Electronically Nonadiabatic Processes in the Interaction of H with a Au Surface Revealed Using MIM Junctions: The Temperature Dependence

Abstract

The chemicurrent response of Au–TaOx–Ta metal–insulator–metal junctions exposed to a flux of atomic hydrogen has been studied in detail for device temperatures between 110 and 300 K. Currents of some 100 pA are observed at an H atom flux of 4 × 1014 atoms cm–2 s–1. The steady-state current closely tracks the rate expected for the Langmuir–Hinschelwood recombination reaction as a function of temperature. The current trace reflects the reaction kinetics when the H-atom flux is modulated. The rate constant is directly determined from the individual trace at each temperature. Moreover, it is observed that the Fermi level of the 20 nm thick top metal film shifts with varying H coverage, giving rise to an additional charging/discharging current. For device temperatures below 200 K, subsurface hydrogen becomes significant.