Attenuating Molecular NDR

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Science  02 Jan 2004:
Vol. 303, Issue 5654, pp. 17
DOI: 10.1126/science.303.5654.17a

Negative differential resistance (NDR), in which current through a device drops with increasing bias voltage, can be seen in resonant tunneling diodes, which are semiconductor devices in which a quantum well is confined by two tunneling barriers. Applying a bias can bring energy levels in a quantum well into and out of resonance with a tunneling electron and thus modulate the current flow. Such devices can be modified by changing the height or width of the tunneling barriers. Wassel et al. report similar modifications in a molecular junction exhibiting NDR—in this case, one formed from a ferrocene-terminated self-assembled monolayer (SAM) on gold probed with gold or platinum-iridium scanning tunneling microscope tips. The barrier between the tip and the molecule was increased in two different ways, either by adsorbing n-alkanethiol SAMs on the tips or by capping the ferrocenyl groups with bulky β-cyclodextrin molecules. In both cases, the NDR peaks were attenuated but not eliminated. — PDS

J. Am. Chem. Soc. 10.1021/ja037651q (2003).

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