M. Suchea

Surface characterization of ZnO transparent thin films

Zinc oxide transparent thin films (ZnO) with different thickness were prepared by dc magnetron sputtering and pulsed laser deposition (PLD) techniques using metallic and ceramic targets onto silicon and Corning glass substrates. Structural investigations carried out by Optical Microscopy (OM), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) have shown a strong influence of the target and deposition technique on the film surface topography. Film roughness (RMS), grain shape and dimensions were found to correlate with the applied deposition technique. On the films grown by PLD high oriented nanostructures were identified and XRD measurements proved that they have a polycrystalline structure following the characteristic zincite XRD spectrum, while the dc magnetron sputtered films were amorphous. Results revealed also that the target composition has a radical effect on film characteristics. In the case of thin films sputtered from a ceramic target AFM analysis has shown the presence of hexagonal shaped grains exhibiting a different surface behavior compared with the films grown from metallic target, the first being also the case of the PLD grown film surfaces. This work indicates that the film surface characteristics are strongly influenced by the deposition technique and conditions applied, thus providing a tool for the enhancement of the film sensing capabilities.

Zinc oxide application in the textile industry: surface tailoring and water barrier attributes as parameters with direct implication in comfort performance

The present study focuses on surface tailoring and water barrier attributes of zinc oxide (ZnO)-polyester composite textile materials. The surface properties, such as surface topography and roughness, composite compositions as well as thermal stability of ZnO-100% polyester textile composite materials treated through a padding process with different concentrations of ZnO dispersions as active agent in water and methanol were studied. The results show that 3% ZnO-textile composite material have enhanced water barrier properties compared with the other compositions; a fact which promises improved properties in terms of comfort. ZnO modification of polyester surfaces leads to a dramatic decrease in their thermal stability.

Surface characteristics of In and Zn oxides by atomic force microscopy

Indium and zinc oxide (InO/sub x/, ZnO) thin films with different thickness were prepared by dc magnetron sputtering onto silicon substrates. Structural investigations carried out by atomic force microscopy (AFM) shown a strong correlation between surface topology and growth parameters. Grain radius (GR) and roughness (RMS) were found to be dependent on film thickness and deposition parameters. The results revealed a linear variation of both GR and RMS as a function of thickness, pressure, substrate temperature, and growth rate. All measurements were made at room temperature using AFM-tapping mode.

Ultra sensitive low temperature metal oxide gas sensors

InO/sub x/ films, in the thickness range of 10-725 nm, were grown by dc magnetron sputtering. Their structural, electrical, and O/sub 3/ and NO/sub 2/ sensing properties were analyzed at various temperatures. Structural investigations carried out by XRD and AFM showed a strong correlation between crystallinity, surface topology and gas sensitivity. Moreover, the electrical conductivity exhibited a change of over six orders of magnitude during the processes of photoreduction and oxidation. The films have shown sensitivities towards O/sub 3/ of <50 ppb and NO/sub 2/ of <100 ppb, at temperatures from RT to 100/spl deg/C.

Electrochemical Deposition of Zinc Oxide on the Surface of Composite Membrane Polysulfone-Graphene-Polystyrene in the Presence of Water Soluble Polymers

The aim of this study consisted in the development of an alternative synthesis procedure for hybrid ultrafiltration membranes for water purification. The membranes were obtained by wet-phase inversion method based on aliquots of polysulfone (PSF) and graphene nanoplatelets modified with poly(styrene) (G-PST). The hybrid materials were modified by electrochemical deposition of zinc oxide (ZnO) on one side of the membranes in the presence of water soluble polymers. Raman, XPS, and TGA analyses were used to characterize the chemical and thermal characteristics of the PST-G. SEM analysis showed the formation of asymmetric porous configuration in all cases and the generation of ZnO with different shapes/structures on the bottom surface of the membrane or inside the porous channels. EDS analysis confirmed the formation of ZnO.

ZnO for photocatalytic air purification applications

Nano and micro-structured ZnO coatings onto various substrates were grown by chemical methods and optimized with respect to their photocatalytic activity against in-doors common air pollutants. Excellent quality coatings with high stability and photocatalytic efficiency were obtained with the scope to be integrated in a novel air-purification system.

