Chemical Vapor Deposition Approach Research Articles

Chemical Vapor Deposition for Advanced Polymer Electrolyte Fuel Cell Membranes

AbstractFuel cells will play a critical role in a renewable energy powered society, whether in mobility or stationary applications. Certain challenges remain to be addressed if performance and cost dynamics of these systems is to achieve large scale, high unit number roll out. This review deals with polymer electrolyte membrane‐based fuel cells with a specific focus on membrane materials and their innovative fabrication based on chemical vapor deposition (CVD) approaches. These deposition techniques are introduced, as are the potential improvements relating to cell performance, namely proton conductivity and stability. The potential benefits of applying CVD‐based synthesis in the fabrication of polymer electrolytes is also discussed with respect to future fuel cell development.

Low Temperature Open-Air Plasma Deposition of SrTiO3 Films for Solar Energy Harvesting: Impact of Precursors on the Properties and Performances.

Strontium titanate (STO) is a well-known oxide used in a wide variety of applications due to its excellent stability and optoelectronic properties. However, its integration in photoelectrocatalytic devices is limited by the lack of fast and scalable methods to produce robust films at a low temperature and atmospheric pressure. Herein, we report an atmospheric pressure plasma-enhanced chemical vapor deposition (AP-PECVD) approach for the synthesis of STO crystalline films and their applications for photoelectrochemical solar energy conversion. The film crystallinity, which plays a determinant role in the photoelectrochemical performance, was linked to the selected strontium precursor and injection method. Through thermal stability studies of the precursors [Sr(dpm), Sr(ipo), Sr(acac), and Ti(ipo)] and analysis of the solution droplet size, it was demonstrated that the closer thermal decomposition behavior and superior miscibility of the Sr(dpm) and Ti(ipo) precursors led to more homogeneous and crystalline films with the highest photoelectrochemical performance (16.5 μA cm-2 at 1.23 V vs RHE under 100 mW cm-2), which can be further improved by a factor of 3.4 using thermal annealing at 500 °C. Evidence of the impact of a strontium precursor on the properties of STO films is provided through thermogravimetric analysis, X-ray diffraction, energy-dispersive system, UV-vis, X-ray photoelectron spectroscopy, HIM-SIMS, and photoelectrochemical analysis.

Selective Antisite Defect Formation in WS2 Monolayers via Reactive Growth on Dilute W‐Au Alloy Substrates (Adv. Mater. 3/2022)

2D Materials In article number 2106674, Kai Xiao and co-workers develop a nonequilibrium chemical vapor deposition approach for selective formation of antisite defects in atomically thin 2D tungsten sulfide monolayer crystals by regulating the diffusion of tungsten into gold substrates. This work demonstrates a novel strategy for the selective formation of defects in 2D materials by tuning their formation energy during synthesis via choice of substrate and alloy design.

Monolayer MoS2/n-Si Heterostructure Schottky Solar Cell

Monolayer MoS2 has a promising optoelectronics property, with a bandgap in the visible range; the material is a potential candidate for solar cell applications. In this work, we grew MoS2 monolayers using a low-pressure chemical vapor deposition approach. To produce uniform wafer-scale MoS2 monolayer films, precursors molybdenum dioxide (MoO2) and sulfur (S) are utilized. Atomic force microscopy was used to quantify the thickness of the monolayers, and the result was validated by Raman spectroscopy. Transmission electron microscopy (TEM) was used to confirm the crystalline quality of the monolayers, and photoluminescence spectroscopy was used to evaluate their optical properties. We were able to create a Schottky solar cell with a MoS2 monolayer up to 1 cm2 area by transferring monolayer film to n-type silicon. The MoS2/n-Si Schottky solar cell demonstrated photovoltaic characteristics with a short circuit current density of 14.8 mA cm−2 and an open-circuit voltage of 0.32 V under 100 mW cm−2 illumination. The fill factor and energy conversion efficiency were 53% and 2.46%, respectively, with the highest external quantum efficiency at 530 nm being 44%.

High-Throughput Production of 1T MoS2 Monolayers Based on Controllable Conversion of Mo-Based MXenes.

