ID-D X-Ray Raman and Inelastic X-Ray Scattering
In an XRS experiment, the incident beam hits the sample, scattered x-ray is collected by spherically-bent single-crystal analyzers and focused to the solid state detector in a nearly backscattering geometry. The incident x-ray energy is scanned relative to the elastic line to determine the inelastic shift. Using the same experimental setup of XRS, we can do an inelastic x-ray scattering experiment to get electronic band structure, excitions, plasmons, and their dispersions under high pressure. During IXS experiments, both incident x-ray energy and scattering angle need to be scanned to obtain the dielectric function and the dynamic structure factor.
To improve the collection efficiency, we have designed, tested and finished commissioning a 17-element analyzer array. The array consists of three columns of 2-inch diameter bent silicon (111) analyzers from NJ-XRSTech in a vertical Rowland circle backscattering geometry. The energy resolution of the instrument is 1.0 eV.To reduce the scattering from the surrounding gasket, at the end of 2016, we have made a comparison of x-ray Raman spectra using post-sample slits versus that of a polycapillary optic. The advantage of the polycapillary is that its field of view is about 50 um, so it does not ‘see’ as much of the gasket scattering. The tradeoff is that the polycapillary has about a 20% transmission efficiency but a wider acceptance angle of collected scattering. The results of our comparison show a significant improvement in the signal/background ratio using the polycapillary. For the same sample and counting times, the background is reduced by an about a factor of 5 using the polycapillary. This is essential to be able to measure samples at mega-bar pressures.