Oxidative Chemical Vapor Deposition Research Articles

4 inch 11 μm high-quality AlN thick films grown on nanopatterned sapphire substrates

A high-quality AlN thick film with 11 μm thickness and low defect density was grown on a 4 inch hexagonal hole nano-patterned sapphire substrate by metal oxide chemical vapor deposition. The density of dislocation etch pits in the AlN heteroepitaxial film reached 1.1 × 107 cm−2. The surface and microstrcutres of the AlN thick film were characterized in detail. The dislocation evolution mechanism and stress evolution of AlN were investigated. Dislocations were mainly generated at the interface between the sapphire and AlN, and the voids above the patterned region were generated by the undesirable grain boundaries caused by the lateral epitaxy of AlN and the substrate during the growth process, which prompted a large number of screw dislocations to bend and merge, and while some mixed dislocations to merge and extend upwards, resulting in a high-quality AlN thick film.

Growth of zinc oxide nanowires by a hot water deposition method.

Recently, various methods have been developed for synthesizing zinc oxide (ZnO) nanostructures, including physical and chemical vapor deposition, as well as wet chemistry. These common methods require either high temperature, high vacuum, or toxic chemicals. In this study, we report the growth of zinc oxide ZnO nanowires by a new hot water deposition (HWD) method on various types of substrates, including copper plates, foams, and meshes, as well as on indium tin oxide (ITO)-coated glasses (ITO/glass). HWD is derived from the hot water treatment (HWT) method, which involves immersing piece(s) of metal and substrate(s) in hot deionized water and does not require any additives or catalysts. Metal acts as the source of metal oxide molecules that migrate in water and deposit on the substrate surface to form metal oxide nanostructures (MONSTRs). The morphological and crystallographic analyses of the source-metals and substrates revealed the presence of uniformly crystalline ZnO nanorods after the HWD. In addition, the growth mechanism of ZnO nanowires using HWD is discussed. This process is simple, inexpensive, low temperature, scalable, and eco-friendly. Moreover, HWD can be used to deposit a large variety of MONSTRs on almost any type of substrate material or geometry.

Triflate Salts as Alternative Non-Chlorinated Oxidants for the Oxidative Chemical Vapor Deposition and Electronic Engineering of Conjugated Polymers.

Oxidative chemical vapor deposition (oCVD) stands as an attractive approach for the synthesis, engineering, and integration of conjugated polymers for advanced electronic and optoelectronic applications. In oCVD, the oxidant significantly influences the conformational and optoelectronic properties of the resulting conjugated polymer thin films. In this work, triflate salts of iron(III) and copper(II) (Fe(OTf)3 and Cu(OTf)2, respectively) are investigated for the first time as suitable alternative oxidants to the widely used iron(III) chloride (FeCl3) for the oCVD of conjugated polymers. Structural and compositional characterizations of the resulting thin films evidenced the successful polymerization of cobalt(II) 5,15-diphenyl porphyrin using either Fe(OTf)3 or Cu(OTf)2. Along with an intermolecular dehydrogenative C-C coupling reaction, the occurrence of side reactions, such as the inclusion of -CF3 groups and demetalation and subsequent insertion of copper(II) in the porphyrin macrocycle when using Cu(OTf)2, were evidenced. Interestingly, the inclusion of -CF3 groups into the polymer backbone when using triflate salts results in a deepening of the frontier energy levels, while the insertion of copper(II) contributes to a reduction in the band gap energy. This work demonstrates that the careful selection of the oxidant agent in oCVD enables fine-tuning the optoelectronic properties of conjugated polymers to suit specific application requirements.

