Prevention of the Reduction of CuO during X-ray Photoelectron Spectroscopy Analysis

A method to prevent the reduction of CuO formed on Cu metal during x-ray photoelectron spectroscopy analysis is presented. When a bias voltage of -250 V was applied to the sample surface in the case of non-monochromatic Mg Kα1,2 irradiation, the reduction of CuO to the lower oxide (Cu2+Cu+) was suppressed by 80–90% as compared with ordinary non-monochromatic x-ray irradiation. The degree of CuO reduction is the same as in the case of monochromatic Al Kα x-ray irradiation. It was found that slow electrons generated from the x-ray window and photoelectrons emitted from the surface by x-ray irradiation cause the reduction. As the reduction can be minimized by applying a bias voltage to the surface, the bias voltage method is very effective for preventing CuO reduction.