Film Growth Research Articles

Growth and characterization of n-type Ga2O3 films on sapphire substrates by APMOVPE

Growth and characterization of n-type Ga2O3 films on sapphire substrates by APMOVPE

Characterization of thin oxide layers formed by Ti-Nb Alloy anodization

Ti-Nb alloys are gaining more prominence in the industrial and scientific environment due to their high biocompatibility, mechanical strength/weight ratio, and exceptional corrosion resistance compared to other metallic materials. Metals exhibiting this passivation characteristic are known as metal valves and may exhibit semiconductive or insulating oxides. Controlling the growth of distinct thickness layer films is possible through tunning anodization conditions. In this work, a Ti-Nb binary system is anodized, and the grown oxide layer is comprehensively characterized using ellipsometry based on its optical properties and thickness at different applied potentials. Confocal Microscopy assessed their surface roughness, and SEM/EDS probed the surface material's elemental composition. CF-LIBS successfully confirmed the 70/30 composition of the Ti-Nb alloy. Raman spectra have detected the presence of amorphous TiO2 and Nb2O5 at potentials higher than 80V, 100V, and 120V. Finally, a linear dependence of the oxide thickness with the applied potential was observed.

Conventional epitaxy of NiO thin films on muscovite mica and c-Al2O3 substrates

Fiber-textured and epitaxial NiO thin films were deposited on Si(100), c-Al2O3, and muscovite mica(001) substrates using reactive magnetron sputtering at substrate temperatures of 300°C and 400°C, to investigate the effect of film thickness and substrate temperature on epitaxial growth of NiO films. The as-deposited films exhibited a face-centered cubic structure with a larger lattice constant, attributed to strain induced during the sputtering process. With an increase in substrate temperature to 400°C, the d-spacing decreased due to strain release, approaching the NiO bulk value for the thickest film. The NiO film grown on Si(100) displayed fiber texture. On c-plane sapphire, NiO thin films exhibited twin domains and three-fold symmetry, consistent with expected crystallographic orientation relationship for NaCl-structured materials on sapphire:(111)NiO∥(0001)Al2O3and[01¯1]NiO∥[1¯010]Al2O3, [011¯]NiO∥[101¯0]Al2O3. On muscovite mica(001) substrates, the observed epitaxial shows that the mechanism is conventional epitaxy, rather than van der Waals epitaxy, consistent with the epitaxial growth of the non-layered non-van-der-Waals compound NiO. The epitaxial relationship was identified as of (111)NiO∥(001)Mica and [01¯1]NiO∥[010]Mica, [011¯]NiO∥[01¯0]Mica.

Electrochemically assisted preparation of defect-rich Co3O4 electrocatalysts in a water-modified deep eutectic solvent for enhanced oxygen evolution in acid

Co3O4-based electrode materials exhibit great potential for utilization as efficient catalysts for the oxygen evolution reaction (OER), especially in acidic media. However, enhancing their catalytic stability remains a crucial challenge. Herein, we present a facile electrochemical deposition approach coupled with calcination treatment to achieve in-situ growth of active Co3O4 films from a deep eutectic solvent with water as the modifier. The incorporation of water optimizes the structure of fabricated Co3O4 by increasing oxygen vacancies and elevating the Co2+/Co3+ ratio, enabling it to sustain the OER in 0.5 M H2SO4. Impressively, the catalyst grown on Pt/Ti substrate exhibits stable operation over 125 h at 10 mA cm−2. Attenuated total reflection-fourier transform infrared (ATR-FTIR) spectroscopy reveals that OER on the defect-rich Co3O4 catalyst occurs through both lattice oxygen mediated mechanism (LOM) and adsorption evolution mechanism (AEM).

