Redox reactions of acetone and ethanol with the surface of N,N′-dimethylperylene-3,4,9,10-biscarboximide (MePTCDI) thin films

Abstract

Thin films of the title compound MePTCDI were deposited by physical vapour deposition on microstructured interdigital Au electrode arrays on a SiO₂–Si substrate. Initial island formation followed by bulk film growth was detected by conductivity measurements during the film growth. Conductivity changes were observed as a consequence of exposure of the films to partial pressures of acetone and ethanol in the range of 10^-7–10^-4 mbar. Following a relative fast decrease at the beginning of exposure the conductivity reached a steady state after about 10 min in each case. The conductivity of the films in the steady state followed a Langmuir adsorption law. Analysis of the time-dependence of the conductivity before the steady state was reached revealed the presence of a redox reaction which leads to the observed changes in charge carrier concentration in the films. Assuming first order kinetics for this reaction the transients as obtained at different partial pressures could be successfully discussed and the validity of the model consisting of a surface reaction in two steps was thereby confirmed.