Phase maps for sputter deposited refractory metal oxide ceramic coatings: review of niobium oxide,yttrium oxide,and zirconium oxide growth

Abstract

Reactive sputter deposition is a widely used glow discharge process for growing high melting point coatings near room temperature, and metastable and multiphase structures not attainable in bulk material grown under conditions of thermodynamic equilibrium. It is therefore ideally suited for growing refractory metal oxide coatings. In this study, ‘phase maps’ are constructed for the sputter deposition of the refractory metal oxides of Nb, Y, and Zr. These diagrams interrelate process parameters, the growth environment, and metallurgical phase in the growth regime of near room substrate temperature, low surface diffusion, and sticking coefficient of unity. Phase boundaries are discussed in terms of: (i) the fractional flux of metal atoms and metal oxide molecules to the substrate; (ii) a complete oxide layer at the metal target surface; (iii) oxygen species in the plasma available for reaction at the substrate.

MST/1693     

Preparation of oxide materials from metal alkoxides

This review covers the works on the sol-gel preparation of oxides from metal alkoxides that were carried out at the Faculty of Chemistry, Moscow State University, and at the Karpov Research Institute of Physical Chemistry. The composition and properties of the oxide powders and films prepared were considered in relation to the nature of alkoxides and solvents and complex formation in solution. The morphology and phase composition of the powders were examined in relation to hydrolysis conditions. Electrical and optical data are presented for titanate, zirconate, niobate, and tantalate powders, ceramics, and films     

Sputter deposition of refractory metal silicides from cold-pressed vacuum-sintered targets

Sputter deposition of refractory metal silicides from cold-pressed vacuum-sintered composite targets of TaSi_x, WSi_x, MoSi_x and TiSi_x is a simple and reproducible technique for very-large-scale integrated metallization. The films were deposited in a Varian 3180 sputtering system onto Si(100) wafers and were annealed in a Varian IA-200 rapid isothermal annealer. The resistivity, stress, stoichiometry, microstructure and morphology were studied before and after annealing. Deposition rate and reflectivity data are also included. Data will be presented for films deposited at 2.0 kW. The effects on film quality of varying the substrate temperature and of applying a d.c. bias voltage during deposition are discussed for tantalum and tungsten silicides. The optimum deposition conditions for obtaining the lowest resistivity silicide films (approximately 70 μΩ cm for TaSi_x, 50 μΩ cm for WSi_x, 80 μΩ cm for MoSi_x and 28 μΩ cm for TiSi_x) are with non-biased substrates at ambient temperature.     

Self-assembly of organic acid molecules on the metal oxide surface of a cupronickel alloy

Corrosion of the metal oxide surface of cupronickel (CuNi) alloys is a problem in applications such as household water pipes, industrial pipelines, and marine vessels. On other substrates, thin films have been used as barriers to corrosion. Here, the formation of self-assembled monolayers (SAMs) on the CuNi metal oxide surface has been investigated. Stable, well-ordered SAMs of octadecylphosphonic acid (ODPA) and 16-phosphonohexadecanoic acid (COOH-PA) were formed on the metal oxide surface of CuNi foils (55% Cu/45% Ni) using a solution deposition method. The ODPA modified surfaces could be used to provide a non-reactive barrier that inhibits corrosion of the CuNi metal oxide surface. Meanwhile, COOH-PA films could be used for further surface reactions such as surface initiated polymerization, in which polymer coatings are grown directly from a well-ordered film. Film-modified surfaces were characterized using diffuse reflectance infrared Fourier transform spectroscopy, contact angle analysis, and matrix assisted laser desorption ionization time of flight mass spectrometry. The ability of the films to inhibit corrosion by limiting oxidation of the CuNi surface was assessed using cyclic voltammetry.     

