High-rate reactive magnetron sputtering of zirconia films for laser optics applications K. Jus ˇkevic ˇius • M. Audronis • A. Subac ˇius • R. Drazdys • R. Jus ˇk _ enas • A. Matthews • A. Leyland Received: 28 August 2013 / Accepted: 19 December 2013 Ó Springer-Verlag Berlin Heidelberg 2014 Abstract ZrO 2 exhibits low optical absorption in the near- UV range and is one of the highest laser-induced damage threshold (LIDT) materials; it is, therefore, very attractive for laser optics applications. This paper reports explorations of reactive sputtering technology for deposition of ZrO 2 films with low extinction coefficient k values in the UV spectrum region at low substrate temperature. A high deposition rate (64 % of the pure metal rate) process is obtained by employing active feedback reactive gas control which creates a stable and repeatable deposition processes in the transition region. Substrate heating at 200 °C was found to have no significant effect on the optical ZrO 2 film prop- erties. The addition of nitrogen to a closed-loop controlled process was found to have mostly negative effects in terms of deposition rate and optical properties. Open-loop O 2 gas- regulated ZrO 2 film deposition is slow and requires elevated (200 °C) substrate temperature or post-deposition annealing to reduce absorption losses. Refractive indices of the films were distributed in the range n = 2.05–2.20 at 1,000 nm and extinction coefficients were in the range k = 0.6 9 10 -4 and 4.8 9 10 -3 at 350 nm. X-ray diffraction analysis showed crystalline ZrO 2 films consisted of mono- clinic ? tetragonal phases when produced in Ar/O 2 atmosphere and monoclinic ? rhombohedral or a single rhombohedral phase when produced in Ar/O 2 ? N 2 . Optical and physical properties of the ZrO 2 layers produced in this study are suitable for high-power laser applications in the near-UV range. 1 Introduction With the rapid development of high-power laser systems, low stability and damage tolerance in optical components have become weak points in the further application of laser systems [1]. Among the various optical thin-film candidate materials, zirconium dioxide (ZrO 2 ) is considered to be one of the most important high index oxides used for optical components in laser systems, since it shows a wide trans- parent range from near-UV (above 350 nm) to mid-IR (*8,000 nm) as well as good optical and mechanical properties and a high laser-induced damage threshold (LIDT) [2–5]. Also, there is great interest in expanding the exploitation of ZrO 2 in the UV range by depositing ZrO 2 / SiO 2 mixtures which are more suitable than pure zirconium oxide for antireflective or high reflectivity multilayer coatings in the UV range [1, 6, 7]. Zirconia films have been deposited by various tech- niques, including electron-beam evaporation (often with ion-beam assistance [8–11]), ion-beam sputtering [12, 13], pulsed laser deposition [14] and magnetron sputtering [15– 18]. A number of studies have reported optical properties of ZrO 2 films in the UV/VIS/NIR regions [1–3, 7–9, 15, 19]. Reactive magnetron sputtering from a metal Zr target is often used for ZrO 2 deposition. As with many other reactive sputtering processes, deposition of an oxide film (particularly an electrically insulating material, such as K. Jus ˇkevic ˇius (&) Á A. Subac ˇius Á R. Drazdys Á R. Jus ˇk _ enas Laboratory of Optical Coatings, State Scientific Research Institute Center for Physical Sciences and Technology, Savanoriu Ave. 231, 02300 Vilnius, Lithuania e-mail: kestutis.juskevicius@ftmc.lt M. Audronis Á A. Matthews Á A. Leyland Department of Materials Science and Engineering, The University of Sheffield, Sir Robert Hadfield Building, Mappin Street, S1 3JD Sheffield, UK e-mail: m.audronis@yahoo.co.uk 123 Appl. Phys. A DOI 10.1007/s00339-013-8214-1