Effects of composition and structure on hydrogen incorporation in tungsten oxide films deposited by sputtering

The effects of composition and structure on hydrogen incorporation in tungsten oxide films were investigated. Films were deposited on carbon and SiO₂ substrates using a reactive sputtering by varying the substrate temperature from 30 to 600 °C in argon and oxygen mixture. The films were characterized using X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), elastic recoil detection analysis (ERDA) and Raman scattering. XRD patterns showed amorphous structure in the films deposited below 400 °C and (0 1 0) oriented monoclinic WO₃ in the films deposited beyond 400 °C. The results of RBS and ERDA indicated that hydrogen concentration in the amorphous films increased from 0.1 to 0.7 H/W with changing the composition from WO_0.25 to WO₃. The hydrogen concentration in WO₃ films decreased to 0.4 H/W with increasing the substrate temperature during deposition. The Raman spectra of the WO₃ films revealed that decreasing of W⁶⁺O terminals was related to decreasing of the hydrogen concentration. It was considered that the incorporated hydrogen in tungsten oxide films was bonded at the end of W⁶⁺O terminals.     

Effects of composition and structure on gasochromic coloration of tungsten oxide films investigated with XRD and RBS

The effects of composition and structure on gasochromic coloration of tungsten oxide films for hydrogen have been investigated. Tungsten oxide films with various O/W atomic ratios from 1.5 to 3.0 are prepared using a reactive rf magnetron sputtering from a tungsten target at different oxygen partial pressures. The films were deposited on quartz and carbon substrates at 200 °C. The O/W atomic ratio and crystallographic structure of the films were determined by Rutherford backscattering spectroscopy and X-ray diffraction. The gasochromic properties of the films were examined by use of optical transmittance in exposure in 1% H₂/Ar atmosphere. The stoichiometric WO₃ film with amorphous structure resulted in superior gasochromic coloration. The decrease in gasochromic performance was caused by non-stoichiometric WO₃ films with amorphous structure or stoichiometric WO₃ films crystallized with post-annealing at temperatures higher than 300 °C in air. It suggests that the gasochromic coloration of tungsten oxide films for hydrogen is strongly influenced by the composition and structure.     

SIMS study of effect of Cr adhesion layer on the thermal stability of silver selenide thin films on Si

Effect of heat treatment on silver selenide films grown from diffusion-reaction of Ag and Se films on Cr-buffered Si substrates was investigated up to 400 °C. X-ray diffraction (XRD), Scanning electron microscopy (SEM), Secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS) were used to characterize the films. XRD patterns of the films showed stress assisted change in preferential orientation of the films upon annealing: the films annealed at 200 °C exhibited a strong orientation along (2 0 0) plane, which changed to (0 1 3) after annealing at 300 and 400 °C. Dynamic SIMS measurements showed that Cr is confined to the interface and that there is no diffusion of Cr into silver selenide.     

Ion beam characterization of rf-sputter deposited AlN films on Si(1 1 1)

Aluminum nitride (AlN) thin films have been deposited on Si(1 1 1) substrates by using reactive-rf-magnetron-sputtering at 250 °C. The crystalline quality and orientation of the films have been studied by X-ray diffraction (XRD). We have observed that the films grow with c- or a-axis orientation. The composition, film thickness, impurities and stress are considered to be factors affecting the orientation and have been analyzed by Rutherford backscattering spectroscopy (RBS), nuclear reaction analysis (NRA) and XRD. Their effects on the film growth will be discussed. Surface morphology of the films will be also presented.     

Structural distortion effect in the cobalt ions implanted TiO2 films

TiO₂ thin films were prepared by direct current magnetron sputtering on glass substrates, then were implanted by cobalt ions, and finally annealed at 400 and 500 °C for 50 min, respectively. They were identified as an anatase structure by X-ray diffraction (XRD). Scanning electron microscope (SEM) images showed that the grain sizes of the films grow with increasing annealing temperature. The energy dispersive X-ray (EDX) measurements indicated that the ratio of the cobalt atoms number and total atoms number of cobalt and titanium in the Co-TiO₂ films was about 2.51%, and X-ray photoelectron spectroscopy (XPS) results revealed that the cobalt existed in the films as Co²⁺. The element distribution of cobalt along cross-section of the films was studied by EDX, as the results showed that the cobalt diffused deeply into the films after annealing. The high resolution transmission electron microscopy (HRTEM) images were used to affirm the anatase structure of the Co-TiO₂ films, and edge dislocations were further found in the HRTEM images, which could be attributed to the effect of the implantation.     