Although transition metal dichalcogenides (TMDs) monolayers are widely applied in electronics, optics, catalysis, and energy storage, their yield or output is commonly very low (<1 wt % or micrometer level) based on the well-known top-down (e.g., exfoliation) and bottom-up (e.g., chemical vapor deposition) approaches. Here, 1T MoS2 monolayers with a very high fraction of ∼90% were achieved via the conversion of Mo-based MXenes (Mo2CTx and Mo1.33CTx) at high temperatures in hydrogen sulfide gas, in which the Mo-layer of Mo-based MXenes could be transformed to MoS2 monolayers and the Mo vacancies facilitate the gliding of sulfur layers to form 1T MoS2. The resultant 1T MoS2 monolayers with numerous vacancies exhibit strong chemisorption and high catalytic activity for lithium polysulfides (LiPSs), delivering a reversible capacity of 736 mAh g-1 at 0.5 C, a superior rate capability of 532 mAh g-1 at 5 C, and a good stability up to 200 cycles at 1 C in lithium-sulfur (Li-S) batteries.

Recent Advances in Processing and Applications of Heterobimetallic Oxide Thin Films by Aerosol-Assisted Chemical Vapor Deposition.

The fabrication of smart, efficient, and innovative devices critically needs highly refined thin-film nanomaterials; therefore, facile, scalable, and economical methods of thin films production are highly sought-after for the sustainable growth of the hi-tech industry. The chemical vapor deposition (CVD) technique is widely implemented at the industrial level due to its versatile features. However, common issues with a precursor, such as reduced volatility and thermal stability, restrict the use of CVD to produce novel and unique materials. A modified CVD approach, named aerosol-assisted CVD (AACVD), has been the center of attention due to its remarkable tendency to fabricate uniform, homogenous, and distinct nano-architecture thin films in an uncomplicated and straightforward manner. Above all, AACVD can utilize any custom-made or commercially available precursors, which can be transformed into a transparent solution in a common organic solvent; thus, a vast array of compounds can be used for the formation of nanomaterial thin films. This review article highlights the importance of AACVD in fabricating heterobimetallic oxide thin films and their potential in making energy production (e. g., photoelectrochemical water splitting), energy storage (e. g., supercapacitors), and environmental protection (e. g., electrochemical sensors) devices. A heterobimetallic oxide system involves two metallic species either in a composite, solid solution, or metal-doped metal oxides. Moreover, the AACVD tunable parameters, such as temperature, deposition time, and precursor, which drastically affect thin films microstructure and their performance in device applications, are also discussed. Lastly, the key challenges and issues of scaling up AACVD to the industrial level and processing for emerging functional materials are also highlighted.

On-wire axial perovskite heterostructures for monolithic dual-wavelength laser

All-inorganic lead halide perovskites have attracted tremendous attention for their tunable bandgaps, excellent photoluminescence efficiency and robust stability. Here, we report on a direct vapor-phase growth of high-quality CsPbCl3/CsPbI3 axial perovskite heterostructure and multi-heterojunction nanowires using a newly developed magnetic-pulling chemical vapor deposition approach. Microstructural characterization and optical investigations reveal that these structures are crystalline with abrupt heterojunctions. Micro-photoluminescence spectra and mapping at the heterojunctions exhibit dual-wavelength emissions at 417 nm and 698 nm, from the adjacent two disparate perovskites, respectively, further demonstrating the formation of unique heterostructures. Additionally, under a focused laser illumination, asymmetrical waveguide behavior along a single CsPbCl3/CsPbI3 wire is clearly observed. Taking a step further, we fabricated a monolithic dual-wavelength laser using an on-wire axial perovskite heterostructure and successfully realized blue and red emissions (425.5 nm and 687.4 nm). The capability to synthesize on-wire heterostructures represents a major step toward high-integration optoelectronic circuits and nanophotonics.

Selective Antisite Defect Formation in WS2 Monolayers via Reactive Growth on Dilute W-Au Alloy Substrates.

Defects are ubiquitous in 2D materials and can affect the structure and properties of the materials and also introduce new functionalities. Methods to adjust the structure and density of defects during bottom-up synthesis are required to control the growth of 2D materials with tailored optical and electronic properties. Here, the authors present an Au-assisted chemical vapor deposition approach to selectively form SW and S2W antisite defects, whereby one or two sulfur atoms substitute for a tungsten atom in WS2 monolayers. Guided by first-principles calculations, they describe a new method that can maintain tungsten-poor growth conditions relative to sulfur via the low solubility of W atoms in a gold/W alloy, thereby significantly reducing the formation energy of the antisite defects during the growth of WS2 . The atomic structure and composition of the antisite defects are unambiguously identified by Z-contrast scanning transmission electron microscopy and electron energy-loss spectroscopy, and their total concentration is statistically determined, with levels up to ≈5.0%. Scanning tunneling microscopy/spectroscopy measurements and first-principles calculations further verified these antisite defects and revealed the localized defect states in the bandgap of WS2 monolayers. This bottom-up synthesis method to form antisite defects should apply in the synthesis of other 2D materials.

