Probing the distribution of hot charge carriers generated in Mg surfaces by oxidation

When Mg surfaces are oxidized the released chemical energy is partly dissipated non-adiabatically by exciting hot charge carriers in the metal surface. Different types of Mg/p-Si(1 1 1) Schottky diodes with homogeneous barrier heights of 0.7 and 0.8 eV are used to detect chemicurrents during exposure of the devices to oxygen. The detected chemicurrent transients represent the kinetics of the chemical reaction which is attributed to an oxide nucleation and growth mode. The current strength is related to the homogeneous Schottky barrier height of the diode. Together with exoelectron emission data the energy distribution of the chemically induced hot charge carriers is deduced and may be described by a Boltzmann type function with an effective temperature of 1730 K. Consequently, the chemicurrent method is found to be almost four orders of magnitude more effective to detect hot charge carriers than exoelectron emission.