AVS 52nd International Symposium
    Electronic Materials and Processing Thursday Sessions
       Session EM1-ThM

Paper EM1-ThM4
Probing Silicon Based Molecular Electronics with Ultra-High Vacuum Scanning Tunneling Microscopy

Thursday, November 3, 2005, 9:20 am, Room 309

Session: Molecular Electronics
Presenter: N.P. Guisinger, Northwestern University
Authors: N.P. Guisinger, Northwestern University
N.L. Yoder, Northwestern University
M.C. Hersam, Northwestern University
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A cryogenic variable temperature ultra-high vacuum (UHV) scanning tunneling microscope (STM) is utilized for measuring the electrical properties of isolated cyclopentene molecules adsorbed to the degenerately p-type Si(100)-2x1 surface at a temperature of 80 K. Current-voltage curves taken under these conditions show negative differential resistance (NDR) at positive sample bias in agreement with previous observations at room temperature.@footnote 1-3@ The enhanced stability of the STM at cryogenic temperatures was utilized for repeated measurements taken over the same molecule. Current-voltage curves on isolated cyclopentene molecules are demonstrated to be repeatable and possess negligible hysteresis for a given tip-molecule distance. Subsequent measurements with variable tip position show that the NDR voltage increases with increasing tip-molecule distance. Using a one-dimensional capacitive equivalent circuit and a resonant tunneling model, this behavior can be quantitatively explained, thus providing insight into the electrostatic potential distribution across a semiconductor-molecule-vacuum-metal tunnel junction. This model also provides a quantitative estimate for the alignment of the highest occupied molecular orbital (HOMO) of cyclopentene with respect to the Fermi level of the silicon substrate, thus suggesting that this experimental approach can be used for performing chemical spectroscopy at the single molecule level on semiconductor surfaces. Overall, these results serve as the basis for a series of design rules that can be applied to silicon-based molecular electronic devices. @FootnoteText@ @footnote 1@ Guisinger, N. P., Basu, R., Baluch, A. S. & Hersam, M. C. (2003) Ann. N. Y. Acad. Sci. 1006, 227-234.@footnote 2@ Guisinger, N. P., Greene, M. E., Basu, R., Baluch, A. S. & Hersam, M. C. (2004) Nano Lett. 4, 55-59.@footnote 3@ Guisinger, N. P., Basu, R., Greene, M. E., Baluch, A. S. & Hersam, M. C. (2004) Nanotechnology 15, S452-S458.