Sensing using nanostructured metal oxide thin films

Metal oxides gas sensing properties particularly for In2O3 and ZnO nanostructures and nanostructured thin films are reviewed. Fabrication methods for these most commonly used metal oxides are presented, followed by a study on how growth techniques lead to nanostructures and nanostructured polycrystalline films with surface features of nanometer scale for film thickness bellow 1μm. The study continues with a discussion on how, a broad range of morphological parameters, affect the thin film response to various gases. After an overview, the study focus on thin films prepared by reactive dc magnetron sputtering and pulsed laser deposition in different growth conditions. In2O3 and ZnO thin films prepared for ozone sensing exhibit resistivity changes of five to eight orders of magnitude at room temperature after exposure to UV light and subsequent ozone treatment. Structural properties, i.e., crystallinity and microstructure investigated by X-ray diffraction (XRD) and Atomic Force Microscopy (AFM) are studied. The nanostructure and nanostructured surfaces are highly controlled by the deposition parameters, which, control the transport properties, and thus the sensing characteristics as measured by conductometric techniques. Analyses on the sensing response of nanostructures and nanostructured In2O3 and ZnO films for different gases are presented. Experiments on Surface Acoustic Wave (SAW) devices based on In2O3 and ZnO thin films fabricated on LiNbO3 substrates indicate the capability of achieving sensing levels in the low ppb range.

Surface Morphology Effects on Photocatalytic Activity of Metal Oxides Nanostructured Materials Immobilized onto Substrates

Structure, shape and surface morphology of the material are directly determined by the substrate and growth method used for material fabrication of nanostructured metal oxides. Those characteristics play a crucial role in the photocatalytic activity of the material. This paper presents a short review of some of the most recent relevant publications regarding pure and doped nanostructured metal oxides used for photocatalytic applications focusing on the structure, shape and surface morphology of the material effects on photocatalytic activity. The cases of TiO₂, ZnO and CuO metal oxides as well as various semiconductors and metal doping were reviewed. It was concluded that, according to the reviewed communications, the most important surface parameters affecting photocatalytic activity are surface area, surface to volume ratio, nanocrystallites size and crystallinity regardless the material. In particular, for each material, more surface parameters may be of significance.

Precursor concentration effect on structure and morphology of ZnO for coatings on fabric substrates

Abstract ZnO is a versatile functional material that has a diverse group of growth morphologies. By controlling the growth kinetics, it is possible to change the growth behavior of ZnO structures. Growth of ZnO structures can be achieved in a cheaper way at low temperature using chemical growth techniques such as aqueous chemical growth, nonaqueous solution growth, sol gel and spray deposition. Up to date, there are quite few reports in the literature presenting state of art approaches of use of ZnO material onto textile substrates for several applications as antibacterial, deodorizing and UV protection, and none regarding any systematic approach of direct growth and optimization with respect to the textile support. The successful exploitation of ZnO particles for use in various technological applications requires the development of techniques for controlling its photocatalytic activity. The present contribution presents a study of precursor concentration effect on structure and morphology of ZnO for coatings on fabric substrates. ZnO particles were obtained by direct growth onto the respective substrate by aqueous chemical growth using suitable precursors for each growth and then characterized regarding their appearance, size and structure using microscopic techniques and X-ray diffraction.

Comparative study on field collected samples of aged silicon rubber composite coatings for high voltage insulators

Abstract : Pollution of high voltage (HV) insulators is a phenomenon with a considerable impact to the performance of transmission and distribution electrical networks. The use of composite materials and especially Silicone Rubber proved to be an efficient improvement, capable of suppressing the problem and diminishing the flashover probability. As a result ceramic insulators in transmission lines are replaced by insulators with composite housing, either HTV Silicone Rubber or LSR. In the case of HV substations however, the replacement of insulators is rather difficult, due to the complexity of the equipment and the corresponding financial cost. In this case the application of RTV Silicone Rubber is an equivalent alternative. The ceramic insulators are covered with a 0.5 mm RTV SIR coating which provides the advantages of composite insulators on a ceramic substrate. After installation the possible material lifetime, which is determined by the service conditions and the material formulation, is of primary concern. In Crete, a large scale application exists and coatings that exceed a service period of 10 years are still in operation. The present study focuses on the structural and morphological characterization of field collected composite insulators of various ages so that the degradation degree can be correlated with their service.