Fabrication of nanoperforated ultrathin TiO 2 films by inkjet printing
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brication of nanoperforated TiO2 thin films (NP-TiO2) on various substrates utilizing evaporation-induced self-assembly has been widely reported during recent years. For many applications, such as solar cells and gas sensors, it would be beneficial if the active material could be deposited onto a desired area or in the form of a pattern or array. In this study, inkjet printing was successfully used to produce NP-TiO2 at both ambient temperature and 60 °C. Especially for intermediate drop spacings (40 and 50 lm), millimeter-sized homogeneous NP-TiO2 patches were obtained with similar NP structure as those being processed by dip coating and drop casting. Compared to ambient temperature, inkjet printing at 60 °C provides a narrower height distribution of the NP structures of about 5 nm. Compared to dip coating and drop casting, inkjet printing enables the deposition of the ink onto target areas, thus enabling the fabrication of microscale arrays and other patterned structures.
I. INTRODUCTION
Nanostructured metal oxide thin films of e.g., Fe2O3, Al2O3, CuO, ZnO, TiO2, and ZrO2 have attracted considerable attention in recent years due to their versatile properties and promising application possibilities in the fields of electronics, gas sensing, catalysis, photocatalysis, and photovoltaics.1–7 These fast emerging application areas put a lot of demands on the fabrication of such metal oxide films, including morphology design, high reproducibility, and possibility to large-scale production. A number of nanopatterning techniques, including scanning probe technique, microcontact printing, and photolithography, have emerged as the predominant methods to fabricate patterns within monolayers of surfactants.8 However, these methods are limited by the patterning rate and the pattern size, and the scaling-up possibilities of these methods are restricted. A promising and cost-efficient technique to produce large-scale nanopatterned structures on a wide range of substrates is to dip coat a metal oxide sol in the presence of block copolymers.9,10 In this method, evaporation-induced self-assembly (EISA) will arrange the block copolymers into micellar structures that will create nanoperforations or nanocraters in the final TiO2, ZrO2, or Al2O3 networks. Faustini et al. have, for example, used this type of substrates to deposit FePt nanoparticles selectively into the nanoperforations to produce magnetic recording devices.11 Recently, we have utilized NP-TiO2 films as substrates in the fabrication of nanopatterned
Contributing Editor: Akira Nakajima a) Address all correspondence to this author. e-mail: qxu@abo.fi DOI: 10.1557/jmr.2015.187 J. Mater. Res., Vol. 30, No. 14, Jul 28, 2015
polymeric films by inkjet printing.12 Inkjet printing has also proven to be a cheap and efficient method for fabrication of electrodes and silica microdot arrays up to millimeter scale.13–16 In this study, we have combined the EISA technique with inkjet printing, to obtain NP-TiO2 surfaces on SiO2 substrates. Comparing to dip-coating and drop-casting methods, inkje
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