No abstract

Polycrystalline transparent semiconducting zinc oxide films have been deposited by the oxidation of diethyl zinc. The film growth rate is controlled by a complex multistep oxidation process which is dominated by radical reactions. The effect of substrate temperature and gas pressures have been studied. Samples deposited between 280 and 350 °C have a conductivity varying from 10−2 to 50 Ω−1 cm−1. The electrical properties of the films which are typical of polycrystalline material with small crystallites are shown to depend very closely on the film growth conditions. A study of oxygen chemisorption at grain boundaries confirms the importance of grain boundary effects in ZnO polycrystalline films.

The work on Franck–Condon factors for radiationless transitions in polyatomic molecules, as reported in Parts I and II of this series, is extended and generalized, starting from the theoretical expression for Franck–Condon factors in aromatic hydrocarbons, which was derived and applied to triplet-to-ground-state transitions in Part II. The role played in this expression by the anharmonicity and symmetry of CH-stretching modes is clarified. As a preliminary step towards application of this expression to singlet-to-ground-state transitions in aromatic hydrocarbons, the appropriate Franck–Condon factors are studied spectroscopically by measuring the long-wavelength part of the fluorescence spectra of anthracene-h10 and -d10. These experimental Franck–Condon factors are used to determine the anharmonicity parameter in the theoretical expression for the singlet-to-ground-state radiationless-transitions rate constant. Theoretical rate constants for the transition calculated on this basis compare favorably with the scarce experimental data. They tend to justify the commonly made assumption that these transitions contribute a negligible amount (about 1% or less) to singlet decay in most simple aromatic hydrocarbons, but with some notable exceptions. Thus, for benzene and tetracene, and possibly also for coronene, contributions of about 10% are obtained, whereas in azulene and all of its known derivatives, the transition dominates the other decay processes of the first excited singlet state. The calculations also account qualitatively for the broadening of the first singlet absorption system and the anomalous fluorescence of azulenes. The isotope rule derived in Part I is corrected for anharmonicity. In its new form it does not account quantitatively for the observed deuterium effects. This indicates that CD-stretching modes, which are much less efficient in taking up electronic energy than CH-stretching modes, have about the same efficiency as some of the skeletal modes, so that these skeletal modes will contribute substantially to the Franck–Condon factors of perdeuterated aromatic hydrocarbons. The analysis of singlet-to-ground-state transitions leads to rate constants of 1013–1014 sec−1 for transitions between closely spaced electronic energy levels of the same multiplicity. Comparison with the results for triplet-to-ground-state transitions indicates a spin-prohibition factor of 108. The dependence of spin-prohibition factors on the energy of the electronic states involved in the transition is briefly discussed.

No abstract

High-quality 800-Å-thick films of tin-doped indium oxide have been prepared by magnetron sputtering. It is shown that films with low resistivity (∼4×10−4 Ω cm) and high optical transmission (≳85% between 4000 and 8000 Å) can be prepared on low-temperature (40–180 °C) substrates with O2 partial pressures of (2–7)×10−5 Torr.