Metalorganic Deposition Process Research Articles

Selector-less crossbar array resistive RAM based on TiO2 fabricated by photochemical metal-organic deposition

In this study, we demonstrated a TiO2-based 32 × 32 crossbar array resistive RAM (ReRAM), a promising candidate for next-generation non-volatile memory (NVM), by utilizing a photochemical metal-organic deposition (PMOD) process. We achieved an interface-type resistive switching device with rectifying characteristics by controlling the oxidation state of directly patterned TiOx films through post-heat treatment. The photochemical reaction induced by UV in the PMOD process and the anatase phase formation during the post-heat treatment were analyzed using Fourier-transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). XPS analysis revealed the immediate formation of Ti peroxide post-PMOD process, underscoring the efficacy of post-heat treatments in controlling oxidation states. Employing 350 °C annealed TiOX as the active material, we successfully fabricated a high-yield (93%), selectorless 32 × 32 crossbar array architecture for ReRAM. Our findings highlight the PMOD process as a viable, cost-effective alternative for memory devices, offering optimized oxidation states crucial for the performance of redox-based ReRAM.

High figure of merit spin polarized electron sources grown via MOCVD

Spin polarized photocathodes are key to the future operation of electron accelerators such as the ones at Thomas Jefferson National Accelerator Facility and Brookhaven National Laboratory. Currently, these photocathodes come in short supply due to limited production by molecular beam epitaxy. By developing a process to implement similar structures using metal organic chemical vapor deposition, the availability of these devices can be increased. In this paper, we detail the implementation of recent photocathode advancements via metal organic chemical vapor deposition process and show an improvement in both polarization and quantum efficiency of our devices compared to those fabricated via molecular beam epitaxy, with devices reaching 82% polarization and 2.9% quantum efficiency.

External catalyst-free InGaN photoelectrode for highly efficient energy conversion and H2 generation

GaN is a well-known material whose energy band edges can straddle the redox potentials deep in the visible and infrared wavelengths, thereby promising a drastically improved photon-to-current efficiency under applied bias. However, the material is still limited by the half-reactions of water splitting due to its high defect density, low light absorption, small reaction area, and large energy band bending. Here, our study provides a turn-key solution to all these issues. The synergistic effect of InGaN/GaN quantum pyramids on nanowires (QPs-NWs) directly addresses the performance degradation of the photocathodes (PCs). New InGaN QP structures on non-polar GaN nanowire show a unique tunable energy band (Eg: ∼2 eV to ∼1.36 eV) by quantum-sliding interface recombination effect. Without the use of external catalysts, the photoelectrochemical water splitting (PEC-WS) of QPs-NWs PC demonstrated enhanced performance with a current density of 34.36 mA cm−2 and a photon-to-current efficiency of 13.75 % under the −0.8 to 0 V applied biasing condition, which is much higher than in previous reports. The current density and the H2 production were measured to be ∼61.81 mA cm−2 and 11.5 mmol cm−2 for 10 h. The external catalyst-free electrode and the metal organic chemical vapor deposition (MOCVD) process will open a new platform for the commercialization of III-nitride based water splitting hydrogen technology.

The MoS2-Graphene-Sapphire Heterostructure: Influence of Substrate Properties on the MoS2 Band Structure

Van der Waals MoS2/graphene heterostructures are promising candidates for advanced electronics and optoelectronics beyond graphene. Herein, scanning probe methods and Raman spectroscopy were applied for analysis of the electronic and structural properties of monolayer (ML) and bilayer 2H-MoS2 deposited on single-layer graphene (SLG)-coated sapphire (S) substrates by means of an industrially scalable metal organic chemical vapor deposition process. The SLG/S substrate shows two regions with distinctly different morphology and varied interfacial coupling between SLG and S. ML MoS2 nanosheets grown on the almost free-standing graphene show no detectable interface coupling to the substrate, and a value of 2.23 eV for the MoS2 quasiparticle bandgap is determined. However, if the graphene is involved in hydrogen bonds to the hydroxylated sapphire surface, an increased MoS2/graphene interlayer coupling results, marked by a shift of the conduction band edge toward Fermi energy and a reduction of the ML MoS2 quasiparticle bandgap to 1.98 eV. The surface topography reveals a buckle structure of ML MoS2 in conformity with SLG that is used to determine the dependence of the ML MoS2 bandgap on the interfacial spacing of this heterostructure. In addition, an in-gap acceptor state about 0.9 eV above the valence band minimum of MoS2 has been observed on locally elevated positions on both SLG/S regions, which is attributed to local bending strain in the grown MoS2 nanosheets. These fundamental insights reveal the impact of the underlying substrate on the topography and the band alignment of the ML MoS2/SLG heterostructure and provide the possibility for engineering the quasiparticle bandgap of ML MoS2/SLG grown on controlled substrates that may impact the performance of electronic and optoelectronic devices therewith.

