Effect of nanostructures formed by oblique co-deposition on transient catalytic reactions

Abstract

We investigated the effects of nanostructures of obliquely co-sputter-deposited thin films in terms of catalytic properties using pulses of reactant molecules as probes. Pt–Al 2O 3 thin films were fabricated on a Si substrate by simultaneous oblique deposition. The films had columnar structures that grew perpendicular to the substrate. We observed the behavior of NO reduction by H 2 with a specially designed apparatus employing pulse valves for the injection of reactant molecules onto the thin film surface and a time-of-flight mass spectrometer to measure plural products. The obliquely co-deposited films, consisting of columnar nanostructures, showed higher NO reduction activity over a wide range of temperatures than the normally co-deposited films, consisting of uniform structures. The yield of N 2 exceeded that of NH 3 and N 2O for both structures in the high temperature range, whereas the yield of N 2O was more significant for the structures with columns than those without columns at low temperatures. Subtle change of the nanometer-scale structures with the deposition angle was clearly discriminated from the viewpoint of transient catalytic activity.