Preparation of high-purity beryllium foils

A technique is described for the preparation of beryllium foils by vapor deposition. The high-purity, pinhole-free foils are vacuum tight and suitable for many x-ray analysis applications. The beryllium is evaporated from an electron beam heated crucible source onto a heated substrated. Substrate temperatures of 450 to 7000C are necessary to obtain the desired mechanical properties of the foils. At these temperatures, contamination of the foils by diffusion of the substrate material into the beryllium can be a significant problem, as impurity levels of more than several hundred ppM are detrimental to the x-ray transparency of the windows. This problem is minimized by careful selection and preparation of the substrate. A clean deposition system and pure source material are necessary to preserve elemental integrity of the vapor-deposited foils