Diamond membrane-based X-ray optics: Fresnel zone plates, beam stops, and grids

The continuous push towards higher photon energies and higher imaging resolution has brought current state- of-theart X-ray focusing zone plates to a limit of 20 nm resolution at & lt;10 keV photon energies. Zone plates for focusing with same or better resolution at energies up to 25 keV are necessary for imaging and elemental analyses of multi-element samples, such as nano-composites, biological or geological samples, and nanofabricated electronic devices. Zone plates with such parameters are not yet available, while even for energies & lt;10 keV, there is a significant shortage of commercially available zone plates, amplified by the demand for these devices in commercial X-ray microscopes. In this Phase I SBIR, Fresnel zone plates will be developed for focusing hard X-rays up to 25 keV with & lt;20 nm resolution, using ultra-nanocrystalline diamond films as a high-performance substrate. These zone plate structures will be patterned by electron-beam lithography, dry-etched into diamond, and coated with an absorbent/phase-shifting X-ray material (Ir) by atomic layer deposition, which also produces a frequency doubling. These devices will utilize a composite zone plate design, known to enhance resolution and efficiency. The benefits of using diamond are: improved mechanical robustness which among other advantages prevents collapse of high-aspect-ratio ring structures, a known high-aspect-ratio etch method, and excellent compatibility with other processes, excellent radiation hardness, extremely low X-ray absorption, and significantly improved thermal/dimensional stability as compared to alternative materials. Key processes such as Ir damascene on diamond and deposition of a second diamond layer atop Ir nano-structures will facilitate the Phase II plan for achieving the final goal of this project: i.e. zone plates with 20 nm outermost zone width and ~2.4 mm Ir absorber thickness. These devices will be produced by repeated lithography steps with self-alignment on the front and/or back-side of the zone-plate-supporting diamond, necessary to reach the desired structure thickness and aspect ratios up to 180:1. Phase I will focus on optimizing the single but challenging patterning step and the diamond properties, while Phase II will exploit a sequential lithography approach and will also develop beam stops, apertures and other X-ray components that can be offered along with zone plates in this market. While developing zone plates for the hard X-ray regime is a significant milestone for X-ray techniques in general with significant ramifications in other sciences, developing stress free/flat diamond membrane devices will also dramatically impact a series of applications, including diamond grids for transmission electron microscopy elemental analysis, electron strippers for proton beam accelerators, diamond windows for laser ablation equipment, pressure sensors, microphones, and many others with large market potential.