Metalorganic Deposition Research Articles

X-Rays Diffraction Study of InGaN/GaN Heterostructures Grown by MOCVD Technique at Different Temperatures

Indium gallium nitride / gallium nitride (InGaN/GaN) heterostructures were grown by using metal organic vapor deposition technique with four different growth temperatures (740 °C, 760 °C, 780 °C, and 800 °C). The structural properties and crystalline quality were investigated using high resolution X-ray diffraction (HRXRD) technique. XRD ω-2θ scan mode at GaN (002) diffraction plane was performed to assess the film’s quality. Through the simulation fitting, the indium composition and the thickness of the thin films were obtained. From the observation, an increase in the growth temperature resulted in higher intensity and smaller full-width at half maximum value of the InGaN (002) diffraction peak, which indicated improvement to the crystalline quality of the InGaN/GaN heterostructure. Moreover, the indium composition of the InGaN epilayer was found to decrease with an increase of the growth temperature due to the thermal decomposition of In-N bond and its re-evaporation from the growing surfaces.

Electrocatalytic Properties of Co3O4 Prepared on Carbon Fibers by Thermal Metal-Organic Deposition for the Oxygen Evolution Reaction in Alkaline Water Electrolysis.

Cobalt oxide (Co3O4) serves as a promising electrocatalyst for oxygen evolution reactions (OER) in water-electrolytic hydrogen production. For more practical applications, advances in dry-deposition processes for the high-throughput fabrication of such Co3O4 electrocatalysts are needed. In this work, a thermal metal-organic deposition (MOD) technique is developed to form Co3O4 deposits on microscale-diameter carbon fibers constituting a carbon fiber paper (CFP) substrate for high-efficiency OER electrocatalyst applications. The Co3O4 electrocatalysts are deposited while uniformly covering the surface of individual carbon fibers in the reaction temperature range from 400 to 800 °C under an ambient Ar atmosphere. It is found that the microstructure of deposits is dependent on the reaction temperature. The Co3O4 electrocatalysts prepared at 500 °C and over exhibit values of 355-384 mV in overpotential (η10) required to reach a current density of 10 mA cm-2 and 70-79 mV dec-1 in Tafel slope, measured in 1 M KOH aqueous solution. As a result, it is highlighted that the improved crystallinity of the Co3O4 electrocatalyst with the increased reaction temperature leads to an enhancement in electrode-level OER activity with the high electrochemically active surface area (ECSA), low charge transfer resistance (Rct), and low η10, due to the enhanced electrical conductivity. On the other hand, it is found that the inherent catalytic activity of the surface sites of the Co3O4, represented by the turnover frequency (TOF), decreases with reaction temperature due to the high-temperature sintering effect. This work provides the groundwork for the high-throughput fabrication and rational design of high-performance electrocatalysts.

Engineering the NASICON electrolyte/Na anode interface with amorphous bismuth oxide for sodium batteries.

Amorphous BiOx, prepared on the surface of NASICON electrolyte by the photochemical metal-organic deposition method, can substantially improve the interfacial properties at the anode side. The Na symmetric cell delivers a critical current density of 1.2 mA cm-2 and cycles stably at 0.5 mA cm-2 for 1000 h at 30 °C.

(Invited) Towards the Development of High-Performance Crystalline Rutile Iridium Dioxide Electrocatalysts for the Oxygen Evolution Reaction

