Organic Chemical Vapor Deposition Process Research Articles

Autoregressive distributed lag-based dynamic uniformity modeling and monitoring approaches for superconductor manufacturing

ABSTRACT High-temperature superconductors (HTS), known for their high efficiency and low energy loss, have found profound applications across various fields, driving the demand for long, uniformly performing tapes. However, ensuring uniform performance over extended lengths of HTS tapes, often characterized by the consistency of critical current, remains challenging due to fluctuations in growth conditions during manufacturing. To elucidate the mechanisms underlying variations in tape uniformity and enable real-time monitoring of associated parameters, we propose an Autoregressive Distributed Lag (ADL)-based Dynamic Uniformity Modeling and Monitoring (ADUM2) approach. This method integrates uniformity measurement, the identification of critical process parameters and real-time monitoring within the manufacturing process. The ADUM2 approach is applied to the advanced metal organic chemical vapor deposition (A-MOCVD) process, a pilot-scale method for superconductor manufacturing. Our model demonstrates superior performance compared to benchmark methods, accounting for over 80% of the total variance in the data and identifying 13 key process parameters influencing the uniformity of HTS tapes. This study offers significant insights into the high-temperature superconductor manufacturing process and holds the potential to facilitate the production of cost-effective, uniformly performing long superconducting tapes in the future.

Lateral heterostructures of WS2 and MoS2 monolayers for photo-synaptic transistor

Von Neumann architecture-based computing, while widely successful in personal computers and embedded systems, faces inherent challenges including the von Neumann bottleneck, particularly amidst the ongoing surge of data-intensive tasks. Neuromorphic computing, designed to integrate arithmetic, logic, and memory operations, has emerged as a promising solution for improving energy efficiency and performance. This approach requires the construction of an artificial synaptic device that can simultaneously perform signal processing, learning, and memory operations. We present a photo-synaptic device with 32 analog multi-states by exploiting field-effect transistors based on the lateral heterostructures of two-dimensional (2D) WS2 and MoS2 monolayers, formed through a two-step metal–organic chemical vapor deposition process. These lateral heterostructures offer high photoresponsivity and enhanced efficiency of charge trapping at the interface between the heterostructures and SiO2 due to the presence of the WS2 monolayer with large trap densities. As a result, it enables the photo-synaptic transistor to implement synaptic behaviors of long-term plasticity and high recognition accuracy. To confirm the feasibility of the photo-synapse, we investigated its synaptic characteristics under optical and electrical stimuli, including the retention of excitatory post-synaptic currents, potentiation, habituation, nonlinearity factor, and paired-pulse facilitation. Our findings suggest the potential of versatile 2D material-synapse with a high density of device integration.

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.

Numerical Simulation of Thermal Performance of GaAs‐Metal‐Organic Chemical Vapor Deposition Reactor Based on 36 × 4 inches’ Wafers

AbstractCurrently, limited studies on 3D models based on thermal and flow fields have investigated the effects of geometric and process parameters on the metal–organic chemical vapor deposition (MOCVD) process in large square reactors under severe temperatures. To address these problems, this study conducts numerical simulations and experiments for a large square Gallium Arsenide (GaAs) MOCVD reactor. A 3D model based on the MOCVD reactor coupled with fluid flow and heat transfer is developed to analyze the influence of the heating mode and process parameters on the temperature uniformity and heating efficiency. At 800 °C, the heating time is decreased less than 300 s, and a temperature uniformity of 7.9 °C is achieved, thereby realizing improved uniformity and excellent reactor performance. The use of cross and lateral lamps promote the controllability of the reactor temperature. As the gas flow rate increases, the velocity at the edge of the reactor increases, which induces the difference in the heat transfer coefficient between the center and edge increased. The variations in the gas composition influence the heating rate and temperature uniformity. The results of this study are useful for the design of heating modules in MOCVD reactors.

