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Bera, Susanta,Lee, Sol A,Kim, Chang-Min,Khan, Hasmat,Jang, Ho Won,Kwon, Se-Hun American Chemical Society 2018 Chemistry of materials Vol.30 No.23
<P>Fabrication of semiconductor thin films with uniform and vertically aligned one-dimensional nanostructures is an active area of research. We report the synthesis of vertically aligned nanograss (NG)-structured SnO<SUB>2</SUB> thin films on a wide range of substrates with a vapor-solid deposition process. In this process, some chemical and physical parameters, such as chemical composition, deposition height from the precursor mixture, deposition temperature, and substrate roughness, are found to play key roles during the growth of SnO<SUB>2</SUB> nanograsses (SNGs). The effects of density change and cross-sectional dimension (width) of the nanograsses (NGs) on surface area improvement of the thin films have been examined by varying the respective parameters. BiVO<SUB>4</SUB> (BV) solution layers were coated onto SNG, forming core-shell type-II heterojunction thin films (SNG-BV). The thickness of the drop-cast BiVO<SUB>4</SUB> solution layers onto the NGs was controlled by the number density of the NGs per unit area. Light absorption efficiency (η<SUB>abs</SUB>) of the core-shell SNG-BV films has been optimized by controlling quasi-arranged periodicity of the core NGs and accessible shell thickness of BiVO<SUB>4</SUB> layers. The charge separation efficiency (η<SUB>sep</SUB>) of SNG-BV films strongly depends on the thickness of the BiVO<SUB>4</SUB> layers onto NGs. Thin layers of BiVO<SUB>4</SUB> coating along the axial direction of thinner SnO<SUB>2</SUB> NGs (25-50 nm) shows enhanced η<SUB>sep</SUB> but lower η<SUB>abs</SUB> due to poor light absorption. On the other hand, the thicker core NGs (40-200 nm) with low surface area provide thick layers of BiVO<SUB>4</SUB>, which drives strong light absorption but suffers from efficient η<SUB>sep</SUB>. However, intermediate layers of BiVO<SUB>4</SUB> onto uniformly arranged SnO<SUB>2</SUB> NGs with 30-70 nm width shows enhanced η<SUB>abs</SUB> as well as efficient η<SUB>sep</SUB> compared to other SNG-BV samples. This result demonstrates that control over the horizontal dimension of the core materials in the core-shell heterojunction (keeping vertical restriction) is a viable approach for optimizing the photoelectrochemical efficiency.</P> [FIG OMISSION]</BR>