| Surface analysis by x-ray photoelctron spectroscopy (XPS), also known as electron spectroscopy for chemical analysis (ESCA), is accomplished by irradiating a
specimen with monoenergetic soft x-rays and energy-analyzing the emitted electrons. Each element has a unique elemental spectrum, and the spectral peaks from a
mixture are approximately the summ of the elemental paks from the individual constituents. Since the mean free path of the electrons is very small, the electrons that
are detected originate from only the top few atomic layers. Quantitative data can be obtained from the peak heights or areas, and identification of chemical states can
be made from the exact positions and separations of the peaks, as well as certain spectral contours.
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