An in situ cell for characterization of solids by soft x-ray absorption

A cell has been designed and fabricated for in situ characterization of catalysts and environmental materials using soft x-ray absorption spectroscopy and spectromicroscopy at photon energies above $\text{250\hspace{0.5em}}\mathrm{eV}$ . “Lab-on-a-chip” technologies were used to fabricate the cell on a glass wafer. The sample compartment is $\text{1.0\hspace{0.5em}}\mathrm{mm}$ in diameter and has a gas path length of $\text{0.8\hspace{0.5em}}\mathrm{mm}$ to minimize x-ray absorption in the gas phase. The sample compartment can be heated to $\text{533\hspace{0.5em}}\mathrm{K}$ by an $\mathrm{Al}$ resistive heater and gas flows up to $\text{5.0\hspace{0.5em}}{\mathrm{cm}}^3\hspace{0.5em}{\min }^{\text{−1}}$ can be supplied to the sample compartment through microchannels. The performance of the cell was tested by acquiring $\mathrm{Cu}$ $L_3$ -edge x-ray appearance near-edge structure (XANES) data during the reduction and oxidation of a silica-supported $\mathrm{Cu}$ catalyst using the beam line 11.0.2 scanning transmission x-ray microscope (STXM) at the Advanced Light Source of Lawrence Berkeley National Laboratory (Berkeley, CA). Two-dimensional images of individual catalyst particles were recorded at photon energies between 926 and $\text{937\hspace{0.5em}}\mathrm{eV}$ , the energy range in which the $\mathrm{Cu}(\mathrm{II})$ and $\mathrm{Cu}(\mathrm{I})$ $L_3$ absorption edges are observed. Oxidation state specific images of the catalyst clearly show the disappearance of $\mathrm{Cu}(\mathrm{II})$ species during the exposure of the oxidized sample to 4% $\mathrm{CO}$ in $\mathrm{He}$ while increasing the temperature from 308 to $\text{473\hspace{0.5em}}\mathrm{K}$ . Reoxidation restores the intensity of the image associated with $\mathrm{Cu}(\mathrm{II})$ . $\mathrm{Cu}$ $L_3$ -edge XANES spectra obtained from stacks of STXM images show that with increasing temperature the $\mathrm{Cu}(\mathrm{II})$ peak intensity decreases as the $\mathrm{Cu}(\mathrm{I})$ peak intensity increases.