Evolution of the oxide structure of 9CrODS steel exposed to supercritical water

The corrosion behavior and oxide structure of 9CrODS steel in supercritical water has been studied. Samples were exposed to supercritical water at 500 and 600 °C for times of 2, 4 and 6 weeks. The oxide structure was studied using microbeam synchrotron X-ray diffraction and fluorescence analysis. The 600 °C samples exhibited a three-layer structure with Fe₃O₄ in the outer layer, a mixture of FeCr₂O₄ and Fe₃O₄ in the inner layer, and a mixture of metal and oxide grains (FeCr₂O₄ and Cr₂O₃) in the diffusion layer. Between the 2 and 4-week samples exposed to 600 °C supercritical water, a Cr₂O₃ film appeared at the diffusion layer-metal interface which appears to be associated with slower oxidation of the metal. The 500 °C samples also showed a three-layer structure, but both the outer and inner oxide layers contained mainly Fe₃O₄, and the diffusion layer contained much fewer oxide precipitates and was a solid solution of oxygen ahead of the oxide front.     

Effects of ion irradiation on the mechanical properties of SiNawOxCyHz sol-gel derived thin films

A study of the effects of ion irradiation of hybrid organic/inorganic modified silicate thin films on their mechanical properties is presented. NaOH catalyzed SiNa_wO_xC_yH_z thin films were synthesized by sol-gel processing from tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) precursors and spin-coated onto Si substrates. After drying at 300 °C, the films were irradiated with 125 keV H⁺ or 250 keV N²⁺ at fluences ranging from 1 × 10¹⁴ to 2.5 × 10¹⁶ ions/cm². Nanoindentation was used to characterize the films. Changes in hardness and reduced elastic modulus were examined as a function of ion fluence and irradiating species. The resulting increases in hardness and reduced elastic modulus are compared to similarly processed acid catalyzed silicate thin films.     

The interdiffusion and solid-state reaction of low-energy copper ions implanted in silicon

At room temperature, single-crystal silicon was implanted with Cu⁺ ions at an energy of 80 keV using two doses of 5 × 10¹⁵ and 1 × 10¹⁷ Cu⁺ cm⁻². The samples were heat treated by conventional thermal annealing at different temperatures: 200 °C, 230 °C, 350 °C, 450 °C and 500 °C. The interdiffusion and solid-state reactions between the as-implanted samples and the as-annealed samples were investigated by means of Rutherford backscattering spectrometry (RBS) and X-ray diffraction (XRD). After annealing at 230 °C, the XRD results of the samples (subject to two different doses) showed formation of Cu₃Si. According to RBS, the interdiffusion between Cu and Si atoms after annealing was very insignificant. The reason may be that the formation of Cu₃Si after annealing at 230 °C suppressed further interdiffusion between Si and Cu atoms.     

Structural and gasochromic properties of epitaxial WO3 films prepared by pulsed laser deposition

The structural and gasochromic properties of epitaxial tungsten trioxide (WO₃) thin films, prepared by ArF excimer pulsed laser deposition under the controlled oxygen atmosphere, have been investigated. The WO₃ films were grown on the α-Al₂O₃ substrates, as the oxygen pressure ranged from 0.57 to 1.20 Pa and the substrate temperature ranged from 432 to 538 °C. The deposited films were characterized by Rutherford backscattering spectroscopy (RBS)/channeling, X-ray diffraction, X-ray pole figures and Raman spectroscopy. RBS and XRD results demonstrated that monoclinic WO₃ (0 0 1) films were successfully grown on the α-Al₂O₃ substrates. The crystal quality was improved by increasing both the oxygen pressure and the substrate temperature. Gasochromic coloration in the WO₃ films by exposure to diluted hydrogen gas was found to correlate with the crystal quality of the films. The gasochromic coloration was suppressed by the epitaxial growth of the films.     

