Development of Sub-nanometer Resolution Depth-Resolved XAFS/XMCD in the Soft X-ray Region towards Operando Measurements

Recent development of the depth-resolved X-ray absorption fine structure (XAFS) and X-ray magnetic circular dichroism (XMCD) techniques in the soft X-ray region is presented. A sub-nanometer resolution in the XAFS/XMCD measurement is achieved by collecting the Auger electrons at different detection angles, which correspond to different probing depths, but it is impossible to apply this technique under magnetic and/or electric fields because the electron trajectory is affected by the external fields. By adopting the fluorescence-yield detection mode using a soft X-ray CCD camera, the depth-resolved XAFS/XMCD technique under the external fields is realized, which leads to the operando measurements for the chemical and magnetic states at the surface and interface. The depth-resolved XAFS/XMCD measurement for an FeCo film under the magnetic field is demonstrated for the first time, which suggests that the 15 ML-thick surface region consists of 60% oxides with little magnetization.