TEM characterization of iron-oxide-coated ceramic membranes

Commercially available porous alumina–zirconia–titania ceramic (AZTC) membranes having a titania surface coating were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), and the Brunauer–Emmett–Teller (BET) method. TEM photomicrographs showed the as-received AZTC membrane to be a multi-layered structure consisting of a porous alumina–zirconia–titania core having ultrafine pore sizes, coated by an additional layer of nanoporous titania. Electron diffraction studies revealed an amorphous surface titania layer while the underlying AZTC membrane was crystalline. The AZTC membranes were coated 20, 30, 40, 45, or 60 times with iron oxide (Fe₂O₃) nanoparticles, after which the membranes were sintered in air at 900 °C for 30 min. TEM revealed a relatively uniform nanoporous Fe₂O₃ coating on the sintered, coated membranes, where the Fe₂O₃ coating thickness increased with increasing number of layers. Electron diffraction patterns showed the Fe₂O₃ coating to be crystalline in nature. This was confirmed by the XRD results showing the structure to be α-Fe₂O₃, while the AZTC membrane was a mixture of the anatase and rutile phase of TiO₂ as well as ZrO₂ and corundum, Al₂O₃. The average pore size of the underlying AZTC membrane increased after the Fe₂O₃-coated membrane was sintered. The nanoporosity in the sintered Fe₂O₃ coating increased until 40 layers, beyond which no significant increases in the average pore size were observed. The iron-oxide-coated membrane improved catalytic properties when used in combination with ozone to treat water. The optimal benefit, in terms of water treatment efficacy, was found at 40 layers of Fe₂O₃.     

Investigation of aluminium thin layer microstructure on BOPP polymer substrate

In this work, 40 μm biaxially oriented polypropylene (BOPP) polymer substrate is coated in a roll coater system. The single- and double-coated aluminium thin layers are analyzed by XRD, SEM, TEM, AFM and optical light microscopy. The size and density of pinholes are investigated by using TEM, the size of the pinholes are in the range of 0.8–8 μm, it is shown that with increasing sample thickness, the dimension of pinholes decreases. SEM and AFM are applied to study the surface morphology. The results show that the surface roughness of double-coated film is better than the single-coated one and the size of pinholes is smaller. The transmittance through the samples is measured on the UV–Vis range. The results show that double-coated film has significantly low transmittance (almost zero transmittance) in UV–Vis region.     

High thermal conductivity composites consisting of diamond filler with tungsten coating and copper (silver) matrix

Tungsten coatings with thickness of 5–500 nm are applied onto plane-faced synthetic diamonds with particle sizes of about 430 and 180 μm. The composition and structure of the coatings are investigated using scanning electron microscopy, X-ray spectral analysis, X-ray diffraction, and atomic force microscopy. The composition of the coatings varies within the range W–W₂C–WC. The average roughness, R _a, of the coatings’ surfaces (20–100 nm) increases with the weight–average thickness of the coating. Composites with a thermal conductivity (TC) as high as 900 W m⁻¹ K⁻¹ are obtained by spontaneous infiltration, without the aid of pressure, using the coated diamond grains as a filler, and copper or silver as a binder. The optimal coating thickness for producing a composite with maximal TC is 100–250 nm. For this thickness the heat conductance of coatings as a filler/matrix interface is calculated as G = (2–10) × 10⁷ W m⁻² K⁻¹. The effects of coating composition, thickness and roughness, as well as of impurities, on wettability during the metal impregnation process and on the TC of the composites are considered.     

PLD bioactive ceramic films: the influence of CaO–P2O5 glass additions to hydroxyapatite on the proliferation and morphology of osteblastic like-cells

This work consists on the evaluation of the in vitro performance of Ti6Al4V samples PLD (pulsed laser deposition) coated with hydroxyapatite, both pure and mixed with a CaO–P₂O₅ glass. Previous studies on immersion of PLD coatings in SBF, showed that the immersion apatite films did not present the usual cauliflower morphology but replicated the original columnar structure and exhibited good bioactivity. However, the influence of glass associated to hydroxyapatite concerning adhesion, proliferation and morphology of MG63 cells on the films surface was unclear. In this study, the performance of these PLD coated samples was evaluated, not only following the physical–chemical transformations resulting from the SBF immersion, but also evaluating the cytocompatibility in contact with osteoblast-like MG63 cells. SEM and AFM confirmed that the bioactive ceramic PLD films reproduce the substrate’s surface topography and that the films presented good adherence and uniform surface roughness. Physical–chemical phenomena occurring during immersion in SBF did not modify the original columnar structure. In contact with MG63 cells, coated samples exhibited very good acceptance and cytocompatibility when compared to control. The glass mixed with hydroxyapatite induced higher cellular proliferation. Cells grown on these samples presented many filipodia and granular structures, typical features of osteoblasts.     

