Effect of O2 Flow Concentration during Reactive Sputtering of Ni Oxide Thin Films on Their Electrochemical and Electrochromic Properties in Aqueous Acidic and Basic Electrolyte Solutions

概要

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Thin films of Ni oxide were deposited by reactive sputtering in argon/oxygen gas mixtures using O2 flow concentrations ranging from 6 to 100% and their electrochemical and electrochromic properties were examined using dilute acidic ($\text{1\,M KCl}+\text{0.5\,mM H$_{2}$SO$_{4}$}$) and basic (1 M KOH) aqueous electrolyte solutions. An electrochromic coloration efficiency of $32\pm 5$ cm2/C was obtained for all the Ni oxide films regardless of O2 concentration in both $\text{KCl}+\text{H$_{2}$SO$_{4}$}$ and KOH. The charge capacity and resultant change in the optical density of the Ni oxide films increased with O2 concentration owing to a decrease in crystal grain size and the resultant increase in the active surface area of the NiO crystal grains. Although the interfacial capacitances of the Ni oxide films in $\text{KCl}+\text{H$_{2}$SO$_{4}$}$ are 2–3 times less than those in KOH, a maximum change in optical density of 0.57 was obtained in $\text{KCl}+\text{H$_{2}$SO$_{4}$}$ for a fine-grained Ni oxide film with a thickness of 400 nm sputtered in 100% O2.
2006-10-15