Gas-MacEtch of Si with a Pt catalyst allows vertical etching nanostructures with an extreme aspect ratio up to 10 000 : 1.

The application of superconformal Bi-catalyzed Au electrodeposition for void-free filling of recessed trenches in X-ray gratings used in phase contrast imaging is detailed. Filling of trenches with aspect ratio (height divided by width) up to 55 is demonstrated. Uniform bottom-up filling of patterned trench arrays across 100 mm (4 inch) diameter Si wafer is accomplished using a welldefined hydrodynamic flow field across the wafer surface. The filling process and microstructure are examined by scanning electron microscopy of cross-sectioned specimens. The importance of process optimization, from the design of potential (current) programming to electrolyte pH and concentrations of Na 3 Au(SO 3 ) 2 and Bi 3+ , for the filling of high aspect ratio trenches is demonstrated. X-ray phase contrast imaging is used to assay the quality and uniformity of the as-formed gratings as well as demonstrate their application to imaging biological tissue. Successful void-free Au filling of micrometer range pitch, high aspect ratio trenches in Si gratings promises to advance X-ray grating interferometry and its application to X-ray phase contrast imaging.