Annealing Of Films Research Articles

Magnetization dynamics of amorphous and nanocomposite CoFeMnNbSiB films with the addition of excess cobalt and boron

We report on the magnetic and structural characterization of Co75.4Fe2.3Mn2.3Nb4Si2B14 (nominal) nanocomposite thin films and compositional derivatives formed by the co-sputtering of additional cobalt and boron followed by ex-situ vacuum annealing at 520 °C for different annealing times. The structural and compositional analyses of these samples were performed using transmission electron microscopy and atom probe tomography (APT). For the quasi-static magnetic measurements, vibrating sample magnetometry (VSM) was used and the magnetization dynamics was studied using a custom-built broadband ferromagnetic resonance (FMR) instrument with a frequency range of 1–65 GHz and fields up to 1.6 T. Two strong resonances were observed for the annealed nominal and B-added samples whereas a dominant single resonance was observed for all as-deposited and all annealed Co-added samples. This observation correlates with APT results where Mn-rich columnar structures were observed in the as-deposited nominal and Co-added annealed films. Whereas, a nearly equiaxed morphology of the crystalline phase was observed for annealed nominal and B-added films. Hence, FMR spectroscopy was found to be sensitive to the different phases present in the samples and differences in morphology. The quasi-static magnetic properties measured using VSM were not able to distinguish between the individual contributions. However, they provide important information regarding the overall magnetization. The VSM results suggested that short time annealing of the nominal composition results in better soft magnetic properties compared to the derivative compositions that were investigated in this study.

Electrochromic Displays via the Room-Temperature Electrochemical Oxidation of Nickel.

Electrochromism refers to the persistent and reversible change in color by applying an electric field. The phenomenon involves the insertion and extraction of electrons and ions within the active material. There is a keen interest in electrochromic (EC) materials, since they exhibit a wide range of potential applications. In recent years, transition-metal oxides have been widely investigated as EC materials due to their low power requirement, high coloration efficiency, and memory effect under an open-circuit condition. Nickel oxide (NiO), a p-type wide band gap semiconductor, exhibits attractive features such as a high color contrast ratio, good chemical stability, cost-effectiveness, and good compatibility with the cathodically coloring tungsten oxide. NiO thin films have been fabricated by various methods, but these are not cost-effective, scalable, or suitable for flexible applications. With the increasing demand for flexible and soft EC devices, it is essential to find routes to fabricate NiO thin films at lower temperatures. In this work, a NiO/Ni(OH)2-based thin EC layer on fluorine-doped tin oxide-coated glass is developed via an electroless nickel (EN) deposition route, followed by room-temperature electrochemical oxidation. The deposition time is optimized to control the film thickness. The EC performance is investigated in an aqueous alkaline electrolyte (1 M KOH) by means of cyclic voltammetry, chronoamperometry, and transmittance measurements. Both the as-deposited and annealed films, after electrochemical oxidation, exhibit excellent EC properties with an optical modulation of approximately 64% (at 550 nm) and good response times of approximately 3 s (coloration) and 14 s (bleaching). A 2 × 2 display obtained by patterning the EN deposition is also demonstrated as part of this work.

Electrochemical and energy storage properties of layer-by-layer assembled vanadium oxide electrode-based solid-state supercapacitor in n+-SnO2:F/n-V2O5 heterostructure device form using ionic liquid gel electrolyte

