Development of Diamond Membrane-Based X-Ray Optics: Fresnel Zone Plates, Beam Stops, and Grids

The continuous push towards higher photon energies and higher imaging resolution in X-ray analysis systems has brought current state-of-theart X-ray focusing zone plates to a limit of 20 nm resolution at <10 keV photon energies. Zone plates for focusing with same or better resolution at energies up to 25 keV are now necessary for imaging and elemental analyses of multi-element samples, such as nanocomposites, biological or geological samples, and nanofabricated electronic devices. Zone plates with such parameters are not yet available, while even for energies <10 keV, there is a significant shortage of commercially available zone plates, amplified by the demand for these devices in commercial X-ray microscopes. What is being done: Hereby, Fresnel zone plates with composite architecture will be developed for focusing hard X-rays up to 25 keV with <20 nm resolution, using ultra-nanocrystalline diamond films as a high-performance substrates, electron-beam lithography, Iridium damascene, and a sequential lithography approach for aspect ratio enhancement. Phase I proved the base steps for achieving such zone plates possible: obtaining flat diamond membranes with different conductivity layers, high resolution electron beam lithography on top of diamond layers, transfer of the pattern into diamond, compatibility of the Iridium films deposited by atomic layer deposition with additional growth of diamond on top, the possibility of polishing metal-coated zone plates without damaging the nanostructures and wafer scale fabrication of zone plates. Phase I also implemented the composite design in conjunction with a novel, superior design of buttresses for preventing the collapse of resist patterns. Phase II will refine some of the processes already proven possible, develop the sequential lithography scheme for enhancing the thickness of the zone plates, and integrate them into one fabrication sequence for obtaining advanced zone plates at wafer scale. The zone plates with composite architecture will be accompanied by suited beam stops and apertures to be tested on X-ray beam lines of the Advanced Photon Source/Argonne National Laboratory, then will become available for commercialization. Commercial Applications: 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, stress free/flat, layered, and nanostructured diamond membranes will dramatically impact a series of other applications, including diamond grids for transmission electron microscopy elemental analysis, electron strippers for proton beam accelerators, pressure sensors, microphones, loudspeakers, and many others with large market potential.