Laws Governing the Pulling of Electrons out of Metals by Intense Electrical Fields

Abstract

Current from thoriated tungsten filaments in vacuum, due to radial fields of up to two million volts per cm. — Three filaments were tested, each .00123 cm in diam. and suspended under tension in the axis of a copper cylinder of 1.6 cm diam. From the dimensions, the radial field at the surface of the filament was 228 times the applied potential difference. The electron currents pulled from the tungsten by the high fields (field currents) rise steadily from 10^-12 to 10^-3 amp. as the field is increased from about 400 to 1100 kv/cm. In the dark, luminous spots were seen on the anode, indicating that these currents come from a few active surface spots. The field current (for a given voltage) depends on the value of the maximum field current previously drawn from it (conditioning current), being reversibly reproducible below the conditioning current. The higher the conditioning current, the lower the field current. A previous heating to high temperatures (2400°C) decreases the field current and also decreases the slope of the current-voltage curve. Both effects (current and heating) show fatigue. Variation with temperature of the filament, to 800°C. The field currents are completely independent of temperature up to 700°, but a temperature of 800° increases the currents due to a given field when this is sufficiently large, by a factor which is roughly independent of the current (10-8 to 10-4 amp.). Electron theory. In explanation of these results, it is suggested that the field currents are due to conduction electrons pulled from minute peaks on the surface, the fatigue effects of both current treatment and heat treatment being due to the rounding off of these peaks by positive ion bombardment or by temperature. Chemical changes may also alter the surface. The lack of dependence of field currents upon temperature furnishes strong evidence that most of the conduction electrons do not share in the energy of thermal agitation. The thermions, however, do share in this energy; they are presumably responsible for the Peltier and thermo-electric effects. In this theory it is assumed that conduction electrons follow the same sort of quantum laws in their escape from the solid as do atoms of a light element at temperatures far below the boiling point.