WORK-FUNCTIONS FOR A HV CATHODE IN NONPOLAR LIQUIDS

When negative HV is applied to a needle of small radius of curvature (r(p) < 0.2 mum) in nonpolar liquids, a detectable field emission current (I > x10(-12) A) is observed above a voltage U(FN), the Fowler-Nordheim law. For larger point radii, only a regular current pulse regime is detected above a threshold voltage U(S) (Trichel regime). Analysis of these voltages U(s) and U(FN) as a function of conduction band energy V0 of different liquids, shows that the apparent work function for high electric field strengths in liquids is lower than the one without applied field (2.1 compared to 4.5 eV for a tungsten cathode). This difference can be explained if one assumes the existence of a plasma-like layer around the HV cathode.