Anatase TiO2 films obtained by cathodic arc deposition

TiO₂ thin films were prepared on glass substrates at different temperatures employing an unfiltered cathodic arc device. The temperature values were varied from room temperature to 400 °C. The crystalline structure of the films was determined by X-ray diffraction. The surface morphology was studied by scanning electron microscopy and atomic force microscopy. Transmittance in UV-visible region was also measured. All films deposited at temperatures lower than 300 °C were amorphous, whereas films obtained at higher temperatures grew in crystalline anatase phase. Phase transition amorphous-to-anatase was observed after post-annealing at 400 °C. The average transmittance value for all films was higher than 80%, a comparison among the films obtained at different temperatures showed a transmittance value slightly higher for films obtained at highest temperatures. Grain size for as-deposited crystalline films was determined approximately in 20 nm, with a surface roughness of about 2 nm.     

Annealing effects on microstructure and properties of Ta-Al thin film resistors

The Ta-Al thin film resistor has been used as a heating element of the thermal bubble inkjet printhead with several millions of thermal cycle operations between room temperature and about 350 °C. In this paper, the thermal stability of Ta-Al alloy films was investigated by the variation of phase transformation, microstructure and resistivity at annealing temperatures of 450-650 °C for 1 h. Three kinds of Ta-Al films were prepared with average Ta/Al atomic composition ratios of about 2/1, 1/1 and 1/2, respectively. The Ta-Al film with composition ratio of about 1/1 exhibits amorphous-like microstructure with nanocrystalline grains embedded in an amorphous matrix. The thermal stability is strongly related to the composition and microstructure in Ta-Al alloy. The best thermal stability of Ta-Al films occurs in Ta-rich alloy up to 650 °C and the worst occurs in Al-rich alloy with phase transformation as low as 450 °C. The amorphous-like Ta-Al alloy is stable up to 550 °C, but then exhibits polycrystalline multiphase formation at 650 °C. The resistivity of Ta-Al films is also related to the annealing temperature. The resistivity of Ta-rich Ta-Al film increases to about 13.5% from as-deposited to after annealing at 450 °C while that is doubled in the Al-rich Ta-Al film. In contrast, the resistivity of the amorphous-like Ta-Al film increased by about 6.1% at 450 °C and then remains nearly stable at 1.5% variation on annealing at 450-550 °C. The as-deposited amorphous-like Ta-Al film has the merits of high resistivity, smooth morphology and good thermal stability at annealing temperatures of up to 550 °C. These attributes are beneficial for the thermal bubble inkjet application with thermal cycling at maximum temperatures below 400 °C.     

Effects of surface dynamic behavior on hydrogen storage properties of sputter-deposited MgNi films

We have studied experimentally the distribution profiles of accommodated oxygen and hydrogen atoms in Mg-Ni films after different stages of hydrogenation at 8 bar pressure in the range of temperatures 210-250 °C by Elastic Recoil Detection Analysis (ERDA) and Nuclear Reaction Analysis (NRA) techniques and performed X-ray diffraction (XRD) structural and surface topography analysis. In agreement with previous publications, it is shown that even small impurity levels of uncontrollable oxygen during hydrogenation result in the formation of the oxide barrier on the surface changing hydrogen permeation properties. It is registered that the quantity of stored hydrogen during the first 3 h of hydrogenation increases up to 40 at.%, decreases up to 20 at.% after 6 h and increases again up to 40 at.% after 72 h. The quantity of the released hydrogen after 3 h hydrogenation increases with the increase in hydrogenation temperature. The observed experimental results are explained assuming that properties of the surface barrier layer changes during hydrogenation and modify hydrogen transport mechanism. The growing hydride phase in the bulk generates stresses that induce cracks and holes in the oxide barrier formed during the initial stages of hydrogenation, and hydrogen release becomes possible. At steady state, the hydrogenation properties adjust to dynamic processes on the surface and in the bulk.     

Hydrogen permeation in Fe-40 at.% Al alloy at different temperatures

The electrochemical permeation technique for studying transport and trapping of hydrogen in Fe-40 at.% Al alloy at temperatures of 5, 25, 45 and 65 °C was used in the paper. The influence of temperature on the effective hydrogen diffusion coefficient, hydrogen permeation rate and hydrogen solubility was determined. The activation energy of hydrogen diffusion in iron aluminide in the studied temperature range was also determined.     

