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Influence of ex-situ annealing on the properties of MgF2 thin films deposited by electron beam evaporation

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@article{e3d3e121638c49788abdee817db5712f,
title = "Influence of ex-situ annealing on the properties of MgF2 thin films deposited by electron beam evaporation",
abstract = "We report on the properties of magnesium fluoride (MgF2) thin films deposited by electron beam evaporation as a function of substrate deposition temperature and ex-situ annealing temperature. In particular, we report on the dependence of refractive index on annealing temperature, which can be used as a tuning parameter of the optical properties. Mechanical and structural properties of the films influenced by the annealing are also examined. Changing the substrate temperature from 50 °C to 240 °C caused a decrease of the refractive index and the lowest value of 1.36 (measured at 632.8 nm) was achieved for the substrate temperature of 240 °C. Rapid thermal annealing further decreased the refractive indices to slightly below 1.32. This could indicate increase in the film porousness and removal of adsorbed water molecules. Prior annealing the film surfaces were very smooth with root mean square and mean roughness below 1 nm. Annealing above 700 °C changed the structure of the films drastically, as they started to form a granular structure, while an annealing temperature of 1000 °C increased the refractive index to a value as high as 1.5. Using X-ray photoelectron spectroscopy we show that the surface of the films consist mainly of Mg and F atoms, but also small traces of C and O are present. The Mg:F ratio remained essentially the same (43:57) between different deposition temperatures. To demonstrate the need for post-deposition annealing treatment, we have also studied the aging effect in the MgF2 based anti-reflective coatings.",
author = "Jarno Reuna and Ville Poloj{\"a}rvi and Pertti P{\"a}{\"a}kk{\"o}nen and Kimmo Lahtonen and Marianna Raappana and Timo Aho and Riku Isoaho and Arto Aho and Mika Valden and Mircea Guina",
year = "2019",
month = "10",
doi = "10.1016/j.optmat.2019.109326",
language = "English",
volume = "96",
journal = "Optical Materials",
issn = "0925-3467",
publisher = "Elsevier",

}

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TY - JOUR

T1 - Influence of ex-situ annealing on the properties of MgF2 thin films deposited by electron beam evaporation

AU - Reuna, Jarno

AU - Polojärvi, Ville

AU - Pääkkönen, Pertti

AU - Lahtonen, Kimmo

AU - Raappana, Marianna

AU - Aho, Timo

AU - Isoaho, Riku

AU - Aho, Arto

AU - Valden, Mika

AU - Guina, Mircea

PY - 2019/10

Y1 - 2019/10

N2 - We report on the properties of magnesium fluoride (MgF2) thin films deposited by electron beam evaporation as a function of substrate deposition temperature and ex-situ annealing temperature. In particular, we report on the dependence of refractive index on annealing temperature, which can be used as a tuning parameter of the optical properties. Mechanical and structural properties of the films influenced by the annealing are also examined. Changing the substrate temperature from 50 °C to 240 °C caused a decrease of the refractive index and the lowest value of 1.36 (measured at 632.8 nm) was achieved for the substrate temperature of 240 °C. Rapid thermal annealing further decreased the refractive indices to slightly below 1.32. This could indicate increase in the film porousness and removal of adsorbed water molecules. Prior annealing the film surfaces were very smooth with root mean square and mean roughness below 1 nm. Annealing above 700 °C changed the structure of the films drastically, as they started to form a granular structure, while an annealing temperature of 1000 °C increased the refractive index to a value as high as 1.5. Using X-ray photoelectron spectroscopy we show that the surface of the films consist mainly of Mg and F atoms, but also small traces of C and O are present. The Mg:F ratio remained essentially the same (43:57) between different deposition temperatures. To demonstrate the need for post-deposition annealing treatment, we have also studied the aging effect in the MgF2 based anti-reflective coatings.

AB - We report on the properties of magnesium fluoride (MgF2) thin films deposited by electron beam evaporation as a function of substrate deposition temperature and ex-situ annealing temperature. In particular, we report on the dependence of refractive index on annealing temperature, which can be used as a tuning parameter of the optical properties. Mechanical and structural properties of the films influenced by the annealing are also examined. Changing the substrate temperature from 50 °C to 240 °C caused a decrease of the refractive index and the lowest value of 1.36 (measured at 632.8 nm) was achieved for the substrate temperature of 240 °C. Rapid thermal annealing further decreased the refractive indices to slightly below 1.32. This could indicate increase in the film porousness and removal of adsorbed water molecules. Prior annealing the film surfaces were very smooth with root mean square and mean roughness below 1 nm. Annealing above 700 °C changed the structure of the films drastically, as they started to form a granular structure, while an annealing temperature of 1000 °C increased the refractive index to a value as high as 1.5. Using X-ray photoelectron spectroscopy we show that the surface of the films consist mainly of Mg and F atoms, but also small traces of C and O are present. The Mg:F ratio remained essentially the same (43:57) between different deposition temperatures. To demonstrate the need for post-deposition annealing treatment, we have also studied the aging effect in the MgF2 based anti-reflective coatings.

UR - http://www.mendeley.com/research/influence-exsitu-annealing-properties-mgf2-thin-films-deposited-electron-beam-evaporation

U2 - 10.1016/j.optmat.2019.109326

DO - 10.1016/j.optmat.2019.109326

M3 - Article

VL - 96

JO - Optical Materials

JF - Optical Materials

SN - 0925-3467

M1 - 109326

ER -