Vanadium oxide film electrodes synthesized by layer-by-layer assembly using sol–gel spin casting and variable 3 & 1 h annealing process over SnO2:F film coated glass substrates are investigated for supercapacitor energy storage using ionic liquid gel-electrolyte. The X-ray photoelectron spectroscopy analysis of V2p3/2 core-level and O1s peak show short-term (1 h) annealing forms vanadium as V2O5 alongside multivalent and oxygen deficient phases, whereas synthesis by 3-h annealing forms stochiometric V2O5 film. In stochiometric V2O5, capacitive contributions are dominantly from redox processes with peaks identified from V5+/V4+, and V4+/V3+ valance states change and partially from electrical double layer (EDL) yielding high specific capacitance of 346.9 Fg−1. Supercapacitor with V2O5 in mixed valence and oxygen defects phases shows enhanced EDL contribution alongside Faradaic yielding 316.2 Fg−1 specific capacitance. These mechanistic differences are analyzed for ionic diffusion limitations. The linear charge/discharge curves at 0.04–0.15 A/g current density show 85–90% Coulomb efficiency and steady energy density 6.8–5.5 Whkg−1 as specific power increases from 1.9 to 5.7 kWkg−1. Oxygen-deficient V2O5-based supercapacitor shows higher 19.2 Whkg−1 energy density declining to 8.9 Whkg−1 with specific power change from 1.1 to 4.6 kWkg−1. Raman spectra show during charge/discharge, the V5+- V3+ redox is mediated by V4.67+, V4.57+, and V3.33+ intermediate valence states. The pseudocapacitive energy storage depends on charge transfer across n+-SnO2:F/n-V2O5 heterostructure with different band alignments for stochiometric and oxygen deficient V2O5. The conduction band shift to the flat band position determines the potential range and extent of V5+ -V3+ redox reaction.

The enhancement of NIR transparency due to annealing and Mg-doping in [formula omitted] thin films

The effect of post-deposition annealing on the structural and optical properties of CuCrO2 and Mg-doped CuCrO2 thin films is reported. The prepared films were annealed in Helium atmosphere at 300 °C. X-ray diffraction analysis revealed the decreased crystallinity and Raman studies clarify the decreased copper defects at interstitials sites with annealing. The NIR wavelength transparency increases and the maximum transmission of 72% was obtained for Mg-doped annealed film of 211 nm thickness.

High mobility of (111)-oriented large-domain (>100 μm) poly-InSb on glass by rapid-thermal crystallization of sputter-deposited films

Rapid-thermal annealing (RTA) of InSb precursor films, deposited by sputtering using an Ar plasma at room temperature, has been investigated to achieve high carrier mobility on low-cost glass substrates. Although InSb films containing residual Ar (∼1%) were partially lost by evaporation during RTA, such evaporation during RTA is suppressed by reducing the residual Ar to ∼0.3%. The crystallinity of the films is significantly increased by RTA at temperatures above 400 °C. The electron mobilities of the films increase with increasing RTA temperature up to 490 °C, showing the maximum values (9000–10 000 cm2 V−1 s−1) at 490 °C, and then, the mobilities decrease at RTA temperatures above 490 °C. The mobilities of 9000–10 000 cm2 V−1 s−1 are obtained for films with a wide range of thickness (300–1000 nm) grown at 490 °C. Detailed analysis indicated that the high carrier mobilities are realized by preferentially (111)-oriented large crystal domains (diameter: >100 μm), obtained by the regrowth of randomly oriented small grains, together with a low barrier height (16 meV) at the sub-domain boundaries (twin boundaries) in the large domains. The RTA after the sputtering technique will facilitate high-performance InSb-based devices with low production costs.

Improving the Performance of Invert Perovskite Solar Cell Devices By a Multifunctional Ammonium Salt

