Charge transfer in metal-polymer contacts and the validity of ’’contact charge spectroscopy’’

Abstract
A number of recent papers have reported measurements which seem to show that charge transferred to polymers by successive contacts to different metals is additive, each metal transferring an amount of charge independent of that deposited by previous metals. These results have been interpreted as showing that a metal may only transfer charge to a narrow range of polymer states close to the metal’s Fermi level, and it has been suggested that this effect may be used to study the energy spectrum of electron states in polymers (’’contact charge spectroscopy’’). We show that if the sample geometry is chosen to define more precisely the region of true contact, charging by a succession of metals is not additive; the charge depends only on the most recent contacting metal. This throws doubt on the hypothesis of charge transfer to a narrow range of states and on the technique of contact charge spectroscopy.

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