Preparation of SiO 2 -pillared layered titanate thin films
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The interlayer space of a thin film of layered titanate, Cs0.68Ti1.83䊐0.17O4, was successfully expanded by SiO2 pillaring. Ion exchange of the Cs ions in the interlayer to alkylammoniuim cations, n-CnH2n+1NH3+ (n ⳱ 8, 12, 18), expanded the interlayer space, and enabled intercalation of tetraethylorthosilicate. X-ray diffraction and the cross section of transmission electron microscopy images revealed that tetraethylorthosilicate-treated thin film maintained the expansion of interlayer space by SiO2 pillaring after calcination at 773 K. X-ray photoelectron spectroscopy after etching the thin film about 100 nm from the surface further confirmed the existence of SiO2 in the interlayer space.
The semiconductor thin films have been utilized as monitor displays, energy conversion apparatuses, and various sensors. The manufacture of thin films that are currently prepared by the chemical vapor deposition technique,1 etc., requires high processing temperature and pressure. On the other hand, a soft chemical method does not require such severe conditions for the preparation of layered thin films. This method takes advantage of exfoliation of layered titanic acid,2– 4 and the obtained thin films had ion-exchange ability of the interlayer cations.2 From the viewpoints of various kinds of applications, it is interesting to modify interlayer space of layered thin films. Each layer of Cs0.68Ti1.83䊐0.17O4 (open square indicates a vacancy) sheet is negatively charged, and Cs cations exist in the interlayer space for compensating the charge balance. In such a structure, the intercalation of neutral large molecules into the interlayer space for modification seems to be difficult. Pillaring of the interlayer space by inorganic oxides has been reported as one of the strategies.5–7 In addition, it was found for layered niobates in powder form that the photocatalytic decomposition of bulky n-alcohols more effectively proceeded over the pillared layered niobates and porous materials made from exfoliated layered niobates than in the original forms.7,8 Because there is no report on such modification as pillaring of layered thin films, we attempted and succeeded in pillaring the interlayer space of Cs0.68Ti1.83䊐0.17O4 by silica in the form of thin film.
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Address all correspondence to this author. CREST, Japan Science and Technology. e-mail: [email protected] J. Mater. Res., Vol. 15, No. 12, Dec 2000
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Layered titanate thin film was prepared by spin coating as in a previously reported preparation method.2,3,9 Briefly, Cs0.68Ti1.83䊐0.17O49–12 was converted into its proton-exchange form, H0.68Ti1.83䊐0.17O4 䡠 H2O, by stirring in HCl aqueous solution (1 N) at room temperature for 2 days. Filtration, followed by washing with distilled water and drying in air, gave H0.68Ti1.83䊐0.17O4 䡠 H2O. The exfoliation of H0.68Ti1.83䊐0.17O4 䡠 H2O was carried out by stirring in ethylamine aqueous solution (H0.68Ti1.83䊐0.17O4 䡠 H2O:ethylamine ⳱ 1:8) at room temperature for 24 h. The suspension was
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