A study of titanium thin films in transmission laser micro-joining of titanium-coated glass to polyimide

Electron beam evaporation (EB-PVD) and cathodic arc physical vapor deposition (CA-PVD) techniques were used for the preparation of titanium (Ti) thin films onto Pyrex borosilicate 7740 glass wafers and the deposited films were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques. The microstructure and surface morphology of the films were studied as a function of the film deposition techniques. Film properties such as, adherence, microstructure and roughness were interconnected to the laser joint strength between Ti coated glass wafers and polyimide films. Ti thin films on glass had a natural oxide layer on the surface as found from XPS. AFM study showed the formation of a uniform Ti coating consisted of packed crystallites with average size of 35 nm by EB-PVD. The root-mean-square surface roughness of the films was 1-2 nm. Whereas, films prepared by CA-PVD had crystallites with an average size of 120 nm and defects in the form of macro-particles which is a common attribute of this deposition system. The surface roughness of the film was 125 nm. The laser joint strength was found to be influenced by the Ti film quality on the glass substrate.     

Thickness dependence of refractive index and optical gap of PMMA layers prepared under electrical field

Optical parameters (refractive index, dispersion energy, optical gap) of polymethylmethacrylate (PMMA) layers prepared by spin coating and modified by electric field have been studied. Refractive index was measured using a refractometer, internal structure was investigated as a structural parameter (E _d) within the One Oscillator Model. Optical gap width (E _g^opt) was assessed using Tauc Approximation from UV-Vis spectra. Surface morphology and roughness was investigated using an AFM. The electric field imposed during preparation of layers increases their refractive index. The highest increase in n (Δn = 0.042) was found for the thinnest PMMA layer (70 nm). Oriented layers have produced higher E _g^opt than non-oriented ones for all studied values of thickness. The electrical field applied at preparation of the oriented layer will not change its surface morphology and roughness.     

Ellipsometric studies of microscopic surface roughness of CdS thin films

Analysis of changes in surface roughness of CdS thin films with preparation temperature was carried out using variable angle spectroscopic ellipsometry (VASE). The films studied were prepared by spray pyrolysis technique, in the substrate temperature range 200–360°C. The VASE measurements were carried out in the visible region below the band gap (E _g=2·4eV) of CdS so as to reduce absorption by the film. The thickness of the films was in the range 500–600 nm. Bruggeman’s effective medium theory was used for analysis of the surface roughness of the film. The roughness of the film had a high value (∼ 65 nm) for films prepared at low temperature (200°C) and decreased with increase in substrate temperature. This reached minimum value (∼ 27 nm) in the temperature range 280–300°C. Thereafter roughness increased slowly with temperature. The growth rate of the films was calculated for different temperature ranges. It was found that the deposition rate decreases with the increase in substrate temperature and have an optimum value at 300°C. Above this temperature deposition rate decreased sharply. The scanning electron micrograph (SEM) of the film also showed that the film prepared at 280–300°C had very smooth surface texture.     

Densification and mechanical properties of mullite-SiC nanocomposites synthesized through sol-gel coated precursors

Mullite-SiC nanocomposites are synthesized by introducing surface modified sol-gel mullite coated SiC particles in the matrix and densification and associated microstructural features of such precursor are reported. Nanosize SiC (average size 180 nm) surface was first provided with a mullite precursor coating which was characterized by the X-ray analysis and TEM. An average coating thickness of 120 nm was obtained on the SiC particles. The green compacts obtained by cold isostatic pressing were sintered in the range 1500–1700°C under pressureless sintering in the N₂ atmosphere. The percentage of the theoretical sintered density decreases with increase in SiC content. A maximum sintered density of 97% was achieved for mullite-5 vol.% SiC. The fractograph of the sintered composite showed a highly dense, fine grained microstructure with the SiC particles uniformly distributed along the grains as well as at the grain boundaries inside the mullite. The Vicker’s microhardness of mullite-5 vol.% SiC composite was measured as 1320 kg/mm² under an applied indentation load of 500 g. This value gradually decreased with an increase in SiC content.     

