Vertical differential charging in monochromatized small spot X‐ray photoelectron spectroscopy

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 different 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.