ZnO nanorods were prepared at relatively low temperatures by homogeneous precipitation from zinc nitrate and urea in a water/ethylene glycol mixture. Crystal size and morphology are controlled by growth time and solvent composition. We observed a strong correlation between nanocrystals’ size/morphology and their optoelectronic defect-related properties. Smaller crystallites exhibited intense deep-defect luminescence and enhanced emission related to near-surface excitonic recombination. Longer growth times lead to formation of well-defined nanorods with hexagonal symmetry exhibiting reduced defect emission.

Homogeneous ZnO/polymethyl methacrylate (PMMA) nanocomposites were prepared by incorporating ZnO nanoparticles synthesized in various diols into a PMMA matrix by the free-radical bulk polymerization. Room temperature photoluminescence spectra of the as-grown and PMMA-embedded ZnO nanoparticles exhibit an excitonic band-gap emission at 3.3 eV, a near band-gap emission at ∼3.1 eV and a broad defect band centered at ∼2.4 eV. Relative intensity of the defect versus band-gap luminescence depends on the parameters of ZnO preparation as well as the average particle size. However, PMMA-embedded particles produce a much stronger excitonic luminescence, whereas the ratio of the 3.1 to 2.4 eV remains approximately constant. There is no indication of random lasing threshold pointing to the ZnO/PMMA interfacial origin of the enhanced band-gap emission.

Er 3þ ions, both with and without a germanium (Ge) sensitizer layer, have been introduced onto the surface of ZnO tetrapod structures. Such structures, characterized by electron microscopy and X-ray diffraction, are found to emit at both the UV/ visible and near-infrared as a consequence of the presence of ZnO/Er 3þ . The presence of selected absorption features in the visible luminescence spectra suggests energy transfer from ZnO to Er 3þ ions in the doped materials. The introduction of Ge onto the tetrapod surface enhances the intensity of Er 3þ photoluminescence significantly with a corresponding blue shift of 11 nm in the emission maxima.

Amorphous carbon (a-C) nanoclusters were synthesized by the implantation of carbon ions (C-) into thermally grown silicon dioxide film (-500 nm thick) on a Si (100) wafer and processed by high temperature thermal annealing. The carbon ions were implanted with an energy of 70 keV at a fluence of 5 x 10(17) atoms/cm2. The implanted samples were annealed at 1100 degrees C for different time periods in a gas mixture of 96% Ar+4% H2. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and High Resolution Transmission Electron Microscopy (HRTEM) were used to study the structural properties of both the as-implanted and annealed samples. HRTEM reveals the formation of nanostructures in the annealed samples. The Raman spectroscopy also confirms the formation of carbon nano-clusters in the samples annealed for 10 min, 30 min, 60 min and 90 min. No Raman features originating from the carbon-clusters are observed for the sample annealed further to 120 min, indicating a complete loss of implanted carbon from the SiO2 layer. The loss of the implanted carbon in the 120 min annealed sample from the SiO2 layer was also observed in the XPS depth profile measurements. Room temperature photoluminescence (PL) spectroscopy revealed visible emissions from the samples pointing to carbon ion induced defects as the origin of a broad 2.0-2.4 eV band, and the intrinsic defects in SiO2 as the possible origin of the -2.9 eV bands. In low temperature photoluminescence spectra, two sharp and intense photoluminescence lines at -3.31 eV and -3.34 eV appear for the samples annealed for 90 min and 120 min, whereas no such bands are observed in the samples annealed for 10 min, 30 min, and 60 min. The Si nano-clusters forming at the Si-SiO2 interface could be the origin of these intense peaks.

In this study we report on the growth behavior of zinc oxide in the presence of different concentrations of silicon. We performed reactions in a continuous tubular reactor in aqueous and ethanolic-aqueous media at different reaction temperatures and for different residence times. It was found that the zinc oxide particles grew from the aqueous medium through the crystallization of amorphous zinc oxide units via different growth stages, i.e., plate-like particles, double-plate-like particles and ellipsoidal particles. The Zn/OH atomic ratio and, consequently, the pH control the particle size and the morphology (i.e., the inclusions on the particle surfaces). The presence of silicon in the reaction solution influences the particle morphology (the formation of planar defects), the particle growth stages (the double-plate-like particles) as well as the particle growth rate. By shifting the UV-VIS absorption maxima of the reaction suspensions we showed that an increased silicon concentration and a decreased reaction temperature significantly retarded the growth rate of the zinc oxide.

A systematic study of the formation of buried b-SiC structures by carbon ion implantation into Si followed by high-temperature thermal annealing has been carried out. A high fluence of carbon ions (8 9 10 17 atoms/cm 2 ) was implanted at 65 keV energy. Formation of the crystalline b-SiC phase was monitored by Fourier-transform infrared (FTIR) spectroscopy, x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) techniques. The implanted samples were annealed at 900°C and 1100°C to observe the effects of annealing temperature on the formation of crystalline b-SiC. Formation of crystalline b-SiC was clearly observed in the sample annealed at 1100°C in a flowing nitrogen environment for a period of 1 h. Graphitic carbon clusters were observed at the implanted carbon profile peak position by XPS depth profile measurements. Various structural defects such as grain boundaries were also visualized in the annealed sample by highresolution TEM.

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Hydrozincite (Zn5(OH)6(CO3)2) is, among others, a popular precursor used to synthesize nanoscale ZnO with complex morphologies. For many existing and potential applications utilizing nanostructures, performance is determined by the surface and subsurface properties. Current understanding of the relationship between the morphology and the defect properties of nanocrystalline ZnO and hydrozincite systems is still incomplete. Specifically, for the latter nanomaterial the structure-property correlations are largely unreported in the literature despite the extensive use of hydrozincite in the synthesis applications. In our work, we addressed this issue by studying precipitated nanostructures of Zn5(OH)6(CO3)2with varying quasi-fractal dimensionalities containing relatively small amounts of a ZnO phase. Crystal morphology of the samples was accurately controlled by the growth time. We observed a strong correlation between the morphology of the samples and their optoelectronic properties. Our results indicate that a substantial increase of the free surface in the nanocrystal samples generates higher relative concentration of defects, consistent with the model of defect-rich surface and subsurface layers.