Mo/Al multilayers have the potential to be used as reflective mirrors in telescopes for cosmic and solar observation in a large spectral range of extreme ultraviolet radiation. Two types of Mo/Al multilayers were deposited by a magnetron sputtering system for comparison: one used pure Al and one used Al doped with 1.5wt. % Si. The structural performance of these two multilayers were characterized by a X-ray diffractometer, atomic force microscope, and optical profilometer. The angular dependence of the reflectivity was measured using a laboratory-based reflectometer at 58.4 nm. Grazing incidence X-ray reflectivity analysis revealed that the Mo/Al (1.5wt. % Si) multilayers possess a significantly improved interfacial structure compared with Mo/Al (pure). Surface morphology observations of the samples indicated that the incorporation of Si smoothes the surface and reduces the surface roughness. X-ray diffraction results suggest that the Si slightly reduces the average grain size of Al and increases the average grain size of Mo, but their crystallinity is improved. Based on the improvement of structural performance, a peak reflectivity of 29.4% at 58.4 nm is achieved for Mo/Al (1.5%Si) multilayers, whereas it is only 17.4% for Mo/Al (pure).
The Solar Upper Transition Region Imager (SUTRI) was proposed to observe for the first time the Ne VII line at 46.5nm emitted from the upper solar transition region. As the key optical elements of the SUTRI, Sc/Si multilayer reflective mirrors are developed to offer high spectral selectivity and high reflectivity at 46.5nm with a normal-incidence angle. To avoid spectral contamination, the reflective bandwidth of the multilayer is required less than 4nm, which is achieved when the Sc layer thickness ratio is tuned to above 0.65. Meanwhile, the mechanical property, resistivity to thermal cycling, and temporal stability of the Sc/Si multilayer are characterized. The addition of an ultrathin Si layer (thickness of 0.6nm) in each Sc layer decreased the crystallization of Sc and flatted the interface, resulting in the enhancement of the mechanical property of the Sc/Si multilayer with new structure. After three times of thermal cycling, the temperature from 5°C to 40°C, the surface morphology of the new Sc/Si multilayer remained unchanged. The grazing incidence reflectometer test results showed that the periodic structure and thickness of the new multilayer were still similar after 2 years of storage. The optimized Sc/Si multilayer has a d-spacing of 24.55nm and a Sc thickness ratio of 0.72, achieving the extreme ultraviolet reflectivity of 28% at 46.1nm obtained from the laboratory-based reflectometer. The optimized Sc/Si multilayer mirrors have been applied in the SUTRI and received bright solar images at 46.5nm.
A laboratory-based reflectometer designed for characterizing the reflectivity of optical coatings in 30- to 200-nm wavelength range was recently developed at IPOE. An RF-produced gas-discharge light source is applied to generate characteristic lines. The light source is mounted on a grazing incident monochromator with a 146-deg deviation angle between the incident and diffracted arms. By precisely adjusting the toroidal grating inside the monochromator chamber, monochromatic lights are acquired through the exit slit. A collimator mirror and two sets of collimation slits with 2 mm × 2 mm dimension are utilized for reducing the divergence of the beam incident on the sample. A high-precision six-axis translation stage, which allows a heavy sample with a maximum diameter of 100 mm, is used to control positions of the samples and the detector. A chopper disk used both for incident light intensity monitor and signal modulation is placed with an incidence angle of 70 deg relative to the incident light beam. The configuration, adjustment process, and test results of the reflectometer are presented in detail. The experimental reflectivity results for Al / LiF / MgF2 film obtained from our laboratory and BESSY-II Synchrotron as well as Hefei Synchrotron Light Source are given and compared for demonstrating the reliability of the system.
Boron carbide coatings were prepared by reactive sputtering with nitrogen and investigated for their optical properties. Different ratios of N2/Ar (4%, 8%, and 15% nitrogen ratio) mixture gas was chosen as the sputtering gas. The atomic concentration distribution and elemental chemical states of coatings were characterized by X-ray photoelectron spectroscopy measurements. The B/C ratio was 3.7:1 and the nitrogen content was 18 at.% in the coating, which was sputtered with 4% N2 mixture gas. And the nitrogen content was increased as the ratio of N2 increases in mixture gas. In the nitridated B4C coatings, the boron mainly existed as the formation of BN and B4C compounds. The theoretical reflectivity was performed, and the increase of nitrogen content would reduce the reflectivity in the soft X-ray, especially in the vicinity of 410 eV.
Boron carbide (B4C) is a commonly used coating material in X-ray mirrors in Free-Electron Laser (FEL) beamlines for its good qualities such as high reflectivity, high hardness and high damage threshold. The B4C coating film fabricated by direct-current magnetron sputtering has large intrinsic compressive stress, which leads to poor adhesion on the substrate. In a traditional way, an adhesive layer of chromium is inserted between the B4C film and the substrate to improve the adhesion, which may also degrade the anti-damage resistance because of the enhanced photoabsorption inside the metal layer. For applications in FEL, the B4C film is generally fabricated under high Argon sputtering gas pressure to reduce the intrinsic stress. However, it is unclear about the impact of the Cr adhesive layer and the sputtering gas pressure on the damage resistances of B4C films. In this study, using a table-top nanosecond EUV damage instrument, single-shot damage experiments were performed on B4C films fabricated at different sputtering gas pressures with or without Cr adhesive layer. The single-shot damage thresholds are reported and the possible damage mechanisms are discussed based on the measurements using scanning electron microscope (SEM) and atomic force microscope (AFM).
Sc/Si multilayer has excellent reflectivity at the wavelength of 35-50 nm and is expected to be fabricated for application in the solar EUV telescope, reflecting Ne VII line (46.5 nm) at normal incidence angle. For obtaining the stable narrow bandwidth, Sc/Si multilayers with different Sc thickness ratios were designed. And the structure and temporal stability of fabricated multilayers were studied. Sc/Si multilayers with a period thickness of about 24 nm were deposited by DC magnetron sputtering. The GIXR measurements indicated that interface diffusion was existed between Sc and Si layers. As the thickness ratio of the Sc increased, the width on Sc-on-Si interfaces increased. The surface roughness of these samples were no obviously different under AFM tests. After two months, the periodic structure and thickness were found to be stable. With a Sc thickness ratio value of 0.67, Sc/Si multilayer not only have the narrow bandwidth, but also have a good temporal stability.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.