Influence of Substrate Polarity on Thermal Stability, Grain Growth and Atomic Interface Structure of Au Thin Films on ZnO Surfaces

Influence of Substrate Polarity on Thermal Stability, Grain Growth and Atomic Interface Structure of Au Thin Films on ZnO Surfaces

Development and Diagnostic Study of the RF nitrogen Atom Source

With the development of thin film technology, particularly the increasing demand for research on group III nitride materials, the need for N ions has significantly increased. A wider and more efficient RF nitrogen atom source specifically designed for nitride film growth has been developed. To evaluate the nitrogen atom density from the RF nitrogen source, a global model of RF nitrogen gas discharge plasma was created. This model was calibrated by measuring the emission spectrum of RF nitrogen gas discharge, and the relationships between nitrogen atom density and actual working pressure, power, and discharge chamber size were determined. It was found that the nitrogen atom density increases with increasing power and initially increases with pressure before decreasing. Finally, the nitrogen atom density was determined, achieving an 18% nitrogen atom dissociation rate and a nitrogen atom density of 5×1012/cm³ at an RF power of 400 W. This density is significantly higher than that of nitrogen ions, indicating that this is a nitrogen atom source with high purity.

Growth and Structure of Ultrathin Iron Silicate and Iron Germanate Films

Growth and Structure of Ultrathin Iron Silicate and Iron Germanate Films

In Situ X‐Ray Photoelectron Spectroscopy Study of Atomic Layer Deposited Cerium Oxide on SiO2: Substrate Influence on the Reaction Mechanism During the Early Stages of Growth

AbstractThermal atomic layer deposition (ALD) of cerium oxide using commercial Ce(thd)4 precursor and O3 on SiO2 substrates is studied employing in‐situ X‐ray photoelectron spectroscopy (XPS). The system presents a complex growth behavior determined by the change in the reaction mechanism when the precursor interacts with the substrate or the cerium oxide surface. During the first growth stage, non‐ALD side reactions promoted by the substrate affect the growth per cycle, the amount of carbon residue on the surface, and the oxidation degree of cerium oxide. On the contrary, the second growth stage is characterized by a constant growth per cycle in good agreement with the literature, low carbon residues, and almost fully oxidized cerium oxide films. This distinction between two growth regimes is not unique to the CeOx/SiO2 system but can be generalized to other metal oxide substrates. Furthermore, the film growth deviates from the ideal layer‐by‐layer mode, forming micrometric inhomogeneous and defective flakes that eventually coalesce for deposit thicknesses above 10 nm. The ALD‐cerium oxide films present less order and a higher density of defects than films grown by physical vapor deposition techniques, likely affecting their reactivity in oxidizing and reducing conditions.

On prognosis of mismatch-induced stress during growth of films in the framework of magnetron sputtering

On prognosis of mismatch-induced stress during growth of films in the framework of magnetron sputtering

Small Molecular Dibenzo[b,d]thiophene-Based Hole Transport Materials for Tin-Lead Perovskite Solar Cell.

The most commonly used hole transport material (HTM) in tin-lead (Sn-Pb) perovskite solar cells (PSCs) is the aqueous poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), and its inherent hygroscopic and acidic features greatly limit the power conversion efficiency (PCE) and stability of PSCs. Concerning this, by selecting dibenzo[b,d]thiophene 5,5-dioxide (DBTDO) as the core and engineering the donor units, 4-methoxy-N-(4-methoxyphenyl)-N-phenylaniline (TPA) and N1-(4-(bis(4-methoxyphenyl)amino)phenyl)-N4,N4-bis(4-methoxyphenyl)benzene-1,4-diamine (DTPA) as peripheral groups, two alternative HTMs are reported. Among them, the HTM TPA-DBTDO-DTPA can form a smoother film, which is conducive to the growth of dense perovskite film on it and shows the most suitable energy level. Meanwhile, the sulfonyl unit can passivate the buried defects of perovskite and improve the open-circuit voltage (VOC) of Sn-Pb mixed PSCs. Correspondingly, the TPA-DBTDO-DTPA-based PSC achieves a champion power conversion efficiency of 22.6% and maintains 75.9% of the initial PCE after aging 1000 h in a nitrogen (N2) environment, which fully outperforms the PEDOT:PSS-based control device.

On Decreasing of Mismatch-Induced Stress During Growth of Films During Magnetron Sputtering

In this paper we analyzed mass transfer during the growth of epitaxial layers during magnetron sputtering. During the analysis we obtained modifications of properties of films with variation of several parameters. We analyzed possibility to decrease mismatch -induced stress on the considered films during their growth. An analytical approach for analyzing mass transfer was introduced, which makes it possible to take into account the nonlinearity of processes, as well as changes in parameters in space and time.

Epitaxial Thin Film Growth on Recycled SrTiO3 Substrates Toward Sustainable Processing of Complex Oxides.

