Time-Resolved Electron Energy Loss Spectroscopy on Copper Oxides

Abstract

In a previous paper it was shown that it is possible to distinguish CuO from Cu metal in a CuO/ZnO catalyst. It was also observed that the CuO showed signs of reduction under the impact of the high current density used in a field emission UHV STEM. This work reports on the efforts so far to study the changes in the L3, 2 edge of Cu as a function of time and hence ultimately to determine the kinetics of whatever radiation damage process is responsible for the changes observed in the catalyst CuO.The first problem to be overcome was to provide a multichannel analyzer system capable of recording the same region of an ELS spectrum repeatedly and yet retain the individual scans. A Kevex 7000 series computer/MCA system was modified and software written which enables the user to select a region of a normal spectrum for subsequent analysis. An additional D to A converter, plus modified Gatan ELS spectrometer electronics, provided the means to offset the spectrometer magnet by an amount equal to the chosen windows so that the same energy window would be scanned sequentially. The electron microscopy was performed using a Philips EM400ST with a field emission gun at 100kV.