High‐performance electronics and optoelectronics of monolayer tungsten diselenide full film from pre‐seeding strategy

AbstractTungsten diselenide (WSe2) possesses extraordinary electronic properties for applications in electronics, optoelectronics, and emerging exciton physics. The synthesis of monolayer WSe2 film is of topmost for device arrays and integrated circuits. The monolayer WSe2 film has yet been reported by thermal chemical vapor deposition (CVD) approach, and the nucleation mechanism remains unclear. Here, we report a pre‐seeding strategy for finely regulating the nuclei density at an early stage and achieving a fully covered film after chemical vapor deposition growth. The underlying mechanism is heterogeneous nucleation from the pre‐seeding tungsten oxide nanoparticles. At first, we optimized the precursor concentration for pre‐seeding. Besides, we confirmed the superiority of the pre‐seeding method, compared with three types of substrate pretreatments, including nontreatment, sonication in an organic solvent, and oxygen plasma. Eventually, the high‐quality synthetic WSe2 monolayer film exhibits excellent device performance in field‐effect transistors and photodetectors. We extracted thermodynamic activation energy from the nucleation and growth data. Our results may shed light on the wafer‐scale production of homogeneous monolayer films of WSe2, other 2D materials, and their van der Waals heterostructures.image

Phase-Tunable Synthesis and Etching-Free Transfer of Two-Dimensional Magnetic FeTe.

Two-dimensional (2D) Fe-chalcogenides (e.g., FeS, FeSe, and FeTe, etc.) have sparked extensive interest due to their rich phase diagrams including superconductivity, magnetism, and topological state, as well as versatile applications in electronic devices and energy related fields. However, the phase-tunable synthesis and green transfer of such fascinating materials still remain challenging. Herein, we develop a temperature-mediated chemical vapor deposition (CVD) approach to grow ultrathin nonlayered hexagonal and layered tetragonal FeTe nanosheets on mica substrates, with their thicknesses down to ∼2.3 and ∼4.0 nm, respectively. Interestingly, we have observed exciting ferromagnetism with the Curie temperature approaching ∼300 K and high conductivity (∼1.96 × 105 S m-1) in 2D hexagonal FeTe. More significantly, we have designed a swift, high-efficiency, and etching-free method for the transfer of 2D FeTe nanosheets onto arbitrary substrates, and such a transfer strategy enables the cyclic utilization of growth substrates. These results should propel the further development of phase-tunable synthesis and green transfer of 2D Fe-chalcogenides, as well as their potential applications in spintronic devices.

On the dynamics in chemical vapor deposition of InN

Epitaxial nanometer-thin indium nitride (InN) films are considered promising active layers in various device applications but remain challenging to deposit. We compare the morphological evolution and characterizations of InN films with various growth conditions in chemical vapor deposition (CVD) by both a plasma atomic layer deposition (ALD) approach and a conventional metalorganic CVD approach. Our results show that a time-resolved precursor supply is highly beneficial for deposition of smooth and continuous InN nanometer-thin films. The time for purging the reactor between the precursor pulses and low deposition temperature are key factors to achieve homogeneous InN. The gas exchange dynamics of the reactor is further studied using computational fluid dynamics. According to our study, 320 °C is found to be the upper temperature where the dynamics of the deposition chemistry can be controlled to involve only surface reactions with surface species. The results highlight the promising role of the ALD technique in realizing electronic devices based on nanometer-thin InN layers.

The synthesis and identification of complete stacking bilayer MoS2 flakes with unconventional shapes via chemical vapor deposition

Two-dimensional complete stacking bilayer molybdenum disulfide (MoS 2 ) crystals with several unconventional morphologies, including four-point star, hexagon, rhomboid, trapezoid, and pentagon, have been attained by employing the space-confined chemical vapor deposition approach. The morphology, structure, and fundamental features of as-produced domains are systematically characterized via utilizing optical microscopy, atomic force microscopy , and Raman/PL system, elucidating bilayer feature of various MoS 2 flakes. The variation of such various bilayer MoS 2 crystals is discussed based on the difference of growth rate between different sides. • Complete stacking bilayer MoS 2 flakes with various shapes have been attained via space-confined chemical vapor deposition. • Evolution of varied shapes, layer-number, and optical properties of bilayer MoS 2 flakes has been evaluated. • Possible growth mechanism of these bilayer MoS 2 flakes with various shapes has been discussed.

