Nanometer-scale depth-resolved hard x-ray absorption spectroscopy based on the detection of energy-loss Auger electrons with low energies

X-ray absorption spectroscopy (XAS) provides information on the chemical state and atomic structure of a target element even without long-range periodicity. A depth-resolved surface-sensitive XAS method for K-edge using hard x rays is proposed herein. The principle of this method is based on the selective detection of low-energy electrons using an electron analyzer. The detected electrons originate from the LMM Auger electrons that cascade from the KLL Auger process caused by K-shell absorption and lose the energy corresponding to their travel distance in a solid. The analysis depth was confirmed to be in the nanometer range using a GaN substrate with a thin oxide film of the defined thickness. In addition, depth-resolved information regarding the local atomic structure, including the interatomic distance and crystallinity, was obtained via the Fourier transformation of the spectral oscillations. Because the proposed technique does not require a change in the detection angle, it is also expected to be used for particles and samples with uneven surfaces.