Proton exchange membrane water electrolysis (PEMWE) offers a promising route for the production of green hydrogen from renewable energy sources and could be the master key to unlocking a future sustainable energy system (1). One of the main barriers delaying the wide-spread adoption of PEMWE technologies is the slow kinetics of the oxygen evolution reaction (OER) occurring at the anode and the need for high-cost, low-abundance precious metal electrocatalysts. Iridium-based oxides are still considered the only feasible option for practical applications due to their high activity and considerable corrosion stability under the harsh electrochemical reaction conditions. To improve the overall efficiency of PEMWEs, future electrocatalyst development strategies must concomitantly address performance metrics in terms of activity, stability and material cost.Towards enhancing iridium utilisation, efforts are aimed at increasing the electrochemical surface area of the catalyst per mass of iridium, thereby increasing the number of available electrocatalytic surface sites. In this regard, amorphous iridium oxide (IrOx) nanoparticles have been shown to achieve a high intrinsic activity (2). However, this comes at the expense of catalyst stability (3) and a loss of intrinsic electronic conductivity (4) associated with the lower degree of crystallinity. By maximising the dispersion of Ir-based nanoparticles, the use of high surface area support materials have also been shown to improve OER performance (5, 6).However, to address long-term stability concerns for Ir-based OER catalysts, highly crystalline rutile iridium dioxide (IrO2) materials may still offer the best prospects. The drawback of using this approach is that the formation of crystalline IrO2 nanoparticles often involves high temperature thermal oxidative treatment causing particle growth and loss of surface area, ultimately leading to decreased OER activities (7). Therefore, novel synthesis methods that retain a high degree of crystallinity without a loss of surface area for IrO2 nanoparticles are required.In this talk, we discuss two synthesis strategies geared towards the preparation of highly crystalline IrO2 nanoparticles with high OER performance. Firstly, we present a novel wet-chemistry synthesis method that avoids the use of reducing agents and eliminates the need for high temperature thermal oxidative treatment. The resultant nano-sized IrO2 nanoparticles were found to have excellent Ir mass-specific OER activity and durability attributed to the small nanoparticle size and high degree of crystallinity.Secondly, we present a novel metalorganic chemical deposition process as a simple, one-step preparation method for highly crystalline IrO2 nanoparticles supported on Sb-doped tin oxide (ATO) (8). The superior OER performance was attributed to the epitaxial anchoring of well dispersed, crystalline IrO2 nanoparticles onto the ATO support. We further discuss the versatility of the method to the application of other conductive oxide support materials such as indium tin oxide and F-doped tin oxide, with the ability of tuning the chemical state of the Ir-based nanoparticles by changing the reaction conditions, i.e., temperature and gas environment as well as the nature of the support.Finally, using a series detailed physico-chemical characterisation techniques to elucidate the nature the iridium phase, composition, morphology and structure, we relate these properties to the electrochemical activity and stability of the prepared materials for the OER. Herein, we highlight some of the challenges often encountered with the analysis of physical and electrochemical characterisation data for IrO2 nanoparticles, particularly when supported on other oxide materials. Acknowledgements This work is funded by the Department of Science and Innovation (DSI, South Africa) Impala Platinum Holdings Limited (Implats) and the Federal Minister of Education and Research (BMBF, Germany). References K. Ayers, Current Opinion in Electrochemistry, 18, 9 (2019). T. Reier, I. Weidinger, P. Hildebrandt, R. Kraehnert and P. Strasser, ECS Transactions, 58, 39 (2013). T. Binninger, R. Mohamed, K. Waltar, E. Fabbri, P. Levecque, R. Kötz and T. J. Schmidt, Scientific Reports, 5, 12167 (2015). M. Bernt, C. Schramm, J. Schröter, C. Gebauer, J. Byrknes, C. Eickes and H. A. Gasteiger, Journal of The Electrochemical Society, 168, 084513 (2021). H.-S. Oh, H. N. Nong, T. Reier, A. Bergmann, M. Gliech, J. Ferreira de Araújo, E. Willinger, R. Schlögl, D. Teschner and P. Strasser, Journal of the American Chemical Society, 138, 12552 (2016). A. Hartig-Weiss, M. Miller, H. Beyer, A. Schmitt, A. Siebel, A. T. S. Freiberg, H. A. Gasteiger and H. A. El-Sayed, ACS Applied Nano Materials, 3, 2185 (2020). J. Quinson, Advances in Colloid and Interface Science, 303, 102643 (2022). Z. S. H. S. Rajan, T. Binninger, P. J. Kooyman, D. Susac and R. Mohamed, Catalysis Science & Technology, 10, 3938 (2020).

Ferroelectric-like behavior in HfO2/Al2O3/AlN metal-insulator-semiconductor capacitor through AlN thermal stress

By modulating the thermal stress during film growth, the strained aluminum nitride (AlN) thin films with ferroelectric-like behavior were successfully grown by metal organic chemical vapor phase deposition (MOCVD) on silicon (Si) (111) substrate. The capacitors with strained AlN were fabricated and experimentally demonstrated, the linear to ferroelectric-like behavior on the fabricated AlN capacitors was observed, and the behavior was explained in terms of residual strains in the film. This work reports the ferroelectric-like properties of AlN film grown under specific deposition conditions for the first time.