Mussel-tailored carbon fiber/carbon nanotubes interface for elevated interfacial properties of carbon fiber/epoxy composites

Based on the Platform effect of polydopamine (PDA), the distribution of metal catalyst on the surface of carbon fiber was investigated in this study. Through PDA-based carbon coating, directional Carbon nanotubes (CNTs) are grown on the high strength carbon fiber body without damaging the interface structure and properties of Carbon fiber reinforced plastic (CFRP) by Chemical vapor deposition (CVD) approach. The results indicated that the PDA coating endows CNTs with a uniform distribution on the fiber surface, which effectively mitigate the corrosion of the fiber body by the high temperature and metal catalyst during the CVD process, thus augmenting the mechanical properties of the carbon fibers and their composites. The failure mechanism of the composite under stress was clarified by the transverse and longitudinal fracture morphology, which further developed the interface theory of CFRP.

Light-Emitting V-Pits: An Alternative Approach toward Luminescent Indium-Rich InGaN Quantum Dots

Realization of fully solid-state white light emitting devices requires high efficiency blue, green, and red emitters. However, challenges remain in boosting the low quantum efficiency of long wavelength group-III-nitride light emitters through conventional quantum well growth. Here, we demonstrate a new direct metal–organic chemical vapor deposition approach to grow In-rich InGaN quantum dots on Si substrates using V-pits, bypassing the need for patterning or unconventional substrates. A correlative nanoscale study on the optical, compositional, and structural properties of intersecting V-pits reveals that the highly textured surface gives rise to localized high intensity red-shifted emission from the apexes of pyramids where InGaN quantum dots spontaneously form. We establish the origin of this efficient long wavelength luminescence to result from both spatially confined higher In-content deposition, as well as smaller bandgap energy basal stacking faults entrapped within a ring of low-emissivity prismatic stacking faults. Our monolithic growth approach on Si would open up new pathways toward attaining CMOS-compatible phosphor-free white light emitting solid-state devices.

Growth Behavior, nucleation control and excellent optical properties of atomically thin WS2 thin films processed via Gas-phase chemical vapor deposition

Improving growth-rate of atomically thin transition metal dichalcogenides (TMDs) with precise thickness-control using a facile-approach is ever growing interest for nanoscale electronic devices. Here, using metalorganic precursors, we demonstrate the growth of WS2 layers on sapphire and SiO2/Si substrates at elevated temperatures via gas-phase chemical vapor deposition (CVD) approach. This choice of precursor for the CVD-process allowed us to rapidly produce the WS2 layers with a growth rate as high as 1-monolayer per 5 min at a growth temperature of 850 ℃. The layer thickness (number of layers), which linearly scales with growth time, can be manipulated with a monolayer precision. Our findings suggest that the initial-nucleation and growth behavior of the WS2 monolayers are very well controlled by reactor pressure and growth temperature. Grain size engineering and possible growth-mode switching from 2D lateral-growth to 3D vertical-growth is demonstrated by tuning the CVD reactor pressure between 10 and 30 Torr. A possible growth behavior is also discussed for the growth temperature range of 650 to 850 ℃. The as-grown WS2 monolayers exhibited excellent photoluminescence emission around 2.0 eV with a linewidth of 49 meV. Our gas-phase-precursor assisted CVD approach would enable a pathway for the rapid-production of atomically thin TMDs for electronic industry.

Probing Ferrimagnetic Semiconductor with Enhanced Negative Magnetoresistance: 2D Chromium Sulfide

AbstractMagnetic 2D materials have emerged as a great interest in spintronics due to atomic thickness scaling, low energy switching, and ease in the manipulation of spins. This report demonstrates a facile, bottom‐up, chemical vapor deposition approach for non‐van der Waals (non‐vdWs), 2D chromium (III) sulfide (Cr2S3) with c‐axis orientation, out‐of‐plane magnetic anisotropy (easy axis), and ferrimagnetic ordering. Importantly, the anisotropic magnetic saturation and resistivity of 10.23 mΩ cm reveal a narrow bandgap ferrimagnetism in Cr2S3 (∆EActivation ≈ 22 meV and Eg ≈ 40 meV). The prototype lateral spin‐channel Al/Cr2S3/Al devices exhibit a negative magnetoresistance of ≈25% and ≈15% at 100 K (below Néel temperature) for few‐layer (≈8 nm) and thin‐film (≈50 nm) device structures, respectively, owing to itinerant ferrimagnetism of Cr2S3. The magnetic field‐induced spin polaron formations are quite resilient and enhance the field‐dependent carrier conduction, making it greatly useful for negative magnetoresistance operation. These prototype Al/Cr2S3/Al structures have demonstrated a low power (≈2 µW for 8 µm channel at 10 µA current) operation with a negative field‐dependent resistance coefficient (rM) of ≈−5 × 10−4 Oe−1. The computed rM magnitude is tenfold higher than the bulk Cr2S3. This study identifies the potential of non‐vdW Cr2S3 toward new and robust 2D‐based spintronic applications.

