Micro-XANES and micro-SRIXE using monocapillary optics

The analytical methods of synchrotron radiation-induced X-ray emission (SRIXE) and X-ray absorption near-edge spectroscopy (XANES) made possible by synchrotron X-ray sources permit the detection of trace levels of elements in materials and the determination of their oxidation state respectively. However, the available X-ray intensity per unit volume of irradiated sample limits the detection sensitivity of these methods. The combination of small sample size (or high desired spatial resolution) and low trace element concentration often conspire to make such measurements unfeasible. We describe the use of a paraboloidally-tapered glass monocapillary to focus X-rays onto a small area to improve the detection sensitivity and spatial resolution. A monocapillary-focused beam produced a 40-μm FWHM diameter focus possessing a factor of 14 greater intensity than that produced by an 8:1 ellipsoidal mirror installed at NSLS beamline X26A. The monocapillary-focused beam was used to obtain XANES and SRIXE data from biological specimens at the same beamline. In particular, XANES spectra were obtained from small numbers of cells containing trace quantities of Cr. Improved signal-to-noise ratio and high spatial resolution were also observed (authors)