Fabrication and Application of 1653.7 nm Methane Sensor

In industries such as coal mining, natural gas transportation and waste-to-energy, methane detection is an essential step. In order to reduce the risk and improve accuracy, laser sensors are used to detect methane. Aiming at the characteristics of the absorption peak of methane gas at 1653.7 nm, the 1653.7 nm distributed feedback laser was obtained from the multi quantum well materials design and ridge-wide pattern design to device packaging by using metal-organic chemical vapor epitaxial deposition, holographic exposure, and nanoimprint lithography. The laser performance achieves a side-mode suppression ratio of 54 dB, a slope efficiency of 0.372 W/A, a threshold current not greater than 12 mA, a saturated optical power greater than 20 mW, and stable optical and electrical properties. Based on this laser, for methane gas with a concentration of 0% to 3%, the loss is stable with the change of gas concentration, and the absorption sensitivity to methane is 0.20237 dB/%.

Magneto-optical property of Ce-substituted YIG films fabricated by metal–organic deposition method

The metal–organic deposition method (MOD) fabricated cerium-substituted yttrium iron garnet (Ce:YIG, CexY3-xFe5O12) films with chemical composition Ce : Y : Fe=1.0:2.0:5.0. We determined the components of the dielectric tensor by measuring the transmittance and reflectance of circularly polarized light. These values are smaller than those obtained by other fabrication methods. Measurements of the cross-section of the samples using scanning electron microscopy (SEM) revealed the layered structures in the backscattered electron (BSE) image, which resulted from the traces of the spin-coating process of the MOD liquid. Energy dispersive X-ray spectroscopy (EDS) measurements revealed a chemical composition of x=0.7. Thus, we consider the small values of the components as the defects in the Ce:YIG crystals and low substitution ratio.

Improvement of epitaxial growth and flux pinning of MOD-derived YBa2Cu3O7−δ nanocomposites films by self-seeding and multi-element doping strategies

YBa2Cu3O7−δ (YBCO) nanocomposite films were fabricated by low-fluorine metal-organic deposition (LF-MOD) route, combining self-seeding and multi-doping strategies with elements of Zr, Hf, Sn and Mn. Under the same growth conditions, due to the self-seeding layer as a template for the c-axis growth of doped films, all the multi-doped films with 200 nm self-seeding layers exhibit good c-axis orientation, even for the heavy doping of 16 mol%. EDS confirmed the four doping elements in the multi-doped YBCO films appear independently, leading to higher density of nano-scale heterogeneous phases than the case of Zr single doping. The pinning force density (Fp) and critical current density (Jc) are improved significantly, which indicates that the optimal doping content is achievable as high as 12 mol% in the case of multi-doping. The multi-12% YBCO films have the highest Fp,max of 6.13 GN/m3 at 77 K, which is about 3.3 times higher than that of the undoped films, and the Jc can reach 4.3 MA/cm2 at 30 K, compared to 3.1 MA/cm2 for the undoped films.

Magnetically aligned metal-organic deposition (MOD) ink based nickel/copper heater surfaces for enhanced boiling heat transfer

We present high boiling heat transfer properties achieved by magnetically aligned nickel precursor inks on copper substrates measured atmospheric pressure. Alignment was performed in a single direction and grid orientation. Pool boiling studies were performed to obtain correlations between the heat flux, heat transfer coefficients, and wall superheat using water and ethanol. The effects of surface wettability and roughness on nucleate boiling heat transfer properties and bubble dynamics are reported. Our studies yielded a critical heat flux (CHF) of 185.9 W/cm2 and a heat transfer coefficient (HTC) of 106.9 kW/m2 °K for water on Ni grid patterned surface, representing an improvement of 49.9% in CHF and 105% in HTC compared to plain copper surface. The alignment of nickel followed by its sintering introduced nucleation characteristics that improved bubble dynamics. This is attributed to a) altered three-phase contact angle via chemically heterogeneity of Ni/Cu surface, and b) increased surface roughness due to nickel microstructures that induced wickability.