Comparative study on the nanomechanical behavior and physical properties influenced by the epitaxial growth mechanisms of GaN thin films

The effect of carrier gas on nanomechanical properties of GaN thin films grown on (0001) sapphire substrates by metal–organic chemical vapor deposition (MOCVD) process, was studied by Berkovich nanoindentation. GaN/H2 and GaN/N2 films were deposited using hydrogen and nitrogen, as carrier gases, respectively. New method was developed to compute the contact stiffness versus the penetration depth using a single load–displacement curve. It was found that the hardness and Young’s modulus of GaN/H2 are lower than those of GaN/N2. Moreover, pop-in events were revealed for GaN/H2, in contrast for GaN/N2. Fracture was only manifested in the imprint of GaN/N2 due to its low fracture toughness. Besides, it was disclosed the high sensitivity of loading rate only for GaN/H2. The GaN/N2 sample experiences plastic strain relaxation, while GaN/H2 is a highly stressed sample; hence, it has less dislocation density compared to GaN/N2 sample. We demonstrated that the used carrier gas influences on GaN epitaxial growth process, which in return deeply affects the resulting dislocation density and dislocation plasticity mechanisms. These latter, tailor the nanomechanical properties of GaN samples and the indentation-induced deformation behavior.

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.

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.

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.

Growth of SmFeAsO1−xFx and NdFe1−xCoxAsO thin films by metal–organic chemical vapor deposition and post diffusion processes

Iron-based ‘1111’ polycrystalline superconducting thin films have been successfully grown on (100) LaAlO3 substrates by metal–organic chemical vapor deposition and an ex situ diffusion process. The viability of the method to grow NdFe1−xCoxAsO and SmFeAsO1−xFx compounds is presented. The x-ray diffraction, scanning electron microscopy and electrical measurements show that the formation of the superconducting quaternary phase is possible by this method. The different behaviors of electrical resistance as a function of temperature are explained and discussed in terms of the amount of ‘doping’ in the different ReFeAsO compounds as well as in terms of the spurious phases that appear together with the superconducting phase.

Dependence of offset voltage in AlGaN/GaN van der Pauw devices under mechanical strain

This work reports the strain dependence of the offset voltage in an AlGaN/GaN van der Pauw device under mechanical strain. The AlGaN/GaN heterostructure was grown on a sapphire (0001) wafer by using a metal organic chemical vapor deposition (MOCVD) process. Taking advantage of the four-terminal configuration, the fabricated van der Pauw device exhibited an excellent repeatability and linearity with a significant change of the offset voltage under application of tensile and compressive strains. In particular, the sensitivity of the device to the applied strain was found to be as large as 3 (μV/V)/ppm, indicating the feasibility of using this effect for mechanical sensing applications. The sensing mechanism of the device is explained via the alteration of the sheet carrier concentration at the AlGaN/GaN interface and the asymmetric current flux in the 2DEG van der Pauw device.

Catalytic wet peroxide oxidation of m‐cresol over novel Fe2O3 loaded microfibrous entrapped CNT composite catalyst in a fixed‐bed reactor

AbstractBACKGROUNDA novel iron‐loaded microfibrous entrapped carbon‐nanotube catalyst (Fe2O3‐MF‐CNT) was synthesized by wet lay‐up papermaking, sintering and metal organic chemical vapor deposition (MOCVD) processes. The catalysts were characterized by N2 adsorption–desorption isotherm, mercury porosimetry, scanning electron microscopy (FE‐SEM), energy dispersive spectroscopy (EDS) and NH3 temperature program desorption (NH3‐TPD), and the catalytic performance was tested by catalytic wet peroxide oxidation (CWPO) of m‐cresol in a fixed‐bed reactor. Finally, the probable multistep reaction pathway for CWPO degradation of m‐cresol over Fe2O3‐MF‐CNT catalyst in a fixed‐bed reactor is presented.RESULTSCharacterization results conclude that the prepared catalysts are acid catalysts containing macropores and mesopores. Active components Fe2O3 are evenly loaded on the support by the MOCVD method. CWPO results show that higher temperature and higher space time promote the catalyst performance. Meanwhile, the Fe2O3‐MF‐CNT catalyst shows perfect reusability with nearly no iron leaching concentration and high m‐cresol conversion (above 95.0%) after four successive runs (24 h). Two possible pathways during degradation of m‐cresol are presented. The hydroxyl radicals turn m‐cresols into aromatic by‐products such as p‐toluquinone, 4‐methylpyrocatechol and methylhydroquinone, followed by evolution to organic acids, and finally to carbon dioxide and water. During the reaction, more m‐cresols are degraded through the pathway in which m‐cresols are first converted into 4‐methylpyrocatechol.CONCLUSIONThe novel Fe2O3‐MF‐CNT catalyst presented herein owns the advantages of both CNTs and stainless steel fibers, and it shows promising performance in CWPO of m‐cresol. © 2018 Society of Chemical Industry

