Branched ZnO nanowires have been fabricated on conductive glass substrates via a solvothermal method for dye-sensitized solar cells (DSCs). The 1D branched nanostructures can afford a direct conduction pathway instead of interparticle hops while using nanoparticles. Furthermore, the short-circuit current density and the energy conversion efficiency of the branched ZnO nanowire DSCs are 4.27 mA/cm 2 and 1.51%, which are twice as high as the bare ZnO nanowire ones. The improvement was a consequence of the enlargement of the internal surface area within the photoelectrode and allowed us to achieve higher dye adsorption to significantly enhance the performance of the DSCs.

We report room-temperature ultraviolet stimulated emission and lasing from optically pumped high-quality ZnO nanowires. Emission due to the exciton-exciton scattering process shows apparent stimulated-emission behavior. Several sharp peaks associated with random laser action are seen under high pumping intensity. The mechanism of laser emission is attributed to coherent multiple scattering among the random-growth oriented nanowires. The characteristic cavity length is determined by the Fourier transform of the lasing spectrum.

Self-assembled ZnO secondary nanoparticles have been fabricated as an effective photoelectrode for dye-sensitized solar cells (DSCs). The hierarchical architecture, which manifested the significant lightscattering, can provide more photon harvesting. In addition, dye-molecule adsorption was sufficient due to enough internal surface area provided by the primary single nanocrystallites. Two indoline dyes, coded D149 and D205, were used as the sensitizers of ZnO DSCs with the optimal energy conversion efficiencies of 4.95% and 5.34%, respectively, under AM 1.5 full sunlight illumination (100 mW cm À2 ). The enhancement of the open-circuit photovoltage (V oc ) and the short-circuit photocurrent density (J sc ) for D205-sensitized ZnO DSCs was ascribed to the effective suppression of electron recombination by extending the alkyl chain on the terminal rhodanine moiety from ethyl to octyl. Further evidence is obtained from the electrochemical impedance spectroscopy (EIS) which exhibits a longer electron lifetime for D205-sensitized ZnO DSC in comparison with the D149-sensitized one.

Optical nonlinearities of ZnO thin films, made by laser deposition, were investigated by the Z-scan method using a mode-locked femtosecond Ti:sapphire laser. The measured bound-electron nonlinear index of refraction ␥ and the two-photon absorption coefficient ␤ at near-IR wavelengths show an enormous enhancement compared with measurements on bulk ZnO at 532 nm. The results reveal that two-photon resonance to the band edge and exciton energy level is responsible for the nonlinear absorption and that the free carrier induced the optical nonlinearity. With the excitation wavelength operated between 810 to 840 nm, a negative ␤ value is measured due to the saturation of linear absorption of the defect states. Finally, we compared the values of ␤ from the closed aperture Z-scan data ͑by considering the multi-photon absorption induced thermal nonlinearity͒ with those obtained from the open aperture Z-scan data. The results show that nonlinear refraction in the near-IR region is dominated by the bound-electron and free-carrier effect, although the thermal optical nonlinearity cannot be completely ignored.

Spatial distributions of the near-field and internal electromagnetic intensities have been calculated and experimentally observed for dielectric cylinders and spheres which are large relative to the incident wavelength. Two prominent features of the calculated results are the high intensity peaks which exist in both the internal and near fields of these objects, even for nonresonant conditions, and the well-defined shadow behind the objects. Such intensity distributions were confirmed by using the fluorescence from iodine vapor to image the near-field intensity distribution and the fluorescence from ethanol droplets impregnated with rhodamine 590 to image the internal-intensity distribution.

Two indoline dyes, coded D149 and D205, were used as the sensitizers of ZnO dye-sensitized solar cells (DSCs) with optimal energy conversion efficiencies of more than 5%, under AM 1.5 full sunlight illumination (100 mW cm( - 2)). Higher interfacial charge transfer rate and retardant fluorescence decay confirmed from transient fluorescence illustrated that D205-sensitized ZnO DSCs could possess better electron transport than D149-sensitized ZnO DSCs. The enhancement of V(oc) and J(sc) for D205-sensitized ZnO DSCs was ascribed to the effective suppression of electron recombination by extending the alkyl chain on the terminal rhodanine moiety from ethyl to octyl. The evidence of enhanced electron diffusion coefficient was further shown by electrochemical impedance spectroscopy (EIS).

We have demonstrated that silicon nanostructures with high aspect ratios, having ϳ400 nm structural height and ϳ55 nm lateral dimension, may be fabricated by scanning probe lithography and aqueous KOH orientation-dependent etching on the H-passivated ͑110͒ Si wafer. The high spatial resolution of fabricated features is achieved by using the atomic force microscope based nano-oxidation process in ambient. Due to the large ͑110͒/͑111͒ anisotropic ratio of etch rate and the large Si/SiO 2 etch selectivity at a relatively low etching temperature and an optimal KOH concentration, high-aspect-ratio gratings with ͑111͒-oriented structural sidewalls as well as hexagonal etch pit structures determined by the terminal etch geometry can be obtained.

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