Study of aluminium oxide from high-alumina refractory ceramics by thermoluminescence

This work is focused on the study of the thermally stimulated blue emission of aluminium oxide (Al₂O₃) that has been removed from twenty different high alumina-rich refractory bricks. The glow curve sensitivity of several alumina grains are defined by (i) a maximum centred at about 165°C that can be deconvoluted into two first order kinetic peaks at 157 and 177°C and (ii) a broad structure over 200–220°C that suggests a continuous trap distribution system. The isolated grains, analysed by means of X-ray diffraction, are composed of 43% of alumina (Al₂O₃), 22% of mullite [72% of Al₂O₃ and 28% of SiO₂], 12% of leucite (KAlSi₂O₆) and 23% of sillimanite [Al₂O₃·SiO₂]. The sample characterization has been performed using X-ray fluorescence and scanning electron microscopy.     

Mechanism of Fe-Mn-Al alloy steel ingot failure from MgO-C refractory corrosion

Fe-Mn-Al alloy steel was melted in a mass production tonnage arc furnace equipped with ladle refining facilities. The ingots were cracked and torn apart on hot rolling. Blue flames erupted from the cracks and became red. A white powder was observed adjacent to the cracks in ingots. The white powder was identified as magnesia. Concentrations of Mg and Ca were high in the centre of the ingot, implying the segregation of impurities. Quantitative elemental analysis and microstructural investigation revealed Mg, Si, Ca and S containing impurities and Cr, Mo and Si carbides were segregated within grain boundaries. The segregation was the main cause of ingot cracking. The 1600°C static cup test for carbon containing MgO-C refractories exhibited the reduction reaction, which raised the Mg concentration up to 0.017 wt% in Fe-Mn-Al alloy steel, whereas the pure MgO refractory cup test showed inertness to Fe-Mn-Al alloy.     

Electrochemical deposition of precious metal on carbon nanotube for methanol oxidation

Precious metal nanoparticles were prepared on carbon nanotube (CNT) by sequential and simultaneous deposition methods for the electrocatalytic study of methanol oxidation. All electrochemical measurements were carried out in a three-electrode cell. A Platinum wire and Ag/AgCl were used as auxiliary and reference electrodes, respectively. Suspension of the CNT and Nafion were mixed and dropped on glassy carbon as a working electrode. Cyclic voltammograms in H₂SO₄ electrolyte solution are attributable to hydrogen adsorption and hydrogen desorption resulting in promising electrochemical performance of the prepared precious metal nanoparticles. Cyclic voltamograms of methanol electrooxidation studied in 2 M CH₃OH in 1 M H₂SO₄ show a distinguishing shape with a prominent oxidation wave in the anodic scan contributed to methanol oxidation while the cathodic scan is associated with the accumulation of carbonaceous species.     

脉冲激光沉积法制备抗近红外/紫外金属氧化物纳米薄膜

用准分子脉冲激光沉积法(PLD)制备了一系列的锌、铁、钛、银、铝、硅、铜等的氧化物单层和多层薄膜,用AFM研究了薄膜的组成和结构;经紫外和红外光谱发现抗紫外性能最好的是氧化锌,在190～380nm区间,其吸收率可达90%以上.抗近红外性能最好的是氧化银薄膜,其次依次是氧化铁、氧化锌、氧化钛、氧化铝、氧化铜;多层薄膜中,含有氧化锌层的抗紫外效果最好;含有氧化银层的抗近红外性能效果最好.如氧化铁/氧化锌/氧化银薄膜,在190～380nm区间,其吸收率接近100%,近红外(780～2500nm)吸收率在70%以上,最高可达90%.在可见光区其透过率在80%左右.     

Manufacture of wire from platinum/metal oxide composites

In order to enhance high‐temperature mechanical properties of platinum a dispersed particle hardening was developed by W. C. Heraeus, Hanau. A suitable compound impeding grain growth and migration of dislocations is zirconia. There are indications that significantly increased amounts of oxides might also stabilise erosion resistance of spark plug electrodes while reducing the percentage of cost‐intensive precious metal. Two different process technologies of manufacturing platinum/metal oxide composites are presented and compared: 1) melting and subsequent oxidation and 2) mixing of metal and oxide powders followed by extrusion. In both cases wires with typical diameters of 0.8 to 0.6 mm are fabricated. Samples with approx. 6 vol.‐% of zirconia dispersed in a platinum matrix were successfully tested under real life conditions in a combustion engine.     

