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

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 him growth was detect ed by conductivity measurements during the film growth. Conductivity change s were observed as a consequence of exposure of the films to partial pressu res 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 reache d a steady state after about 10 min in each case. The conductivity of the f ilms in the steady state followed a Langmuir adsorption law. Analysis of th e time-dependence of the conductivity before the steady state was reached r evealed the presence of a redox reaction which leads to the observed change s in charge carrier concentration in the films. Assuming first order kineti cs for this reaction the transients as obtained at different partial pressu res could be successfully discussed and the validity of the model consistin g of a surface reaction in two steps was thereby confirmed.