Metallic-mode reactive sputtering of nickel oxide thin films and characterization of their electrochromic properties

Abstract

Nickel oxide is a promising electrochromic (EC) material, and it is a material that changes color upon undergoing electrochemical oxidation and reduction. In this study, we prepared nickel oxide thin films by sputtering a nickel metal target using water vapor (H2O) as a reactive gas, and investigated the effects of substrate cooling and water vapor flow ratio in the atmosphere of argon (Ar) gas, RH2O = H2O/(Ar + H2O). High and constant target voltage and plasma emission peaks of Ni atoms were obtained up to RH2O = 75% at ‒80 °C, indicating that the Ni target maintained a metallic state. The deposition rate increased with increasing RH2O when the substrates were cooled, and a maximum deposition rate of 34.6 nm min−1 was obtained at RH2O = 50%. The nickel oxide thin films that were formed in the metallic target mode showed high transmittance in the as-deposited state and good EC properties.

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

“…The number of supplied H 2 O molecules was calculated to be 1.1 × 10 −4 mol min −1 , and the amount of sputtering Ni atoms was estimated to be 2.2 × 10 −5 mol min −1 by weighing the mass of the deposited Ni film. 24) The ratio of the number of supplied H 2 O molecules to that of sputtered Ni atoms is considered to be sufficiently large for the Ni(OH) 2 formation.…”

“…Some previous studies on the sputter deposition of Ni(OH) 2 and hydrated NiO thin films are summarized in Table I. [15][16][17][18][19][20][21][22][23][24] In these studies, a Ni(OH) 2 target was sputtered in an Ar + O 2 atmosphere, or Ni metal targets were reactively sputtered in reactive gasses containing O 2 + H 2 or H 2 O. Substrate cooling below (RT, around 20 °C) was applied in some studies. Although these papers reported good EC properties for the deposited films, the Ni(OH) 2 thin film formation was not fully confirmed.…”

Two-color electrochromic devices using a tungsten oxide and nickel oxide double layer

“…H 2 O was used as the reactive gas to form nickel hydroxide films with high electrochemical activity. 12,[29][30][31][32] Although the H 2 O-deposited films are expected to contain OH groups and H 2 O molecules, it is denoted as NiO in this paper for simplicity. ITO films with a thickness of 300 nm were prepared by sputtering an ITO target (SnO 2 concentration of 5 wt%, 4 N purity) in an Ar atmosphere.…”

Coloring and Bleaching Properties of 500–1000 nm‐Thick Electrochromic Tungsten Oxide Films Deposited by Reactive Direct Current Magnetron Sputtering

“…Oxides such as tungsten oxide (WO 3 ), [1] molybdenum trioxide MoO 3 , [2] vanadium oxide (VO x ), [3] and nickel oxide (NiO x ) [4,5] are well-known electrochromic (EC) materials. WO 3 has attracted particular interest as it changes from colorless to deep blue; [6][7][8][9][10][11] this phenomenon is reversible and occurs at a low voltage.…”