Rapid phase formation and interfacial reaction of YBa2Cu3O7−δ coated conducts by using high-rate crystallization of fluorine-free chemical solution

In the present work, the high-rate epitaxial growth for superconducting YBa2Cu3O7-δ (YBCO) films on the substrates of LaMnO3(LMO)/IBAD-MgO/Y2O3/Al2O3/Hastelloy is achieved by fluorine-free metal organic deposition (FF-MOD) by rapidly switching the partial oxygen pressure (pO2) at a fixed temperature. Further investigation into the effects of temperature and switching pO2 on the phase transition of YBCO elucidates that the growth mode and microstructural characteristics of the studied films. BaMnO3 heterogeneous particles are observed in localized regions in the films by cross-sectional transmission electron microscopy, which may be generated by the interfacial reactions between the substrate and transient liquid phases. The present work implies the feasibility of FF-MOD for the rapid growth of YBCO films on LMO buffered metallic substrates, regardless of interfacial reactions during the preparation.

Effect of Chlorine Addition on Texture and Superconducting Performance of YBa2Cu3O7−δ-Coated Conductors

YBa2Cu3O7−δ (YBCO) thin films with the addition of Cl were prepared on Hastelloy tape by the extremely low fluorine metal-organic deposition (MOD) technique. The composition and microstructure of the present samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was revealed that the Cl-added YBCO thin films achieved better texture and density compared with the pure YBCO films. The superconducting properties at magnetic fields were measured using the magnetic property measurement system (MPMS). The results showed that the sample onset transition temperature (Tc, on) did not change significantly after the addition of Cl. The critical current density (Jc) in the presence of YBCO with the addition of Cl increased significantly. Meanwhile, both the Jc and gravitational force (Fp) of the (Cl, Hf) co-added YBCO films were further enhanced at different magnetic fields. The thermodynamic analysis of the BaCO3 removal reaction revealed that the addition of Cl to YBCO formed chlorine compounds, which were effective in avoiding the formation of BaCO3. Further, the calculation results of the Gibbs free energy at different pressure quotients showed that the stability of the relevant chlorine compounds occurred in the order of BaCl2 > CuCl2 > YCl3 and the oxidation of BaCl2 to BaO required a higher temperature compared to BaF2, implying the potential advantages of inhibiting the a-axis growth.

Nucleation and epitaxy growth of high-entropy REBa2Cu3O7–δ (RE= Y, Dy, Gd, Sm, Eu) thin films by metal organic deposition

High-entropy REBa2Cu3O7–δ (RE = Y0.7 + Dy0.2 + Gd0.2 + Sm0.2 + Eu0.2) (HE-REBCO) superconducting films doped with multiple rare earth elements were successfully fabricated with thickness up to 800 nm by a trifluoroacetate-metal organic deposition (TFA-MOD). The enhanced entropy change ΔS of the HE-REBCO system promotes the c-axis growth of REBCO thin film in the competition with a/b-axis growth. The microstructure and element distribution were investigated by the transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). The results show that HE-REBCO films have a great amount of stacking defects, lattice distortions and various rare earth oxides. Furthermore, the microstrain of HE-REBCO films increases significantly compared to the undoped YBCO and (Y, Dy)BCO films. Finally, the superconducting critical temperature (Tconset) of HE-REBCO films is about 93 K, and the in-field properties are significantly improved, especially at the temperature of about 77 K. The maximum pinning force density (Fp,max) of the HE-REBCO samples at 77 K is 1.7 times higher than that of the undoped YBCO films.

