Investigation of partial oxidation of copper deposited on pyrolytic boron nitride

Abstract

Copper clusters with diameters of approximately 2.0 to 4.0 nm (355 to 2840 atoms) served as models to obtain more detailed information of the complicated oxidation process of copper surfaces. In addition to the cluster size, the amount of oxygen embedded in the clusters and their structure were chosen as key parameters. SEELFS (surface extended electron energy loss fine structure) above the M_2,3 edge of copper and HRTEM (high resolution transmission electron microscopy) were used for the insitu investigations. The combination of the two techniques allowed a clear and sound interpretation of the spectroscopic results. SEELFS measurements on copper clusters prepared by inert gas aggregation and on clusters primarily oxidised by adding pure oxygen of different partial pressures to the aggregation gas during the metal evaporation, i.e., during the nucleating process, were performed. Thereby a positive shift of the first nearest neighbour distance (FNND) was observed when compared to pure copper clusters. This dilatation is caused by oxygen embedded in the clusters. The shape of the FNND peaks indicate heavy distortions within the primarily oxidised clusters. Furthermore, oxygen reduces the fractional amount of multiply twinned particles (MTPs) and the critical diameter D_crit for the structural change to fcc in a significant way compared to pure copper clusters.