Room-Temperature Preparation of Ta Ions-Containing Ionic Liquid and its Vapor Deposition toward Ta-Oxide Film Coating

Abstract

Ta ions-containing solutions, which are brown in color with no precipitation, were successfully prepared through an electroelution process with ionic liquid (IL). An as-delivered Ta metal plate covered with a passivation oxide film could be easily eluted even at room temperature by simply applying an anodic potential of, e.g. +2.2 V vs. Ag in [Bmim][PF6] IL. According to the quantity of electric charge required for oxidation of Ta, most Ta ions in the IL were suggested to be in an oxidation state of +5, which was also confirmed by x-ray photoemission spectroscopy (XPS). Ta ions in IL were found to thermally evaporate together with IL molecules by heating in a vacuum, forming a deposit of the Ta ions-containing IL on a substrate. The Ta concentrations in the deposits were reduced uniquely by about one order of magnitude from those in the original bulk source through the evaporation process under the present conditions. Furthermore, a possibility of the formation of thin film-like Ta oxide from such a Ta ions-containing IL deposit and its bulk droplet prepared on substrates by annealing in air at 1000oC will be discussed.

Recent Progress in Vacuum Engineering of Ionic Liquids

“…For example, the thermal evaporation of Ta metal, whose melting temperature is approximately 3000 °C [ 64 ], is so difficult that the thin films of Ta metal and its compounds, such as Ta oxides, have been fabricated by chemical vapor deposition (CVD) [ 65 ]. In this section, the vacuum deposition of Ta ions-containing IL and its following conversion into a Ta-oxide film is introduced as a model application of metal-ions containing ILs [ 66 ].…”

“…In the electrodeposition of Ta metal in IL, as demonstrated by the F. Endres group, Ta ions-containing IL solutions are conventionally prepared by dissolving Ta salts, such as TaF 5 , in IL [ 64 , 67 ]. On the other hand, we have recently succeeded in the preparation of Ta ions-containing IL solutions through a direct electroelution process with an IL of [bmim][PF 6 ] in a glove box [ 66 ]. In this process, the concentration of Ta ions is well adjusted by controlling the application time of electroelution, with a good linear relationship between them.…”