A method for measuring the specular X-ray reflectivity with millisecond time resolution

A method for quick measurement of the specular X-ray reflectivity using a tapered undulator source is described. It uses a convergent X-ray beam with a one-to-one correspondence between X-ray energy and direction, which is produced by diffraction of a white X-ray beam at a curved silicon crystal. To increase the momentum transfer range, the sample is rotated 45 degrees from the horizontal around the incident beam direction, so that both the X-ray energy and the incident angle change continuously with direction. The specularly reflected beam is observed with a two-dimensional detector. The X-ray reflectivity curve in a wide momentum transfer range can be observed in a single detector exposure with a time resolution in the millisecond range. Test measurements were done for a commercial silicon wafer and a gold thin film on silicon.