SCLC diode thin film rate monitor

Abstract

The injection of a vapour beam into a thermionic vacuum diode in a Kingdom cage type configuration modifies the diode characteristics considerably. The anode current increases on injection, the increase being dependent on the anode voltage. This is attributed to the partial neutralization of the space charge by the presence of positive ions in the vapour beam (produced by the electron bombardment in the Kingdon cage configuration). The increase in the plate current in the space charge region of the diode is linearly proportional to the number of atoms in the vapour beam for various metal evaporants at low rates of evaporation. A theory to explain the neutralization effect has been developed. The observed effect lends itself to a useful device to monitor the vapour beam density and, therefore, the evaporation and deposition rates of materials. Vapour beam densities as low as 10¹³/cm² sec and hence deposition rates as low as 0.1 Å/sec can be measured. Unlike the ionization gauge type of monitor, this device is not seriously affected by the presence of background (ambient) gases during vacuum evaporation.