ZnO Matrices Research Articles

FTIR and Raman Spectroscopy of Carbon Nanoparticles in SiO2, ZnO and NiO Matrices

Coatings of carbon nanoparticles dispersed in SiO2, ZnO and NiO matrices on aluminium substrates have been fabricated by a sol–gel technique. Spectrophotometry was used to determine the solar absorptance and the thermal emittance of the composite coatings with a view to apply these as selective solar absorber surfaces in solar thermal collectors. Cross-sectional high resolution transmission electron microscopy (X-HRTEM) was used to study the fine structure of the samples. Raman spectroscopy was used to estimate the grain size and crystallite size of the carbon clusters of the composite coatings. X-HRTEM studies revealed a nanometric grain size for all types of samples. The C–SiO2, C–ZnO and C–NiO coatings contained amorphous carbon nanoparticles embedded in nanocrystalline SiO2, ZnO and NiO matrices, respectively. Selected area electron diffraction (SAED) showed that a small amount of Ni grains of 30 nm diameter also existed in the NiO matrix. The thermal emittances of the samples were 10% for C–SiO2, 6% for the C–ZnO and 4% for the C–NiO samples. The solar absorptances were 95%, 71% and 84% for the C–SiO2, C–ZnO and C–NiO samples, respectively. Based on these results, C–NiO samples proved to have the best solar selectivity behaviour followed by the C–ZnO, and last were the C–SiO2samples. Raman spectroscopy studies revealed that both the C–ZnO and C–NiO samples have grain sizes for the carbon clusters in the range 55–62 nm and a crystallite size of 6 nm.

Investigation of silicon nanoclusters embedded in ZnO matrices deposited by cosputtering system

A co-sputtering system was used to deposit silicon nanoclusters embedded in zinc oxide matrix (Si:ZnO) at low temperature without post-annealing. By adjusting the radio frequency power of the Si target during co-sputtering, Si:ZnO films with various crystallographic structures can be obtained. Silicon nanoclusters embedded in the zinc oxide matrix were examined using a high-resolution transmission electron microscope, x-ray diffractometer, and Fourier transformation infrared spectrometry. By comparing with photoluminescence spectra, we can clearly identify quantum confinement effect of silicon nanoclusters embedded in the ZnO matrix.

Optical, thermal and structural characteristics of carbon nanoparticles embedded in ZnO and NiO as selective solar absorbers

Selective solar absorber coatings of carbon embedded in ZnO and NiO matrices on aluminium substrates have been fabricated by a sol–gel technique. Spectrophotometry was used to determine the solar absorptance and the thermal emittance of the composite coatings. The surface morphology of the samples was studied by scanning electron microscopy (SEM). Cross-sectional high-resolution transmission electron microscopy (X-HRTEM) was used to study the fine structure of the samples. Chemical composition analysis was done by energy dispersive spectroscopy (EDS) and electron energy loss spectroscopy (EELS). The crystal structure of ZnO and NiO samples was also investigated with an X-ray diffraction (XRD) technique. Samples were subjected to an accelerated ageing test for 95 h, with condensation at relative humidity of 95% and at a climate chamber temperature of 45 °C. The thermal emittances of the samples were 6% for the ZnO and 4% for the NiO matrix materials. The solar absorptances were 71% and 84% for ZnO and NiO samples, respectively. The SEM revealed a smooth featureless surface for both C–ZnO and C–NiO samples. Some C–NiO samples showed dentritic features. X-HRTEM, EDS and EELS studies revealed a nanometric grain size for both types of samples. The C–ZnO and C–NiO coatings contained amorphous carbon embedded in nanocrystalline ZnO and NiO matrices, respectively. Selected area electron diffraction (SAED) showed that a small amount of Ni grains of 30 nm diameter also existed in the NiO matrix. The accelerated ageing tests produced performance criterion (PC) values of 0.15 and 0.054 at 95 h for the C–ZnO and C–NiO samples, respectively. Based on these results, C–NiO samples proved to have better solar selectivity behaviour than the C–ZnO counterparts.

Solar selective absorber functionality of carbon nanoparticles embedded in SiO2, ZnO and NiO matrices

AbstractIt is possible to design an optical material, through control of the substrate and coatings, to absorb a large fraction of the solar spectrum and to emit very little radiation energy in the near and far infra‐red wavelength range. This requires a coating structure that transmits in the ultraviolet and visible, but reflects in the near and far infrared, with a sharp drop in transmission near 2 (m. In this paper, we report on selective solar absorber coatings of carbon nano‐particles embedded in SiO2, ZnO and NiO matrices, fabricated by a sol‐gel technique. The coatings were tested on aluminium substrates. UV‐VIS and FTIR spectroscopies were used to determine the spectral response of the composite coatings, from which the solar absorptance and thermal emittance were determined. We show that the NiO matrix samples have the best solar selective behaviour, and suggest a theoretical evaluation framework for future comparison of such materials. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth by Electrochemistry of Zinc Oxide Films with Controlled (nano)Structure and Properties

