Single and multi-channel Al-based multilayer systems for space applications in EUV range

Abstract

We report on further development of reflective multilayer coatings containing aluminum as low absorbing material for the extreme ultra-violet (EUV) applications, in particular for solar physics. Optimizations of the multilayer design and deposition process have allowed us to produce Al-based multilayers having relatively low interface roughness and record EUV reflectances in the range from 17 to 40 nm. The peak reflectance values of 56 % at 17.5 nm, 50 % at around 21 nm, and 42 % at 32 nm were achieved with new three-material multilayers Al/Mo/SiC and Al/Mo/B 4 C at near-normal incidence. We observe a good temporal stability of optical parameters of the multilayers over the period of 4 years. Moreover, the multilayer structure remains stable upon annealing at 100 °C in air during several weeks.We will discuss the optical properties of more complex Al-based systems with regard to the design of multilayer coatings that reflect more than one wavelength and reject some others within the spectral range from 17 to 40 nm. Such multichannel systems with enhanced reflectance and selectivity would provide a further advance in optical performance and compactness of EUV solar imaging instruments. We will discuss general aspects of design, optimization and fabrication of single-and multi-channel multilayer mirrors made with the use of aluminum. We will present recent results on the EUV reflectivity of multilayer coatings based on the Al/Mo/SiC and Al/Mo/B 4 C material combinations. Al-based multilayer systems are proposed as optical coatings in EUV telescopes of future space missions and in other EUV applications.

Optical, structural and aging properties of Al/Sc-based multilayers for the extreme ultraviolet

“…It turns out that 8026 reached 31.9% reflectance at 19.1 nm (-2.2% absolute), 8028 reached 27.6% at 39.7 nm (-0.8%) and 8031 showed a reflectance of 16.6% at 42.4 nm (-1.0%). These changes are in the typical range of EUV coating evolution in the first year after deposition [16] and may be explained by a modification of the top layer (oxidization and/or contamination) [17]. These results demonstrate adequate temporal stability of the EUV performance of Al/Sc multilayers protected with a 3 nm thick SiC capping layer.…”

“…We protected all the "thickness study" samples with a 3 nm thick SiC top layer. We have previously demonstrated that such SiC capping layers are able to assure a good temporal stability of Al-based multilayers [16,17]. For the optimized samples, we adjusted the SiC top layer thickness in order to reach the highest reflectance (see Table 1).…”

Extreme Ultraviolet Multilayer Nanostructures and Their Application to Solar Plasma Observations: A Review

“…The best results in terms of the EUV reflectance and long-term stability were obtained both with Al/Mo/SiC 97 and Al/Mo/B 4 C structures: the reflectance peaks of about 56% at 17.4 nm and about 50% at 21 nm were demonstrated to be stable over four years. 95 Furthermore, Al/Mo/B 4 C reached a reflectance of 42% at 32 nm. 95 Such coatings showed a fair drop in reflectance after annealing of nearly 6 sweeks at 100 C in air atmosphere, probably due to surface oxidation; 95 in contrast, they remained stable after many vacuum thermal cycles ranging from −50 C up to +70 C. 96 In Figure 7 the peak reflectance expected with Al/Mo/B 4 C at each wavelength is reported and compared with the experimental results available in Ref.…”

“…95 Furthermore, Al/Mo/B 4 C reached a reflectance of 42% at 32 nm. 95 Such coatings showed a fair drop in reflectance after annealing of nearly 6 sweeks at 100 C in air atmosphere, probably due to surface oxidation; 95 in contrast, they remained stable after many vacuum thermal cycles ranging from −50 C up to +70 C. 96 In Figure 7 the peak reflectance expected with Al/Mo/B 4 C at each wavelength is reported and compared with the experimental results available in Ref. [95].…”

Analyses of tabulated optical constants for thin films in the EUV range and application to solar physics multilayer coatings

“…However, the influence of the SiO2 top layer on the reflectance spectra out of the Bragg peak region is negligible. 1) have been developed simultaneously with Al/Mo/SiC and provide high efficiencies with near normal incidence reflectance up to 50% at 21 nm 13 (not shown in this paper) and 42% at 30 nm for an incidence angle θ = 80° (Figure 5).…”