Tungsten contamination of vacuum-deposited permalloy films

Abstract

An experiment was performed to determine the extent of contamination introduced into Permalloy* magnetic thin films, evaporated in vacuo from a tungsten block heat source, by material of the heat source. The measurement was accomplished by labelling the blocks with radioactive tungsten 185 via thermal neutron irradiation, and producing films using the labelled blocks as heat sources. The films so produced were then counted for tungsten radioactivity content. From this information the corresponding mass of tungsten was calculated. A comparative study of the effect of the residual gases in the vacuum system on the transport of tungsten from the block in the absence of Permalloy was also performed. The results of the experiment indicated that contamination of films by the material of the source is due primarily to an interaction between the evaporant and the source material, rather than due to an interaction between the source and the residual gases in the system. Contamination of the films due to the interaction of the residual gases with the material of the sources was found to comprise substantially less than 20 per cent of the total contamination of the films by source material.