Electrodeposition is a versatile method for the preparation of ZnO films with controlled nanostructures and properties. In the present paper we describe two approaches for the preparation of ZnO hybrid films with red/green adjustable luminescence. ZnO is imparted with luminescence properties by bipyridine (dcbpy)- lanthanide complexes. In the first route, ZnO/ dcbpy hybrid films are prepared and subsequently chelated with Ln3+ ions (with Ln being Eu or Tb) to form the luminescent complex. In the second proposed route, highly porous ZnO matrices are prepared by electrodeposition with help of eosin Y molecules. The matrices are loaded with in- situ assembled Ln3+:dcbpy luminescent complexes. In both cases, the ligand is anchored to ZnO by its carboxylic acid groups. The film emission and excitation characteristics show UV absorption by the ligand bipyridine group and an efficient energy transfer to Ln3+.

Tailored synthesis of ZnO:Er(III) nanosystems by a hybrid rf-sputtering/sol-gel route

The rational design of rare-earth doped materials represents one of the major goals of current research in the field of optoelectronics. In this study, ZnO:Er(III) nanosystems were synthesized by means of a hybrid rf-sputtering/sol-gel (SG) route, consisting of the erbium (guest) rf-sputtering on porous zinc oxide xerogels (host) obtained by the SG method, followed by ex situ thermal treatments in air (300–600°C, 1–5h). Particular attention was focused on tailoring the erbium content and distribution in the resulting systems by optimization of the processing conditions. The structural, morphological, and compositional characteristics and their interplay with the synthesis procedure were investigated by glancing incidence x-ray diffraction, x-ray photoelectron spectroscopy, x-ray excited Auger electron spectroscopy, secondary ion mass spectrometry, UV-visible-near IR absorption spectroscopy, and atomic force microscopy. The obtained results highlight the advantages and versatility of the adopted preparation strategy in tailoring the amount and distribution of Er(III) species in high purity ZnO matrices, resulting in nanosystems endowed with compositional and morphological homogeneity at nanoscale level.

Highly Porous Electrodeposited Zinc Oxide Films Functionalized for Red/Green Luminescence

A stepwise method for the preparation of red/green luminescent thin films based on zinc oxide and lanthanide-organic complexes is described. The synthesis of highly porous ZnO matrices is performed by electrodeposition with help of eosin Y molecules. The matrix is loaded with in situ assembled Ln 3 + :dcbpy luminescent complexes (with Ln being Eu or Tb). The ligand is anchored to ZnO by its carboxylic acid groups. The film excitation and emission characteristics show UV absorption by the ligand at 310 nm and by ZnO below 250 nm with an efficient energy transfer to Ln 3 + for light emission.

Magnetism in V-doped ZnO thin films

Ferromagnetism at room temperature, along with a spin-glass-like behaviour at lowtemperatures, has been observed in laser ablated V-doped ZnO thin films. It is found thatV atoms were well substituted for Zn atoms and resulted in a very uniform distributionamong the ZnO matrices.

Piezoelectric Photothermal Spectra of Co Doped ZnO Semiconductor

Piezoelectric photothermal spectroscopy (PPTS) is a powerful tool for investigating optical properties of semiconductors. Temperature dependence of the PPT signal intensity of the Co-doped ZnO semiconductor was measured from 4.2 to 300 K. The Co concentration dependence of the PPT signal intensity was also studied to clarify the effect of doping with transition metals. In the case of doping at a low level, Co atoms form deep impurity levels in the ZnO matrices in the spectral region from 1.2 to 1.7 eV. However, for samples doped at higher levels, many crystal field split-off levels from localized Co2+ ions appeared at approximately 0.7–1.2 and 1.7–2.4 eV and these two bands became dominant in the spectra. The doping effect was investigated from the point of view of nonradiative transition for the first time.

Effects of Shape and Size of Inclusions on the Sintering of ZnO—ZrO2 Composites

The densification behavior and microstructure development of ZnO matrices containing rigid Zro2 inclusions were studied, with special emphasis on the effect of inclusion shape and size. The inclusions retarded the densification of the matrix, regardless of the inclusion shape and size. For large inclusions with diameters of 10 μm, dense regions developed between inclusion particles. The inclusion particles and dense regions formed a continuous network, which constrained the densification of the composites. The inclusion shape had a small effect on the development of dense regions. Severe retardation in densification was observed for compacts containing inclusions with diameters of 10 μm. In these cases, dense regions between inclusion particles did not develop. The formation of the continuous network cannot be applicable to small inclusions as an origin of retardation of densification.