Transparent Ag nanowire arrays embedded in anodic alumina membranes were prepared by a template-based approach combined with ac electrodeposition and subsequent etching of substrate. The optical response of the structure could be attributed to surface plasmon resonance (SPR) of Ag nanowires. When the incident light was perpendicular to the surface of the composite film, only the transverse resonant mode was excited, and a dual peak line shape appeared at about 400 nm in the optical absorption spectrum. The longitudinal resonance mode appeared at a longer wavelength when polarized light illuminated the film with an angle of incidence of about 70°, where the angle was defined with respect to the surface normal. The resonant positions and relative intensities of the two resonant modes were affected by the diameter and aspect ratio of nanowires as well as the polarization direction of incident light. In contrast to the prediction of quasistatic theory, the longitudinal resonance peak did not red shift any more while the aspect ratio was large enough.

The development of novel nanostructured materials with controlled shapes and ordered morphology has stimulated great research interest for seeking novel properties and tailorable functions. In particular, nanostructured ZnO, a remarkable semiconducting oxide with a broad, direct bandgap, received much attention for its potential applications such as UV lasing, electro-optical switches, chemical sensors, photocatalysts, and dye-sensitized solar cells. A series of ZnO nanostructures, such as nanowires, [1][2][3][4] nanorod arrays, [3,[5][6][7] nanobelts, [8] nanoneedle arrays, [9] nanorings, [10] and nanosheets [11,12] have been successfully synthesized. Recently, Eiji et al. [12] reported that ZnO films formed with upright standing nanosheets on substrates induce a very high conversion efficiency for dye-sensitized solar cells because of the easy diffusion of electrolytes in the direction perpendicular to the substrates. However, because the diffusion of electrolytes in the direction parallel to the substrate is still difficult in the nanosheet films, the conversion efficiency would further increase if the nanosheet was macroporous. On the other hand, nanosheets with ordered pore periodicity have a wide range of potential applications including photonic crystals, [13] nanosieve filters, [14,15] masks, [16] and catalysts. [17] Moreover, the modulation induced by both nanoscale thickness and periodic macroporous structure may result in more exciting properties, for example, subwavelength imaging by a photonic-crystal slab.[18]The 3D colloidal crystal template technique is one of the most versatile and efficient techniques for creating 3D periodic macroporous structures, such as inverse opals. [19][20][21][22] However, the fabrication of 2D ordered pore periodicity in a nanosheet whose direction is nearly vertical to the substrate using this method has not been reported. Here, we extend the colloidal crystal template technique to assist the electrochemical deposition of ZnO nanosheet structures and, thus, create 2D hexagonal pore periodicity on nanosheets. Indium tin oxide (ITO) coated glass is used as an electrochemical deposition working electrode. The synthetic polystyrene colloidal crystals are coated onto the ITO glass as templates. ZnO nanosheets with ordered pore periodicity are obtained by the electrochemical deposition of zinc hydroxide nitrate hydrate (ZHNH) into the interstices of colloidal-crystal arrays and the subsequent removal of the templates under calcination. The spatial arrangement of ZnO nanosheets with ordered pore periodicity on ITO substrates is largely affected by the colloidal crystal template assisted crystallization process. Figure 1a shows a scanning electron microscopy (SEM) image of the cross section of a colloidal crystal template that was made from polystyrene microspheres with a diameter of 270 nm on an ITO substrate. The colloidal crystal microspheres have a high degree of order in all directions on the substrate. The thickness of the microsphere arrays is estimated to be 6-7 lm, co...

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Nucleation of water on solid surface can be promoted noticeably when the lattice parameter of a surface matches well with the ice structure. However, the characteristic length of the surface lattice reported is generally less than 0.5 nm and is hardly tunable. In this paper, we show that a surface with nanoscale roughness can also remarkably promote ice nucleation if the characteristic length of the surface structure matches well with the ice crystal. A series of surfaces composed of periodic grooves with same depth but different widths are constructed in molecular dynamics simulations. Water cylinders are placed on the constructed surfaces and frozen at constant undercooling. The nucleation rates of the water cylinders are calculated in the simulation using the mean first-passage time method and then used to measure the nucleation promotion ability of the surfaces. Results suggest that the nucleation behavior of the supercooled water is significantly sensitive to the width of the groove. When the width of the groove matches well with the specific lengths of the ice crystal structure, the nucleation can be promoted remarkably. If the width does not match with the ice crystal, this kind of promotion disappears and the nucleation rate is even smaller than that on the smooth surface. Simulations also indicate that even when water molecules are adsorbed onto the surface structure in high-humidity environment, the solid surface can provide promising anti-icing ability as long as the characteristic length of the surface structure is carefully designed to avoid geometric match.