Chemistry

Biased Switching

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Science  08 Oct 2004:
Vol. 306, Issue 5694, pp. 201
DOI: 10.1126/science.306.5694.201a

The conductivity of highly conjugated oligo(phenylene-ethynylene) (OPE) molecules has been explored in a number of settings. When these molecules are thiol-derivatized and surrounded with alkanethiol molecules on gold films, random switching in their conductance from a high “on” state to a low “off” state has been observed by scanning tunneling microscopy (STM), and the switching has been attributed to hybridization changes in the OPE-surface bond.

Lewis et al. report that the rate of stochastic switching can be slowed by chemically adding hydrogen-bonding interactions and that it can be controlled to a large extent by the bias of the STM tip. They introduce an amide functionality into the alkanethiol and add a nitro substituent to the center ring of the OPE. A negative tip bias of 1 V increases the on/off ratio, and a positive tip bias repopulates the off state. The authors note that the ability to cycle the OPE molecules between these on and off states argues against mechanisms that attribute the changes to desorption and adsorption of the OPE molecules. — PDS

J. Am. Chem. Soc. 126, 12214 (2004).

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