Electrochemical Manufacturing of Coated Silicon X-ray Mirror Optics

Currently available X-ray optics technologies such as compound refractive lenses, diffraction zone plates, and Kirkpatrick- Baez (K-B) mirrors allow for significant scientific discovery in modern synchrotron facilities. However, these optics each have limitations, variously including significant chromaticity (focal length dependence on photon energy), very long focal distances, and requirements for extremely high surface finish. One approach to mitigating the long focal distance of K-B mirrors is to combine mirror pairs into a single, bi- axially curved mirror form. This Phase I program seeks to demonstrate the feasibility of attaining the required surface form in (doped) silicon mirror substrates by pulsed- waveform electrochemical polishing. As well, the program aims to demonstrate the feasibility of pulsed- waveform electrodeposition of a suitable high-Z reflective material (viz., nickel) onto the prepared silicon surfaces. Pulsed electrochemical processing has significant established potential for both processing steps and is anticipated to provide an economical, effective means to achieving the required material forms for reflective X-ray optics in challenging geometries. In the Phase I program, custom-designed, patented electrochemical processing cells will be retrofitted to carry out polishing and nickel electrodeposition tests on doped silicon wafers. Preliminary electroanalysis will be performed as a means for informing and directing exploration of the electropolishing parameter space. Surface analysis will be accomplished by on-site non-contact optical profilometry, combined with cross-sectioning and microscopy, if required. A preliminary scale-up and economic analysis of the technology will be performed. In order to increase our capabilities to perform detailed scientific studies of complex materials and chemical systems, continued improvements in X-ray optics are required. In the proposed program, electrochemical processing techniques will be investigated as a potential means for fabricating such improved optics. Commercial Applications and Other Benefits: Future applications of the technology encompass the primary target market of X-ray optics, as well as potentially optics for lower-energy photons which pose challenges to current fabrication methods. The scientific investigations enabled by advancement of X-ray optics designs are substantial, especially as pertains to compositional surface mapping and high-resolution (large-scale) imaging and elemental/chemical analysis. While specific public benefits from such enabled activities are difficult to elaborate precisely, they are anticipated to be substantial.