Chongwu Zhou


Research Assistant Center for Microelectronic Materials and Structures Yale Univ. P.O. Box 208284 New Haven, CT 06520

tel: (203) 432-7567 fax: (203) 432-7769 e-mail: zhou@optik.eng.yale.edu

Education:
Ph.D Yale University, 1998 (expected)
B.A. University of Science and Technology of China, China, June 1993

Research interest:

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Break Junctions: Interesting physics and potential applications are expected when we are able to characterize the electrical properties of a single molecule. We report our approach to address a single molecule with mechanically controllable break junctions. We demonstrate that a quantum point contact consisting of a few atoms can be realized with break junctions and pronounced conductance quantization is observed at room temperature. Molecules of benzene-1,4-dithiol are self-assembled onto the two facing gold electrodes of a conventional mechanically controllable break junction to form a statically stable gold-sulfur-aryl-sulfur-gold system, which allows for direct observation of charge transport through the molecules. Current-voltage I(V) measurements at room temperature demonstrate a highly reproducible apparent Coulomb blockade gap of ~0.7V. The conductance-voltage G(V) curves show two steps in both bias directions with the first step ~0.045 5S (22 M) and the second step ~0.075 5S (13.3 M).

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Micrimachined Break Junctions: As a further advancement of the break junction technology, we report micromachined break junctions in silicon, which are one hundred times smaller than the conventional ones. Unmatched static stability in tunneling regime has been achieved: the variation of tunneling distance is about 3 pm in a 1kHz bandwidth.

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Fully Integrated Break Junctions: We present a detailed description of the fabrication and operation at room temperature of a new type of fully integrated break junction. The junction consists of a narrow metal wire bridging the gap between a suspended silicon nitride membrane and the bulk substrate. A gate electrode on the membrane controls the junction. In contrast to previous break junctions which use an external piezo, electrostatic force induced by the voltage bias between the gate electrode and the s ubstrate is used to adjust the contact size and tunneling distance. Both theoretical calculation and experimental results show that deflection of the suspended beam with atomic resolution can be achieved by fine tuning the gate-substrate bias. In the contact regime the conductance of the junction takes on discrete values close to multiples of the fundamental conductance unit when the constriction is reduced atom by atom. When the junction is tuned from tunneling to contact, it is demonstrated that the condu ctance can be controllably tuned to the first few quantization levels at room temperature.

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Nanopore: We present the investigation of a novel metal/organic monolayer/metal heterostructure diodes. Our technique provides well-defined, stable and reproducible metallic contacts to a self-assembled monolayer of 4-thioacetate-biphenyl with nanoscale area. Electronic transport measurements show a prominent rectifying behavior arising from the asymmetry of the heterostructure. Varying-temperature measurements reveal that thermal emission of electrons over a barrier of 0.22 eV dominates at positive bia s and the transport under negative bias is carried by hopping conduction.

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Publications:

1 C. Zhou, C.J. Muller, M.R. Deshpande, J.W. Sleight, and M.A. Reed, "Microfabrication of a mechanically controllable break junctionin silicon", Appl. Phys. Lett. 67, 1160 (1995).

2 C. Zhou, C.J. Muller, M.A. Reed, T.P. Burgin and J.M. Tour, "Mesoscopic phenomena studies with mechanically controllable break junctions at room temperature", in Molecular Electronics, edited by M. Ratner, in press.

3 C. Zhou, C.J. Muller, M.R. Deshpande, J. McCormack and M.A. Reed, "Conductance quantization in fully integrated break junctions at room temperature", in Nanowires, NATO Advanced Research Workshop, edited by P.A. Serena and U. Landman, in press.

4 M.A. Reed, C.Zhou, C.J. Muller, T.P. Burgin, J.M. Tour, "Conduction of single molecules", submitted to Science.

5 C. Zhou, M.R. Deshpande, M.A. Reed and J.M. Tour, "Fabrication of nanoscale metal/self-assembled monolayer/metal heterostructures", submitted to Appl. Phys. Lett.