Influence of Cobalt and Cobalt–Manganese Oxide Coating Thickness Deposited by DLI-MOCVD as a Barrier Against Cr Diffusion for SOC Interconnect

The influence of cobalt and cobalt–manganese oxide coating thickness on its ability to be a good diffusion barrier against Cr outward diffusion was investigated for stainless steel interconnects (AISI 441) of a solid oxide cell (SOC). The coatings were all synthesized using a DLI-MOCVD (Direct Liquid Injection-Metal Oxide Chemical Vapor Deposition) hot wall reactor. The study shows that a minimum cobalt oxide thickness of 300 nm was needed to be a good diffusion barrier against Cr for the 500-h exposure test. This observation was linked to the Mn concentration reached in the cobalt spinel during exposure. Indeed, during exposure at high temperature, Mn diffused from the substrate into the cobalt coating and transformed cobalt spinel into Co-Mn spinel. Whereas pure cobalt spinel was a good Cr diffusion barrier, cobalt-manganese spinel, Co3-xMnxO4, was not when x > 2. The thickness of the cobalt coatings must be chosen so that the Mn quantity coming into it from diffusion from the substrate does not degrade the protectiveness of the coating.

Advancements in oxidative chemical vapor deposition (oCVD) with liquid oxidant: A true dry vacuum manufacturing approach for optoelectronic devices

Advancements in oxidative chemical vapor deposition (oCVD) with liquid oxidant: A true dry vacuum manufacturing approach for optoelectronic devices

Reel-to-Reel Coating of a Conductive Polymer on Synthetic Textile Yarns in a Semi-closed Batch Oxidative CVD System

In this manuscript, we demonstrate the ability to use a reel-to-reel processing technology for conductive surface functionalization of textile yarns using oxidative chemical vapor deposition in a continuous manner. We designed and built a vacuum deposition system, which allows the winding of yarns into the oCVD reactor by unreeling from the outside atmosphere, where the yarn is pre-treated with oxidant solution. Iron(III)chloride (FeCl3) and 3,4-ethylenedioxythiophene were used as the oxidant and monomer, respectively, to deposit thin films of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films on the synthetic PET yarn surfaces. FTIR and XPS analyses were carried out to verify the chemical structure of as-deposited PEDOT films. Effects of temperature, oxidant concentration, and winding speed on the electrical conductivities of the yarns after oCVD were studied. All yarns exhibited non-zero conductivity values independent of the deposition conditions studied. Very high conductivity uniformities were observed along the longitudinal direction of the yarns even at the highest studied winding speed of 24 cm/min.

Enhancing Capacitance of Carbon Cloth Electrodes via Highly Conformal PEDOT Coating Fabricated by the OCVD Method Utilizing SbCl5 Oxidant

AbstractCarbon cloth shows potential for flexible energy storage electrodes but encounters challenges such as low specific capacitance and limited wettability. This study addresses these limitations by fabricating a highly conformal coating of poly(3,4‐ethylenedioxythiophene) (PEDOT) around 3D carbon fibers via the oxidative chemical vapor deposition (oCVD) method, employing antimony pentachloride (SbCl5) as the oxidant. The oCVD stands out as a robust manufacturing technique for fabricating highly conformal conducting polymer films on porous structures, ensuring the preservation of geometric features and the maintenance of active sites for redox reactions. The resulting PEDOT‐coated carbon cloth electrodes exhibit improved pseudocapacitance and specific capacitance compared to their pristine counterparts. Particularly, oCVD PEDOT‐coated carbon cloth fabricated at various deposition temperatures exhibit a substantial 1.5‐ to 2.3‐fold enhancement in specific capacitance compared to pristine carbon cloth. The highest specific capacitance (170.94 F g⁻¹) is attained in the oCVD PEDOT‐coated carbon cloth fabricated at a deposition temperature of 80 °C, representing a 2.3‐fold enhancement over its pristine counterpart. The PEDOT‐coated carbon cloths demonstrate lower charge transfer resistance compared to their pristine counterparts, further confirming their superior electrochemical performance. This investigation highlights oCVD's effectiveness in fabricating highly conformal PEDOT coating on carbon cloth electrodes for electrochemical energy storage devices.

Comparative Study of Field-Effect Transistors Based on Graphene Oxide and CVD Graphene in Highly Sensitive NT-proBNP Aptasensors.

