Ionic liquid, ethyltrimethylammonium bis(trifluoromethylsulfonyl), (IL: [N 1112 ] [TFSA]) that has a melting point of 109 °C, was deposited at room temperature on α-Al 2 O 3 (0001) substrates by continuous-wave infrared laser deposition in a vacuum. No decomposition of IL molecules occurred during the thermal evaporation and the polycrystalline nature of the deposits at RT was found identical to that of the corresponding powder IL. The thin film IL (TF-IL) on a non-treated α-Al 2 O 3 (0001) substrate, with droplet-like shapes in morphology, exhibited almost no ionic conductivity even above the melting point because the IL would not spread over the non-treated substrate. In contrast, the TF-IL, with more dense, granular structures in morphology, deposited on a chemically-modified, wettable α-Al 2 O 3 (0001) substrate, did exhibit a substantial ionic conductivity even at temperatures lower than the melting point, and it was then followed by a drastic increase of the ionic conductivity through its solid-liquid phase transition. The behaviors of the deposited IL growing and melting on the substrate are discussed based on the results of in situ laser microscope and ionic conductivity measurement experiments.
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