The influence of plasma power on the temperature-dependant conductivity and on the wet chemical etch rate of sputter-deposited alumina thin films

Aluminum oxide (Al₂O₃) thin films are synthesized by reactive d.c. magnetron sputter deposition on silicon substrates. The impact of varying plasma power P_p (i.e. 400 to 1000 W) and of thin film temperatures T up to 540 °C on the electrical performance are evaluated, as these dielectric layers with a thickness of 450 nm are targeted as potential candidates for high temperature sensor applications. From 150 °C to 500 °C, the current-voltage measurements show a leakage current behavior according to the Poole-Frenkel electron emission with an activation energy of 1.16 eV. At T > 500 °C, the conductivity increases above average, in respect to the extrapolated Poole-Frenkel behavior at T < 500 °C, most probably due to the migration of charged ions, such as Ar⁺, incorporated into the film during deposition. Basically, samples synthesized at higher plasma levels show an enhanced electrical insulation behavior. This result is supported by measurements applying optical ellipsometry as well as by the determination of the wet chemical etching behavior in phosphoric-based acid at different bath temperatures. At higher plasma power, the refractive index shows a slight tendency to increase, staying, however, below the value of single-crystalline Al₂O₃. In contrast, the etch rate decreases by a factor of 1.5 at samples deposited at 1000 W when lowering the temperature of the etchant from 90 °C to 60 °C. These results indicate an enhanced film density at higher P_p values as the microstructure of the Al₂O₃ films is X-ray amorphous independent of plasma power and post-deposition annealing temperatures up to 650 °C.     

Tribological properties of pulsed laser deposited Mo-S-Te composite films at moderate high temperatures

Tribological investigations of Mo-S-Te composite films were conducted on films grown at room temperature by pulsed laser deposition. The chemistry and microstructure of the films were characterized by X-ray diffraction, scanning electron microscopy, X-ray energy dispersive spectroscopy, and micro Raman spectroscopy. The films showed a granular morphology and a preferred basal plane growth of 2H-MoS₂ parallel to the substrate after annealing at high temperatures. The friction coefficients of the films were 0.05 at 300 °C and 0.10 at 450 °C for more than 10,000 cycles in air. Smeared hexagonal MoS₂ lubricant films were observed inside wear tracks while the tribochemical formation of wear debris occurred both inside and outside the wear tracks. The Te additives for increasing the film durability were proposed to slow oxidation of the lubricants at elevated temperatures by thermally-induced tellurium migration to the surface and the subsequent formation of the Te diffusion barrier. This mechanism could be significantly effective in high-temperature tribotests because of the increased tellurium mobility at high temperatures.     

Characterization of nanostructured Cr2Nx/Cu multilayers deposited by reactive DC magnetron sputtering

Nitride/metal nanostructured multilayers of Cr₂N_x/Cu were deposited by reactive DC magnetron sputtering with various bilayer periods (2.5-30 nm) and substrate temperatures (25-400 °C). All films had a total thickness of about 470 nm and the overall chemical composition of the chromium nitride layers was close to Cr₂N_0.8. The deposited films were characterized by Rutherford Backscattering (RBS), low-angle X-ray reflectivity (XRR), high-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM). The hardness and elastic modulus were measured by nanoindentation. The films deposited at 25 °C had a well-defined multilayer structure and the chromium nitride layers were found to crystallize into N-deficient fcc CrN_0.4 with traces of hexagonal Cr₂N_0.8. The layers were strongly textured with fcc CrN_0.4[002] and Cu[002] oriented along the growth direction — the fcc CrN_0.4 and Cu grains growing with a cube-on-cube relationship. The measured hardness values were about 8 GPa, and showed no dependence on the bilayer period. Higher deposition temperatures caused the multilayer structure to degrade, and at 400 °C the films were better described as non-textured nanocomposites with the chromium nitride crystallized entirely into the equilibrium hexagonal Cr₂N_0.8 structure. Hardness values of the high-temperature films in the range of 4-8 GPa were measured. Multilayer films deposited at 25 °C were found to be thermally stable against post-deposition annealing at temperatures up to about 400 °C. Annealing at 500 °C caused severe structural changes — the fcc CrN_0.4 phase transformed into hexagonal Cr₂N_0.8 accompanied by degradation of the periodic multilayer structure. The hardness decreased from the originally 8 GPa to about 5 GPa upon annealing.     

