Thickest x-ray masks to date

Extending phase-based methods to higher x-ray energies would be beneficial for a series of applications where high Z and/or thick and dense samples need to be imaged. Using commercially procured masks with a thickness of ~300 micron, we have been able to perform quantitative phase imaging at spectral energies of up to 150 kVp (see Reliable phase retrieval at 150 kVp below). To enable reaching higher energy, we have created deep trenches in silicon wafers via deep reactive ion etching, and established a collaboration with NIST to enable filling them completely with gold using their bismuth-mediated super-conformal approach. This resulted in 500 micron thick gold masks, producing stronger phase contrast from high-Z materials such as Cu compared to their 300 micron thick counterparts. 

Left: 500 micron thick Si structure midway through superconformal filling with Au; right: edge-enhancement from a Cu detail extracted from images acquired with 500 and 300 thick masks; the x-ray spectrum is hardened by increasing the threshold in a photon-counting detector.