Interfacial and chemical properties of Pt/TiO2, Pd/TiO2, and Pt/GaN catalytic nanodiodes influencing hot electron flow

The influence of physical and chemical properties of Pt/TiO2, Pd/TiO2, and Pt/GaN metal-semiconductor Schottky diodes on the yield of collected hot electron flow (number of hot electrons per product molecule) was investigated. We measured both the chemicurrent (electron flow) and chemical turnover rate during oxidation of carbon monoxide (at pressures of 100 Torr of O-2 and 40 Torr of CO in the 373-513 K range) using reaction systems equipped for simultaneous reaction rate and current measurements. The chemicurrent was found to be correlated with the turnover rate and can be used to detect the turnover rate for the three diodes. Thermoelectric current was observed in the presence of O-2 or CO gas in the absence of catalytic reaction. The chemicurrent was observed only under catalytic reaction condition. The chemicurrent yield of Pt/GaN ((3.5 +/- 0.8) x 10(-3)) was higher than that of Pt/TiO2 or Pd/TiO2 ((2-3) x 10(-4)) by 1 order of magnitude. We found that the metal-semiconductor interface structure (roughness, grain size, and step-terrace) is important in controlling the magnitude of chemicurrent yield.