Facile Synthesis of Carbon Film with High Carrier Concentration Using Coal Tar and the Application in Joule Heating

The excellent electrical, thermal, and mechanical properties of carbon films make them promising for application in functional devices. As the byproduct of the coking industry with low cost and large quantity, coal tar can be an alternative feedstock for preparing high-performance carbon films. This work adopts the negative-pressure chemical vapor deposition (NPCVD) approach to prepare thin films on a glass substrate with tunable electrical properties and thickness using coal tar as carbon source. The sheet resistance of as-prepared carbon films can be adjusted within 3 orders of magnitude due to its high carrier density (up to 2.1 × 1022/cm3). As potential Joule heater, carbon film is characterized by fast heating rate (up to 12.5 °C/s) and high temperature (up to 300 °C at 40 V in 24 s). The thickness and sp2 cluster size affect the carrier density and carrier mobility of carbon film. These results verify the feasibility of using coal tar to synthesis high-performance carbon films suitable for electronic applications.

Direct one-stage plasma-chemical synthesis of chalcogenide films doped with ytterbium

In this paper we descried the plasma-enhanced chemical vapor deposition (PECVD) approach for preparation of the arsenic sulfide thin films modified by ytterbium. Radio frequency (40.68 MHz) plasma discharge at low pressure (0.1 Torr) was used for the initiation of chemical interactions between precursors. Arsenic monosulfide (As4S4), elemental high-pure S and Yb were employed as the starting materials. The composition of the films was controlled by regulating of the temperature of the ytterbium source supplied with external heater. The Yb concentration in the Yb:AsxSy films was from 1 to 7 at%. The chalcogenide materials were also studied by Scanning Electron Microscopy (SEM), Optical spectroscopy in the range of 250-1000 nm, and Raman spectroscopy.

Single-Step Fabrication Method toward 3D Printing Composite Diamond-Titanium Interfaces for Neural Applications.

Owing to several key attributes, diamond is an attractive candidate material for neural interfacing electrodes. The emergence of additive-manufacturing (AM) of diamond-based materials has addressed multiple challenges associated with the fabrication of diamond electrodes using the conventional chemical vapor deposition (CVD) approach. Unlike the CVD approach, AM methods have enabled the deposition of three-dimensional diamond-based material at room temperature. This work demonstrates the feasibility of using laser metal deposition to fabricate diamond-titanium hybrid electrodes for neuronal interfacing. In addition to exhibiting a high electrochemical capacitance of 1.1 mF cm-2 and a low electrochemical impedance of 1 kΩ cm2 at 1 kHz in physiological saline, these electrodes exhibit a high degree of biocompatibility assessed in vitro using cortical neurons. Furthermore, surface characterization methods show the presence of an oxygen-rich mixed-phase diamond-titanium surface along the grain boundaries. Overall, we demonstrated that our unique approach facilitates printing biocompatible titanium-diamond site-specific coating-free conductive hybrid surfaces using AM, which paves the way to printing customized electrodes and interfacing implantable medical devices.

Chemical Vapor Deposition for N/S-Doped Single Fe Site Catalysts for the Oxygen Reduction in Direct Methanol Fuel Cells

Single metal site catalysts are the most promising candidates to replace platinum-group-metal (PGM) catalysts for the oxygen reduction reaction (ORR), yet insufficient performance and scalable preparation approaches remain great challenges. Here, we report a nitrogen (N)/sulfur (S) codoped single Fe site catalyst (Fe–N/S–C) through a chemical vapor deposition (CVD) strategy. Using the cyclopentadiene-shielded Fe atom ferrocene (Fc) as the precursor, atomically dispersed single Fe sites were successfully embedded into the N, S codoped 2D carbon nanosheets. The superior catalytic activity for the ORR in alkaline media is stemmed from the N, S codoping, tuning the optimal charge distribution of Fe sites. In addition, the CVD approach could surpress the formation of iron-carbide-containing iron clusters (“FexC/Fe”), thereby leading to high surface areas and porosity. Furthermore, the Fe–N/S–C catalyst was further studied as a cathode catalyst in direct methanol fuel cells showing encouraging performance.