Effect of microstructure on the sulphide stress cracking susceptibility of a high strength pipeline steel

The sulphide stress cracking (SSC) susceptibility of a newly developed high strength microalloyed steel with three different microstructures has been evaluated using the slow strain rate testing (SSRT) technique. Studies were complemented with potentiodynamic polarization curves and hydrogen permeation measurements. Material included a C–Mn steel having Ni, Cu, and Mo as main microalloying elements with three microstructures: martensitic, ferritic and ferritic + bainitic. Testing temperatures included 25, 50, 70 and 90 °C. Detailed SEM observations of the microstructure and fracture surfaces were done to identify possible degradation mechanisms. The results showed that in all cases, the corrosion rate, number of hydrogen atoms at the surface and the percentage reduction in area increased with temperature. The steel with a martensitic microstructure had the highest SSC susceptibility at all temperatures, whereas the ferritic steels were susceptible only at 25 °C, and the most likely mechanism is hydrogen embrittlement assisted by anodic dissolution.     

Amorphous hafnium oxide thin films for antireflection optical coatings

Hafnium oxide (HfO₂) thin films were grown on silicon and quartz substrates by radio frequency reactive magnetron sputtering at temperature < 52 °C. X-ray diffraction of the films showed no structure, suggesting that the films grown on the substrates are amorphous. The optical properties of these films have been investigated using spectroscopic ellipsometry with wavelength range 200-1400 nm and ultraviolet-visible spectrophotometer techniques. Also, the effects of annealing temperatures on the structure and optical properties of the amorphous HfO₂ (a-HfO₂) have been investigated. The films appeared to be monoclinic structure upon high temperature (1000 °C) annealing as confirmed by X-ray diffraction. The results show that the annealing temperature has a strong effect on the optical properties of a-HfO₂ films. The optical bandgap energy of the as-deposited films is found to be about 5.8 eV and it increases to 5.99 eV after the annealing in Ar gas at 1000 °C. The further study shows that the measurement of the optical properties of the amorphous films reveals a high transmissivity (82%-99%) and very low reflectivity (< 8%) in the visible and near-infrared regions at any angle of incidence. Thus, the amorphous structure yields HfO₂ film of significantly higher transparency than the polycrystalline (68%-83%) and monoclinic (78%-89%) structures. This means that the a-HfO₂ films could be a good candidate for antireflection (AR) optical coatings.     

Formation of crystalline Al-Ti-O thin films and their properties

The article reports on the effect of addition of Ti into Al₂O₃ films with Ti on their structure, mechanical properties and oxidation resistance. The main aim of the investigation was to prepare crystalline Al-Ti-O films at substrate temperatures T_s ≤ 500 °C. The films with three different compositions (41, 43 and 67 mol% Al₂O₃) were reactively sputtered from a composed Al/Ti target and their properties were characterized using X-ray diffraction (XRD), X-ray fluorescent spectroscopy (XRF), microhardness testing, and thermogravimetric analysis (TGA). It was found that (1) the addition of Ti stimulates crystallization of Al-Ti-O films at lower substrate temperatures, (2) Al-Ti-O films with a nanocrystalline cubic γ-Al₂O₃ structure, hardness of 25 GPa and zero oxidation in a flowing air up to ∼ 1050 °C can be prepared already at low substrate temperature of 200 °C, and (3) the crystallinity of Al-Ti-O films produced at a given temperature improves with the increasing amount of Ti. The last finding is in a good agreement with the binary phase diagram of the TiO₂-Al₂O₃ system.     

Determining substrate temperature in an AC inverted cylindrical magnetron sputtering PVD system

The substrate temperature achieved during physical vapor deposition significantly affects the properties and phases of thin films. An Isoflux ICM-10 Dual Target Inverted Cylindrical Magnetron Sputtering system is used to deposit low temperature alpha-phase alumina, for which an experimentally determined substrate temperature is desired. Constraints inherent to the Isoflux system limit the use of a thermocouple. Instead, a pressure vessel containing numerous samples of temperature indicating liquids is placed in the chamber during operation. These indicator paints are observed upon completion of the deposition process to record the substrate temperature. Measurements indicate a temperature range of 343 °C to 399 °C for our alpha-phase alumina films deposited at a pressure of 0.27 Pa (2 mTorr), a substrate bias of − 35 V, and a power of 5 kW. Theoretical heat transfer calculations support the experimental measurements. A parametric investigation showed that the removal of the − 35 V substrate bias decreases the substrate temperatures by approximately 35 °C and that the substrate temperature increases about 50 °C for each additional kilowatt of power in the range of 1 kW to 6 kW.     

