Artificial opals consisting of polystyrene spheres ordered into a fcc lattice are grown with control over the orientation and thickness. A thorough study of the formation of the pseudogap in these structures is carried out by means of reflectivity and transmission spectra. Special attention is paid to discriminating those features inherent to the photonic crystal, and those to the substrate on which the crystal is grown. Further, a characterization of the photonic band structure in the hexagonal facet of the Brillouin zone is made using angle resolved reflectivity measurements.

The surface electrical properties of ZnO thin films grown along the nonpolar $[11\overline{2}0]$ direction have been investigated by Kelvin probe microscopy on a nanometer scale. Two different charge domains, with a 75 meV work function difference, coexist within the ZnO surface, which is covered by rhombohedral pyramids whose sidewalls are shown to be $\{10\overline{1}1\}$-type planes. The presence and relative orientation of the two kinds of charge domains are explained in terms of the atomic arrangement at the $\{10\overline{1}1\}$ polar surfaces.

An optical and morphological study has been carried out to understand the role of intrinsic defects in the optical properties of opal-based photonic crystals. By doping poly(methylmethacrylate) (PMMA) thin-film opals with larger polystyrene (PS) spheres, structural disorder has being generated perturbing the PMMA matrix periodicity. It is shown that this disorder dramatically affects the optical response of the system worsening its photonic properties. It has been found that the effect of doping is highly dependent not only on the concentration but also on the relative size of the dopant with reference to the matrix. Through a detailed scanning electron microscopy inspection, the sort of structural defects involved, derived from the different particle size used, has been characterized. A direct relationship between the observed optical response with the different perturbations generated in the lattice has been found. In addition, from this study it can be concluded that it is possible to grow high quality alloyed photonic crystals, exhibiting intermediate photonic properties between pure PMMA and pure PS opals by simple sphere size matching and variation of the relative concentration of both components.