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    Photoinduced hydrophilic behavior of TiO2 thin film on Si substrate

    Year: 2021

    Journal: J. Alloy. Compd., Volume 872, AUG 15

    Authors: Rudakova, Aida, V; Emeline, Alexei, V; Romanychev, Andrey, I; Bahnemann, Detlef W.

    Organizations: Research Grant of the Saint-Petersburg State University [73032813]; Russian Foundation for Basic Research grant [18-03-00855]

    Keywords: Titanium dioxide; Photoinduced superhydrophilicity; Silicon; Type-II heterostructure; Substrate; TiO2-Si; Thin film

    Photoinduced hydrophilic behavior of TiO2 thin film synthesized by atomic layer deposition method on p-Si wafer as well on SiO2-coated glass has been studied. In contrast to the TiO2 film on SiO2-coated glass, the TiO2 film on the Si wafer initially had a moderate hydrophobicity and became more hydrophobic upon visible light exposure. Such a significant difference was explained by the formation of a type-II TiO2 -Si heterostructure that was confirmed by the alteration of the work function. The role of photoelectrons in the mechanism of light-induced hydrophilic conversion of the TiO2 surface was elucidated, which reduces to the deactivation of both active surface sites responsible for the superhydrophilic transition and already existing hydrophilic sites. Reversible hydrophilic-to-hydrophobic surface conversion upon switching UV exposure by visible light has been demonstrated for TiO2 /Si coatings. Similar to the tensiometric data, a cyclic change in the work function value was found. The observed cycles in values of water contact angle and work function were gradually ceasing. This phenomenon was associated with the formation of the interfacial SiOx layer as a result of light-induced passivation of silicon at the TiO2-Si interface. (C) 2021 Elsevier B.V. All rights reserved.
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