Focusing multilayer mirror detection system for carbon K edge soft x-ray absorption spectroscopy (invited)

Fluorescence yield carbon K edge soft x-ray absorption measurements of mixed element samples are impeded by background scattered x-rays and fluorescence from noncarbon atoms within the sample induced by the incident x-ray beam (first and higher orders). We describe a high efficiency near-normal incidence focusing multilayer mirror detection system for carbon K edge fluorescence yield soft x-ray absorption spectroscopy. A spherical focusing multilayer mirror collects nearly 60% of the available solid angle with a reflectivity of 6% and a resolution of 2% (dE/E) for carbon K radiation in combination with a high efficiency proportional counter detector. The focusing multilayer system is able to effectively discriminate the background fluorescence and scattered light signals originating at the sample during a carbon K edge soft x-ray absorption experiment. A signal-to-background ratio in excess of 100 is possible for very dilute carbon samples, enabling a whole new class of in situ photon-in photon-out soft x-ray absorption measurements of carbon chemistry in catalysts to be made, even in a reactive chemical environment. (C) 2002 American Institute of Physics.