In this work, a masking technique was used to improve the thickness uniformity of a Mo/Si multilayer deposited on a curved spherical mirror by direct current (DC) magnetron sputtering with planetary rotation stages. The clear aperture of the mirror was 125 mm with a radius of curvature equal to 143.82 mm. Two different shadow masks were prepared; one was flat and the other was oblique. When using the flat mask, the non-uniformity considerably increased owing to the relatively large gap between the mask and substrate. The deviation between the designed and measured layer thickness and non-uniformity gradually reduced with a smaller gap. The second mask was designed with an oblique profile. Using the oblique mask, the deviation from multilayer thickness uniformity was substantially reduced to a magnitude below 0.8% on the curved spherical substrate over the clear aperture of 125 mm. Multilayers still achieved a smooth growth when deposited with obliquely incident particles. The facile masking technique proposed in this study can be used for depositing uniform coatings on curved spherical substrates with large numerical apertures for high-resolution microscopes, telescopes, and other related optical systems.

<!-- *** Custom HTML *** --> Driven by the growing demand for large-size x-ray mirrors used in synchrotron radiation and free-electron laser facilities, a linear deposition system based on magnetron sputtering technique is built. The layer growth quality and thickness uniformity are optimized by adding masks in front of the cathode to reduce the oblique-incidence particles and tune the sputtering flux distribution. Based on this, a 0.5-m-length W/Si multilayer mirror is demonstrated. The multilayer has a d-spacing of 3 nm and a bilayer number of 60. The surface roughness of the multilayer is only 0.33 to 0.25 nm in the spatial frequency range of 3.0 × 10^−  3 to 1.0 μm^−  1, and the average interface width is 0.32 nm. The hard x-ray reflectivity and uniformity of the large mirror were characterized at the Optics Beamline in Shanghai Synchrotron Radiation Facility. A maximum reflectivity of 62.5% and 62.7% was measured at 8 and 18 keV, respectively, with an angular resolution of Δθ / θ = 2.7 % . The d-spacing uniformity over the 0.5-m-length and 60-mm-width area of the mirror is 1.0% and 1.2% (peak-to-valley), respectively. These results indicate a good and uniform quality of the nanoscale multilayer over the large mirror area. The measured second- and third-order reflectivities of the multilayer are more than 2 orders magnitude lower than the first order, implying a good suppression of high harmonics in the monochromator application.

The Mo/Si multilayer mirror has been widely used in EUV astronomy, lithography, microscopy and other fields because of its high reflectivity at the wavelength around 13.5 nm. During the fabrication of Mo/Si multilayers on large, curved mirrors, shadow mask was a common method to precisely control the period thickness distribution. To investigate the effect of shadow mask on the microstructure of Mo/Si multilayers, we deposited a set of Mo/Si multilayers with and without the shadow mask on a curved substrate with aperture of 200 mm by direct current (DC) magnetron sputtering in this work. Grazing incidence X-ray reflectivity (GIXR), diffuse scattering, atomic force microscope (AFM) and X-ray diffraction (XRD) were used to characterize the multilayer structure and the EUV reflectivity were measured at the National Synchrotron Radiation Laboratory (NSRL) in China. By comparing the results, we found that the layer microstructure including interface width, surface roughness, layer crystallization and the reflectivity were barely affected by the mask and a high accuracy of the layer thickness gradient can be achieved.

Grating optics lie in the heart of X-ray spectroscopy instruments. The low efficiency and angular dispersion of conventional single-layer-coated gratings significantly limit the transmission and energy resolution of monochromators and spectrometers, particularly in the tender X-ray region (E=1−5 keV). Multilayer-coated blazed gratings (MLBGs) operating at high diffraction orders offer the advantage of achieving both high efficiency and high dispersion simultaneously. Tender X-ray monochromators and spectrometers using different high-order MLBGs have been designed, all demonstrating one to two orders of magnitude higher transmission compared to conventional systems. By employing a 2400 l/mm MLBG at the −4th or −8th diffraction order, the theoretical energy resolution of the instrument is improved by two to three times at 2.5 keV. Two MLBGs operating at the −2nd and −4th orders have been fabricated, showcasing remarkable efficiencies of 34%–12% at 2.5 keV, surpassing that of single-layer-coated gratings by an order of magnitude. Further optimization of manufacturing accuracy can yield even higher efficiencies. The measured angular dispersion agrees well with theoretical predictions, supporting the potential for high resolution. High-order MLBG optics pave the way for a new generation of tender X-ray monochromators/spectrometers that offer both high transmission and high resolution.