Characterization of magnesium fluoride thin films deposited by direct electron beam evaporation

Dumas, L.; Quesnel, Etienne; Robic, Jean-Yves; Pauleau, Y.

doi:10.1116/1.582210

Cited by 33 publications

(28 citation statements)

References 11 publications

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“…Figure 5 (b) shows that density of MgF 2 films increased with substrate temperature from ∼81% of bulk density (3.16 g/cm −3 ) for the film deposited at room temperature up to ∼100% of bulk density for the films deposited at 250°C. This result is compatible with those reported in Ref [9]. Density increase must be due to a reduction of voids in the film, leaving less room for water and contaminants and thus reducing MgF 2 extinction coefficient values as reported by Wood II et al [12].…”

Section: Density Roughness and Pinholessupporting

confidence: 93%

“…Yet, the absorption of thin films of MgF 2 in the transparency range is several orders of magnitude higher than in MgF 2 crystals, and this absorption increases towards the cut-off wavelength. The absorption in thin films deposited by evaporation is related with the columnar growth that leaves room for water and contaminants [9]; columnar growth also generates scattering losses [10,11]. All this limits Al/MgF 2 mirror reflectance.…”

Section: Introductionmentioning

confidence: 99%

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Optimization of MgF₂-deposition temperature for far UV Al mirrors

et al. 2018

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Progress towards far UV (FUV) coatings with enhanced reflectance is invaluable for future space missions, such as LUVOIR. This research starts with the procedure developed to enhance MgF-protected Al reflectance through depositing MgF on a heated aluminized substrate [Quijada et al., Proc. SPIE 8450, 84502H (2012)] and it establishes the optimum deposition temperature of the MgF protective film for Al mirrors with a reflectance as high as ~90% at 121.6 nm. Al films were deposited at room temperature and protected with a MgF film deposited at various temperatures ranging from room temperature to 350°C. It has been found that mirror reflectance in the short FUV range continuously increases with MgF deposition temperature up to 250°C, whereas reflectance decreases at temperatures of 300°C and up. The short-FUV reflectance of mirrors deposited at 250°C only slightly decreased over time by less than 1%, compared to a larger decay for standard coatings prepared at room temperature. Al mirrors protected with MgF deposited at room temperature that were later annealed displayed a similar reflectance enhancement that mirrors protected at high temperatures. MgF and Al roughness as well as MgF density were analyzed by x-ray grazing incidence reflectometry. A noticeable reduction in both Al and MgF roughness, as well as an increase of MgF density, were measured for films deposited at high temperatures. On the other hand, it was found a strong correlation between the protective-layer deposition temperature (or post-deposition annealing temperature) and the pinhole open area in Al films, which could be prevented with a somewhat thicker Al film.

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Section: Density Roughness and Pinholessupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Optimization of MgF₂-deposition temperature for far UV Al mirrors

et al. 2018

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“…3(a), the stress transformed from compressive stress into tensile stress which mainly originated from thermal stress due to the difference in thermal expansion coefficient between the films and the substrate. The compress tensile of the films prepared at room temperature was thought to be related to the reaction between the adsorbed water molecules and the inner face of the pores [10]. The tensile stress increased with the deposition rate as shown in Fig.…”

Section: Film Characterizationmentioning

confidence: 96%

Laser-induced damage resistance of AlF₃films

Sun

Zhang

et al. 2013

SPIE Proceedings

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AlF 3 thin films were prepared by thermal evaporation at different substrate temperatures and deposition rates. The relationships between optical properties, mechanical properties and laser-induced damage threshold (LIDT) at 355nm of AlF 3 films were discussed. Both absorption and stress increased with increasing substrate temperatures and deposition rates, which was a disadvantage to laser-induced damage resistance. Meanwhile, interfacial adhesion and hardness increased with substrate temperatures and deposition rates, which was an advantage to enhance the LIDT. The LIDT increased from room temperature to 200℃ duo to increasing interfacial adhesion and hardness, and then decreased to 300℃ duo to increasing absorption and stress. The LIDT decreased with deposition rates due to increasing absorption and stress.

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“…When the MgF 2 film grows on a substrate at room temperature (RT), it grows more absorbing and more porous than bulk MgF 2 crystals, which is a source of light scattering and causes the presence of contaminants, starting with water vapor, to fill the pores. The absorption in thin films deposited by evaporation is related with the columnar growth [2]. Both scattering and absorption result in a lower reflectance of the Al/MgF 2 coating.…”

Section: Introductionmentioning

confidence: 99%

Enhanced far-UV reflectance of Al mirrors protected with hot-deposited MgF2

Marcos

Gutiérrez-Luna

Espinosa-Yáñez

et al. 2018

Advances in Optical Thin Films VI

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Mirrors based on Al protected with a MgF 2 film provide high reflectance over a broad spectral range down to the wavelength of 120 nm in the Far UV (FUV). After more than 50 years since the development of this technology, a significant FUV reflectance enhancement has been obtained in the last years. Such enhancement originates mostly in the higher transparency of the MgF 2 protective layer deposited on a hot Al-coated substrate. Research has been conducted at GOLD to measure the dependence of the FUV reflectance enhancement with MgF 2 deposition temperature. A reflectance enhancement was found for freshly-prepared samples; moreover, the reflectance degradation over time of Al films protected with hot-deposited MgF 2 was also smaller than for the coatings deposited at room temperature. A reflectance as high as 90% was measured at 121.6 nm (hydrogen Lyman α line) for aged samples. A FUV reflectance enhancement was also obtained on samples fully deposited at room temperature and later annealed in vacuum. The reflectance of Al mirrors as a function of MgF 2 deposition temperature, as well as of post-deposition annealed mirrors, and their stability over time is presented. Structural data on film roughness, density, and main crystal orientations for mirrors with a MgF 2 film deposited both at room temperature and at 250°C are also presented.

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Characterization of magnesium fluoride thin films deposited by direct electron beam evaporation

Cited by 33 publications

References 11 publications

Optimization of MgF₂-deposition temperature for far UV Al mirrors

Optimization of MgF₂-deposition temperature for far UV Al mirrors

Laser-induced damage resistance of AlF₃films

Enhanced far-UV reflectance of Al mirrors protected with hot-deposited MgF2

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Characterization of magnesium fluoride thin films deposited by direct electron beam evaporation

Cited by 33 publications

References 11 publications

Optimization of MgF2-deposition temperature for far UV Al mirrors

Optimization of MgF2-deposition temperature for far UV Al mirrors

Laser-induced damage resistance of AlF3films

Enhanced far-UV reflectance of Al mirrors protected with hot-deposited MgF2

Contact Info

Product

Resources

About

Optimization of MgF₂-deposition temperature for far UV Al mirrors

Optimization of MgF₂-deposition temperature for far UV Al mirrors

Laser-induced damage resistance of AlF₃films