One-step growth of thin film SnS with large grains using MOCVD

Thin film tin sulphide (SnS) films were produced with grain sizes greater than 1 μm using a one-step metal organic chemical vapour deposition process. Tin–doped indium oxide (ITO) was used as the substrate, having a similar work function to molybdenum typically used as the back contact, but with potential use of its transparency for bifacial illumination. Tetraethyltin and ditertiarybutylsulphide were used as precursors with process temperatures 430–470 °C to promote film growth with large grains. The film stoichiometry was controlled by varying the precursor partial pressure ratios and characterised with energy dispersive X-ray spectroscopy to optimise the SnS composition. X-ray diffraction and Raman spectroscopy were used to determine the phases that were present in the film and revealed that small amounts of ottemannite Sn2S3 was present when SnS was deposited on to the ITO using optimised growth parameters. Interaction at the SnS/ITO interface to form Sn2S3 was deduced to have resulted for all growth conditions.

Measuring the dielectric and optical response of millimeter-scale amorphous and hexagonal boron nitride films grown on epitaxial graphene

Monolayer epitaxial graphene (EG), grown on the Si face of SiC, is an advantageous material for a variety of electronic and optical applications. EG forms as a single crystal over millimeter-scale areas and consequently, the large scale single crystal can be utilized as a template for growth of other materials. In this work, we present the use of EG as a template to form millimeter-scale amorphous and hexagonal boron nitride (a-BN and h-BN) films. The a-BN is formed with pulsed laser deposition and the h-BN is grown with triethylboron (TEB) and NH3 precursors, making it the first metal organic chemical vapor deposition (MOCVD) process of this growth type performed on epitaxial graphene. A variety of optical and non-optical characterization methods are used to determine the optical absorption and dielectric functions of the EG, a-BN, and h-BN within the energy range of 1 eV–8.5 eV. Furthermore, we report the first ellipsometric observation of high-energy resonant excitons in EG from the 4H polytype of SiC and an analysis on the interactions within the EG and h-BN heterostructure.

Multi-Aperture Shower Design for the Improvement of the Transverse Uniformity of MOCVD-Derived GdYBCO Films.

A multi-aperture shower design is reported to improve the transverse uniformity of GdYBCO superconducting films on the template of sputtered-LaMnO3/epitaxial-MgO/IBAD-MgO/solution deposition planarization (SDP)-Y2O3-buffered Hastelloy tapes. The GdYBCO films were prepared by the metal organic chemical vapor deposition (MOCVD) process. The transverse uniformities of structure, morphology, thickness, and performance were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), step profiler, and the standard four-probe method using the criteria of 1 μV/cm, respectively. Through adopting the multi-aperture shower instead of the slit shower, measurement by step profiler revealed that the thickness difference between the middle and the edges based on the slit shower design was well eliminated. Characterization by SEM showed that a GdYBCO film with a smooth surface was successfully prepared. Moreover, the transport critical current density (Jc) of its middle and edge positions at 77 K and self-field were found to be over 5 MA/cm2 through adopting the micro-bridge four-probe method.

Development of Multipass MOCVD Process for Fabricating (Gd,Y)Ba2Cu3O7-δ Coated Conductors

A multipass metal organic chemical vapor deposition (MOCVD) process has been optimized to fabricate REBa2 Cu3O7-δ (REBCO) ( $\text{RE}= \text{Gd}+ \text{Y}$ with $\text{Gd}/ \text{Y} = \text{1}$ ) thin-film superconducting tapes with high critical currents. Some optimum MOCVD parameters for multipass process are found to be different from those for single-pass process, including RE:Ba:Cu ratio in precursor and deposition temperature. An X-ray diffraction analysis on the effect of changing rare-earth (RE) content on the structural property indicates that an RE-rich composition can improve the in-plane alignment of an REBCO film and favor the multipass process. A 280-m-long REBCO tape made by a three-pass MOCVD process achieved an average critical current of 256.4 A in a 4-mm width with a standard deviation of 9.4 A at 77 K and self-field.