Graphene-based materials are actively being investigated as sensing elements for the detection of different analytes. Both graphene grown by chemical vapor deposition (CVD) and graphene oxide (GO) produced by the modified Hummers' method are actively used in the development of biosensors. The production costs of CVD graphene- and GO-based sensors are similar; however, the question remains regarding the most efficient graphene-based material for the construction of point-of-care diagnostic devices. To this end, in this work, we compare CVD graphene aptasensors with the aptasensors based on reduced GO (rGO) for their capabilities in the detection of NT-proBNP, which serves as the gold standard biomarker for heart failure. Both types of aptasensors were developed using commercial gold interdigitated electrodes (IDEs) with either CVD graphene or GO formed on top as a channel of liquid-gated field-effect transistor (FET), yielding GFET and rGO-FET sensors, respectively. The functional properties of the two types of aptasensors were compared. Both demonstrate good dynamic range from 10 fg/mL to 100 pg/mL. The limit of detection for NT-proBNP in artificial saliva was 100 fg/mL and 1 pg/mL for rGO-FET- and GFET-based aptasensors, respectively. While CVD GFET demonstrates less variations in parameters, higher sensitivity was demonstrated by the rGO-FET due to its higher roughness and larger bandgap. The demonstrated low cost and scalability of technology for both types of graphene-based aptasensors may be applicable for the development of different graphene-based biosensors for rapid, stable, on-site, and highly sensitive detection of diverse biochemical markers.

Enhanced doping and structure relaxation of unsubstituted polythiophene through oxidative chemical vapor deposition and mild plasma treatment

We report on the enhancement of electrical properties of unsubstituted polythiophene (PT) through oxidative chemical vapor deposition (oCVD) and mild plasma treatment. The work function of p-type oCVD PT increases after the treatment, indicating the Fermi level shift toward the valence band edge and an increase in carrier density. In addition, regardless of initial values, nearly the same work function is obtained for all the plasma-treated oCVD PT films as high as ∼5.25 eV, suggesting the pseudo-equilibrium state is reached in the oCVD PT from the plasma treatment. This increase in carrier density after plasma treatment is attributed to the activation of initially not-activated dopant species (i.e. neutrally charged Br), which is analogous to the release of trapped charge carriers to the valence band of the oCVD PT. The enhancement of electrical properties of oCVD PT is directly related to the improvement of the thin film transistor performance such as drain current on/off ratio, ∼103 and field effect mobility, 2.25 × 10−2 cm2 Vs−1, compared to untreated counterparts of 102 and 0.09 × 10−2 cm Vs−1, respectively.

Morphological and molecular control of chemical vapor deposition (CVD) polymerized polythiophene thin films.

Oxidative chemical vapor deposition (oCVD) has emerged as one of the most promising techniques for conjugated polymer deposition, especially for unsubstituted polythiophene thin films. oCVD overcomes the insolubility challenge that unsubstituted polythiophene (PT) presents and adds the ability to control morphological and molecular structure. This control is important for enhancing the performance of devices which incorporate organic conductors. In this work, Raman spectroscopy, UV-vis spectroscopy, and AFM reveal that the relative amount of distortion in the polymer chains, the conjugation length and the film roughness are all affected by the CVD deposition conditions, in particular the reactor pressure. PT films deposited at 150 mT and 300 mT are found to have lower chain distortion, longer conjugation lengths and lower surface roughness compared to other deposition pressures. The oCVD PT film is also directly grafted to the trichloro(phenylethyl)silane (PTS) treated substrates, where the effect of PTS grafting is observed to significantly affect film roughness. In addition, we report the first study of the effect of oCVD PT films on the performance of lithium-ion battery electrodes. These oCVD PT films are used to engineer a LiCoO2 cathode in lithium-ion batteries. The observed improvements are a 52% increase in the discharge capacity (67 mA h g-1 to 102 mA h g-1) at 10C and a 500% improvement in cycling stability tested at 5C within the voltage range of 3.0-4.5 V (capacity fading rate is reduced from 1.92%/cycle to 0.32%/cycle).

