch, with an estimated picosecond switching time, was suggested. An energy band diagram was built for explaining the electron transport behavior in the device operation.

To study the scalability of the molecular rotor devices, we extend our discussions to the general scalability of the electron and ion transport phenomena in semiconductor and molecular devices. Finally, we describe possible chip architectures to integrate molecular switches into the conventional CMOS circuits and to achieve a CMOL logic system.