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Nanocrystalline Low‐Refractive Magnesium Fluoride Films Deposited by Reactive Magnetron Sputtering: Optical and Structural Properties
Author(s) -
Mertin Stefan,
Marot Laurent,
Sandu Cosmin S.,
Steiner Roland,
Scartezzini JeanLouis,
Muralt Paul
Publication year - 2015
Publication title -
advanced engineering materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.938
H-Index - 114
eISSN - 1527-2648
pISSN - 1438-1656
DOI - 10.1002/adem.201500129
Subject(s) - materials science , magnesium fluoride , nanocrystalline material , analytical chemistry (journal) , ellipsometry , sputter deposition , x ray photoelectron spectroscopy , thin film , sputtering , amorphous solid , optics , magnesium , nanotechnology , metallurgy , crystallography , chemistry , chemical engineering , physics , chromatography , engineering
In this work, we study MgF 2 thin‐film synthesis by reactive pulsed DC magnetron sputtering from a metallic magnesium target in a gas mixture of argon, oxygen, and carbon tetrafluoride (CF 4 ). Nanocrystalline films on silicon and glass substrates with excellent properties for optical application are achieved. The plasma discharge is analyzed with a differentially pumped mass spectrometer before and during the deposition process. Without breaking the vacuum, monochromatic photoelectron spectroscopy (XPS) is performed for in situ determination of the atomic C and O concentration. Film microstructure, topography, and thickness are investigated by electron microscopy (SEM and TEM), atomic force microscopy (AFM), and X‐ray diffraction (XRD). The optical constants n and k are determined by spectroscopic ellipsometry and spectrophotometry: a consistent parametric fit of the ellipsometric angles and spectral transmittance and reflectance based on three Lorentz oscillators to determine n and k is achieved for a wide spectral range (300–2 300 nm). At 550 nm, a refractive index of 1.382 and near‐zero absorption is obtained, which is in excellent agreement with n = 1.383 of polycrystalline MgF 2 . The measured light reflection at 760 nm is reduced by 3% for a quarter‐wave nanocrystalline MgF 2 coating on glass compared to the uncoated glass substrate.