A linear zone plate named multilayer laue lens （MLL） is fabricated using a depth-graded multilayer structure. The lens shows considerable potential in focusing an X-ray beam into a nanometer scale with high efficiency. In this letter, a depth-graded multilayer consisting of 324 alternating WSi2 and Si layers with a total thickness of 7.9μm is deposited based on the thickness sequence according to the demands of the zone plate law. Subsequently, the multilayer sample is sliced and thinned to an ideal depth along the cross-section direction using raw abrasives and diamond lapping. Finally, the cross-section is polished by a chemical mechanical polishing （CMP） technique to remove the damages and improve the surface smoothness. The final depth of the MLL is approximately 7 μm with an achieved aspect ratio greater than 400. Results of scanning electron microscopy （SEM） and atomic force microscopy （AFM） indicate that interfaces are sharp, and the multilayer structure remains undamaged after the thinning and polishing processes. The surface roughness achieved is 0.33 nm.
Aperiodic molybdenum/silicon （Mo/Si） multilayer designed as a broadband reflective mirror with mean reflectivity of 10% over a wide wavelength range of 12.5-28.5 nm at incidence angle of 5° is developed using a numerical optimized method. The multilayer is prepared using direct current magnetron sputtering technology. The reflectivity is measured using synchrotron radiation. The measured mean reflectivity is 7.0% in the design wavelength range of 12.5-28.5 nm. This multilayer broadband reflective mirror can be used in extreme ultraviolet measurements and will greatly simplify the experimental arrangements.
Theoretically,the spectral resolution of a multilayer can be improved through a combination of utilizing high reflectance orders and by decreasing the thickness of the scattering layer.We fabricate Mo/Si multilayers in the first,second,third,fourth and fifth reflectance orders with Mo layer thicknesses of 3.0 nm and 2.0 nm,respectively,using direct current magnetron sputtering.The structure of the multilayers is characterized with a grazing angle x-ray diffractometer(XRD).Then the reflectivity of the multilayers is measured in a synchrotron radiation facility.The results show that the spectral resolution increases with the increasing reflectance order and with the decreasing Mo layer thickness.The highest spectral resolution is improved to 117.5 in the 5th order for dMo=2 nm,where the reflectivity is 18%.
To develop high quality dispersion optics in the X-ray region, the sliced multilayer transmission grating is examined. Dynamical diffraction theory is used to calculate the diffraction property of this volume grating. A WSi2/Si multilayer with a d-spacing of 14.3 nm and bi-layer number of 300 is deposited on a super- polished silicon substrate by direct current magnetron sputtering technology. To make the transmission grating, the multilayer is sliced and thinned in the cross-section direction to a depth of 23-25 ttm. The diffraction efficiency of the grating is measured at E = 8.05 keV, and the lst-order efficiency is 19%. The sliced multilayer grating with large aspect ratio and nanometer period can be used for high efficiency and high dispersion optics in the X-ray region.
A WSi2/Si multilayer, with 300 bi-layers and a 2.18-nm d-spacing, is designed for X-ray monochroma- tor application. The nmltilayer is deposited using direct current magnetron sputtering technology. The reflectivity of the 1st-order Bragg peak measured at E = 8.05 keV is 38%, and the angular resolution （△θ/θ） is less than 1.0%. Fitting results of the reflectivity curve indicate a layer thickness drift of 1.6%, mainly accounting for the broadening of the Bragg peaks. The layer morphology is further characterized by transmission electron microscopy, and a well-ordered multilayer structure with sharp interfaces is observed from the substrate to the surface. The material combination of WSi2/Si is a promising candidate for the fabrication of a high-resolution nmltilayer monochromator in the hard X-ray region.
