Electrical current oscillations in vapor-adsorbed ferrocene derivatives having two substituted groups

Abstract

Oscillations in electrical current as a function of time have been observed in a specific temperature range in the samples of 1,1′-diacetylferrocene and 1,1′-ferrocenedicarboxylic acid with adsorbed ethanol vapor in a sandwich-type cell. The frequency of current oscillations has been found to decrease with bias voltage and sample temperature and to increase with vapor pressure. The frequency of current oscillations for the mono-group substituted derivatives is higher than the corresponding frequency for the derivatives having two substituted groups. Again, the frequency of oscillations for –COCH 3 group substituted derivatives is higher than the corresponding value for –COOH group substituted derivatives. The observation of current oscillations is possibly associated with some kind of time dependent phase changes, arising from the structural nonrigidity of the molecules, in the solid-ethanol vapor system at the sample surface layer. The “ball-bearing” motion of the cyclopentadienyl rings of ferrocene unit, nature and number of substituted groups, cooperative interaction of the neighboring molecules influence the structural nonrigidity and hence the oscillatory behavior of current. Reasons are given for ruling out other models of current oscillations in semiconductors.