Performance of a flat-field grating spectrometer for tender x-ray emission spectroscopy.

A flat-field grating spectrometer for tender x-ray emission spectroscopy has been developed. The grating has been coated with an aperiodic Ni/C multilayer that improves the diffraction efficiency in the range 1-3.5 keV at a constant angle of incidence. The aperiodic layer structure originates from the topmost bilayer with a larger thickness compared to other Ni/C bilayers. The performance of the spectrometer has been evaluated by measuring characteristic x rays such as the L series emitted from a Cu(In,Ga)Se-based thin-film solar cell specimen. It is shown that the Lα x-ray emission spectra of Cu, In, Ga, and Se can be clearly simultaneously observed in the range from 0.9 to 3.3 keV, and the linewidths are 4.9, 26.1, 4.6, and 6.1 eV, respectively, corresponding to a spectral resolution of 100-300.