Low-energy ion-induced electron emission in metal-insulator-metal sandwich structures

Abstract

An ${\text{Ag-AlO}}_{x}\text{-Al}$ sandwich structure is used to investigate the electronic excitation induced by ${\text{Ar}}^{+}$ ions at the surface of the top 15 nm Ag film. The internal electron emission yield, i.e., the number of electrons emitted per impinging ion into the bottom Al film, is determined as a function of the kinetic energy of the ions in the range of 300--6000 eV. A comparison to the external electron emission yield, i.e., the number of electrons per projectile ejected into the vacuum, reveals two interesting aspects. First, unlike in the external emission, no significant contribution of the potential energy to the internal electron emission yield is observed. Second, the kinetic part of the electron emission yield exceeds the external one over the entire energy range. Another interesting result is that the internal emission yield shows a power-law dependence on ion kinetic energy. A Monte Carlo simulation, based on a simple theoretical treatment of the kinetically induced electron emission, supports the experimental findings. Finally, we discuss the influence of excitation properties (e.g., anisotropy) as well as of device properties (e.g., film thickness, barrier height) on the computed electron emission yields.