Parylene-AlOx Stacks for Improved 3D Encapsulation Solutions

The demand for ultra-tight encapsulation solutions with excellent barrier and high conformality properties has increased in recent years. To meet these challenges, thin-film barrier coatings have emerged as a promising solution. In this study, we investigate well-established silicon-based plasma-enhanced chemical vapor deposition (PECVD) and metal oxide atomic layer deposition (ALD) barrier coatings deposited at low temperatures (≤100 °C) regarding their abilities to address high-level 3D encapsulation applications. Various combinations of such layers are evaluated by measuring the water vapor transmission rate (WVTR) and considering the conformality properties. The impact and the benefits of the organic film integration, namely parylene VT4 grade, on the barrier performances is assessed. Among these combinations, parylene-AlOx stack emerges as one of the most effective solutions, obtaining a WVTR of 3.1 × 10−4 g m−2 day−1 at 38 °C and 90% relative humidity conditions.

Improving the oxidation resistance of carbon fibers via B4C coating by modified boron oxide chemical vapor deposition

Carbon fiber is one of the engineering materials frequently used in high-temperature applications despite its very poor oxidation resistance. To enhance the oxidation resistance of C fibers and improve the service temperature, boron carbide coatings were prepared by the modified reactive boron oxide chemical vapor deposition (BOCVD) method. For the coating process, a tube furnace system was utilized. Experiments were performed at 1100–1400 °C for up to 6 h under a flowing Ar atmosphere. Coatings were analyzed by SEM, Raman, XRD, and XPS analysis. B4C coatings were found to be in nodular form around 30–50 nm. Oxidation tests performed in flowing air up to 1500 °C by DTA-TG analysis and oxidation mechanisms were explained in details. We revealed that the base oxidation resistance increased up to 180 °C with no net mass gain or loss.

Regulating Li Nucleation and Growth Heterogeneities via Near-Surface Lithium-Ion Irrigation for Stable Anode-Less Lithium Metal Batteries.

The inhomogeneous nucleation and growth of Li dendrite combined with the spontaneous side reactions with the electrolytes dramatically challenge the stability and safety of Li metal anode (LMA). Despite tremendous endeavors, current success relies on the use of significant excess of Li to compensate the loss of active Li during cycling. Herein, a near-surface Li+ irrigation strategy is developed to regulate the inhomogeneous Li deposition behavior and suppress the consequent side reactions under limited Li excess condition. The conformal polypyrrole (PPy) coating layer on Cu surface via oxidative chemical vapor deposition technique can induce the migration of Li+ to the interregional space between PPy and Cu, creating a near-surface Li+-rich region to smooth diffusion of ion flux and uniform the deposition. Moreover, as evidenced by multiscale characterizations including synchrotron high-energy X-ray diffraction scanning, a robust N-rich solid-electrolyte interface (SEI) is formed on the PPy skeleton to effectively suppress the undesired SEI formation/dissolution process. Strikingly, stable Li metal cycling performance under a high areal capacity of 10mAhcm-2 at 2.0mAcm-2 with merely 0.5×Li excess is achieved. The findings not only resolve the long-standing poor LMA stability/safety issues, but also deepen the mechanism understanding of Li deposition process.

A Polymer-Derived Co(Fe)Ox Oxygen Evolution Catalyst Benefiting from the Oxidative Dehydrogenative Coupling of Cobalt Porphyrins.

