This second field had a direct and long lasting consequence on the research activity of John (Jack) Mitchell. Mott's accomplishments include explaining theoretically the effect of light on a photographic emulsion (see latent image). His work on oxidation, besides fostering new research in the field (notably by J. Bénard and Nicolás Cabrera), was the root of the concept of the band gap produced in semiconductors by gradients in the distribution of donor and acceptor impurities.