Low-Vacuum Pyrolysis of YBCO Films by Using Fluorine-Free Metal Organic Chemical Deposition

The preparation of YBCO superconducting films by using metal organic chemical deposition (MOD) involves low-temperature pyrolysis and high-temperature treatment. The former process generally requires the introduction of water vapor and other gases. The study on pyrolysis in a low vacuum environment and non-carrier gas atmosphere has never been reported. In this work, we explored a low vacuum pyrolysis scheme with simple Argon gas decompression and a carrier-free atmosphere. The effects of heating rate on the microstructure of pyrolysis films were investigated, and the high-temperature treatment temperature (Th) was also optimized. Compared with conventional pyrolysis, the present low-vacuum pyrolysis does not employ the flowing dry or wet gases, facilitating the internal gas release during film decomposition. More importantly, the efficiency was greatly improved with reduced pyrolysis time. The obtained film surface is free of CuO particle, which leads to a lower roughness. We also investigated the effect of Th on the final YBCO film texture and superconductivity. As Th increased from 810 °C to 815 °C, the BaCuO2 phase decreased with enhanced c-axis orientation being evident by XRD and Raman spectra. As a result, the critical current density (Jc) increased from 0.38 MA/cm2 to 1.2 MA/cm2 (77 K, self-field).

Analysis and optimization of MOCVD flow ratio based on machine learning and PSO algorithm

Metal-Organic Chemical Vapor Deposition (MOCVD) is a widely used technology for epitaxial growth. The metal-organic (MO) source enters the reaction chamber through several pairs of gas inlets, and the flow ratio among these inlets has a significant influence on epitaxial results. Based on Computational Fluid Dynamics (CFD) software, a numerical model of MOCVD was established to study the influence of the flow ratio of MO source inlets on the flow states in reaction chamber. It was found that the flow ratio has no effect on the flow states in general, though there are some differences in the flow field. Back Propagation (BP) neural network was used to approximate the relationship between MO flow ratio and deposition results, which showed high accuracy. Swarm Intelligence algorithm was used to optimize the flow ratio of MO source. The coefficient of variation was reduced by 38.1%, which indicated that it was an efficient way to adjust the flow ratio and improve the film quality.

Enhancement of self-field critical current density by several-tens-MeV ion irradiation in YBa2Cu3O7 films prepared by fluorine-free metal-organic deposition

An up to 63% enhancement in critical current density (J c) was achieved for 1 μm thick YBa2Cu3O7 (YBCO) films at self-field at 77 K by irradiation with 24–84 MeV Au ions. This enhancement is highly unusual, since in YBCO films, J c at self-field (J c sf) is generally insensitive to ion irradiation, unlike J c in magnetic fields. Our observed film-thickness dependence of the irradiation effect and our microstructure imaging indicate that this rare observation is attributed to an extremely “clean” (i.e. less-disordered) microstructure in the top 700 nm of the layer of our 1 μm thick films prepared via fluorine-free metal-organic deposition. Our results directly indicate that discontinuous 1D vortex-pinning centers (pins) that have the following features effectively enhance MA cm−2-order J c sf at 77 K of YBCO films; namely, 5–10 nm in diameter, ∼20 nm in size along a pin track, have a ∼20 nm gap between the pins in a pin track, and are directed in the c-axis.

Development of Quaternary InAlGaN Barrier Layer for High Electron Mobility Transistor Structures.

A quaternary lattice matched InAlGaN barrier layer with am indium content of 16.5 ± 0.2% and thickness of 9 nm was developed for high electron mobility transistor structures using the metalorganic chemical-vapor deposition method. The structural, morphological, optical and electrical properties of the layer were investigated planning realization of microwave power and terahertz plasmonic devices. The measured X-ray diffraction and modeled band diagram characteristics revealed the structural parameters of the grown In0.165Al0.775Ga0.06N/Al0.6Ga0.4N/GaN heterostructure, explaining the origin of barrier photoluminescence peak position at 3.98 eV with the linewidth of 0.2 eV and the expected red-shift of 0.4 eV only. The thermally stable density of the two-dimension electron gas at the depth of 10.5 nm was experimentally confirmed to be 1.2 × 1013 cm−2 (1.6 × 1013 cm−2 in theory) with the low-field mobility values of 1590 cm2/(V·s) and 8830 cm2/(V·s) at the temperatures of 300 K and 77 K, respectively.

Improved ORR/OER bifunctional catalytic performance of amorphous manganese oxides prepared by photochemical metal-organic deposition.

