Microwave induced hydrogen plasma is used to fabricate ZnO thin films at low ambient gas pressure and controlled oxygen content in the gas mixture. The emission spectra have been observed. Optical emission spectroscopy was used to identify the chemical reaction mechanism. Structural quality of the so-obtained nanoparticles was studied by X-ray diffraction (XRD) and high resolution scanning electron microscopy (SEM). SEM results showed that nanorods were formed in the process, and XRD results along with nanorod dimensions obtained from SEM are consistent with the formation of single and poly-crystalline ZnO nanorods. The alignment of these nanorods with respect to the substrates depends on the lattice mismatch between ZnO and the glass substrate. The minimum crystallite grain size as obtained from the SEM measurements was $24 nm and the average diameter is 70 nm with a length of 1-2 lm. The deposited ZnO thin films have a wide energy band gap that equals $3 eV. ª 2014 The Authors. Production and hosting by Elsevier B.V. on behalf of King Saud University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

Polymer nanocomposites exhibit unique physical properties inaccessible from their individual constituents, which are tunable through the type of the polymer matrix, the type and size of the incorporated nanoparticles, and the doping level, and therefore, can be utilized in a wide range of potential applications. Here, we report the fabrication of pure Polyvinyl chloride (PVC) and PVC-based nanocomposites containing different loadings of pure and Cr-doped ZnO nanoparticles, using solvent casting method. Scanning electron microscopy images of the obtained nanocomposite films confirmed the successful incorporation of nanoparticles within the PVC matrix, with higher dispersion quality for the Cr-doped ZnO samples. The prepared nanocomposite samples were found to possess higher thermo-mechanical stability, compared to pure PVC, resulting from the strong interaction between the nanoparticles and polymeric chains, as inferred from their thermogravimetric and dynamic mechanical analysis (TGA and DMA) profiles. Specifically, the temperatures corresponding to the onset and 50% weight loss as well as the glass transition temperature are increased by ~ 88, ~ 34, and ~ 16 °C, respectively, after loading selected amounts of the nanoparticles. In addition to the thermo-mechanical stability, the nanocomposites revealed potentially relevant dielectric response, where the dielectric permittivity exhibits remarkable enhancement, by 400%, compared to pristine PVC. The optical transmission of the PVC is strongly suppressed over the entire visible spectral regime, upon loading the nanoparticles, and its optical band gap (~ 4.1 eV) is red shifted toward the value of pristine ZnO nanoparticles (~ 3.3 eV), while the distinct Cr3+ and Cr6+ optical transitions are preserved for the nanocomposites. The obtained thermo-mechanical stability, required for working devices, together with the here reported improvements in the dielectric response for the nanocomposite samples may alter the typical applications of PVC polymers from being insulating materials to be utilized in energy storage and capacitors manufacture, while the preserved optical properties of the incorporated nanoparticles render these nanocomposites suitable candidates for optoelectronic devices.

Pristine and chromium-doped ZnO nanowires were prepared following the traditional coprecipitation method. X-ray diffraction data identified a pure wurtzite hexagonal crystal structure characteristic for ZnO, irrespective of the doping level. The particle size, as deduced form Williamson-Hall plots, was found to be 45-55 nm for all samples. Scanning electron microscopy revealed a clear nanowires morphology for the pure and doped samples, while elemental analysis ensured the successful Cr-doping. Distinct spectroscopic signatures of Cr-doping were revealed from a detailed deconvolution process applied to optical spectra of doped samples, where Cr 3+ optical transitions were unambiguously identified at ~420 and ~665 nm. Particularly relevant, is the spectral decomposition here performed for the superimposed absorption edge (~385 nm) and Cr 3+ optical resonance at ~420 nm, allowing to claim practically doping-independent optical band gap behavior in the present doping regime. This is further supported by identifying the characteristic ZnO near edge photoluminescence peak (~ 392 nm) which maintains fixed wavelength after Crdoping. These findings contrast earlier studies on Cr-doped semiconductor nanoparticles and glass systems where the optical band gap has been largely underestimated. We attribute the inconsistence band gap values reported in literature for Cr-doped semiconductors to the proximity of Cr optical transitions to the semiconductor absorption edge.