Kinetic electronic excitation of solids by fast-particle bombardment

Abstract

The kinetic excitation of hot electrons and conduction-band vacancies following the impact of an energetic particle onto a solid surface was studied using metal-insulator-metal tunnel junctions. The top metal layer polycrystalline silver was bombarded by charged and neutral Ar projectiles of kinetic energies between 1 and 15 keV. Hot charge carriers generated within the collision cascade initiated by the projectile impact were detected as a tunneling current across the oxide barrier into the underlying substrate metal electrode. The tunneling yield is shown to depend monotonously on the kinetic impact energy with no notable contribution of potential emission. The dependence, however, is different for singly charged and neutral projectiles. Applying a bias voltage between the two metal electrodes, information about the energy spectrum of the excited carriers is obtained. The experimental data are interpreted in terms of a simple two-temperature tunneling model, yielding a kinetically induced transient electron “temperature” on the order of 10 4 K.