Der Vordurchschlagsstrom im Hochvakuum. I. Die Spannungsabhängigkeit des Stromes bei konstantem Feld

Pre‐breakdown currents were measured in the range from 10 −17 to 10 −9 A in a vacuum of 10 −9 Torr. The cathode was the extended (100) surface of a nickel single crystal. In the range from 10 −15 to 10 −11 A the current curves could be measured in times ≦ 1 s. It was found that the emission is not constant in times < 1 s. The currents show a fluctuation in times < 1 s which is voltage depending. The average current (measured in times > 1 s) rises with the total voltage at constant field. This is interpreted by a voltage depending work function which varies by the influence of ionic bombardment on adsorbed gas layers. This view is supported by a pronounced effect of oxygen adsorption. The total voltage effect causes a considerably error in the field enhancement factor β and the emitting surface which are calculated from the Fowler‐Nordheim plots.