In past years, halide perovskite solar cells (PSCs) have attracted much attention and are considered as the next-generation solar cells due to their excellent performance. Compared to the conventional structure, the inverted perovskite solar cell device has great potential in large-scale practical applications due to the low-temperature manufacturing process. However, the power conversion efficiency (PCE) is still lower than conventional structure devices, which is because of the high trap density in the surface and grain boundary of perovskite film. One kind of defect is the iodine vacancy caused by methylammonium iodide (MAI) volatilization during perovskite film annealing. I- could be oxidized into I2 and then volatilize out during the perovskite film annealing, the vacancy of I- could form trap states in the surface and grain boundary of the perovskite film. The surface traps induce many defects and increase the charge recombination rate in the inverted polycrystalline perovskite film, which causes PCE loss in the devices. Although lots of efforts are to improve the PCE of devices, perovskite solar cell device is still hard to practical applicate due to poor stability under light exposure conditions. Under light soaking especially UV light, perovskite film would degrade which means I3 - easily change to I2 and induce the lattice defects of perovskite film, which further influence the performance of PSCs. Herein, we present a strategy to suppress the I2 generation to decrease the trap density, reduce the charge recombination in perovskite film and further improve the performance of devices by an ammonium salt named tetrabutylammonium chloride (TBACl) modified. The PCE of devices increase from 18.52% to 20.36% after TBACl was modified, and TBACl also reduce the Voc loss in the perovskite solar cell devices. Furthermore, TBACl passivation enhances the light stability of devices and slows down PSCs degradation with UV light soaking. Because TBACl distributes in the surface and GBs of perovskite film that could absorb the UV light and decrease the effects on the perovskite layer. Benefiting from the influence of TBACl on perovskite solar cell devices, the devices could maintain over 90% with light soaking 120 h and UV light irradiation 450 min, respectively. However, the control devices only could maintain ~47% and ~51% of the initial PCE values under light exposure and UV light soaking conditions, respectively. Thus, we provide a low-cost, easy, and effective post-treatment strategy to enhance the device performance and improve the light stability of perovskite solar cell devices.

PbS and PbO Thin Films via E-Beam Evaporation: Morphology, Structure, and Electrical Properties.

Thin films of lead sulfide (PbS) are being extensively used for the fabrication of optoelectronic devices for commercial and military applications. In the present work, PbS films were fabricated onto a soda lime glass substrate by using an electron beam (e-beam) evaporation technique at a substrate temperature of 300 °C. Samples were annealed in an open atmosphere at a temperature range of 200–450 °C for 2 h. The deposited films were characterized for structural, optical, and electrical properties. Structural properties of PbS have been studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), and Rutherford backscattering spectrometry (RBS). The results of XRD showed that the PbS thin film was crystalline in nature at room temperature with cubic crystal structure (galena) and preferential (111) and orientation (022). The morphology of the thin films was studied by FESEM, which also showed uniform and continuous deposition without any peel-off and patches. EDS analysis was performed to confirm the presence of lead and sulfur in as-deposited and annealed films. The thickness of the PbS film was found to be 172 nm, which is slightly greater than the intended thickness of 150 nm, determined by RBS. Ultraviolet-Visible-Near-Infrared (UV-Vis-NIR) spectroscopy revealed the maximum transmittance of ~25% for as-deposited films, with an increase of 74% in annealed films. The band gap of PbS was found in the range of 2.12–2.78 eV for as-deposited and annealed films. Hall measurement confirmed the carriers are p-type in nature. Carrier concentration, mobility of the carriers, conductivity, and sheet resistance are directly determined by Hall-effect measurement. The as-deposited sample showed a conductivity of 5.45 × 10−4 S/m, which gradually reduced to 1.21 × 10−5 S/m due to the composite nature of films (lead sulfide along with lead oxide). Furthermore, the present work also reflects the control of properties by controlling the amount of PbO present in the PbS films which are suitable for various applications (such as IR sensors).

Deposition of tungsten oxide films by reactive magnetron sputtering on different substrates

Tungsten oxide films are deposited with the help of reactive magnetron sputtering in an argon/oxygen gas mixture. Films are deposited on different substrates, in particular, on soda lime glass, fluorine-doped tin oxide coated glass, silicon (Si), and quartz (SiO2). Thin films from three different discharge modes, in particular, high power impulse magnetron sputtering, midfrequency magnetron sputtering, and radiofrequency magnetron sputtering, are compared. Deposited films are characterized by x-ray diffraction, Raman spectroscopy, and spectroscopic ellipsometry. Composition, crystal structure, and optical properties of as-deposited and annealed films are found to depend on the deposition mode and on the substrate.

