Combinatorial approach to the growth of α-(Al1 − x,Crx)2O3 solid solution strengthened thin films by reactive r.f. magnetron sputtering

The development of new coatings with superior functionalities for high performance cutting tools is a key challenge in manufacturing. In this context, the synthesis of aluminium oxide and derivative oxide thin films is attracting large scientific and technical interests. The present paper addresses fundamental materials science-based aspects of the physical vapour deposition (PVD) growth of Al-Cr-O thin films at a substrate temperature of 500 °C. A combinatorial experimental approach was chosen to describe the growth and microstructure evolution of Al-Cr-O thin films by means of reactive r.f. magnetron sputtering. A segmented target consisting of two half plates of Al and Cr was used for the deposition carried out under stationary conditions in a laboratory-scale PVD coater. Opposite to the cathode five substrate samples were placed in a line. The r.f. cathode power was set to 500 W and the r.f. substrate bias was set to − 100 V. The total gas pressure was kept constant at 0.4 Pa for all experiments with a fixed ratio of oxygen to argon gas flow. Detailed results on the coatings composition, constitution, microstructure and properties as a function of the elemental composition are presented. X-Ray Diffraction (XRD), X-Ray Reflection (XRR), Transmission Electron Microscopy (TEM) and Electron Probe Microanalysis (EPMA) studies prove the growth of nanocrystalline, stoichiometric, metastable corundum-like solid solution strengthened α-(Al_1 − x,Cr_x)₂O₃ thin films with a high degree of crystallinity, grain sizes between 27 ± 6 nm (in the case of Al-rich coatings) and 44 ± 17 nm (in the case of Cr-rich coatings), Vickers micro hardness values up to 2620 ± 80 HV0.05 and thin film densities between 4.00 g/cm³ (in the case of Al-rich coatings) and 4.86 g/cm³ (in the case of Cr-rich coatings).     

Development of a novel cathodic plasma/electrolytic deposition technique part 1: Production of titanium dioxide coatings

A new atmospheric pressure plasma electrolytic deposition process has been developed for the production of crystalline titanium dioxide films on metal substrates. The process occurs in a liquid precursor composed of titanium tetraisopropoxide and absolute ethanol. A plasma discharge is created and confined around the cathode in a superheated vapour sheath surrounded by the liquid phase, inducing the production of a nano-crystalline TiO₂ coating at the surface of the cathode. The analysis of the structure and composition of these TiO₂ coatings have been carried out by Scanning Electron Microscopy, Transmission Electron Microscopy, Raman and X-Ray Photoelectron Spectroscopies and X-Ray Diffraction. The produced crystalline titanium dioxide coatings are very adherent to the substrate and present a dendritic-like structure. We have moreover demonstrated that it is possible to adjust easily its composition by a post-processing calcination. Such characteristics make these films very interesting for photocatalysis, solar cells and gas sensing applications, and promise therefore some useful industrial benefits.     

TiOxNy coatings grown by atmospheric pressure metal organic chemical vapor deposition

Titanium oxynitride coatings were deposited on various substrates by an original atmospheric pressure metal organic chemical vapor deposition (MOCVD) process using titanium tetra-iso-propoxide as titanium and oxygen precursors and hydrazine as a nitrogen source. The films composition was monitored by controlling the N₂H₄ mole fraction in the initial reactive gas phase. The variation of the N content in the films results in significant changes in morphological, structural and mechanical properties. When a large excess of the nitrogen source is used the resulting film contains ca 17  at % of nitrogen and forms dense and amorphous TiO_xN_y films. Growth rates of these amorphous TiO_1.5N_0.5 coatings as high as 14 μm/h were obtained under atmospheric pressure. The influence of the deposition conditions on the morphology, the structure, the composition and the growth rate of the films is presented. For the particular conditions leading to the growth of amorphous TiO_1.5N_0.5 coatings, first studies on the mechanical properties of samples grown on stainless steel have revealed a high hardness, a low friction coefficient, and a good wear resistance in unlubricated sliding experiments against alumina which make them very attractive as protective metallurgical coatings.     