Effects of duty ratio at high frequency on growth mechanism of micro-plasma oxidation ceramic coatings on Ti alloy

The aim of this work is to study the effects of duty ratio on the growth mechanism of the ceramic coatings on Ti–6Al–4V alloy prepared by pulsed single-polar MPO at 2,000 Hz in NaAlO₂ solution. The phase composition of the coatings was studied by X-ray diffraction, and the morphology and the element distribution in the coating were examined through scanning electron microscopy and energy dispersive spectroscopy. The thickness of the coatings was measured by eddy current coating thickness gauge. The corrosion resistance of the coated samples was examined by linear sweep voltammetry technique in 3.5% NaCl solution. Duty ratio influenced the composition and structure of the coatings. Many residual discharging channels on the coating surface showed that the spark discharge at 2,000 Hz was mainly attributable to the breakdown of the oxide film, which was suitable for the elements both from the electrolyte and from the substrate to join MPO process, and therefore, the coating was mainly composed of Al₂TiO₅. Because of the increase of the congregation and the adsorption of Al from the electrolyte with increasing duty ratio, the redundant Al on the electrode surface led to the formation of γ-Al₂O₃. And Al and Ti in the coating existed in the form of the reverse gradient distribution. Meantime, ceramic coatings improved the corrosion resistance of Ti alloy, and the coating surface morphology and thickness determined the coated samples prepared at D = 20% had the best corrosion resistance among the coated samples.     

Hydrophobic properties and color effects of hybrid silica spin-coatings on cellulose matrix

A novel sol–gel derived organic–inorganic hybrid silica sol consisting of organic direct red dye 4BS and inorganic silica (SiO₂) is successfully synthesized by adding coupling agent γ-chloropropyltriethoxysilane (CPTS). Hybrid silica coatings are deposited on cellulose matrix surface via spin-coating approach to introduce effective hydrophobic and color properties. Compared to the dye hybrid silica sol (DHSS), the particle size of CPTS/dye hybrid silica sol (CDHSS) increases from 64.51 to 129.70 nm, while the surface tension reduces from 34.27 × 10⁻³ N m⁻¹ to 31.22 × 10⁻³ N m⁻¹. The hydrostatic pressure of the cellulose matrix coating with CDHSS is 4530.5 Pa, the contact angle is 131.48°, and the wetting time is ~150 min, which attributes to the alkyl chloride aliphatic chain and sharp micro-surface roughness of the hybrid coatings validated directly by AFM and SEM images. The K/S value (5.15) of the cellulose matrix coated with CPTS/dye hybrid silica (CMCCDHS) is 12.44% higher than that of the cellulose matrix coated with dye hybrid silica (CMCDHS), and increased by 30.38% relative to the control coated sample. The maximum absorption wavelengths of the matrixes treated with different processes are the same as the maximum absorption wavelength of the silica sols (510 nm).     

Aluminum nitride on silicon: Role of silicon carbide interlayer and chloride vapor-phase epitaxy technology

A new approach to the deposition of aluminum nitride (AlN) layers with thicknesses ranging within ∼0.1–10 μm on silicon single crystal substrates by hydride-chloride vapor-phase epitaxy (HVPE) has been developed and implemented, which involves the formation of thin (∼100-nm-thick) intermediate silicon carbide (3C-SiC) interlayers. It is established that wavy convex bands with a height of about 40 nm are present on the surface of as-grown AlN layers, which are situated at the boundaries of blocks in the layer structure. It is suggested that the formation of these wavy structures is related to morphological instability that develops due to accelerated growth of AlN at the block boundaries. Experiments show that, at low deposition rates, AlN layers grow according to a layer (quasi-two-dimensional) mechanism, which allows AlN layers characterized by half-widths (FWHM) of the X-ray rocking curves of (0002) reflections about ω_θ = 2100 arc sec to be obtained.     

