Field Emission in Liquids

Abstract

Field emission from tungsten emitters into liquid H2, D2, He, Ar, N2, O2, and C6H6 has been carried out in modified field emission tubes, which permitted switching from ultrahigh vacuum to very pure liquids and back to vacuum. In all cases space-charge-limited behavior was found at >10−9 A, from which the following mobilities (in centimeter2 volt−1·second−1/units) could be estimated: 3 × 10−2 cm2 V−1·sec−1 for H2 at 21°K, 0.9∼10−2 for D2 at 21°K, 4 × 10−2 for He at 4.2°K, 0.36 for He at 1.8°K, 8 × 10−3 for O2, 8 × 10−3 for N2, and 4 × 10−3 for C6H6. In the case of Ar a limiting velocity of 5 × 106 cm/sec rather than a field-dependent mobility was observed. For He and Ar onset of high emission (10−9 A) is abrupt, indicating electron avalanching with concomitant gas-bubble formation at the tip which leads to sputtering. In the case of O2 electrochemical etching occurred even at low currents. For H2 and D2 a true Fowler–Nordheim field emission regime could be observed for i≤10−10 A, from which an energy barrier of 0.1–0.5 eV to the solution of free electrons in H2 was estimated.