Hydrogen behavior in gasochromic tungsten oxide films investigated by elastic recoil detection analysis

Changes in the composition and crystalline structure of gasochromic tungsten oxide films resulting from the incorporation of hydrogen were investigated; the oxide films were prepared by reactive RF magnetron sputtering on SiO₂ and glassy carbon substrates simultaneously. X-ray diffraction analysis of the deposited films at 600 °C showed a uniaxial oriented structure in the (0 1 0) plane of monoclinic WO₃ for both substrates. The elastic recoil detection analysis (ERDA) and Rutherford backscattering spectroscopy (RBS) for the films on glassy carbon revealed that the hydrogen impurity was uniformly distributed up to a concentration of 0.24 H/W. The Pd-coated films on SiO₂ turned blue when they were exposed to a mixture of Ar and 5% H₂ gases. When the sample became colored, the hydrogen concentration in the film increased to 0.47 H/W and the crystalline structure of the film changed from monoclinic to tetragonal. These results indicated that the gasochromic coloration of the tungsten oxide films coincided with incorporation of hydrogen atoms into the crystalline lattice, corresponding to the formation of hydrogen tungsten bronze (H_xWO₃).     

Microstructure evolution of Ge implanted silicon oxide thin films upon annealing treatments

The structural evolution of silicon oxide films with Ge⁺ implantation was traced with a positron beam equipped with positron annihilation Doppler broadening and lifetime spectrometers. Results indicate that the film structure change as a function of the annealing temperature could be divided into four stages: (I) T < 300 °C; (II) 300 °C ? T ? 500 °C; (III) 600 °C ? T ? 800 °C; (IV) T ? 900 °C. In comparison with stage I, the increased positron annihilation Doppler broadening S values during stage II is ascribed to the annealing out of point defects and coalescence of intrinsic open volumes in silicon oxides. The obtained long positron lifetime and high S values without much fluctuation in stage III suggest a rather stable film structure. Further annealing above 900 °C brings about dramatic change of the film structure with Ge precipitation. Positron annihilation spectroscopy is thereby a sensitive probe for the diagnosis of microstructure variation of silicon oxide thin films with nano-precipitation.     

N-TiO2 nanoparticles embedded in silica prepared by Ti ion implantation and annealing in nitrogen

Room-temperature Ti ion implantation and subsequent thermal annealing in N₂ ambience have been used to fabricate the anatase and rutile structured N-doped TiO₂ particles embedded in the surface region of fused silica. The Stopping and Range of Ions in Matter (SRIM) code simulation indicates a Gaussian distribution of implanted Ti, peaked at ∼75 nm with a full width at half maximum of ∼80 nm. However, the transmission electron microscopy image shows a much shallower distribution to depth of ∼70 nm. Significant sputtering loss of silica substrates has occurred during implantation. Nanoparticles with size of 10-20 nm in diameter have formed after implantation. X-ray photoelectron spectroscopy indicates the coexistence of TiO₂ and metallic Ti in the as-implanted samples. Metallic Ti is oxidized to anatase TiO₂ after annealing at 600 °C, while rutile TiO₂ forms by phase transformation after annealing at 900 °C. At the same time, N-Ti-O, Ti-O-N and/or Ti-N-O linkages have formed in the lattice of TiO₂. A red shift of 0.34 eV in the absorption edge is obtained for N-doped anatase TiO₂ after annealing at 600 °C for 6 h. The absorbance increases in the ultraviolet and visible waveband.     

Positron annihilation study of structural effect on photocatalytic activity of mesoporous TiO2 thin films

Mesoporous TiO₂ films were synthesized by using triblock copolymers via a sol-gel process in aqueous solution. It was found that a film calcined at 600 °C has the highest photocatalytic activity. By application of positron annihilation Doppler broadening spectroscopy combined with XRD, SEM, and N₂ adsorption desorption techniques, the film structural properties were examined systematically. It is revealed that an excellent photocatalytic activity could be achieved only if a film maintains a suitable TiO₂ grain size, i.e. ∼7.5 nm in the present study, a median specific surface area and a high crystallinity in anatase state.     