Corrosion barrier alumina/zirconia bilayer stack on low Cr steel by direct liquid injection metalorganic chemical vapor deposition

Numerous industrial fields necessitate the development of advanced metallic materials presenting high corrosion resistance in aqueous media and being less expensive than classical high chromium steels. In the present work, amorphous zirconia, alumina and alumina/zirconia coatings have been deposited on 2 wt% chromium steel coupons using an innovative direct liquid injection metal organic chemical vapor deposition process. Scanning electron microscopy and X-ray diffraction reveal that the alumina sublayer acts as an efficient barrier against steel oxidation occurring during the amorphous zirconia deposition performed under O2 at 400 °C. They also show that the steel oxidation occurring concomitantly to the zirconia coating modifies the film morphology by increasing its roughness and thickness, in comparison with the same zirconia coating on alumina. The anticorrosive properties of the thin films have been studied by an immersion test of the bare and coated coupons in deionized water at 80 °C during 6 days and by electrochemical impedance spectroscopy in aqueous sodium chloride solution for 48 h. They reveal that, in contrast to alumina and zirconia monolayers alone, the alumina/zirconia stack acts as a corrosion protection coating in pure water through a synergetic barrier effect against (i) oxidation by alumina and (ii) aqueous corrosion by zirconia.

(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).

An advanced electrical heating technique for double-sided Y(Gd)BCO coated conductor: gaining high engineering current density based on MOCVD

An advanced electrical heating technique was proposed and adopted for the reel-to-reel deposition of double-sided Gd x Y1−x Ba2Cu3O7−δ (Y(Gd)BCO) films on the surface of LaMnO3/epitaxial-MgO/IBAD-MgO/Y2O3/Al2O3/Hastelloy tapes based on the metal organic chemical vapor deposition process. In this technique, heating current is introduced into alloy tape to produce heat through the electric brushes. The use of thin Hastelloy tapes is an effective method to obtain a high engineering current density. However, the reduction of the substrate thickness will directly attenuate its mechanical strength, which will lead to the deformation of tapes at high temperature based on original electric heating device. More seriously, the electrical contact between the alloy substrate and the brush will deteriorate, which could cause ignition and ablation at the edge of the tapes. Therefore, in order to improve mechanical and electrical stability, we redesigned a novel electrical heating device to deposit Y(Gd)BCO films. Furthermore, through adopting the multiple-deposition process based on the new electrical heating device, the J e of Y(Gd)BCO film can reach 900 A mm−2 (at self-field, 77 K), which has been significantly improved compared with the J e before optimization.

Material proposal for 2D indium oxide

Realization of semiconductor materials at the two-dimensional (2D) limit can elicit exceptional and diversified performance exercising transformative influence on modern technology. We report experimental evidence for the formation of conceptually new 2D indium oxide (InO) and its material characteristics. The formation of 2D InO was harvested through targeted intercalation of indium (In) atoms and deposition kinetics at graphene/SiC interface using a robust metal organic chemical vapor deposition (MOCVD) process. A distinct structural configuration of two sub-layers of In atoms in “atop” positions was imaged by scanning transmission electron microscopy (STEM). The bonding of oxygen atoms to indium atoms was indicated using electron energy loss spectroscopy (EELS). A wide bandgap energy measuring a value of 4.1 eV was estimated by conductive atomic force microscopy measurements (C-AFM) for the 2D InO.