Complex oxide thin films cover a range of physical properties and multifunctionalities that are critical for logic, memory, and optical devices. Typically, the high-quality epitaxial growth of these complex oxide thin films requires single crystalline oxide substrates such as SrTiO3 (STO), MgO, LaAlO3, a-Al2O3, and many others. Recent successes in transferring these complex oxides as free-standing films not only offer great opportunities in integrating complex oxides on other devices, but also present enormous opportunities in recycling the deposited substrates after transfer for cost-effective and sustainable processing of complex oxide thin films. In this work, the surface modification effects introduced on the recycled STO are investigated, and their impacts on the microstructure and properties of subsequently grown epitaxial oxide thin films are assessed and compared with those grown on the pristine substrates. Detailed analyses using high-resolution scanning transmission electron microscopy and geometric phase analysis demonstrate distinct strain states on the surfaces of the recycled STO versus the pristine substrates, suggesting a pre-strain state in the recycled STO substrates due to the previous deposition layer. These findings offer opportunities in growing highly mismatched oxide films on the recycled STO substrates with enhanced physical properties. Specifically, yttrium iron garnet (Y3Fe5O12) films grown on recycled STO present different ferromagnetic responses compared to that on the pristine substrates, underscoring the effects of surface modification. The study demonstrates the feasibility of reuse and redeposition using recycled substrates. Via careful handling and preparation, high-quality epitaxial thin films can be grown on recycled substrates with comparable or even better structural and physical properties toward sustainable process of complex oxide devices.

200 cm2/Vs electron mobility and controlled low 1015 cm−3 Si doping in (010) β -Ga2O3 epitaxial drift layers

We report on metalorganic chemical vapor deposition (MOCVD) growth of controllably Si-doped 4.5 μm thick β-Ga2O3 films with electron concentrations in the 1015 cm−3 range and record-high room temperature Hall electron mobilities of up to 200 cm2/Vs, reaching the predicted theoretical maximum room temperature phonon scattering-limited mobility value for β-Ga2O3. Growth of the homoepitaxial films was performed on Fe-doped (010) β-Ga2O3 substrates at a growth rate of 1.9 μm/h using TEGa as the Gallium precursor. To probe the background electron concentration, an unintentionally doped film was grown with a Hall concentration of 3.43 × 1015 cm−3 and Hall mobility of 196 cm2/Vs. Growth of intentionally Si-doped films was accomplished by fixing all growth conditions and varying only the silane flow, with controllable Hall electron concentrations ranging from 4.38 × 1015 to 8.30 × 1015 cm−3 and exceptional Hall mobilities ranging from 194 to 200 cm2/Vs demonstrated. C-V measurements showed a flat charge profile with the ND+–NA− values correlating well with the Hall-measured electron concentration in the films. SIMS measurements showed the silicon atomic concentration matched the Hall electron concentration with carbon and hydrogen below detection limit in the films. The Hall, C-V, and SIMS data indicate the growth of high-quality 4.5 μm thick β-Ga2O3 films and controllable doping into the mid 1015 cm−3 range. These results demonstrate MOCVD growth of electronics grade record-high mobility, low carrier density, and thick β-Ga2O3 drift layers for next-generation vertical β-Ga2O3 power devices.

High-Temperature Steam Oxidation and Surface Microstructure Evolution of Fe13Cr6Al(1–4)Mo0.15Y Alloys

The current study investigated the microstructure evolution and anti-corrosion behavior of low Y doping alloys of Fe13Cr6Al(1–4)Mo0.15Y subjected to high-temperature steam (800 °C to 1300 °C). The results indicate that steam oxidation induces the growth of high-quality oxidation film that is thermodynamically driven, with rapid increases in the thickness from 800 °C to 1300 °C without film convolution and spallation. The film convolution and spallation were successfully suppressed through on-site formation of the high-temperature stable ternary crystalline phase (Y2Mo3O12) and decreasing of the thickness of α-Al2O3 oxidation film during the fabrication and oxidation scenario. The on-site steam oxidation rate has been significantly suppressed, with lower weight gain and less oxidizing film convolution than monolithic FeCrAlMo alloy, through the addition of a low concentration of Y.

