Classical hard x-ray transmission gratings fabricated using lithography are limited by a small aspect ratio of less than 20 when the grating periods are smaller than 2 microns. State of the art X-ray phase contrast imaging techniques require high density transmission gratings with smaller periods and higher aspect ratio to cover larger energy range for thicker samples. This problem may be addressed with a sliced multilayer technique, similar to that used in multilayer Laue lenses and multilayer transmission mask gratings. To increase the acceptance area of the grating, it was proposed [1] to use a thin Si substrate that is asymmetrically etched to a staircase with each stair supporting a multilayer parallel to its surface. Using an X-ray beam shining through the layers at an oblique angle to the substrate and parallel to the layer surfaces, one hopes to have a large-area transmission grating with small multilayer periods. The first fabrication test is completed using W/Si multilayers with dc magnetron sputtering deposition. The layer thickness d is designed to be (stair height)/2N, where 2N is the total number of layers. Preliminary results and challenges are presented.

[1] S. K. Lynch and H. H. Wen et al. “Multilayer-Coated Micro-Grating Array for X-Ray Phase-Contrast Imaging,” SPIE Proceedings 2011, submitted.

* This work is supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. SKL and HHW are supported by Division of Intramural Research, National Heart, Lung and Blood Institute, National Institutes of Health.