Thin films of cobalt porphyrin conjugated polymers bearing different substituents are prepared by oxidative chemical vapor deposition (oCVD) and investigated as heterogeneous electrocatalysts for the oxygen evolution reaction (OER). Interestingly, the electrocatalytic activity originates from polymer-derived, highly transparent Co(Fe)Ox species formed under operational alkaline conditions. Structural, compositional, electrical, and electrochemical characterizations reveal that the newly formed active catalyst greatly benefited from both the polymeric conformation of the porphyrin-based thin film and the inclusion of the iron-based species originating from the oCVD reaction. High-resolution mass spectrometry analyses combined with density functional theory (DFT) calculations showed that a close relationship exists between the porphyrin substituent, the extension of the π-conjugated system cobalt porphyrin conjugated polymer, and the dynamics of the polymer conversion leading to catalytically active Co(Fe)Ox species. This work evidences the precatalytic role of cobalt porphyrin conjugated polymers and uncovers the benefit of extended π-conjugation of the molecular matrix and iron inclusion on the formation and performance of the true active catalyst.

Effect of various dopants on titanium dioxide nanorod arrays: A review

In recent years, titanium dioxide (TiO2) has emerged as one of the most exceptional nanomaterials, attracting interest from experts throughout the globe. In addition to having a band gap of 3.2 eV, TiO2 has outstanding optical, structural, electrical, and photocatalytic capabilities that may be used in the semiconductor industry. However, because of its weak conductivity and capacitance, TiO2 has not been able to reach its full potential. In order to realise its full potential, researchers have devised a variety of methods, including hydrothermal deposition, sol-gel-assisted template deposition, chemical vapor deposition, electrochemical anodisation, hydrothermal deposition, and metal oxide doping. Doping TiO2 with metal oxides has been shown to significantly enhance its properties, which may improve its qualities. The primary goal of this study is to provide an overview of various research studies on the influence of the metal oxide dopant on the final properties of titanium dioxide (TiO2) nanorod arrays.

Mold-Free Manufacturing of Highly Sensitive And Fast Response Pressure Sensors Through High-Resolution 3d Printing And Conformal Oxidative Chemical Vapor Deposition Polymers.

In this work, w e showcase a new manufacturing paradigm to exclude conventional mold-dependent manufacturing of pressure sensors, which typically requires a series of complex and expensive patterning processes. Our mold-free manufacturing leverages high-resolution 3D printed multiscale microstructures as substrate and a gas-phase conformal polymer coating technique to complete the mold-free sensing platform. The array of dome and spike structures with a controlled spike density of a 3D-printed substrate ensures a large contact surface with pressures applied and extended linearity in a wider pressure range. For uniform coating of sensing elements on the microstructured surface, oxidative chemical vapor deposition is employed to deposit a highly conformal and conductive sensing element, poly(3,4-ethylenedioxythiophene) at low temperatures (< 60 °C). The fabricated pressure sensor reacts sensitively to various ranges of pressures (up to 185 kPa-1 ) depending on the density of the multiscale features and shows an ultra-fast response time (∼36 μs). The mechanism investigations through the finite element analysis identify the effect of the multiscale structure on the figure-of-merit sensing performance. Our unique findings are expected to be of significant relevance to the technology that requires higher sensing capability, scalability, and facile adjustment of a sensor geometry in a cost-effective manufacturing manner. This article is protected by copyright. All rights reserved.

Oxidative chemical vapor deposition of polypyrrole onto carbon fabric for flexible supercapacitive electrode material

Polypyrrole has been a promising conjugated polymer for application in electrochemical energy storage devices. One primary feature is its pseudocapacitive behavior, which makes it suitable for hybridization with traditional carbon-based electrical double layer capacitive materials. The processing condition for such a hybridization is a critical aspect for the electrode performance in long term. Oxidative chemical vapor deposition was used to deposit polypyrrole onto 3D carbon fiber fabric. This allowed uniform and conformal deposition of polypyrrole on individual fibers as well as a control over its thickness depending on the reaction time. The obtained composite was characterized for electrochemical energy storage application using cyclic voltammetry and galvanostatic charge discharge measurements. Additionally, the stability of the polypyrrole-carbon fiber electrode was tested using microscopy and energy dispersive spectroscopy in order to obtain insights into physical and chemical degradation of polypyrrole during electrochemical aging. Results showed thickness-dependence of electrode stability, tuning of which in the correct voltage window is necessary for optimal long-term performance.

