Surface Gas Eruption and Van der Waals Cohesion on Tungsten

Abstract

IN some experiments on the detection of single atoms and molecules reported earlier1, it was noticed that, in the early stages of the conditioning of the point, there were occasions when, on increasing the field by some 20 per cent, an abrupt instability in the field current occurred; this invariably produced excessively large currents. The field emission pattern of the emitting facets of the point, previous to this, was, of course, badly blurred, with no definition comparable with that from clean points, but it was possible to discern ‘out of focus’ non-emitting areas on the fluorescent anode; as soon as the instability arose, there was complete loss of resolution, and the pattern showed a uniform streaming as if a sheet of gas was moving across the point. When the point had been fully ‘conditioned’, it required a much higher field to produce the effect. If, however, the whole vacuum system was let down to air at atmospheric pressure and soon after pumped out, it was possible to obtain repeated gas eruption and current instability without further increase of field.