Ceramics International 47 (2021) 9691–9700 Available online 15 December 2020 0272-8842/© 2020 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Hydrolysis corrosion of alumina thin flms produced by pulse DC reactive magnetron sputtering at various operating pressures Chatpawee Hom-on a , Napat Triroj b , Mati Horprathum c , Tossaporn Lertvanithphol c , Chanunthorn Chananonnawathorn c , Sakson Limwichean c , Noppadon Nuntawong c , Prayoon Songsiriritthigul d , Hideki Nakajima e , Annop Klamchuen f , Papot Jaroenapibal a, * a Sustainable Infrastructure Research and Development Center, Department of Industrial Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen, 40002, Thailand b Department of Electrical Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen, 40002, Thailand c Spectroscopic and Sensing Devices Research Group, National Electronics and Computer Technology Center, Pathum Thani, 12120, Thailand d NANOTEC-SUT Center of Excellence on Advanced Functional Nanomaterials and School of Physics, Suranaree University of Technology, Nakhon Ratchasima, 30000, Thailand e Synchrotron Light Research Institute, Nakhon Ratchasima, 30000, Thailand f National Nanotechnology Center, National Science and Technology Development Agency, Pathum Thani, 12120, Thailand A R T I C L E INFO Keywords: Aluminum oxide Thin flms Operating pressure Sputtering Corrosion ABSTRACT Alumina thin flms were prepared by pulsed DC reactive magnetron sputtering using operating pressures that were varied from 3 to 20 mTorr. The flms were immersed in DI water at temperatures of 55 ◦ C and 65 ◦ C for 30 min to study their hydrolysis corrosion behaviors. Unlike bulk crystalline Al 2 O 3 materials, sputtered alumina flms fabricated at operating pressures of 7 mTorr and higher were found to react with DI water within minutes, even under mild conditions. X-ray diffraction (XRD) and spectroscopic ellipsometry (SE) showed that the as- sputtered flms had amorphous structures with various degrees of porosity within the flms. The calculated porosity was found to increase from 17% to 25% as the operating pressure increased from 3 to 20 mTorr, respectively. Field-emission scanning electron microscopy (SEM) was employed to characterize the morphologies of the corroded flms. Attenuated total refectance Fourier transform infrared (ATR-FTIR) spectroscopy showed the presence of hydroxide-containing functional groups on surfaces of alumina flms, suggesting that the corrosion was due to a hydrolysis reaction. X-ray photoelectron spectroscopy (XPS) revealed distinct features in the non-corroded and corroded sample groups. For the corroded group (7–20 mTorr), the Al 2p peak showed two transitions, at 74.2 and 75.5 eV, attributed to Al–O and Al–OH, respectively. The O 1s peak intensities associated with the hydroxide content of samples in this group were found to be stronger than those associated with the lattice oxygen. The O 1s signal from adsorbed water at 533.7 eV became much stronger in corroded samples. The results also show that flms fabricated at higher operating pressures yielded higher levels of pre-adsorbed hy- droxide. Corrosion may progress through collective processes, including the formation of soluble aluminum hydroxide complex species and Al–O bond breaking during the proton transfer reactions between adsorbed water and hydroxide. 1. Introduction Alumina (Al 2 O 3 ) is considered a thermally stable material with high strength, chemical inertness and excellent electrical insulating proper- ties [1,2]. Crystalline alumina materials have two main phases, α-Al 2 O 3 (corundum) and γ-Al 2 O 3 (spinel). Both phases are generally assumed to be water-insoluble at room temperature. Thus, they are used as anti-corrosion materials in many applications. Several research groups have studied the reactivity of alumina with water [3–7]. Corrosion of alumina was normally found at elevated temperature by exposing it to water vapor [3,4] or under extreme conditions such as an alkaline so- lution at 150–200 ◦ C [5]. Some reports have shown that γ-Al 2 O 3 can react with water at 25 ◦ C resulting in the formation of bayerite. How- ever, the reaction rate is so slow that bayerite crystallization can only be * Corresponding author. E-mail address: papoja@kku.ac.th (P. Jaroenapibal). Contents lists available at ScienceDirect Ceramics International journal homepage: www.elsevier.com/locate/ceramint https://doi.org/10.1016/j.ceramint.2020.12.108 Received 17 August 2020; Received in revised form 30 November 2020; Accepted 12 December 2020