Unveiling the growth mode and structure relaxation of Polytetrafluoroethylene film by radio-frequency magnetron sputtering

Relying on radio-frequency (RF) magnetron sputtering, Polytetrafluoroethylene (PTFE) films with a series of thicknesses in the range from 80 to 2000 nm were prepared on silicon substrates. The surface morphology and roughness of the PTFE films were measured by atomic force microscope (AFM) technology at microscale. Results indicated that the PTFE film grew in an island pattern during sputtering, while the surface roughness of PTFE films was almost invariable throughout the sputtering process. Then the structure relaxation of PTFE film annealed at 100 °C for 15–480 min was investigated. Annealing treatment induced columnar protrusions on the PTFE surface, which was due to the flow and rearrangement of molecules. During annealing duration, the columnar structures could continuously rearrange and decompose, and therefore lowering film thickness from 2000 to 1110 nm with increasing annealing time. Due to molecule flow and redistribution of the annealed film, the columnar structures were formed on the surface, which resulted in the higher roughness. Finally, the effects of film thickness and annealing time on the hydrophobicity were also studied.

Mechanical, electrical properties and microstructures of combinatorial Ni-Mo-W alloy films

Nickel-molybdenum-tungsten (Ni-Mo-W) alloys have been suggested for applications of advanced micro-electro-mechanical systems (MEMS) in extreme environments due to their high strength, good electrical conductivity, and excellent thermal stability. In this work, we have carried out combinatorial experiments to reveal composition-dependent phase formation, physical properties, and thermal stability of Ni-Mo-W alloy films. Combinatorial synthesis through a magnetron sputtering process fabricated thin films with a composition range of Ni 56–92 Mo 6–38 W 0.5–7.5 . Structural analysis for the as-deposited combinatorial film revealed that a nanotwinned and strongly textured nano-columnar fcc structure was formed in the Ni-rich compositions, while solute content greater than 30% resulted in the formation of metallic glasses. The specimen exhibited very high hardness (8.8–12.5 GPa) and moderate electrical resistivity (85–135 μΩ ∙ cm), and both the properties were found to increase with solute concentration. Annealing of the combinatorial film at 600 ℃ for 1 h revealed that nanotwinned structure is thermally stable for high Ni concentrations. Metallic glasses with high solute concentration also exhibited high thermal stability and were not crystallized after annealing. Alloys with intermediate solute content experienced the transformation from the amorphous to fcc nanocrystalline phase with nanotwins. The annealed combinatorial film maintained high hardness and moderate electrical resistivity after annealing. • Composition-dependent phase formation and physical properties of Ni 56–92 Mo 6–38 W 0.5–7.5 alloy films were investigated. • A nanotwinned (NT) and nano-columnar fcc structure was formed in the Ni-rich compositions. • The solute content greater than 30% resulted in the formation of metallic glasses. • The specimen exhibited high hardness (8.8–12.5 GPa) and moderate electrical resistivity (85–135 μΩ · cm). • The NT structure with high Ni content and metallic glasses with high solute concentration were thermally stable.

Influence of annealing temperature on structural, electrical, and optical properties of 80 nm thick indium-doped tin oxide on borofloat glass

The influences of annealing temperature (473–573 K) on the crystal structure, linear/nonlinear optical parameters, and electrical characteristics of 80 nm thick indium-doped tin oxide (ITO) thin films are investigated. Thermal annealing induces the crystal structure in the ITO. As-prepared and annealed ITO have various morphologies depending on the annealing temperature, such as nanoplates and dendritic and spherical nanoparticles. As the substrate temperature increased up to 370 K, the electrical resistivity and sheet resistance of as-prepared ITO decreased dramatically and then slightly decreased as the substrate temperature further increased. The electrical conductivity and activation energy for the various processes were estimated. The reflectance (R) and transmittance (T) data are used to calculate the linear/nonlinear optical constants and parameters. The optical bandgap increased from 3.18 to 3.8 eV as the annealing temperature increased from room temperature to 573 K. Crystallinity is improved due to the annealing and hence an enhancement in the optical energy bandgap is achieved. Meanwhile, high-temperature annealing reversibly affected the optical bandgap energy of ITO thin films via reduction and oxidation reactions. Thermal annealing of ITO films improves crystal structure, visual transparency, and electrical conductivity, making it the preferred material for optoelectronic devices and solar cells.

