Reactive sputter deposition of β-Ni(OH)₂ thin films in Ar + H₂O mixed gas atmosphere at a substrate temperature of −80 °C

Abstract

Nickel hydroxide [Ni(OH)2] is an electrochemically-active material used for rechargeable batteries, electrochemical capacitors, and electrochromic devices. Although there have been some studies on nickel hydroxide thin films deposited by sputtering, the Ni(OH)2 formation has not been fully confirmed. In this study, a Ni metal target was reactively sputtered in atmospheres of O2 and Ar + H2O at substrate temperatures of room temperature (RT, around 20 °C), −80 °C, and −170 °C, and the aging treatment effects in the air at RT were studied. From optical, X-ray diffraction, and infrared absorption measurements, β-Ni(OH)2 thin films were found to be formed after aging the films deposited at −80 °C in Ar + H2O, however, NiO thin films were formed at RT. These results corresponded well with a thermodynamic consideration of Ni(OH)2. At −170 °C, mixed metal and oxide films were formed, presumably because of insufficient Ni oxidation.