Magnetic and photocatalytic properties of nanocrystalline ZnMn<Subscript>2</Subscript>O<Subscript>4</Subscript>

The present study describes the synthesis of ZnMn₂O₄ nanoparticles with the spinel structure. These oxide nanoparticles are obtained from the decomposition of metal oxalate precursors synthesized by (a) the reverse micellar and (b) the coprecipitation methods. Our studies reveal that the shape, size and morphology of precursors and oxides vary significantly with the method of synthesis. The oxalate precursors prepared from the reverse micellar synthesis method were in the form of rods (micron size), whereas the coprecipitation method led to spherical nanoparticles of size, 40–50 nm. Decomposition of oxalate precursors at low temperature (∼ 450°C) yielded phase pure ZnMn₂O₄ nanoparticles. The size of the nanoparticles of ZnMn₂O₄ obtained from reverse micellar method is relatively much smaller (20–30 nm) as compared to those made by the co-precipitation (40–50 nm) method. Magnetic studies of nanocrystalline ZnMn₂O₄ confirm antiferro-magnetic ordering in the broad range of ∼ 150 K. The photocatalytic activity of ZnMn₂O₄ nanoparticles was evaluated using photo-oxidation of methyl orange dye under UV illumination and compared with nanocrystalline TiO₂. Dedicated to Prof. C N R Rao on his 75th birthday     

Characteristics of pulse plated ZnTe films

Stoichiometric films of ZnTe are electrodeposited on stainless steel and conducting glass substrates from an aqueous solution consisting of ZnSO₄ (50 mM), TeO₂ (17 μM) and H₂SO₄ to maintain a pH of 2.5. Structure, morphology, composition, and optical are studied using XRD, SEM, EDAX and optical transmittance spectroscopy The films are composed of small crystallites (50 nm) with cubic crystal structure. The films were polycrystalline in nature with peaks corresponding to the cubic phase. Direct band gap of 2.30 eV was observed. XPS studiers indicated the formation of ZnTe. EDAX measurements were made on the films and it was found that there was a slight excess of Te. AFM studies indicated a surface roughness of 15 nm and a crystallite size of 10–50 nm.     

Morphology, surface topography and optical studies on electron beam evaporated MgO thin films

Electron beam evaporated thin films of MgO powder synthesized by burning of magnesium ribbon in air and sol-gel technique are studied for their microstructure (SEM), surface topography (AFM), and optical transmission behaviour (UV-visible spectroscopy). MgO thin films are shown to be either continuous or have mesh like morphology. The bar regions are believed to be of magnesium hydroxide formed due to absorption of moisture. Their AFM images exhibit columnar/pyramidal/truncated cone structure, providing support to the 3D Stranski-Krastanov model for film growth. Further, they are shown to have high transmittance (∼90%) in the wavelength range 400–600 nm, but absorb radiation below 350 nm substantially giving signature of a band transition.     

Structure, mechanical properties and corrosion resistance of nanocomposite coatings deposited by PVD technology onto the X6CrNiMoTi17-12-2 and X40CrMoV5-1 steel substrates

This article presents the research results on the structure and mechanical properties of nanocomposite coatings deposited by PVD methods on the X6CrNiMoTi17-12-2 austenitic steel and X40CrMoV5-1 hot work tool steel substrates. The tests were carried out on TiAlSiN, CrAlSiN and AlTiCrN coatings. It was found that the structure of the PVD coatings consisted of fine crystallites, while their average size fitted within the range 11–25 nm, depending on the coating type. The coatings demonstrated columnar structure and dense cross-sectional morphology as well as good adhesion to the substrate, the latter not only being the effect of adhesion but also by the transition zone between the coating and the substrate, developed as a result of diffusion and high-energy ion action that caused mixing of the elements in the interface zone. The critical load L _C2 lies within the range 27–54 N, depending on the coating and substrate type. The coatings demonstrate a high hardness (~40 GPa) and corrosion resistance.     

Chromaticity,brightness and aging of silica spray coated zinc sulfide silver phosphor particles

A spray drying approach was used to coat 15 nm SiO₂ continuous films onto ZnS:Ag phosphor particles. The coating was deposited on the particles by simultaneously spraying a slurry consisting of a solution of TEOS and ethanol with the solid phosphor particles into a heated drying column. The cathodoluminescent spectra of silica coated phosphor has CIE 1931 chromaticity coordinates of X ∼ 0.055, Y ∼ 0.085, brightness that is 90% of the uncoated phosphor brightness, and improved aging behavior under laboratory testing conditions.     