Elaboration of cerium oxide from polyacrylate–metal complexes

The complexes formed between poly(acrylic acid) (PAA) and Ce(III) were studied. Two main complexes are formed depending on the degree of ionization α of PAA (α is defined as the ratio of ionized carboxyl groups over the total number). It is suggested that one of these complexes is a binuclear one. The thermal decomposition of the two complexes gave cerium oxide in the same conditions of temperature. The use of a low-molecular weight PAA sample allowed the formation of CeO₂ at low temperature compared to high-molecular weight PAA and model polyacids like oxalic or citric acids. Cerium oxide with fine granulometry and good surface area was obtained.     

Kinetics of subcritical cracking under the chloride and sulphide environments in a low alloy steel

The effects of two aqueous environments, namely chloride and sulphide have been investigated using fracture mechanics approaches in a Ni-Cr-Mo alloy, tempered between 200–600°C temperatures after quenching. The experimental investigation included tensile and fracture toughness tests in the ambient condition, environmental tests to determine the threshold, K_ISCC and the crack growth rate values $\text{da}\text{dt}$ and fracture surface studies. An attempt has been made to substantiate the role of microstructure and the source of hydrogen on the susceptibility to failure by computing $\text{C}{}_{\mathrm{c}}\text{C}{}_{\mathrm{o}}$ ratios for the hydrogen induced cracking process. A crack growth rate expression of the type, $\text{da}\text{dt}\text{= c'(K)}{}^{\mathrm{n}}$ is proposed for Stages I and II to account for the discrepancy between the theoretically calculated and the experimental $\text{da}\text{dt}$ data. The experimental values of the constants c' and n are determined. For all the tempering conditions investigated, the H₂S environment appears to be more hostile than the NaCl medium. However, the susceptibility to both the environments is more pronounced for yield strength values greater than 1500 MPa. The $\text{K}{}_{\mathrm{If}}\text{K}{}_{\mathrm{IC}}$ ratio is bound to be less than 1 under the H₂S, and greater than 1 under the NaCl solution.     

Failure mechanisms in alloy of polyamide 6,6/polyphenylene oxide under severe conditions

Toughening mechanisms of a polyamide 6,6/polyphenylene oxide alloy containing an elastomer tested under a slow rate, an impact rate, and a low temperature have been investigated using various microscopy techniques. It is found that the toughening mechanisms of the alloy may change from crazing/shear yielding, to crack bridging/crazing, and to transparticle failure, depending on the testing conditions. Except for the low temperature high strain rate testing condition and in the plane stress region of the crack, the crazing mechanism has been observed in all the conditions we studied. When the testing rate is high, the shear yielding mechanism is suppressed; multiple crazing and particle bridging mechanisms appear to dominate.     

Compressive and shear buckling analysis of metal matrix composite sandwich panels under different thermal environments

Combined inplane compressive and shear buckling analysis was conducted on flat rectangular sandwich panels using the Rayleigh-Ritz minium energy method with a consideration of transverse shear effect of the sandwich core. The sandwich panels were fabricated with titanium honeycomb core and laminated metal matrix composite face sheets. The results show that slightly slender (along the unidirectional compressive loading axis) rectangular sandwich panels have the most desirable stiffness-to-weight ratios for aerospace structural applications; the degradation of buckling strength sandwich panels with rising temperature is faster in shear than in compression; and the fiber orientation of the face sheets for optimum combined-load buckling strength of sandwich panels is a strong function of both loading condition and panel aspect ratio. Under the same specific weight and panel aspect ratio, a sandwich panel with metal matrix composite face sheets has a much higher buckling strength than one having monolithic face sheets.     