A study of the oxidation behavior of CrN and CrAlN thin films in air using DSC and TGA analyses

Freestanding CrN_x and Cr_1 − xAl_xN films with two different Al atomic percentages with respect to the metal sublattice (x = 0.23 and x = 0.60) were produced by pulsed closed field unbalanced magnetron sputtering (P-CFUBMS). The dynamic oxidation behavior of the films has been characterized by thermal analysis using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The structure of the films at different thermal-annealing temperatures were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) in an effort to understand different phase transitions and oxidation reactions observed on the DSC curves. The peak temperatures of the main exothermic/endothermic oxidation reactions in the DSC signals at different heating rates were applied to the Kissinger model for determination of activation energies. The mechanical properties of the films at different heat-annealing states were measured by nano-indentation.It was found that the CrN_x films oxidized in air after 600 °C by the dissociation of fcc (face center cubic)-CrN to h(hexagonal)-Cr₂N and nitrogen and, after 900 °C by the dissociation of h-Cr₂N to Cr and nitrogen in the film. The addition of Al to CrN film can further improve the oxidation resistance, especially for the high temperature above 800 °C. The oxidation degradation in two Cr-Al-N films started with dissociation of fcc-CrAlN to h-Cr₂N and nitrogen in the film. The presence of thermally stable Al-N bonding in the fcc-CrAlN structure can suppress the reduction of nitrogen in the film. A dense (Cr,Al)₂O₃ layer (either amorphous or crystalline) formed at early oxidation stage (< 700 °C) can act as an effective diffusion barrier slowing down the inward diffusion of the oxygen at high temperatures. Precipitation of h-AlN phase in Cr_0.77Al_0.23N and Cr_0.40Al_0.60N films were found at 900 and 1000 °C respectively, accompanied with crystalline Al₂O₃ formation. After that, both Cr-Al-N films oxidized rapidly after the dissociation of h-Cr₂N to Cr and nitrogen. In addition, Cr_0.40Al_0.60N films exhibit higher oxidation resistance than Cr_0.77Al_0.23N films. The fcc-CrAlN was retained up to 900 °C and the precipitation of h-AlN phase took place after 1000 °C in Cr_0.40Al_0.60N films. Cr_0.40Al_0.60N films also retained a hardness of 25 GPa after annealing at 800 °C in ambient air for 1 h. The activation energies of the final oxidation exothermic peaks in CrN_x, Cr_0.77Al_0.23N and Cr_0.40Al_0.60N films in the current study were found to be 2.2, 3.2 and 3.9 eV atom^− 1 respectively.     

Thermal stability and oxidation resistance of Ti-B-N, Ti-Cr-B-N, Ti-Si-B-N and Ti-Al-Si-B-N films

Films Ti-B-xN-y(Al,Si,Cr) with different compositions x = 25-33 at.% and y = 11-14 at.% were deposited by DC magnetron sputtering of TiBN, TiCrB, TiSiB, and TiAlSiB composite targets in a gaseous mixture of argon and nitrogen. The structure and phase composition of films were studied by means of X-ray diffraction, transmission electron microscopy, Raman and X-ray photoelectron spectroscopy. To evaluate the thermal stability and oxidation resistance, the Ti-B-N, Ti-Cr-B-N, Ti-Si-B-N, and Ti-Al-Si-B-N films were annealed at 600, 800, and 1000 °C in vacuum and at 600, 700, 800, and 900 °C in air, respectively. The elemental depth profiles for the oxidized films were obtained by focused ion beam equipped with secondary ion mass spectrometer. The Ti-B-N and Ti-Cr-B-N films demonstrated thermal stability up to 1000 °C. A threshold temperature of 800 °C was determined, below which these films acted as a diffusion barrier for Ni diffusion from metallic substrate. Annealing in the range of 600-800 °C improved mechanical and tribological characteristics of the films. The Ti-Cr-B-N and Ti-Al-Si-B-N films were more resistant against high-temperature oxidation than the Ti-B-N and Ti-Si-B-N films.     

Fabrication and characterization of ITO thin films on heat-resistant transparent flexible clay films

Transparent conductive indium tin oxide (ITO) thin films were deposited on transparent flexible clay films with heat resistant and high gas barrier properties by rf magnetron sputtering. The electrical, structural, and optical properties of these films were examined as a function of deposition temperature. A lowest resistivity of 4.2 × 10^− 4 Ωcm and an average transmittance more than 90% in the visible region were obtained for the ITO thin films fabricated at deposition temperatures more than 300 °C. It was found that ITO thin films with low resistivity and high transparency can be achieved on transparent flexible clay film using conventional rf magnetron sputtering at high temperature, those characteristics are comparable to those of ITO thin films deposited on a glass substrate.     