High homogeneity 10 cm long BaTiO3-doped YBa2Cu3O7-δ films by the trifluoroacetate metal-organic deposition process

The trifluoroacetate metal-organic deposition (TFA-MOD) is one of the most appealing routes for the growth of high-quality YBa2Cu3O7-δ (YBCO) coated conductors (CCs) due to its advantages of low cost and high efficiency. However, the puzzle of the inhomogeneities in microstructures and superconducting properties of YBCO CCs prepared based on the TFA-MOD route remain still a challenge. In this paper, 10 cm long YBCO films were prepared under different low-pressure conditions. These YBCO films were deposited on buffered Hastelloy C276 tapes using a dip coater. The effect of different ambient pressures on the microstructure and critical current density of YBCO films was investigated. High critical current density (JC) YBCO coated conductors with good homogeneity were obtained. The JC values (77 K, self-field) at different positions along the length direction of YBCO coated conductor were around 3.5–4 MA/cm2. The results showed that only under a suitable pressure the homogeneities of the microstructure and critical current density along the length direction of coated conductor can be greatly improved. The improvement was mainly ascribed to good texture and the absence of impurity phases BaF2 and Ba4Y2O7 in the films.

Investigation of epitaxial growth of La2Zr2O7 thin films with different carbonaceous phases

During the metal–organic deposition (MOD) process, the carbon-rich impurities remaining in a film are harmful to the epitaxial growth of the oxide film. Thus, it is of great importance to investigate epitaxial growth of oxide films with different carbonaceous phases. To control the carbonaceous phases in the as-fabricated LZO film, different dopant concentrations and annealing atmospheres have been suggested during the MOD process. A characterization of specimens was performed using X-ray diffraction θ–2θ scans, out-of-plane and in-plane scans, X-ray photoelectron spectroscopy, electron backscattering diffraction, and atomic force microscopy. It was found that a small number of carbonaceous phases, regardless of their type, has no obvious negative influence on the growth orientation of the film. Moreover, because some bridge-pillar spots in the graphene layer enable the epitaxial growth of oxide film, the texture degree of LZO film doped with a high concentration of reduced graphene oxide (RGO) is even sharpened. With increasing doping RGO concentration, the surface roughness of the LZO film increases, which indicates an exaggerated impact of the surface defects on the metallic substrate on the grain size of the LZO film doped with RGO. Different oxygen partial pressures in the annealing atmosphere determine the type of carbonaceous phase in the as-prepared oxide film. The carbonate species formed in the film under high oxygen partial pressure have a negative influence on the texture degree and the surface flatness of LZO film, while low oxygen partial pressure favors the reduction of the residual carbon in the film. Therefore, oxide films with high performance can be achieved by controlling the presence of the positive carbonaceous phases in the film during the introduction of an appropriate artificial doping source and the selection of a suitable annealing atmosphere.

Resistive switching characteristic of Ce0.9Y0.1O2/TiO2 bi-layer structure by photochemical metal-organic deposition

Sneak current is one of the main bottlenecks for dense crossbar array resistive random access memory. This study reports highly non-linear resistive switching characteristic from Ce0.9Y0.1O2/TiO2 bi-layer (1S/1R device) structure, fabricated by photochemical metal-organic deposition, as a solution for sneak current issue. Ce0.9Y0.1O2 material, possessing oxygen vacancies, was used as a potential barrier as well as oxygen reservoir which rectified the current of low resistance state without an electrical breakdown in 1S/1R device. TiO2 was adopted for resistive switching property, and TiO2 layer having mixed phase (anatase and brookite) showed typical diode switching behavior. The photochemical reaction of photochemical metal-organic deposition process and phase formation were monitored and established using by Fourier-transform infrared spectroscopy and X-ray diffraction, respectively. The 1S/1R device showed highly non-linear resistive switching characteristic, large on/off ratio of above three orders of magnitude with low operating current.

Microstructure and electrical transport mechanisms of the Ca-doped LaMnO3 films grown on MgO substrate

La0.7Ca0.3MnO3 (LCMO) thin films have been grown on MgO substrate using the metal organic deposition process. The lattice mismatch between LCMO and MgO is relatively large around 8.14% imposing large in-plane-tensile strain and out-of-plane-compressive strain on the film. Hence the structural, microstructural and electrical properties have been found to be strongly correlated to the strain degree and relaxation. Cross-section transmission electron microscopy observations demonstrate the presence of microstructural defects due to the large lattice mismatch between the LCMO and MgO. In addition to structural and microstructural defects, X-ray diffraction and Raman spectroscopy measurements show the existence of a minor phase of MnO in the film. Magnetization versus temperature measurement show a relatively low Curie temperature around 75 K. The electrical behavior is found to be semiconducting over a large temperature interval. The electrical transport mechanisms have been investigated using the small polaron hopping and variable range hopping models and correlated to their microstructural properties.