Nanotechnology-associated coatings for aircrafts

Polymeric epoxy-based composites are modified with nanopowders of silicon oxide (∼ 100 nm). By the method of spraying, these composites are applied to specimens of 2024-T3 aluminum alloy preliminary treated with molybdate solutions to get conversion layers. Three types of polymeric coatings are considered: reference, treated by silica, and with additional polyurethane coatings. The aim of modification of polymeric coatings is to absorb and/or block unwanted ions/molecules (Cl⁻, O₂, OH⁻, H₂O, etc.) and improve the protective properties of the films. The tests carried out by the method of electrochemical impedance spectroscopy, in a salt-fog chamber, and by immersion in a 0.5 M NaCl solution reveal high anticorrosion characteristics of the coating. New coatings are promising for the corrosion protection in the aircraft industry. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 3, pp. 103–108, May–June, 2007.     

AFM study of the surface morphology of L-CVD SnO2 thin films

In this paper we present the results of Atomic Force Microscopy (AFM) characterisation of the surface morphology of the L-CVD SnO₂ thin films prepared by L-CVD technology and studied after exposure to air, dry air oxidation, and ion beam profiling. The L-CVD SnO₂ thin films after air exposure have a very smooth surface morphology with an average surface roughness (RMS) smaller than 0.5 nm, and average and maximal grain heights of about 1 and 2 nm, respectively. After dry air oxidation the L-CVD SnO₂ thin films exhibit an average surface roughness (RMS), as well as the average and maximal grain height, increased by one order of magnitude. Finally, after the ion beam profiling the L-CVD SnO₂ thin films exhibit an evidently disordered structure with a lot of craters. These experiments showed that the L-CVD SnO₂ thin films exhibit a very high quality surface morphology, what can be useful for solar cells and gas sensors application.     

Synthesis and characterization of copper telluride nanowires via template-assisted dc electrodeposition route

Using polycarbonate track-etch membranes (Whatman), copper telluride (Cu_1.75Te) nanowires of diameter 100 nm and 50 nm have been synthesized electrochemically via template-assisted electrodeposition technique on indium tin oxide (ITO) coated glass from aqueous acidic solution of copper (II) sulphate (CuSO₄·5H₂O) and tellurium oxide (TeO₂) at room temperature (30 °C). Scanning electron microscopy (SEM) reveals the morphology of the nanowires having uniform diameter equal to the diameter of the template used. X-ray diffraction (XRD) pattern showed the structure corresponding to the hexagonal structure of copper telluride and single-crystalline. Using UV–visible spectrometry, the optical band gap of copper telluride nanowires was found to be 3.092 eV for 100 nm and 3.230 eV for 50 nm diameters. The photoluminescence (PL) studies shows higher intensity and broad spectrum in the blue region (450–475 nm) of visible light spectrum.     

Effect of Mn doping on the structural,morphological, optical and magnetic properties of indium tin oxide films

We report on the preparation and characterization of high purity manganese (3–9 wt.%) doped indium tin oxide (ITO, In:Sn = 90:10) films deposited by sol–gel mediated dip coating. X-ray diffraction and selected area electron diffraction showed high phase purity cubic In₂O₃ and indicated a contraction of the lattice with Mn doping. High-resolution transmission electron microscopy depicted a uniform distribution of ∼20 nm sized independent particles and particle induced x-ray emission studies confirmed the actual Mn ion concentration. UV-Vis diffuse reflectance measurements showed band gap energy of 3.75 eV and a high degree of optical transparency (90%) in the 100–500 nm thick ITO films. X-ray photoelectron spectroscopy core level binding energies for In 3d_5/2 (443.6 eV), Sn 3d_5/2 (485.6 eV) and Mn 2p_3/2 (640.2 eV) indicated the In³⁺, Sn⁴⁺ and Mn²⁺ oxidation states. Magnetic hysteresis loops recorded at 300 K yield a coercivity H_c ∼ 80 Oe and saturation magnetization M_s ∼ 0.39 μ_B/Mn²⁺ ion. High-temperature magnetometry showed a Curie temperature T _c > 600 K for the 3.2% Mn doped ITO film.