Shaping single-walled metal oxide nanotubes from precursors of controlled curvature

We demonstrate new molecular-level concepts for constructing nanoscopic metal oxide objects. First, the diameters of metal oxide nanotubes are shaped with angstrom-level precision by controlling the shape of nanometer-scale precursors. Second, we measure (at the molecular level) the subtle relationships between precursor shape and structure and final nanotube curvature. Anionic ligands are used to exert fine control over precursor shapes, allowing assembly into nanotubes whose diameters relate directly to the curvatures of the 'shaped' precursors.     

High-voltage nanoimprint lithography of refractory metal films

Local oxidation of metal, semiconductor, and polymer surfaces has provided a common basis from which to explore fundamental principles of nanolithography and prototype functional nanostructures for many years now. This article summarizes an investigation of local oxidation for iron and Group IV metal thin films using both scanning probe microscopy and high-voltage nanoimprinting methods. We illustrate how the underlying kinetics of metal oxidation in the presence of nitrogen, which is incorporated into the metal film during the growth process, is dramatically enhanced compared with that of single-crystal silicon. We then go on to demonstrate subsequent selective etching of latent features and a potential magnetic application.     

Plasma-assisted deposition of metal and metal oxide coatings

A combination of physical vapour deposition and plasma-assisted chemical vapour deposition techniques were used to deposit Cu-, Ni- and Sn-rich SnO/SnO2 coatings on metal and ceramic substrates. Cu and Ni were deposited on Al alloy 6061 substrates and Ni deposition was also performed on glass microscope slides and commercially pure alumina substrates. Sn-rich SnO/SnO2, on the other hand, was coated on stainless steel and pure Cu substrates. A direct-current plasma system was used to deposit the pure metals in vacuum with a resistively heated tungsten boat that was coated with alumina. All samples were sputtered for 20 min in an argon:hydrogen (1:1) atmosphere at a pressure of 300 mTorr. To reduce contamination and oxidation of both substrates and deposited layers, Cu and Ni coatings were made with argon:hydrogen (2:1) carrier gas. Sn-rich tin oxide coatings were deposited in a pure argon atmosphere (no hydrogen) to allow for the oxidation of Sn deposits on the stainless steel and copper substrates. Investigations of coated surfaces by scanning electron microscopy and X-ray diffraction showed coatings to be smooth, continuous and pure. Deposition rates showed this application to provide a very high rate when compared with chemical vapour deposition and metal–organic chemical vapour deposition techniques. Scratch tests results prove good attachment of the coatings to their respective substrates. © 1998 Chapman & Hall     

Green nanochemistry: metal oxide nanoparticles and porous thin films from bare metal powders

A universal, simple, robust, widely applicable and cost-effective aqueous process is described for a controlled oxidative dissolution process of micrometer-sized metal powders to form high-purity aqueous dispersions of colloidally stable 3-8 nm metal oxide nanoparticles. Their utilization for making single and multilayer optically transparent high-surface-area nanoporous films is demonstrated. This facile synthesis is anticipated to find numerous applications in materials science, engineering, and nanomedicine.     

Development of oxide diffusion-barrier on refractory metals

A new approach to the development of diffusion-barrier coatings which can effectively reduce the interaction of refractory filaments such as tungsten and tantalum with a nickel-alloy matrix is presented. This consists of reacting the oxide film deliberately grown on these metals with a nickel coating prior to fabricating the composite. The nickel-oxide film reactions proceed under vacuum conditions in the temperature range 650 to 800° C with the formation of intermediate phases which produce sufficiently strong bonds for composite strengthening. The details of the reaction mechanisms are not known but two types of reaction are identified. Type 1 which is a common reaction to both the Ni/oxide/Ta and the Ni/oxide/W systems constitutes a displacement reaction at the Ni/oxide interface leading to the formation of new phases and type 2 is controlled by the bulk diffusion of nickel through the compact oxide film with the development of a diffusion zone at the oxide/substrate interface. Type 2, which is only observed in the Ni/oxide/W system, is believed to confer remarkable chemical stability at 800° Cin vacuo.