Optimization of interim heat-treatment condition on TFA-MOD process for fabrication of Y0.77Gd0.23Ba2Cu3Oy coated conductors with BaHfO3

We have optimized the interim heat-treatment (IHT) time in trifluoroacetate based metal organic deposition process on fabrication of the BaHfO3 (BHO) doped Y0.77Gd0.23Ba2Cu3Oy (YGdBCO) coated conductor (CC) in order to further improve the in-field critical current density (Jc) performance. The in-field Jc values of 0.6 μm-thick BHO doped YGdBCO CCs increased with increasing the IHT time within 90 min. The highest critical current density (Jc) value of 0.86 MA/cm2 at 77 K in 3 T (B//c) was obtained for 0.6 μm-thick BHO doped YGdBCO CC with IHT time of 90 min. CCs with IHT time shorter than 90 min had relative low in-field Jc performance but high self-field Jc performance. It can be caused by the insufficient transformation to BaF2 in IHT which is a reason for the relatively large BHO particles. In the case of applying IHT for longer time than 90 min, coarsening of CuO particles in precursor films was suggested and degradation of self- and in-field Jc performances were observed.

Study of Chemical Enhancement Mechanism in Non-plasmonic Surface Enhanced Raman Spectroscopy (SERS).

Surface enhanced Raman spectroscopy (SERS) has been intensively investigated during the past decades for its enormous electromagnetic field enhancement near the nanoscale metallic surfaces. Chemical enhancement of SERS, however, remains rather elusive despite intensive research efforts, mainly due to the relatively complex enhancing factors and inconsistent experimental results. To study details of chemical enhancement mechanism, we prepared various low dimensional semiconductor substrates such as ZnO and GaN that were fabricated via metal organic chemical vapor deposition process. We used three kinds of molecules (4-MPY, 4-MBA, 4-ATP) as analytes to measure SERS spectra under non-plasmonic conditions to understand charge transfer mechanisms between a substrate and analyte molecules leading to chemical enhancement. We observed that there is a preferential route for charge transfer responsible for chemical enhancement, that is, there exists a dominant enhancement process in non-plasmonic SERS. To further confirm our idea of charge transfer mechanism, we used a combination of 2-dimensional transition metal dichalcogenide substrates and analyte molecules. We also observed significant enhancement of Raman signal from molecules adsorbed on 2-dimensional transition metal dichalcogenide surface that is completely consistent with our previous results. We also discuss crucial factors for increasing enhancement factors for chemical enhancement without involving plasmonic resonance.

Formation of Erbia-Yttria double layer fabricated by metal organic chemical vapor deposition process with changing oxygen flow rates

Er2O3 and Y2O3 are promising materials for advanced breeding blanket system of nuclear fusion reactor because they have high electrical resistivity and effective tritium permeation suppression. In this report, Er2O3 thin films were fabricated by metal organic chemical vapor deposition (MO-CVD) process with changing oxygen flow rates on the stainless steel 316 (SUS316) substrate with Y2O3 layer fabricated via radio frequency (RF)-sputtering. Samples were prepared with four conditions of oxygen rate, 0.08, 0.13, 0.25, 0.42 Pa∙m3/s (50, 75, 150 and 250 sccm, respectively) and only on Er2O3 / Y2O3–0.42 Pa∙m3/s sample was added thermal cycles. Four samples were observed with using X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). Increasing oxygen flow rate during MO-CVD process increased the thickness of Er2O3 thin film and decreased columnar width and succeeded in fabricating Er2O3 thin film and dense microstructure on the SUS 316 substrate with Y2O3 layer.

High Performance Coated Conductors Fabricated by UTOC-MOD Process

A new metal organic deposition (MOD) process using precursor solution containing metal trifluoroacetates was developed to improve in-field performance. In this process, the pinning centers of BaMO3 (M: metal elements such as Zr and Hf) materials could be made to be finer by reducing the once coating thickness in the coating and calcination step. This is referred to as the ultra-thin once coating (UTOC)-MOD process. This process improves the in-field performance. The UTOC-MOD process also has the advantage of uniformity of 2-dimensional Jc-distribution, which was determined using a scanning hall-probe microscopy analysis. Improvement of the Jc uniformity was also confirmed based on scribed tapes. A smaller dispersion of the filament-critical current values in the UTOC-MOD tape was determined based on a comparison with the results for obtained by a conventional process. With respect to the mechanical strength, it was established that the dispersion of the delamination strength, which was evaluated using stud-pull equipment, was suppressed. Microstructural analysis revealed that, the UTOC films were pore-free, although large pores are present in the films when conventional MOD is utilized. This difference in the microstructure can be attributed to the aforementioned improvement in the uniformity of the UTOC-MOD films.