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.     

Study of the electrochemical permeation of hydrogen in iron

Hydrogen permeation through iron membranes of different thicknesses was studied by the electrochemical permeation technique. The membranes were charged with hydrogen by galvanostatic cathodic polarization in 0.1 M NaOH at 25 °C.The measured build-up and decay permeation current transient had been examined.The experimental results revealed that the diffusion apparently increases with decreasing membrane thickness. This result suggests that the hydrogen transport through membrane was mainly governed by hydrogen trapping at the trap sites present at the grain boundaries.The influence of the passive layer on the hydrogen permeation and its influence on the evaluation of diffusion and trapping characteristics were discussed.     

Phase transformation in κ- and γ-Al2O3 coatings on cutting tool inserts

The phase transformation in as-deposited, metastable κ- and γ-alumina coatings on cutting inserts has been studied by a combination of X-ray diffraction, scanning electron microscopy and cathodoluminescence. In the case of κ-alumina, mechanical forces during metal cutting lower the transformation temperature of the metastable phases to the thermodynamically stable α-alumina phase from 1050 °C to 930 °C. This is the reason why that coating has a similar performance during metal cutting when compared to the stable α-alumina phase. The transformation temperature in γ-alumina coated cutting tools is found to be as low as 950-975 °C. Cathodoluminescence (CL) has been demonstrated as a possible method for differentiation between the various alumina phases. Specifically, both κ- and γ-alumina films have revealed a strong room temperature CL with different peak energies depending on the phase. CL of the metastable alumina coatings annealed at the transformation temperatures corresponds to the stable α-alumina phase.     

Formation of nanostructured YSZ/Ni anode with pore channels by plasma spraying

YSZ/Ni is the conventionally most used material for making the anode of a solid oxide fuel cell. Agglomerated nanostructured YSZ/NiO powders and plasma spray are applied to produce nanostructured YSZ/NiO coatings on porous support substrates. After reduction in an ambient atmosphere of 7% hydrogen and 93% argon at about 800 °C for 4 hours, a novel SOFC anode with nanostructured characteristics such as nano YSZ particles, nano Ni particles, nano pores and nano pore channels is produced. This new YSZ/Ni anode provides larger triple phase boundaries for hydrogen oxidation reactions. X-ray diffraction patterns of these YSZ/NiO coatings after 1 h of heat treatment at temperatures from 700 to 1100 °C are obtained and Scherrer analysis is conducted to study the effect of temperature on grain size. The results obtained from SEM, TEM, XRD and EDX measurements and analyses are presented in this investigation.     

The cracking behavior of anodic films on cast aluminum alloy after heating in the temperature range up to 300 °C

The cracking behavior of sealed anodic films on cast aluminum alloy after heating in the temperature range up to 300 °C was studied and the effects of anodizing temperature, heating temperature and heating rate on cracking behavior were investigated. The results showed that before heating some micro-cracks were present in sealed anodic films on the aluminum alloy tested. After heating between 100 °C and 300 °C, the initial micro-cracks became wider and deeper, and new cracks also may be initiated in the film. As anodizing temperature increased, both the crack density and the crack width increased after heating, which was attributed to increase of the porosity of the anodic films formed at higher temperatures. At higher heating temperature, the cracks obviously got wider, but the crack density remained almost unchanged. Increased heating rate resulted in more cracks in the anodic film, indicating that higher strain rate may promote initiation of the micro-cracks, while cooling rate had little influence on cracking behavior.     

Combustion chemical vapour deposition of Al2O3 films: Effect of temperature on structure, morphology and adhesion

Alumina films were synthesized on Si(100) substrates at different temperatures in the range of 600 to 900 °C using open atmosphere combustion chemical vapour deposition (C-CVD) technique. A custom made premixed-diffusion type burner with an extra coaxial oxygen inlet close to the burner mouth enabled variation of deposition temperature from 600 to 900 °C in steps of 100 (± 10) °C. The presence of γ- and θ-alumina phases were observed in films synthesized in the temperature range of 600-800 °C, whereas at 900 °C single phase θ-alumina films were obtained. Adherent coatings were obtained at temperatures ≥ 700 °C. The grain size and roughness of the films increased with deposition temperature. The films underwent two types of adhesion failures, a continuous ductile perforation and a tensile type hertzian crack due to the presence of interfacial oxide layer, during scratch test. The presence of SiO₂ interfacial layer between substrate and film was discerned from ellipsometric studies.