Oxidation tuning in AlCrN coatings

In this work, we have studied the influence of the coating design and composition on the oxidation behavior of Al_xCr_1−xN (x = 0.70) coatings. In particular, we have studied the effect brought about by the deposition of an additional subsurface titanium nitride barrier layer as well as by the doping of the AlCrN-based coatings by tungsten, boron and silicon. The coatings studied have been deposited using the cathodic arc vacuum (CAV) technique. The multilayered AlCrN/TiN coatings with TiN sublayer were oxidized in air at 900 °C over 3 h and then analyzed by Glow Discharge Optical Emission Spectroscopy (GDOES) and X-ray photoelectron spectroscopy (XPS). Oxidation tests were performed in air at 900 and 1100 °C for the AlCrN and AlCrWN, AlCrSiN, and AlCrBN coatings. In each case weight gain was measured and the surface morphology of the oxidized samples were studied using Secondary Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The results obtained showed that the oxidation behavior of the aluminum rich AlCrN-based coatings could be improved in two ways: (1) by controlling the chromium outward diffusion rate in multi-layered coatings and (2) by alloying the AlCrN-based coatings with Si. Both improvements are related to the enhancement of the protective oxide film formation.     

Structural characterisation of High Velocity Suspension Flame Sprayed (HVSFS) TiO2 coatings

The microstructural features of TiO₂ coatings, deposited by High Velocity Suspension Flame Spraying (HVSFS) from a suspension of titania nanoparticles, were investigated by Focused Ion Beam (FIB) + Scanning Electron Microscopy (SEM) techniques, by Transmission Electron Microscopy (TEM) and by micro-Raman spectroscopy, and were compared to those of conventional HVOF-sprayed TiO₂. Proper selection of the HVSFS deposition parameters results in coatings consisting of a dense matrix, made up by the efficient superposition of well-flattened micrometric lamellae, with homogeneously distributed porosity containing sub-micrometric re-solidified spherical particles. Unlike conventional HVOF coatings, lamella boundaries are hardly discernible, no intralamellar cracking occurs and equiaxed crystals appear instead of columnar ones. A homogeneous distribution of anatase and rutile is also found. Modifications to the spray parameters can give rise to large, unmelted agglomerates, scattered throughout the coating and having poor cohesion to the surrounding material. These agglomerates retain the original phase composition of the nanopowder.     

Anti-corrosion coatings on SS 304 by incorporation of Pr6O11–TiO2 in siloxane network

This paper describes an attempt to develop anticorrosive siloxane coatings based on Pr₆O₁₁–TiO₂ composite films for SS 304 substrate by sol-gel technique. We demonstrate for the use of praseodymium oxide doped Titanium oxide (Pr₆O₁₁–TiO₂) nanocomposites loaded in a hybrid sol-gel layer, to effectively protect the underlying steel substrate from corrosion attack. The influence of Pr₆O₁₁–TiO₂ gives the surprising aspects based on active anti-corrosion coatings. The silica sol was treated with Pr₆O₁₁–TiO₂ to achieve different level of add-on i.e.) 0–1 wt % of nanocomposites. The influence of different weight percent of nanocomposites on silica matrix for anticorrosion performance was investigated by Electrochemical Impedance Spectroscopy (EIS). Pr₆O₁₁–TiO₂ nanocomposites loaded in a hybrid sol-gel layer effectively protect the underlying substrate from corrosion attack. The results showed significant improvement in anticorrosion property for higher add-ons up to the optimized percent of nanocomposites. Furthermore, Transmission Electron Microscopy (TEM) and Scanning Electron Microscope Microscopy (SEM) were used to characterize the surface morphology of doped and undoped coatings. The studied showed a synergistic effect between Pr₆O₁₁–TiO₂ and siloxane matrix has leads to a self-healing coatings.     

Chemical compositions of organosilicon thin films deposited on aluminium foil by atmospheric pressure dielectric barrier discharge and their electrochemical behaviour

Atmospheric pressure dielectric barrier discharge (AP-DBD) deposition of organosilicon thin films on aluminium foils was investigated over a range of discharge parameters. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) analyses showed how variations of the plasma gas composition and deposition conditions affect the composition, structure and morphology of the films. The corrosion behaviour of the films was characterised by electrochemical techniques. Relationships between the deposition parameters, film chemistry and electrochemical properties of these films are reported.     

