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Differential charging (DC) is a charging effect in x-ray photoelectron spectroscopy (XPS or ESCA) that results from the spatial variation of sample potentials in the XPS sampling volume. It can be conceptually categorized into two Werent aspects--lateral (LDC) and vertical (VDC)-according to the difference in the directions of the inhomogeneous distribution of the potentials in the surface phases of the sample. The phenomenon of VDC, which leads to a shift of the peak position, to a broadening of the peak width or even to a dramatic distortion of the peak shape, was observed in the following systems: semiconductors and conductors with ultrathin oxidized or insulating overlayers. The suggested approach to overcome the problem of VDC is simply to isolate the sample and neutralize it with electrons from a monoenergtic flood gun.

Modern analytical methods for the investigation of surfaces have been greatly improved during the last decade, and the number of instruments offered by manufacturers has increased accordingly. In this article, four of the most frequently applied methods are discussed, with emphasis on those which have found wider application in industry. The aim of this report is to give an easily understandable introduction to all those who are not yet familiar with surface analytical methods. Emphasis is on the Auger electron spectroscopy (AES), the most popular technique for elemental analysis of surfaces. The numerous analytical methods differ widely in information depth, lateral resolution, level of nondestructiveness, detection limits, and the possibility of getting quantitative results. Compared with the well known x‐ray microprobe analysis, the surface‐sensitive methods have a lower information depth of up to four orders of magnitude and are therefore well suited to analyze extremely thin films down to a few atomic layers. First, the fundamental physical principles of the atomic excitation and emission processes are described, then the main characteristics of the four methods and their information content are discussed. Finally, some applications are given for the characterization of interesting technical materials.

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