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Development of Grating Technology for High-Resolution Spectrometers Using Nanofabrication Techniques

Drew Miles
The Pennsylvania State University

Several of astronomy’s key future science objectives as identified by NASA can be achieved with soft X-ray spectroscopy. This study seeks to develop a new technique for fabricating X-ray reflection gratings to be integrated in future X-ray spectrometer designs. The fabrication method developed in this study will create a reflection grating with a true radial profile, which is a requirement in order to eliminate grating-induced aberrations to the telescope focus and achieve the required resolving power of future missions. If successful, the technology developed in this study will lead to the realization of theoretical X-ray spectrometer performance on timescales consistent with the next decadal survey. This study will build on our research group’s strong heritage in the development of X-ray reflection gratings and introduce a new fabrication technique that retains current state-of-the-art grating efficiency while also achieving order-of-magnitude improvements in resolving power. The new fabrication technique is centered around piezoelectric materials and will be approached as follows: first, I will model grating applications of piezoelectric materials and conduct trade-study to determine most suitable piezoelectric materials to be used in grating fabrication. I will then obtain materials and begin implementation of the planned fabrication procedures: create a “master” grating with parallel grooves current electron-beam lithography (EBL) employed in our grating fabrication efforts in order to retain the precise groove facets achievable with EBL; the EBL “master” will then be imprinted into a soft resist that is coated upon a wafer of piezoelectric material, beneath which are electrodes to control the current through the material; with the parallel-groove profile imprinted into the resist, a variable current will be applied across the piezoelectric material to force the resist to conform to a pre-selected pattern, which will transform the parallel grooves into a radial profile without sacrificing the precise facets introduced in the original EBL write; the pattern will then be UV-cured in order to solidify the resist and lock the radial profile into place; finally, this new piezoelectric master will be used to imprint dozens of replicas. The entire process will certainly require a significant amount of development and trial-and-error, which includes testing intermediate prototypes at NASA centers for both efficiency and resolution. However, if implemented successfully, this technology will make possible both the order-of-magnitude gains in effective area and resolving power over current observatories that is required for future X-ray missions.

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