Hot-electron transmission through thin amorphous films of tetratetracontane: Effects of the density of gap states on the band-gap current and its anomalous temperature dependence

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Abstract
Low-energy electron transmission experiments were performed for two types of amorphous films (solid amorphous and molten amorphous films) of tetratetracontane [CH3(CH2)42CH3]. The temperature dependence of the transmission spectra and the spectral changes due to the amorphous-to-crystal transition of the films were measured. We observed that (1) the transmitted current through the band gap did not show a large decrease by the solid-amorphous–to–crystal change, and (2) for crystalline films it decreased abruptly and almost disappeared at a temperature just below the melting point, while the electron transmission through the conduction bands existed clearly even at this temperature. These results indicate that the gap current cannot be explained by the electron inelastic scattering to the localized gap states originating in the crystalline defects followed by a diffusion through the gap states. Further, we found a large difference between the spectra of the solid amorphous and molten amorphous films. The solid amorphous film showed a negative electron affinity of -0.1 eV, while the molten amorphous film gave positive electron affinity.