Mechanical properties of SiOx gas barrier coatings on polyester films

This paper reports the impressive mechanical properties of 1 μm thick carbon-containing SiO_x gas barrier coatings, characterised using the uniaxial fragmentation test. Such coatings have been found to act as excellent barriers to water vapour permeation partly because they can be made so thick without stress induced cracking. The impressive mechanical properties are thought to be due in part to the high amount of carbon they contain, which gives them a more organic character, as well as the fact that they are deposited as a succession of thinner layers. The adhesion of the coatings to the polyester film is good in all cases, reflecting a high density of covalent bonding at the interface. Improvement of the mechanical properties of a SiO_x/PET composite can be achieved by altering the substrate. By replacing the PET with a heat-stabilised (HS) PET film, a HS film with an acrylate layer or PEN, it is found that the coating displays improved mechanical properties and adhesive strength (as well as barrier). This is thought to be due to the superior surface thermal and mechanical properties of these substrates. Deposition temperatures are at least 80 °C, which causes molecular motion at the surface of a plain PET film and creates defects in the SiO_x coating as it grows, making it more brittle and permeable to gas flow.     

Effect of the internal stress relaxation during the post-annealing on the photo-induced properties of TiO2 coatings reactively sputtered

Photocatalyst TiO₂ coatings have been reactively sputtered at high pressure on cold glass substrates pre-coated by a SiN_x sodium diffusion barrier. The as-deposited coatings were amorphous and the TiO₂/SiN_x/glass samples were subsequently heated at different temperatures under air. The TiO₂ films crystallise in the anatase structure above temperatures of 250 °C with a [001] preferential orientation. The structural analyses have demonstrated that the crystallites are elongated following the c axis direction, perpendicularly to the surface. No modifications of grain size and texture have been observed over the complete temperature range studied (250-550 °C). However, the lattice parameters evolution shows a decrease of the tensile stress with a rise in annealing temperature. The microstructure is then completely relaxed around 400 °C and finally compressive stress is observed at higher temperature. The study of the photo-induced (photocatalytic and hydrophilic) properties shows an activity maximum at 400 °C. These results suggest that the photo-induced properties would be favoured by a relaxed microstructural state of titanium dioxide.     

The adhesion of SiNx thin layers on silica–acrylate coated polymer substrates

Plasma Enhanced Chemical Vapor Deposition (PECVD) was used to grow 200, 300 and 400 nm thick silicon nitride layers (SiN_x) on a high temperature aromatic polyester substrate spin coated with a silica–acrylate hybrid coating (hard coat). Layers deposited without oxygen plasma treatment remained attached to the substrate, while spontaneous buckle delamination of the layer deposited with oxygen plasma treatment was observed directly after layer deposition. This effect was investigated using Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS), Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM). SIMS analyses showed a considerable increase of silicon oxide by exposing the substrate to oxygen plasma treatment, while AFM showed an increased roughness. Bright-field transmission electron micrographs show the presence of a particulate SiO₂ layer. The oxygen plasma treatment thus removes the acrylate from the hard coat layer leaving behind the SiO₂ particles leading to lower adhesion and thus to spontaneous buckle delamination.     

Ion-plasma protective coatings of CdTe surface for X- and gamma-ray detectors

Comparative study of I-V characteristics of “metal-semiconductor-metal” structures without coatings and with protective coatings is presented. Regimes for radio frequency deposition of dielectric coatings on the surface of pixeled Schottky junction based on Cl-doped CdTe single crystals with high resistivity (10⁷-10¹⁰) Ω·cm were determined. In particular, the films with composition of (TeO₂)_x-(SiO₂)_1 − x have demonstrated high isolation properties. Possible applications of new CdTe pixeled detectors with the studied protective coatings for high resolution spectrometry in X- and gamma-ray sensor devices are discussed.     

Plasma functionalization of silicon carbide crystalline nanoparticles in a novel low pressure powder reactor

In order to functionalize silicon carbide nanopowders with carboxylic groups, an r.f. (13.56 MHz) low pressure plasma reactor has been developed so that particles can be stirred during the processing to try to coat them on their whole surface. Coatings in an O₂/hexamethyldisilazane (HMDSN) mixture have first been optimized on flat substrates; X-ray Photoelectron Spectroscopy (XPS) analysis showed that the O₂/HMDSN gas mixture resulted in a coating evolving from a polymer-like structure to a more inorganic SiO_x-like structure as the oxygen ratio increased. For a large O₂/HMDSN value, carboxylic groups were detected on the sample surface. Silicon carbide nanoparticles have then been plasma processed in such a reactive atmosphere. XPS, Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) and Transmission Electron Microscopy (TEM) analyses evidenced the surface modification of the processed powder and confirmed the grafting of carboxylic groups.     

