Partial Fluorescence Yield XAFS Measurements in Soft X-ray Region Using a Large-Area Silicon Drift Detector

X-ray absorption fine structure (XAFS) spectra in the soft X-ray region are obtained in the electron and fluorescence yield modes, which are sensitive to surface and bulk, respectively. A micro-channel plate (MCP) can be used as the detector for the total fluorescence yield (TFY) method by applying a sufficiently high negative bias to a grid in front of the MCP. However, this method often suffers from low signal to back ground (S/B) and signal to noise (S/N) ratios. We have introduced a silicon drift detector (SDD) with a large acceptance area of 80 mm in order to perform the highly sensitive partial fluorescence yield (PFY) XAFS experiments. Then the S/N and S/B ratios were improved significantly compared to those in the TFY-XAFS obtained by using the conventional MCP. By introducing the PFY method using the SDD to the ultra-soft XAFS beamline BL-2, XAFS spectra could be collected from a sample in three different modes simultaneously, i.e. PFY, the partial electron yield (PEY) by using an MCP with a retarding grid, and the total electron yield (TEY) by recording the sample current. Since these methods have different detection depths each other, a depth profile can be studied by comparing these three spectra. We demonstrate the performance of the present system applied to the typical cathode materials of lithium ion secondary battery.