Controlling single-molecule negative differential resistance in a double-barrier tunnel junction

ORAL

Abstract

Negative differential resistance (NDR), the phenomenon of decreasing current with increasing voltage over certain voltage range, has found applications such as high frequency oscillators and high speed switches. NDR has been observed with a low temperature scanning tunneling microscope (STM) in the differential conductance spectra of single copper phthalocyanine (CuPc) molecules adsorbed on one and two atomic layers of NaBr film grown on a NiAl(110) surface. However, there is no NDR for single CuPc molecules adsorbed on three atomic layers of NaBr on NiAl(110). This is explained as the result of competing effects of increasing sample bias on tunnel barrier heights across vacuum junction and NaBr junction for resonant tunneling through the lowest unoccupied molecular orbital (LUMO) of CuPc. Whereas increasing positive sample bias increases tunnel barrier height across the vacuum junction, it decreases tunnel barrier height across the NaBr junction. The overall behavior, NDR versus the absence of NDR, depends on which of these two effects dominates. Numerical simulation supports this mechanism. Our results show that transition from NDR to the absence of NDR can occur as sharply as the addition of one atomic layer of NaBr.

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Authors

  • Xiuwen Tu

    University of California, Irvine

  • Gareguin Mikaelian

    University of California, Irvine

  • Wilson Ho

    Department of Physics and Astronomy, University of California, Irvine, CA 92614, Department of Physics and Astronomy and Department of Chemistry,University of California, Irvine, CA 92697-4575, USA., Department of Physics and Astronomy and Department of Chemistry, University of California, Irvine, CA 92697-4575, USA., University of California, Irvine, Department of Physics and Astronomy and Department of Chemistry, University of California, Irvine, California 92697-4575, USA