Transition metal oxide nanomaterials or nanocomposites containing transition metal oxides have the potential to replace traditional catalysts for electrochemical applications, photocatalysis, and energy storage. Amorphous manganese oxide catalysts were prepared via photochemical metal–organic deposition (PMOD). Through XRD, SEM-EDS, Raman spectroscopy, FTIR spectroscopy, HRTEM-EDS, and XPS, we confirmed that amorphous manganese oxide catalysts were successfully prepared. Amorphous catalysts prepared with different photolysis times were compared in terms of their performance for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), and catalyst MnOx-PMOD48 showed the best performance because of its high Mn3+ proportion and electrochemically active surface area. MnOx-PMOD48 showed better ORR/OER performance than the crystalline MnOx and MnOx/Ti4O7 catalysts from our previous work. Following our previous work on crystalline manganese oxide catalysts, we added Ti4O7 during the PMOD process with 48 h of treatment and obtained the amorphous catalyst MnOx/Ti4O7-PMOD. MnOx/Ti4O7-PMOD was supported by Ti4O7 particles, which led to improved stability. The ORR/OER catalytic activity of MnOx/Ti4O7-PMOD was better than that of crystalline catalyst MnOx/Ti4O7-300, which was the best crystalline catalyst in our previous work. We also compared lithium-oxygen batteries assembled with MnOx/Ti4O7-PMOD and MnOx/Ti4O7-300. The battery performance tests confirmed that the amorphous manganese catalyst had better ORR/OER bifunctional catalytic performance than the crystalline manganese catalyst because of its high defect state with more abundant edge active sites and more surface-exposed catalytic active sites.

Highly efficient amorphous binary cobalt-cerium metal oxides for selective oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran

This study reports for the first time the use of amorphous mixed cobalt-cerium metal oxides (Co10-aCeaOx), obtained by photochemical metal-organic deposition, for 5-hydroxymethylfurfural (HMF) oxidation. The optimized Co8Ce2Ox exhibites a good electrocatalytic activity toward HMF oxidation with a current density of 2.8 mA cm−2 at 1.60 V, which is 1.4 times higher than that of pure CoOx. Operando Raman spectra reveal that the incorporation of Ce alters the electronic structure of the composite by facilitating the formation of CoOOH/CoO2, thus promoting catalytic activity. Notably, it is found that the oxidation of HMF proceeds dominantly via the oxidation of the alcohol group, followed by its subsequent oxidation in both alkaline and neutral media. Due to the stability of the aldehyde group in neutral media, high valuable 2,5-diformylfuran (DFF) with the selectivity of 60%–92% is obtained, thus open the new route for electrocatalytic DFF production.

Simulation study on the diversity and characteristics of twin structures in GaN

Gallium nitride (GaN) is a promising material for high-frequency and high-power electronics owing to its high thermal stability, wide bandgap, and high breakdown voltage. Monocrystalline GaN films are usually produced by metal organic chemical vapor phase deposition using Si, SiC, or Al 2 O 3 as the substrate. However, the difference in lattice constants and thermal expansion coefficients causes many defects in GaN epilayers . In particular, the formation of twins will strongly influence the electronic properties of GaN-based devices. In this study, the solidification process of GaN was simulated by molecular dynamics at a cooling rate of 10 12 K/s, and the twin structures in GaN were discussed. The results of this simulation showed two types of twins, including coherent twin and rotating twin, which were analyzed by visualization technology. The formation of twins was related to the coexistence of zinc blende and wurtzite phases. Furthermore, the types of twins were closely associated to the stacking ways of zinc blende and wurtzite structures. In general, it is essential to study the microstructure and the structural evolution of twin GaN, in order to give references to experiments about the growth and characteristics of twins. • Zinc blende and wurtzite nucleated randomly and formed lots of complex structures at the beginning of crystallization. • Coherent and rotating twins were formed according to different stacking methods of zinc blende and wurtzite structures. • The rules for the combination of twin structures in GaN crystals have been summarized and it can be generalized. • An error in the stacking sequence can cause the metastable phase c-GaN to start seeding the h-GaN phase.

An electric field-assisted photochemical metal–organic deposition allowing control of oxygen content for resistive switching in directly patterned TiOx films

An electric field-assisted photochemical metal–organic deposition allowing control of oxygen content for resistive switching in directly patterned TiOx films