Influence of composition and temperature on oxide film formation for Fe-Cr-Ni alloys in simulated PWR primary water

ABSTRACT The growth of oxide films on Fe-Cr-Ni alloys in simulated pressurized water reactor (PWR) primary system environments was investigated, with focus on the influence of alloy composition and temperature. Oxide film thicknesses were measured for 90 specimens prepared from compact tension (CT) test pieces. Cross-sectional observations were also conducted on coupon specimens using scanning transmission electron microscopy (STEM). The behavior of Ni-based alloys, specifically Alloy 600, and Fe-based alloys, specifically Type 316 stainless steel, were compared. Ni-based alloys exhibit superior corrosion resistance due to slower Fe diffusion kinetics compared to Fe-based alloys, leading to the formation of a nickel-enriched protective layer at the metal-oxide interface. The oxidation rates of Ni-based alloys follow an Arrhenius-type temperature dependence. In contrast, Fe-based alloys show a more complex temperature-dependent behavior, with reduced oxidation rates at higher temperatures that are likely due to changes in oxide dissolution. Higher chromium concentrations in both alloy types improve the protectiveness of the oxide film towards corrosion by forming a more compact inner oxide layer. The study identifies three primary factors influencing oxide film growth: reactions at the metal-oxide interface, diffusion within the oxide layer, and processes at the oxide-solution interface. The relative significance of these processes varies depending on the alloy composition and temperature.

Dynamic Response of a Rotor Supported on Hybrid Bearings in Air, Water, and Liquid Nitrogen: Measurements and Comparisons to Predictions

Abstract Modern liquid rocket engine turbopumps implement hybrid bearings, which combine hydrostatic and hydrodynamic fluid film principles, in compact and lightweight units known for their superior reusability, durability, and reliability. This study aims to provide extensive and reliable test data for the purpose of anchoring and benchmarking predictive tools for these bearings. This paper provides comprehensive dynamic response measurements of a rotor weighing 10.40 kg and approximately 60 mm in diameter at the bearing locations. The test rotor is supported on two hybrid journal bearings with a bearing length to bearing diameter ratio of approximately 0.42 and a bearing radial clearance to rotor radius ratio of around 0.0017. The bearings are tested with air, water, and liquid nitrogen, serving as surrogate test fluids for common propellants in liquid rocket engines. Rotor run-up and speed coast-down tests are conducted to measure shaft motion responses. The results clearly demonstrate that the rotordynamic characteristics of the test rotor supported on the hybrid journal bearings largely rely on properties of the test fluids and their feeding conditions. Notably, when air is pressurized into the test bearings, the shaft motion responses differ markedly from those observed with water and liquid nitrogen, primarily due to significantly lower stiffness and damping coefficients. Furthermore, rotor speed coast-down tests for each test fluid exhibit notable differences in coast-down speed over time characteristics, depending on the test fluid properties. The predicted rotor imbalance responses exhibit excellent correlation with the measurement data. The steady increase of demand and growth of the fluid film bearing technology for reusable rocket engines require accurate bearing design tools, the extensive component testing, and the implementation of the technology. The validated and developed bearing predictive models from previous research demonstrate well the characteristics of bearings under various operating fluids conditions. The findings and database presented in this work contribute not only to comprehending the performance of hybrid bearings but also to understanding and enhancing the dynamic characteristics of rotor systems supported on hybrid bearings.

Constructing Morphotropic Phase Boundary in Epitaxial BiFeO3 on SrTiO3 by Suppression of Strain Relaxation

AbstractThe strain‐driven morphotropic boundary in BiFeO3 can enhance the piezoelectric properties. However, the tetragonal phase has generally been observed in BiFeO3 films grown on substrates with intense compressive strain (more than −4.5%) within a limited thickness range (<300 nm) due to significant thickness‐dependent strain relaxation during film growth at high deposition temperatures. This work proposes suppressing thickness‐dependent strain relaxation by decreasing growth temperature. Utilizing a hydrothermal method, the growth temperature of epitaxial BiFeO3 films decreases to 200 °C. As a result, the tetragonal phase is observed in 600‐nm‐thick BiFeO3 film on (001) SrTiO3 substrates (strain equals only −1.5%), accompanied by the monoclinic phase. This SrTiO3‐available morphotropic phase boundary significantly enhances the piezoelectric response in epitaxial BiFeO3 film. Ex situ and in situ measurements, theoretical calculations, and simulation confirm that the SrTiO3‐available morphotropic phase boundary originates from the suppressed strain relaxation. Furthermore, a critical temperature (400 °C), below which the tetragonal phase can be maintained, is identified to offer an applicable strategy for extending strain‐driven morphotropic phase boundary for high‐performance piezoelectric films.