Morpho-Structural Investigations and Carbon Nanoclustering Effects in Cr-Al-C Intermetallic Alloys.

Intermetallic Cr-Al-C thin films from the 211 class of MAX phases were fabricated via ion beam deposition and structural investigations were undertaken to obtain information about morpho-structural effects propelled by carbon excess in the stoichiometry of the films. In order to promote the occurrence of the Cr2AlC MAX phase, the stoichiometric thin films were subsequently annealed at two temperature values: 650 °C and 700 °C in UHV conditions for 30 min. The morpho-structural effects in both as-deposited and annealed films were monitored using scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. XRD analysis showed that the as-deposited sample was almost completely crystallized in the hexagonal Cr2AlC structure, with a remaining amorphous fraction of about 17%, most probably rich in carbon. Raman analysis allowed the identification of three spectral regions, two of them encompassing the Raman optical modes belonging to the Cr2AlC 211 MAX phase, while the third one gave strong evidence of highly intense and large D- and G-bands of carbon. Structural parameters such as the crystal lattice parameters as well as the volume of the crystal unit cell were found to decrease upon annealing; this decrease is attributed to the grain growth. The average crystallite dimension was proven to increase after annealing, while the lattice micro-strain lowered to approximately 63% in the annealed thin film compared to the as-deposited one. Well-formed and intense Raman peaks attributed to D- and G-bands of carbon were also observed and, corroborated with the structural data, seemed to indicate an overall increased level of crystal ordering as well as potential carbon nanoclustering after thermal treatments with thin Cr2AlC films. This observed phenomenon concords with previously documented reports on ab initio modelling of possible Cr2AlC structures with carbon excess.

Annealing Effects on SnO2 Thin Film for H2 Gas Sensing.

Hydrogen (H2) is attracting attention as a renewable energy source in various fields. However, H2 has a potential danger that it can easily cause a backfire or explosion owing to minor external factors. Therefore, H2 gas monitoring is significant, particularly near the lower explosive limit. Herein, tin dioxide (SnO2) thin films were annealed at different times. The as-obtained thin films were used as sensing materials for H2 gas. Here, the performance of the SnO2 thin film sensor was studied to understand the effect of annealing and operating temperature conditions of gas sensors to further improve their performance. The gas sensing properties exhibited by the 3-h annealed SnO2 thin film showed the highest response compared to the unannealed SnO2 thin film by approximately 1.5 times. The as-deposited SnO2 thin film showed a high response and fast response time to 5% H2 gas at 300 °C of 257.34% and 3 s, respectively.

Effect of Zr contents and covering Ag layer on microstructure and SERS properties of Cu nanoparticles / Cu-Mo-Zr alloy films on flexible substrates

Cu-Mo-Zr alloy films with different Zr contents were prepared by magnetron sputtering. The microstructure and SERS properties of alloy films were characterized by SEM, TEM, XRD and Raman spectroscopy. A large number of Cu nanoparticles are formed spontaneously on the surface of alloy film after annealing. Moreover, the number, size and particle spacing of Cu nanoparticles are found to be highly sensitive to annealing temperature, annealing time, Zr content and film thickness. Results of the local electric field between Cu particles on the alloy films surface simulated by FDTD reveal that larger particles and smaller spacing can produce stronger local electric fields. Furthermore, a 10 nm Ag layer coating on the alloy film has a significant effect on the size, spacing of Cu particles, and the synergistic enhancement between Ag layer and Cu nanoparticle can significantly increase the local electric field thereby improving the SERS performance of Cu-Mo-Zr alloy films. The Raman signal of 10-13 mol/L Rhodamine 6G solution can be detected by using Ag layer/Cu-30 at% Mo-22.9 at% Zr alloy films as SERS substrates. The present study provides a method for preparing SERS substrates with low cost, high sensitivity and excellent repeatability.

