Fabrication of x-ray absorption gratings via micro-casting for grating-based phase contrast imaging

Abstract

Grating-based x-ray differential phase contrast (DPC) imaging has shown huge potential. For broad applications, it is essential that the key components are low-cost, especially the absorption gratings. We therefore proposed and developed a micro-casting process for fabricating x-ray absorption gratings with bismuth. This process is feasible for mass production at low cost, with a large format, and a high aspect ratio. To develop this kind of absorption grating, an array with deep trenches was fabricated by photo-assisted electrochemical etching in a silicon wafer. The trenches were then filled with bubble-free, molten bismuth via capillary action and surface tension. Bismuth was attractive as a filling material because of its great mass absorption coefficient, low cost and broad environmental compatibility. Furthermore, our micro-casting process provided bismuth absorption gratings with a clean surface and no need for post treatment. To test their performance in x-ray DPC imaging, two bismuth absorption gratings, one as a periodic source and another as the analyzer, were used with periods of 42 and 3 µm and depths of 110 and 150 µm, respectively. The acquired phase-contrast images demonstrated that the micro-casting process produces qualified gratings for x-ray DPC imaging.