Effects of synthesis, doping methods and metal content on thermoluminescence glow curves of lithium tetraborate

Lithium tetraborate: Li₂B₄O₇, (LTB) has been synthesized and doped with various Mn content by different methods, such as, high temperature solid state synthesis and solution assisted synthesis methods. Powder XRD results proved the formation of solid-solution by replacing Mn with Li ions in LTB lattice at lower amount of Mn doping, for example 0.1-3.0% Mn doping. In this research TL glow curves of Mn doped lithium tetraborate (LTB:Mn) produced by using different synthesis and doping methods and the effects of Ag, P and Mg as co-dopant were investigated. Structural and morphological analyses of products were done by using Fourier Transform Infrared spectroscopy (FTIR), Powder X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Raman Spectroscopy.     

Growth and characterization of chemical bath deposited Cd1−xZnxS thin films

Cd_1−xZn_xS (0 ≤ x ≤ 1) thin films have been deposited by chemical bath deposition method on glass substrates from aqueous solution containing cadmium acetate, zinc acetate and thiourea at 80 ± 5 °C and after annealed at 350 °C. The structural, morphological, compositional and optical properties of the deposited Cd_1−xZn_xS thin films have been studied by X-ray diffractometer, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), photoluminescence (PL) and UV-vis spectrophotometer, respectively. X-ray diffraction analysis shows that for x < 0.8, the crystal structure of Cd_1−xZn_xS thin films was hexagonal structure. For x > 0.6, however, the Cd_1−xZn_xS films were grown with cubic structure. Annealing the samples at 350 °C in air for 45 min resulted in increase in intensity as well as a shift towards lower scattering angles. The parameters such as crystallite size, strain, dislocation density and texture coefficient are calculated from X-ray diffraction studies. SEM studies reveal the formation of Cd_1−xZn_xS films with uniformly distributed grains over the entire surface of the substrate. The EDX analysis shows the content of atomic percentage. Optical method was used to determine the band gap of the films. The photoluminescence spectra of films have been studied and the results are discussed.     

Effect of lanthanum doping on linear and nonlinear-optical properties of Bi3TiNbO9 thin films

Lanthanum doped Bi₃TiNbO₉ thin films (LBTN-x, La³⁺ contents x = 5%, 15%, 25% and 35 mol.%) with layered perovskite structure were fabricated on fused silica by pulsed laser deposition method. Their linear and nonlinear optical properties were studied by transmittance measurement and Z-Scan method. All films exhibit good transmittance (>55%) in visible region. For lanthanum doping content are x = 5%, 15% and 25 mol.%, the nonlinear absorption coefficient of LBTN-x thin films increases with the La³⁺ content, then it drops down at x = 35 mol.% when the content of La³⁺ in (Bi₂O₂)²⁺ layers is high enough to aggravate the orthorhombic distortion of the octahedra. We found that, 25 mol.% is the optimal La³⁺ content for LBTN-x thin films to have the largest nonlinear absorption coefficient making the LBTN-x film a promising candidate for absorbing-type optical device applications.     

Effect of refluxing time on the morphology of pencil like zinc oxide nanostructures prepared by solution method

This paper presents the fabrication of pencil like zinc oxide nanorods by solution method using precursor zinc acetate di-hydrate (Zn(Ac)₂.2H₂O) and alkali sodium hydroxide (NaOH) at a very low refluxing temperature (75 °C) for different ageing/ refluxing (12 h, 24 h, 36 h, 48 h and 60 h) time intervals. The morphological observation was carried out by using Field Emission Scanning Electron Microscopy (FESEM). The FESEM revealed that as the aging/refluxing time increased, the size (length and diameter) of the zinc oxide nanorods also increased. Furthermore, the morphology and crystallinity of the products grown were also confirmed by Transmission Electron Microscopy (TEM), high-resolution TEM, and Selected Area Electron Diffraction (SAED) patterns, which indicated that grown pencils grew along a [0001] direction with an ideal lattice fringe distance of ∼0.52 nm. The optical properties of the grown pencil-like zinc oxide nanorods were characterized by using UV-vis spectroscopy. Strong absorbance peaks were observed at ∼375 nm to 378 nm, which is the characteristic peak for the wurtzite hexagonal phase of ZnO. The FTIR spectroscopic measurement showed a standard peak of zinc oxide in the range of 428 cm⁻¹ to 520 cm⁻¹. Additionally, on the basis of chemical and morphological analysis, we have also proposed a possible growth mechanism for pencillike zinc oxide nanostructures.     

