A variety of scattering processes occur within the metal—oxide—metal tunnel cathode, with the result that most of the injected electrons fail to escape into vacuum. By considering the over-all behavior it is possible to identify the most important loss mechanisms and where they occur. Electron emission measurements suggest that the internal hot electron velocity distribution in the exit metal films is isotropic as a result of numerous phonon scattering events. It is also found that the electron attenuation length in the exit metal film is not a strong function of energy over most of the observable range. As a direct consequence one obtains the result that the shape and mean energy of the emitted electron energy distribution are determined principally by the scattering in the oxide layer. Collision ionization is unlikely; hence optical phonon scattering is believed to be the principal oxide energy loss mechanism. If the scattering is random and independent of energy, both the mean energy loss (ΔE) and mean square deviation (δ2) should depend linearly on oxide thickness (x). Within the limits of the available data this is shown to be reasonably correct, and a mean rate of energy loss dE/dx≈0.03 eV/Å is obtained. This corresponds to about one optical phonon emission event for every 4-Å travel measured along the field direction. The consistency of the argument is tested by showing that δ2 also varies linearly with oxide thickness. The minimum ingredients for a model of the hot electron scattering processes are outlined.

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Barium and calcium stearate Langmuir films from 1 to 10 monolayers in thickness (approximately 25–250Aå) have been investigated for use as ultrathin insulating barriers between evaporated metal electrodes. These metal‐insulator‐metal sandwiches showed highly nonlinear and temperature dependent conduction characteristics, from which a thermal barrier height of 0.25–0.30 ev is calculated. Reproducibility of electrical properties however was poor, apparently due to voids and inhomogeneities in the organic insulating films. It is calculated that even in the best samples, 2 to 3 monolayers were required to eliminate voids penetrating completely through the organic films. A reactive and hence oxidized surface was found to be necessary for the formation and retention of low porosity layers, tin being the most successful substrate electrode material. Insulating behavior could not be obtained from films transferred onto gold electrodes. Film structure and adhesion was investigated by studying the layering process and the autoradiographs obtained from C14 tagged films. The autoradiographs did not reveal any significant defects in the layers down to the resolution of the negatives (∼25μ). It was found that the physicochemical nature of the substrate surface affected the adhesion of more than the first monolayer, and that porosity alone was unlikely to account for the long‐range effect. Positive ion adsorption, as described by Goranson and Zisman, is suggested as a possible alternative and shown to be consistent with some aspects of the electrical measurements.