Template-Assisted Growth of High-Quality α-Phase FAPbI3 Crystals in Perovskite Solar Cells Using Thiol-Functionalized MoS2 Nanosheets.

Formamidinium lead iodide (FAPI) has gained attention for hybrid perovskite solar cell (PSC) applications due to its enhanced stability and narrow bandgap. However, a significant challenge remains in inducing and stabilizing the elusive perovskite "black phase"─photoactive cubic α-FAPI─as the relatively bulky FA+ cations tend to favor the thermodynamically stable nonphotoactive "yellow phase". In this study, we present a templated growth strategy employing thiol-functionalized MoS2 nanosheets as templates. By introduction of 3-mercaptopropionic acid (MPA)-functionalized MoS2 as a growth template, precise control over crystal formation was achieved, favoring the growth of high-quality α-FAPI films. These advanced templated films exhibited substantial improvements in charge transport properties, efficient light absorption, and enhanced charge extraction. As a result, the PSCs achieved a significantly enhanced power conversion efficiency (PCE) compared to the nontemplated control device, increasing from 20.6 to 22.5%. The MoS2-incorporated device also demonstrated excellent shelf stability, maintaining 91% of the initial PCE even after 1600 h of storage without device encapsulation.

Out‐Diffusion and Uphill‐Diffusion of Mg in Czochralski‐Grown (100) β‐Ga2O3 Under High‐Temperature Annealing and Its Influence on Lateral MOSFET Devices

AbstractIn this work, the out‐diffusion and uphill‐diffusion of Mg inside (100) β‐Ga2O3 epilayers and substrates are reported. The Mg accumulates toward the (100) surface upon annealing under an oxidizing environment, whereas the concentration profile changes with annealing temperatures and durations. Furthermore, the out‐diffusion of Mg from the substrate into the epilayer is observed at temperatures above 800 °C, which continues during the film growth. The substitutional‐interstitial‐diffusion (SID) mechanism is suggested to be the driving mechanism for the former, and the latter is related to the diffusion of mobile Mg interstitials. The accumulation profile of Mg can be used to identify the interface between the epilayer and the substrate. Furthermore, significant differences in device performance are observed for power transistors fabricated on annealed and non‐annealed epitaxial β‐Ga2O3 wafers. Increased breakdown voltages of annealed samples are attributed to the Mg diffusion into the first few nanometers of the epitaxial layer close to the interface to the semi‐insulating substrate, leading to compensation of residual dopants (donors) in that region.

Bridging to Commercialization: Record-Breaking of Ultra-Large and Superior Cyclic Stability Tungsten Oxide Electrochromic Smart Window.

Electrochromic smart windows (ESWs) can significantly reduce energy consumption in buildings, but their cost-effective, large-scale production remains a challenge. In this study, the instability of black phosphorus is leveraged to induce the growth of the tungsten oxide film through its decomposition process, inspired by the 2D material-assisted in situ growth (TAIG) method. This approach results in the preparation of large-scale, high-performance WO3-x·nH2O (n<2) films. Characterization techniques and DFT calculations confirm efficient regulation ofstructural water and oxygen vacancies during TAIG preparation. The WO3-x·nH2O films exhibit excellent electrochromic (EC) properties, including high transmittance modulation (74.2%@1100nm), fast switching time (tc=5.5s, tb=3.8s), high coloration efficiency (124.7cm2C-1), and superior cyclic stability (transmittance modulation retained 94.7% after 20000 cycles). Ultra-largeWO3-x·nH2O film are prepared via a simple immersion process, and fabricated into a large-area ESW under facile laboratory conditions, demonstrating the economic and practical feasibility of this approach in industrial-scale production. Operated by the intelligent control circuit, the ESWexhibits remarkable EC properties and cyclic stability This research represents a milestone in improving the performance and industrial-scale production of ESWs, bridging the gap to the commercialization of EC technology.