Modulating preferred crystal orientation for efficient and stable perovskite solar cells—From progress to perspectives

AbstractThe perovskite solar cell (PSC) has been recognized as a promising candidate for the next generation of photovoltaics due to its excellent power conversion efficiency (PCE), potential low cost and straightforward solution preparation processes. With efforts around the world, the PCE of PSCs has reached 25.7%. As the perovskite film is the most important part of a PSC, its quality dramatically affects the efficiency and stability of the PSC. Numerous works have focused on controlling crystallization to realize oriented growth of perovskite films. Particularly, considering the photoelectric anisotropy of perovskite materials, it is very meaningful to investigate the relationship between preferred crystal orientation and device efficiency and stability. This review highlights various approaches for realizing preferred crystal orientation of polycrystalline perovskite films, including optimizing the perovskite precursor solution and film annealing process, additive engineering, and interface engineering. Furthermore, the key factors affecting oriented crystal growth are carefully discussed, which provides effective guidance to obtain highly‐oriented perovskite films for highly efficient and stable PSCs.image

Electronic structure, magnetic, transport, and optical properties of bulk and film Fe2CrGa Heusler alloy. Effect of structural disorder

Magnetic, transport, and optical properties of thin film and bulk Fe2CrGa alloy samples with different types of atomic order were experimentally investigated. The obtained data were discussed in terms of first-principle calculation results made for the stoichiometric Fe2CrGa alloy with different types of atomic order and disorder. An ultimate atomic disorder in Fe2CrGa alloy films was obtained by employing vapor quenching deposition onto substrates cooled by liquid nitrogen. Annealing of as-quenched Fe2CrGa alloy films causes their crystallization at Tann=750 K with the formation of the disordered A2-type structure, which is accompanied by the rapid growth of alloy resistivity in a narrow temperature range, formation of multi-phase magnetic structure and changes in the optical properties. Crystalline bulk and film Fe2CrGa alloy samples show the dome-like temperature dependence of the resistivity with maximums near their Curie temperatures and explained in terms of competition between negative with temperature contribution from highly resistive media and positive from the electron–magnon scattering. The big resemblance between calculated for Hg2CuTi type of atomic order and experimental optical conductivity spectra for annealed Fe2CrGa alloy films proves that Hg2CuTi type of atomic order is more probable for this alloy.

Microstructure evolution and highly sensitive surface enhanced Raman scattering properties of self-formation dual-scale Ag nanoparticles/ Ag-Zr alloy film

• Simple method was proposed to prepare monodisperse Ag particles/Ag-Zr films. • Ag nanoparticles (NPs) directly formed on the surface of as-deposited Ag-Zr films. • Size, number and nanogap of Ag NPs are sensitive to Ag-Zr film thickness. • Ag NP/Ag-Zr granular film displays effective Raman enhanced properties. Ag-22%Zr alloy films with different thicknesses were fabricated on flexible polyimide substrate by co-sputtering method. It is interested in finding that a lot of Ag nanoparticles are spontaneously formed on the as-deposited Ag-Zr films at room temperature. The phase, crystal structure, particle number and size, and surface enhanced Raman scattering (SERS) properties of as-deposited and annealed Ag-Zr alloy films were characterized by X-ray diffraction, high resolution transmission electron microscope, field emission scanning electron microscope and Raman spectrometer, respectively. Results show that Zr grains dispersed around Ag grains and had a coherent growth relation with Ag grains in the alloy film. Dual scale Ag nanoparticles were formed on the annealed Ag-Zr alloy films without template. An intense SERS effect was obtained by covering the Ag layer on the Ag-Zr alloy films. The SERS substrate showed good repeatability and revealed high sensitivity of enhancement factor with the detection limit concentration of Rhodamine 6G as low as 5 × 10-15 mol/L. It was demonstrated that the nanogaps between Ag nanoparticles behaved as hot spots, and thus enhanced local electromagnetic fields substantially. Furthermore, densely and uniformly distributed Ag nanoparticles enlarged the surface roughness and the surface area, resulting in further enhanced Raman signals.