A sulfur cathode design strategy for polysulfide restrictions and kinetic enhancements in Li-S batteries through oxidative chemical vapor deposition

Lithium-sulfur (Li-S) batteries offer a promising solution for achieving high-density and low-cost energy storage devices. However, the practical utilization of Li-S batteries is hindered by the main bottleneck of polysulfides transport from the cathode to the electrolyte and anode, which leads to the detrimental degradation of the electrolyte and non-uniform microstructure evolution on the anode, ultimately resulting in rapid capacity fading. To overcome this limitation, we propose a groundbreaking mitigation strategy that leverages the oxidative chemical vapor deposition (oCVD) technique to limit the shuttling of polysulfides in the cathode. This gas-phase approach is unique in that highly conducting and conformal polymer coating entirely eliminates the use of traditional binders in the cathode while enhancing the kinetic conditions of the sulfur conversion and inhibiting the shuttling of polysulfides during battery operation. Complementary experimental and theoretical investigations identify that polysulfides are physically and chemically confined in the cathode region. The sulfur cathode manufactured using this approach demonstrates high active material loading (90 wt%), a high sulfur utilization ratio of 84.4% (∼1413 mAh g−1 at 0.1 C), and capacity retention of 85% after 300 cycles (∼810 mAh g−1) at 0.5 C. The pouch cell also showcases a high specific energy of up to 202 Wh kg−1 with a low electrolyte/sulfur ratio of 4.55, proving the immense potential for practical applications.

Effect of graphene coatings on the morphology of submillimeter thin copper wires after salt spray aging

Unprotected copper conductors are prone to oxidation and corrosion, especially when in contact with salt water or at high temperature. In this study, we compared commercially available coating with graphene oxide and plasma-enhanced chemical vapor deposition (PECVD) graphene coated wires in terms of antioxidation and anticorrosion protection. Samples were subjected to aging tests in a salt spray chamber. Thereafter, both the degree of coverage and surface protection were assessed by X-ray photoelectron spectroscopy measurements and scanning electron microscope images, which showed significant surface protection for both graphene coatings. Raman spectra obtained from the transferred coatings revealed their structural stability, which shows that it is possible to successfully use few atomic-layers-thick coatings to protect commercially available wires. Wire resistance tests performed at temperatures up to 320°C showed similar or better results for graphene coatings than for commercially coated wires. Additionally, images of the wires after high temperature tests showed high antioxidation protection for graphene coatings, especially for PECVD. The results of this study can be applied for further research on mechanical suitability of the coatings and wires themselves, especially after high-temperature CVD processes. Such studies may lead to novel Cu wire processing technologies.Graphical abstract

Photo-electrocatalytic performance of poly(3,4-ethylenedioxythiophene)/TiO2 nano-tree films deposited by oCVD/CVD for H2 production

The hydrogen production from photo-electrocatalytic water splitting attracts extensive attention as a direct way to convert solar energy into chemical fuels. In this work, innovative photo-anodes composed of TiO2 which has a preferable growth orientation [211] conjugated with PEDOT as bi-layers are prepared by a dry process strategy, combining oxidative and metalorganic chemical vapor deposition (CVD). Pure anatase, dendritic TiO2 films of variable thickness are obtained at 500 °C by varying the deposition time. Increase of films thickness from 474 to 2133 nm results in morphologies that evolve from dense and angular structures to isolated and nanostructured tree-like columns with a concomitant decrease of the charge transfer resistance due to the enhancement of active facets of anatase structure. The PEDOT/TiO2 bi-layer with an overall thickness of 1350 nm and a 50 nm thick upper-PEDOT layer exhibits the highest photocurrent response (0.26 mA cm−2 at 1.8 V/RHE), a fast photocurrent response under illumination, and the best hydrogen yield up to 4.1 µmol cm-2h−1 with electronic conductivity being three order of magnitude higher than pristine TiO2.