Superconducting Joint of GdBa2Cu3Oy Coated Conductors by Crystallization of an Additionally Deposited Precursor Layer

A superconducting joint of REBa 2 Cu 3 O y (REBCO) coated conductors (CCs) has been demanded strongly to fabricate long length CCs for high field magnet applications such as nuclear magnetic resonance and magnetic resonance imaging. In the previous reports of superconducting joint, specimens of REBCO CCs were jointed via melting REBCO phases or via solid state diffusion of REBCO phases. In our study, we propose a new method of joint for REBCO CCs. A precursor layer is additionally deposited on GdBCO CC by a metal organic deposition process, and then two pieces of them are stuck together face-to-face and crystallized the precursor to form 123 phase under mechanical pressure in an oxygen atmosphere. The microstructures and temperature dependence of resistance of the jointed sample are characterized by a cross-sectional transmission electron microscopy (TEM) and a four-probe method, respectively. As a result, TEM observation reveals that two CCs are jointed together without formation of secondary phases at the joint interface. Also, temperature dependence of resistance shows Tc onset and Tc zero of 93 K and 82 K, respectively. Consequently, a superconducting joint has been completed successfully. The concept of this method is combining film growth and solid-state diffusion for the additionally deposited precursor layers.

Growth of Multi-Layer hBN on Ni(111) Substrates via MOCVD

In this paper we demonstrate a metal organic chemical vapor deposition (MOCVD) process for growth of few layer hBN films on Ni(111) on sapphire substrates using triethylborane (TEB) and ammonia (NH3). Ni(111) was selected as a substrate due to its symmetry and close lattice matching to hBN. Using atomic force microscopy (AFM) we find hBN is well aligned to the Ni below with in plane alignment between the hBN zig zag edge and the <110> of Ni. We further investigate the growth process exploring interaction between precursors and the Ni(111) substrate. Under TEB pre-exposure Ni-B and graphitic compounds form which disrupts the formation of layered phase pure hBN; while NH3 pre-exposure results in high quality films. Tunnel transport of films was investigated by conductive-probe AFM demonstrating films to be highly resistive. These findings improve our understanding of the chemistry and mechanisms involved in hBN growth on metal surfaces by MOCVD.

Integration effect of O2‐plasma to an excimer‐laser‐assisted metal organic deposition process for functionalization of photoelectrodes

AbstractTo prevent photocorrosion of a Cu2O photocathode, composition of a TiO2 layer onto the Cu2O is one of the most effective solutions. For crystallization of the TiO2 layer alone without heat‐damage to the underlying Cu2O layer, which is easy to oxidize to CuO, we developed the integration process of O2‐plasma and an excimer‐laser irradiation, that a metal‐organic precursor film is crystalized by irradiation of the excimer‐laser in O2‐plasma. The TiO2 layer could be crystalized with lower oxygen vacancies by the laser irradiation in O2‐plasma compared to that prepared by the irradiation in air. Furthermore, the oxidation of Cu2O to CuO was drastically restricted due to the highly crystalized TiO2 in which oxygen ions were hard to diffuse to the interface of TiO2/Cu2O. The photocorrosion of the obtained film during water reduction reaction was also restricted. This O2‐plasma integrated process is effective for selective crystallization of metal‐oxide films for functionalization of photoelectrodes.

Orientations of Al4C3 and Al films grown on GaAs substrates

A method for growth of aluminum epilayers on III-V substrates using metalorganic chemic vapor deposition (MOCVD) processes could be beneficial for optoelectronic and photovoltaic device fabrication. However, deposition from common precursors under standard MOCVD conditions results in polycrystalline Al4C3. Both Al4C3 films grown on GaAs (100) substrates, and those grown on GaAs (111) B substrates, show strong alignment of the rhombohedral [110] for the Al4C3 crystallites with the in-plane GaAs <110> directions. However, by using plasma-enhanced MOCVD at low growth temperatures, elemental Al can be deposited. Al growth by this method on (001), (111) B and (110) GaAs substrates gave textured, polycrystalline films. In all cases, the Al crystallites are primarily oriented with a <110> aligned with an in-plane <110> of the substrate at initial growth stages. These insights may lead towards growth of large-grained or epitaxial Al films.