Figure 5.

Intrinsic relationship between nanoporous geometry and optical properties in nanoporous anodic alumina photonic crystals (NAA-PCs). (a) Structural engineering of effective medium of NAA-PCs with details of the intrinsic relationship between nanoporous geometry and effective medium approximation. (b) NAA-PC as a metamaterial platform with negative refraction of light (reproduced from [45], with copyright permission from The American Association for the Advancement of Science, 2008). (i) Illustration showing negative refraction from air into composite NAA-PC filled with silver nanowires (left) and schemed showing the structure of the composite NAA-PC-Ag nanowires and SEM images of these photonic structures (scale bars = 500 nm); (ii) and (iii) beam intensities at the surface of the composite NAA-PC-Ag nanowires at 660 and 780 nm, respectively; (iv) dependence of refraction angles on incident angles and polarizations at 780 nm wavelength. (c) Schematic showing the structure of a 2D NAA-PC with incident light flowing perpendicularly to its nanopores. (d) Self-ordering regimes in MA (filled symbols) and HA (open symbols) in the most representative acid electrolytes used to produce NAA. Reproduced from [28], with copyright permission from American Chemical Society, 2014.