Insight into the photoinduced phenomena in ternary Ge-Sb-Se sputtered thin films

The kinetics of photoinduced changes, namely, photobleaching and photodarkening in sputtered ternary Ge 29 Sb 8 Se 63 thin films, was studied. The study of time evolution of the absorption coefficient Δ α ( t ) upon room-temperature near-bandgap irradiation revealed several types of photoinduced effects. The as-deposited films exhibited a fast photodarkening followed by a dominative photobleaching process. Annealed thin films were found to undergo photodarkening only. The local structure studied by Raman scattering spectroscopy showed significant structural changes upon thermal annealing, which are presumably responsible for a transition from the photobleaching observed in as-deposited and reversible photodarkening in annealed thin films. Moreover, a transient photodarkening process was observed in both as-deposited and annealed thin films. The influence of the initial film thickness and laser optical intensity on the kinetics of photoinduced changes is discussed.

Initial nucleation of metastable γ-Ga2O3 during sub-millisecond thermal anneals of amorphous Ga2O3

Beta-phase gallium oxide (β-Ga2O3) is a promising semiconductor for high frequency, high temperature, and high voltage applications. In addition to the β-phase, numerous other polymorphs exist and understanding the competition between phases is critical to control practical devices. The phase formation sequence of Ga2O3, starting from amorphous thin films, was determined using lateral-gradient laser spike annealing at peak temperatures of 500–1400 °C on 400 μs to 10 ms timescales, with transformations characterized by optical microscopy, x-ray diffraction, and transmission electron microscopy (TEM). The resulting phase processing map showed the γ-phase, a defect-spinel structure, first nucleating under all annealing times for temperatures from 650 to 800 °C. The cross-sectional TEM at the onset of the γ-phase formation showed nucleation near the film center with no evidence of heterogeneous nucleation at the interfaces. For temperatures above 850 °C, the thermodynamically stable β-phase was observed. For anneals of 1–4 ms and temperatures below 1200 °C, small randomly oriented grains were observed. Large grains were observed for anneals below 1 ms and above 1200 °C, with anneals above 4 ms and 1200 °C resulting in textured films. The formation of the γ-phase prior to β-phase, coupled with the observed grain structure, suggests that the γ-phase is kinetically preferred during thermal annealing of amorphous films, with β-phase subsequently forming by nucleation at higher temperatures. The low surface energy of the γ-phase implied by these results suggests an explanation for the widely observed γ-phase inclusions in β-phase Ga2O3 films grown by a variety of synthesis methods.

On thermal stability and oxidation behavior of metastable W–Zr thin-film alloys

The thermal stability and oxidation behavior of metastable W–Zr thin-film alloys with up to 83 at.% Zr were thoroughly investigated with a focus on the effect of gradual substitution of Zr for W. The films were prepared by dc magnetron co-sputtering of W and Zr targets in argon on unheated and unbiased substrates. The experiments showed that a supersaturated α-W(Zr) solid solution structure of as-deposited W-rich films with up to 19 at.% Zr is highly thermally stable up to 1200 °C in argon and the thermal stability of the W–Zr thin-film metallic glasses (33–83 at.% Zr) decreases with increasing Zr content. Nevertheless, the thermal stability of the W–Zr thin-film metallic glass with 33 at.% Zr reaches 1420 °C, which is very high value for binary metallic glass. The annealing of W-rich films (0–24 at.% Zr) in air leads to the formation of a protective surface oxide layer, which serves as a more effective oxygen diffusion barrier due to an increasing packing factor and amorphization with Zr addition. On the other hand, no protective surface oxide layer is grown during the annealing in air in the case of the W–Zr thin-film metallic glasses and the oxidation leads to the formation of compact, homogeneously oxidized substoichiometric W–Zr–O films with an amorphous structure and enhanced mechanical properties before reaching the final mass gain.