Nano-grain Al2O3 crystals grown by sputtering of aluminium on CoCrPt thin films for potential application in ultra-high-density recording media

Designing supraceramic assemblies based on Al₂O₃ has remained a challenge due to the problems associated with the suitable dispersion in neat compounds and ability to control the preferred orientation in a unique fashion. Herein, granular HCP-(CoCrPt)_100−X(Al₂O₃)_X (X represents the percent weight) thin films with Si(1 0 0) substrates have been fabricated using sputtering technique followed by annealing treatment. Structural and magnetic properties of thin film have been investigated for potential application in magnetic recording media. It was shown that coercivity increased from 0.5 to 2.5 kOe by increasing the nano-grain Al₂O₃ content in the CoCrPt magnetic layers. In CoCrPt-Al₂O₃ thin films coercivity of 2.5 kOe has been obtained with increasing the Al₂O₃ content from 3 to 13 wt.% in the annealed thin films. The structural properties of the samples were studied using X-ray diffraction (XRD) and transmission electron microscope (TEM) equipped with selected area electron diffraction (SAED). The magnetic properties of the samples were measured with a vibrating sample magnetometer (VSM). The VSM results showed that the HCP-CoCrPt-Al₂O₃ granular films are a promising candidate for ultra-high-density recording media because of its low Al₂O₃ content and simple manufacturing process.     

Synthesis, structural and microwave dielectric properties of Al2W3−xMoxO12 (x = 0-3) ceramics

Low dielectric ceramics in the Al₂W_3−xMo_xO₁₂ (x = 0-3) system have been prepared through solid state ceramic route. The phase purity of the ceramic compositions has been studied using powder X-ray diffraction (XRD) studies. The microstructure of the sintered ceramics was evaluated by Scanning Electron Microscopy (SEM). The crystal structure of the ceramic compositions as a result of Mo substitution has been studied using Laser Raman spectroscopy. The microwave dielectric properties of the ceramics were studied by Hakki and Coleman post resonator and cavity perturbation techniques. Al₂Mo_xW_3−xO₁₂ (x = 0-3) ceramics exhibited low dielectric constant and relatively high unloaded quality factor. The temperature coefficient of resonant frequency of the compositions is found to be in the range −41 to −72 ppm/°C.     

Synthesis and characterization of cuprous oxide dendrites: New simplified green hydrothermal route

Cuprous oxide (Cu₂O) dendrites were prepared by simple hydrothermal route at two different temperatures using starch as reducing and stabilizing agent. Scanning Electron Microscopy (SEM) revealed the alterations in morphology with reaction temperature and time. The spherical nanoparticles obtained at lower reaction temperature self-assembled into distinct dendritic nanostructures at high temperature. The mechanism of formation of dendrite over the polysaccharide template has been discussed. Transmission Electron Microscopy (TEM) revealed that the crystalline size of these dendrites in one dimension is about 50 nm. The nanoparticles were characterized by UV-vis and photoluminescence (PL) spectroscopy, X-ray diffraction (XRD), FT-IR and Thermal Gravimetry Analyzer (TGA). Impedance analysis of the nanostructures showed conductivity to be a function of temperature.     

Laser chemical vapor deposition of titanium nitride films with tetrakis (diethylamido) titanium and ammonia system

Wide-area and thick titanium nitride (TiN_x) films were prepared on Al₂O₃ substrate by laser chemical vapor deposition (LCVD) using tetrakis (diethylamido) titanium (TDEAT) and ammonia (NH₃) as source materials. Effects of laser power (P_L) and pre-heating temperature (T_pre) on the composition, microstructure and deposition rate of TiN_x films were investigated. (111) and (200) oriented TiN_x films in a single phase were obtained. The lattice parameter and N to Ti ratio of the TiN_x films slightly increased with increasing P_L and was close to stoichiometric at P_L > 150 W. TiN_x films had a cauliflower-like surface and columnar cross section. The deposition rate of TiN_x films increased from 42 to 90 µm/h at a depositing area of 10 mm by 10 mm substrate, decreasing with increasing P_L and T_pre. The highest volume deposition rate of TiN_x films was about 10² to 10⁵ times greater than those of previous LCVD using Nd:YAG laser, argon ion laser and excimer laser.