Angular intensity modulation in angle‐resolved XPC and AES of non‐crystalline ultrathin surface layers: The phenomenon and its implications

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Abstract
The well‐known phenomenon of forward (elastic) scattering of x‐ray photoelectrons and Auger electrons, which gives rise to prominent diffraction peaks for emission from monocrystalline materials, can lead to a much less prominent, yet significant, angular intensity modulation of emission from nominally non‐order materials in which stoichiometric or other constraints enforce some short to medium‐rang order. A seemingly small intensity modulation can have a drastic effect on the determination of layer thickness or of effective attenuation length from angle‐resolved measurements. This conclusion is arrived at by applying the known facts o forward scattering (summarized here) to the currently structural model of oxide layers on the semiconductors Si and GaAs (serving as examples). The predictions are compared with experimental data on carbonaceous contamination in the native oxide layers on Si (111) and GaAs (001), obtained by angle‐resolved XPS and AES and evaluated for angle‐dependent effective attenuation length. It is concluded that angular intensity modulation can be expected to be a frequently occurring phenomenon with serious implications for the study of ultrathin layers and ultraslow depth profiles by the electron spectroscopes XPS and AES.