Optical and structural characterization of orthorhombic LaLuO3 using extreme ultraviolet reflectometry

Mirrors are a subset of optical components essential for the success of current and future space missions. Most of the telescopes for space programs ranging from Earth Observation to Astrophysics and covering all the electromagnetic spectrum from X-rays to Far-Infrared are based on reflective optics. Mirrors operate in diverse and harsh environments that range from Low-Earth Orbit, to interplanetary orbits and the deep space. The operational life of space observatories spans from minutes (sounding rockets) to decades (large observatories), and the performance of the mirrors within the optical system is susceptible to degrade, which results in a transient optical efficiency of the instrument. The degradation that occurs in space environments depends on the operational life on the orbital properties of the space mission, and it reduces the total system throughput and hence compromises the science return. Therefore, the knowledge of potential degradation physical mechanisms, how they affect mirror performance, and how to prevent it, is of paramount importance to ensure the long-term success of space telescopes. In this review we report an overview on current mirror technology for space missions with a particular focus on the importance of degradation and radiation resistance of the coating materials. Particular detail will be given to degradation effects on mirrors for the far and extreme UV as in these ranges the degradation is enhanced by the strong absorption of most contaminants.

Mirrors for space telescopes: degradation issues

Reflectance versus incidence angle measurements have been performed from 5 to 152 nm on samples of SiC with a different C/Si ratio deposited with rf magnetron sputtering. The optical constants of the material at different wavelengths have been determined by using a curve-fitting technique of reflectance values versus incidence angle. Complementary measurements of the incident beam polarization, film thickness, surface roughness, and stoichiometry were performed to complete the analysis of the samples.

Reflectance measurements and optical constants in the extreme ultraviolet-vacuum ultraviolet regions for SiC with a different C/Si ratio

B4C optical coating represents, together with Ir, Pt, SiC, one of best choice for high reflectance in the extreme ultraviolet
region (EUV 160-30 nm). This material is also used in multilayer for soft X-ray applications, such as Si/B4C or W/B4C,
or as interlayer in Mo/Si multilayer to avoid interdiffusion also because of its high thermal stability. Our work concerns
on B4C thin films deposited on Si [100] substrates by means of three different deposition techniques: RF plasma
magnetron sputtering, e-beam evaporation, pulsed laser ablation (PLD). We performed reflectance vs incidence angle
measurements from 5 nm to 152 nm on different samples deriving the optical constants with a least-square fitting
method. Complete films characterization have been carried out with compositional (XPS), structural (XRD) and
morphological (AFM, SEM) analyses.

Optical constants in the EUV soft x-ray (5÷152 nm) spectral range of B4C thin films deposited by different deposition techniques

We have deposited SiC thin films using two different deposition tech- niques, Pulsed Electron Deposition (PED) and Pulsed Laser Deposition (PLD). The PED technique is a relatively new technique where a pulsed electron flux with high energy directly hits the target surface producing a plasma in a very similar way to PLD, where, instead, a pulsed laser beam is used. These two techniques can give very dense thin films with stoichiometry much closer to the target one's compared to others physical vapour deposition techniques (sputtering, e-beam). The major drawback of PED is that the thin film surface is affected by the pres- ence of particulate, due to the impact of the high energy electron beam with the target. In the PLD system we used a magnetic field to curve the plasma path in the vacuum and we placed the substrate at 90 ◦ with respect to the target allowing the deposition of particulate-free samples. The characterization of the films has been made by measuring the optical reflectance vs angle of incidence in the EUV region (from 121.6 nm down to 40.7 nm), taking measurements at different time from deposition. X-ray photoemission measurements have been also carried out to show stoichiometry and the presence of contaminants. Other measurements such as X-ray diffraction, atomic force microscopy and profiling were also carried out to check crystalline domains and surface roughness.

Silicon carbide thin films for EUV and soft X-ray applications

VUV reflectance measurements and optical constants of SiC thin films

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Reflectance measurements and optical constants in the extreme ultraviolet-vacuum ultraviolet regions for SiC with a different C/Si ratio

VUV reflectance measurements and optical constants of SiC thin films