The annealing behavior of Cu nanoparticles in Ar-ion implanted spinel

Magnesium aluminate spinel crystals (MgAl₂O₄ (1 1 0)) deposited with 30 nm Cu film on surface were implanted with 110 keV Ar-ions to a fluence of 1.0 × 10¹⁷ ions/cm² at 350 °C, and then annealed in vacuum condition at the temperature of 500, 600, 700, 800 and 900 °C for 1 h, respectively. Ultraviolet-visible spectrometry (UV-VIS), scanning electron microscopy (SEM), Rutherford backscattering (RBS) and transmission electron microscopy (TEM) were adopted to analyze the specimens. After implantation, the appearance of surface plasmon resonance (SPR) absorbance peak in the UV-VIS spectrum indicated the formation of Cu nanoparticles, and the TEM results for 500 °C also confirmed the formation of Cu nanoparticles at near-surface region. In annealing process, The SPR absorbance intensity increased at 500 and 700 °C, decreased with a blue shift of the peak position at 600 and 800 °C, and the peak disappeared at 900 °C. The SPR absorbance intensity evolution with temperature was discussed combined with other measurement results (RBS, SEM and TEM).     

Crystal structure, corrosion kinetics of new zirconium alloys and residual stress analysis of oxide films

Corrosion kinetics of NZ2 alloy were investigated after autoclave treatments in 360 °C/18.6 MPa lithiated water and 400 °C/10.3 MPa steam. The crystal structure and the residual stress of oxide films of NZ2 alloys after corroded in both conditions were investigated by XRD method. The kinetics analysis indicates that the resistance of NZ2 alloy treated in 360 °C lithiated water is higher than that treated in 400 °C steam. The crystal structure analysis shows that the content of tetragonal t-ZrO₂ in the oxide films decreases smoothly and the content of monoclinic m-ZrO₂ increases with the duration of corrosion time, independent of the kinetics transition. Stress measurements show that high compressive stresses were developed in the oxide layers. Furthermore, the transitions of kinetics can be associated with the sudden decrease of macroscopic compressive stresses in the oxide films. The higher t-ZrO₂ content is, the higher compressive stress in the oxide film is, the lower is the corrosion rate. Therefore it is considered that t-ZrO₂ is mainly stabilized by the macroscopic compressive stresses in the oxide films. In addition, local stresses in the oxide films, grain size and the oxygen vacancies play an important role in the t-ZrO₂ stabilization.     

Corrosion behaviors of US steels in flowing lead-bismuth eutectic (LBE)

Corrosion tests of several US martensitic and austenitic steels were performed in a forced circulation lead-bismuth eutectic non-isothermal loop at the Institute of Physics and Power Engineering (IPPE), Russia. Tube and rod specimens of austenitic steels 316/316L, D-9, and martensitic steels HT-9, T-410 were inserted in the loop. Experiments were carried out simultaneously at 460 °C and 550 °C for 1000, 2000 and 3000 h. The flow velocity at the test sections was 1.9 m/s and the oxygen concentration in LBE was in the range of 0.03-0.05 wppm. The results showed that at 460 °C, all the test steels have satisfactory corrosion resistance: a thin protective oxide layer formed on the steel surfaces and no observable dissolution of steel components occurred. At 550 °C, rod specimens suffered rather severe local liquid metal corrosion and slot corrosion; while tube specimens were subject to oxidation and formed double-layer oxide films that can be roughly described as a porous Fe₃O₄ outer layer over a chrome-rich spinel inner layer. Neglecting the mass transfer corrosion effects by the flowing LBE, calculations based on Wagner’s theory reproduce the experimental results on the oxide thickness, indicating that the oxide growth mechanism of steels in LBE is similar to that of steels in air/steam, with slight modification by dissolution and oxide dissociation at the liquid metal interface.     

