Field evaporation of tungsten in the presence of adsorbed water

The field evaporation of tungsten at T=300 and 600 K in the presence of water vapor in the residual atmosphere was studied using a static mass spectrometer with a moderate resolution (M/ΔM=200). The room-temperature mass spectrum of field-evaporated particles displayed only the peaks of triply charged ions; an increase in the temperature to 600 K added the peaks of doubly charged ions of approximately the same intensity. The presence of adsorbed water reduced the evaporating field strength by a factor of 2-2.5. At 300 K, an increase in the water content in the residual atmosphere markedly enhanced the field etching. No singly or quadruply charged tungsten ions were observed. The results are indicative of the activation mechanism of field evaporation at the temperatures studied and show evidence of a substantial decrease in the magnitude of evaporating field caused by the presence of water.