QDev Seminar: Karolis Parfeniukas
High aspect ratio nanofabrication for hard x-ray zone plates
Diffractive zone plate optics are routinely used to produce the highest resolution focus for nanoscale x-ray imaging. The devices are circular diffraction gratings with radially decreasing grating constant, and the obtainable resolution depends on the smallest grating line width. However, optimal focusing efficiency of a zone plate requires a certain lens thickness. Therefore, high aspect ratio nanofabrication processes are required.
In this talk, two methods will be presented. First, reactive ion etching of tungsten, capable of aspect ratios up to 22:1 at 30 nm line width. Such tungsten optics were used in the commissioning experiment of the nanoimaging beamline NanoMAX at the synchrotron facility MAX IV. Second, metal-assisted chemical etching of silicon as a cutting-edge alternative. Etching reaction control, fabrication strategies, and limitations of the method will be discussed.