Fig. 1A shows typical FESEM micrograph of ZTNW that were grown on an ITO substrate using a growth solution containing 5 mL of 0.5 M (NH4)2TiF6, 1 mL of 0.5 M Zn(NO3)2·xH2O and 1 mL of 0.5 M HMT for 5 h at temperature of 90 °C. As can be seen from the Fig. 1A, typical for the ZTNW prepared using the present method, they grow effectively on the substrate covering up to approximately 70% of the substrate surface. Regarding the morphology, ZTNW exhibits perfect square-shape with width and length can be up to several micrometers and thickness is in the range of 30–60 nm ( Fig. 1B). Unique to the ZTNW, their surface is not solid structure, instead it is a porous-like structure, resulting from being constructed by protruded growth of nanobrick like structure (diameter and length are ca. 5 and 10 nm, respectively) (see Fig. 1C and D). This property is thought to be potential for DSSC application because this could provide wide-surface area for surface reaction. As can also be seen from the image ( Fig. 1A), most of the ZTNW form branches that is emerged from the centre of a “parent” wall; which could be formed due to a high-energy nature at this site, facilitating secondary nucleation and growth. However, ZTNW with branches emerged from different position are also observed. We thought it is due to a collision amongst the adjacent growing branches. Typical TEM analysis result of ZTNW are shown in Fig. 1E. As can be seen from the TEM image and in good agreement with the FESEM images in Fig. 1C and D, the bulk structure of the ZTNW is constructed by the effective arrangement on nanocuboids structure. As also can be seen from the TEM result, white spots are observed throughout the bulk structure of ZTNW. This is actually the hole on the structure, indicating the porous nature of the structure, that allows electron beam sees trough the background behind the ZTNW. This condition is certainly ideal for an expanded surface reaction and adsorption of dye molecules. In addition to this interesting feature, as judged from the HRTEM image in Fig. 1F, the nanocuboid that constructs the ZTNW is interestingly characterized by a (0 0 1) plane of anatase TiO2. This plane is one of the highest energy plane in anatase phase so that an active physicochemical process is expected to occur on the ZTNW. Thus, enhanced performance in application could be obtained. Fig. 1G shows typical XRD spectrum of ZTNW. From the XRD spectrum, it is confirmed that the ZTNW is anatase with obtained peaks match with the JCPDS File no 21-1272. The peaks at 24.8, 37.5, 48.0 and 54.2° can be labelled as diffraction from lattice plane of (1 0 1), (0 0 4), (2 0 0) and (2 1 1), respectively. From the spectrum, it is revealed that no peak related to Zn or ZnO is observed in the spectrum, inferring effective substitution of Zn into TiO2 lattice. Hence, successful Zn doping onto TiO2 nanowall is achieved [6].
Fig. 1A shows typical FESEM micrograph of ZTNW that were grown on an ITO substrate using a growth solution containing 5 mL of 0.5 M (NH4)2TiF6, 1 mL of 0.5 M Zn(NO3)2·xH2O and 1 mL of 0.5 M HMT for 5 h at temperature of 90 °C. As can be seen from the Fig. 1A, typical for the ZTNW prepared using the present method, they grow effectively on the substrate covering up to approximately 70% of the substrate surface. Regarding the morphology, ZTNW exhibits perfect square-shape with width and length can be up to several micrometers and thickness is in the range of 30–60 nm ( Fig. 1B). Unique to the ZTNW, their surface is not solid structure, instead it is a porous-like structure, resulting from being constructed by protruded growth of nanobrick like structure (diameter and length are ca. 5 and 10 nm, respectively) (see Fig. 1C and D). This property is thought to be potential for DSSC application because this could provide wide-surface area for surface reaction. As can also be seen from the image ( Fig. 1A), most of the ZTNW form branches that is emerged from the centre of a “parent” wall; which could be formed due to a high-energy nature at this site, facilitating secondary nucleation and growth. However, ZTNW with branches emerged from different position are also observed. We thought it is due to a collision amongst the adjacent growing branches. Typical TEM analysis result of ZTNW are shown in Fig. 1E. As can be seen from the TEM image and in good agreement with the FESEM images in Fig. 1C and D, the bulk structure of the ZTNW is constructed by the effective arrangement on nanocuboids structure. As also can be seen from the TEM result, white spots are observed throughout the bulk structure of ZTNW. This is actually the hole on the structure, indicating the porous nature of the structure, that allows electron beam sees trough the background behind the ZTNW. This condition is certainly ideal for an expanded surface reaction and adsorption of dye molecules. In addition to this interesting feature, as judged from the HRTEM image in Fig. 1F, the nanocuboid that constructs the ZTNW is interestingly characterized by a (0 0 1) plane of anatase TiO2. This plane is one of the highest energy plane in anatase phase so that an active physicochemical process is expected to occur on the ZTNW. Thus, enhanced performance in application could be obtained. Fig. 1G shows typical XRD spectrum of ZTNW. From the XRD spectrum, it is confirmed that the ZTNW is anatase with obtained peaks match with the JCPDS File no 21-1272. The peaks at 24.8, 37.5, 48.0 and 54.2° can be labelled as diffraction from lattice plane of (1 0 1), (0 0 4), (2 0 0) and (2 1 1), respectively. From the spectrum, it is revealed that no peak related to Zn or ZnO is observed in the spectrum, inferring effective substitution of Zn into TiO2 lattice. Hence, successful Zn doping onto TiO2 nanowall is achieved [6].
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