Deposition of titanium nitride on Si(1 0 0) wafers using plasma focus

Titanium nitride thin films were deposited on Si(1 0 0) substrates by using a low energy (2.3 KJ) Mather-type plasma focus device. The composition of the deposited films was characterized by X-ray diffraction (XRD). The crystallite size has strong dependence on the numbers of focus shots. The crystallinity of TiN thin films is found to increase with increasing the number of focus shots. The effect of different number of focus shots on micro structural changes of thin films was characterized by Scanning Electron Microscope (SEM) and Atomic Force Microscope (AFM). SEM results showed net-like structure for film deposited for 15 numbers of shots, which are elongated grains of Si₃N₄ in amorphous form embedded into TiN crystals. The average surface roughness was calculated from AFM images of the thin films. These results indicated that the average surface roughness increased for films deposited with increased number of focus shots. The least crystallite size and roughness are observed for film deposited with 25 focus shots.     

Influence of post-annealing time on blistering evolution in Si 〈1 0 0〉 implanted with high-fluence H ions

The influence of post-annealing time on blistering characteristics induced by 5 × 10¹⁶ cm⁻² ion-implanted H in Si <1 0 0> was studied in terms of the formation and growth of blisters. Ion energies consisted of 40 and 100 keV. Post-annealing treatments were carried out using furnace annealing (FA) at 400 and 500 °C for a duration of 0.25-3 h in a nitrogen ambient. Raman scattering spectroscopy (RSS), optical microscopy (OM), atomic force microscopy (AFM), and secondary ion mass spectrometry (SIMS) were utilized to analyze the defect complex phases, the appearance of optically-detectable blisters and craters, the average depth of craters, and the hydrogen and oxygen depth profiles in the implanted layer, respectively. Furthermore, a characteristic time for the growth of optically-detectable blisters which was determined from the blister-covered fractions for various post-annealing times is proposed and used as a criterion to identify the effectiveness in the formation and growth of optically-detectable blisters. The results revealed that the characteristic time for the 400 °C-annealed specimens in the 40 keV implant is much shorter than it is in the 100 keV one. However, the characteristic time for the 500 °C-annealed specimens in the 40 keV implant is slightly longer than it is in the 100 keV implant. In addition, both the characteristic times for the 500 °C-annealed specimens are much shorter than those for the 400 °C ones. The above-mentioned phenomena hold true for craters.     

Channeling study of thermal decomposition of III-N compound semiconductors

GaN thermal stability is the limiting factor of the growth rate for epitaxially grown films and of the thermal annealing of defects. As a consequence, this issue has been extensively studied for more than one decade. There are, however, substantial differences in the reported kinetics and presumed mechanisms of decomposition, which are primarily related to the reactor design thus, reflecting the complexity of chemical reactions involved. We report here on the use of 1.7 MeV He-ion RBS/channeling for the study of thermal decomposition of MOVPE grown GaN and Al_xGa_1−xN (x = 0.05-0.5) layers. These layers with thickness of 320 nm were grown on sapphire substrates with 20 nm AlN nucleation layer. Prior to annealing samples were characterized by RBS/channeling, selected samples were also studied by SEM. Thermal treatment was performed in the MOVPE reactor in the temperature range 900-1200 °C in the N₂ atmosphere. RBS/channeling analysis provided data on layer thickness, composition and evolution of ingrown defects. GaN decomposition starts at 900 °C and results in the reduction of the layer thickness without observable changes of the film composition. The presence of large density of GaN hillocks on the surface was revealed by SEM after annealing at 1000-1050 °C. Remarkable stability of Al_xGa_1−xN was observed, this alloy remains unchanged upon annealing at 1200 °C/6 h even for x as low as 0.05.     

Effect of annealing on structure and hardness of oxygen-implanted layer on Ti6Al4V by plasma-based ion implantation

Ti6Al4V was treated by oxygen plasma-based ion implantation at the voltage pulses of −30 and −50 kV with a constant fluency of 0.6 × 10¹⁷ O/cm². After implantation, the annealing in vacuum was applied to the implanted samples to control phase structure of the implanted layer. The higher voltage implantation forms nano-size rutile in the implanted layer, but the subsequent annealing at 600 °C induces the resolution of the previous rutile. Although, the lower voltage implantation does not lead to rutile, the annealing can precipitate anatase and rutile in the implanted layer. The higher voltage implantation results in a higher hardness of the implanted layer. The annealing at 500 °C leads to an apparent increase in hardness of the implanted layer, but the annealing at 600 °C induces a rapid decrease in hardness.