Chemical Vapor Deposition Approach Research Articles

UV-to-IR highly transparent ultrathin diamond nanofilms with intriguing performances: Anti-fogging, self-cleaning and self-lubricating

Fouling and abrasive wear severely affect the transparency of optical sensors and windows employed in marine, biomedical and aerospace applications. Herein, we report a strategy to create a robust and superhydrophilic surface based on ultrathin transparent diamond nanofilms synthesized by an enhanced self-assembly seeding and chemical vapor deposition approach. A quartz glass coated with an ultrathin (~50 nm) and smooth diamond nanofilm exhibits a high optical transparency of 90% in air and 98% underwater in UV–Vis range. Especially, an IR transmittance of 85% is recorded, which is even 10% higher than that of uncoated quartz. The transparent diamond nanofilms are superhydrophilic and underwater superoleophobic after oxygen plasma treatment, leading to the anti-fogging capability in air and underwater self-cleaning of oil. Importantly, the quartz coated with the diamond nanofilms shows excellent mechanical robustness with unchanged morphology and transparency under severe sandblasting condition. Moreover, this ultrathin diamond nanofilm can make the deposited substrates self-lubricating, which significantly decreased the friction coefficient of the quartz from 0.18 to 0.05. High transparence from ultraviolet to infrared and intriguing performances of the ultrathin diamond nanofilms make them promising for several important applications, such as aircraft fairing and window, optical lens, and marine exploration, etc.

Atmospheric Plasma-Enhanced Spatial Chemical Vapor Deposition of SiO2 Using Trivinylmethoxysilane and Oxygen Plasma

SiO2 constitutes one of the most widely used dielectric materials in the microelectronics, packaging, and optical industries. Therefore, the development of new processes to deposit SiO2 at low temperature and in an affordable and scalable way are desirable. In this work, we present a low-temperature, open-air process based on spatial atomic layer deposition (SALD) that yields high purity SiO2 films at temperatures down to room temperature. The films were obtained by operating our SALD system in CVD mode (i.e., allowing precursor crosstalk), using an oxygen plasma in combination with trivinylmethoxysilane (TVMS). TVMS is an appealing precursor since it is highly volatile, is affordable, and does not contain halogen elements, thus being very suitable for application in atmospheric-pressure spatial deposition systems. Conversely, water, oxygen, hydrogen peroxide, or ozone did not show any reactivity with TVMS at temperatures up to 260 °C. Thus, when operating our system in ALD mode, no film could be obtained due to the lack of reactivity of the precursor with OH* surface groups. 3D printing was employed to fabricate custom heads integrating both the precursor injector and the atmospheric plasma generator. Our results show that conformal SiO2 thin films can be deposited by our atmospheric plasma-enhanced spatial chemical vapor deposition (APE-SCVD) approach at low temperatures (RT–180 °C) on different substrates, including silicon wafers, microglass slides, or even polymeric substrates with a high growth rate up to 2–5 nm/min. The deposition rate increased when increasing the power applied to the plasma reactor but decreased when increasing the deposition temperature due to the faster decay of the metastable oxygen radical species. FTIR results showed no differences for films deposited with different plasma powers. Conversely, temperature had an effect on the ratio between the AS1 and the AS2 bands. Even though the deposition of SiO2 was carried out at low temperatures in the open air using a metalorganic precursor, no contamination from SiNx or SiCx was observed by FTIR and XPS measurements. Our results open the door to the low-temperature, fast printing of Si-based devices.

Plasma-Synthesized Nanoparticles for Hybrid CNT/Nanoparticles Composites

Carbon nanotubes (CNTs) have attracted a lot of attention due to their unique electrical, thermal and mechanical properties [1-3]. CNTs are also highly suitable to achieve multi-functional materials when combined with a range of nanoparticles (NPs)[4-6].In this work, CNT macroscopic ribbon structures are synthesized using the floating catalyst chemical vapor deposition (FC-CVD) approach, using Iron as a catalyst, sulfur to limit the iron growth and to enhance the growth rate of the CNTs and methane as a carbon precursor [7].Plasma-induced non-equilibrium electrochemistry (PiNE) was then used to synthesize NiO QDs and subsequently spray coated them onto CNT ribbons. The PiNE process used a Ni foil as the anode and a nickel tube as the cathode powered by direct current supply (45 min, 2 kV, 5mA). The NiO QDs exhibited a diameter of 3nm and were spray coated onto the CNTs which had been pre-treated with HNO3 to remove the Fe catalysts. The CNT-NiO QDs composite were tested for H2 generation with promising results.As the two-step process highlighted limitations in the NP loading, a second approach was devised, developed and tested for high loading with Zn-based NPs. An RF helium microplasma reactor was integrated in-line with the CNT synthesis set-up to produce CNT-NPs in one-step process. Transmission and scanning electron microscopy confirmed the presence of ZnO NPs with a good coverage of the CNT ribbons. X-ray photoelectron spectroscopy shows that up to 40% of Zn can be loaded on the CNT ribbons, which represents a substantial improvement towards energy storage applications.

(Invited) Controlling Monolayer and Few-Layer MoS2 and WS2 Optoelectronic and Catalytic Properties

By functionalizing, doping, and changing phases, we can control the optoelectronic and catalytic properties of 2D transition metal dichalcogenides (TMDCs), specifically MoS2 and WS2. These 2D layered nanomaterials can be made via a top-down (exfoliation) or bottom-up (chemical vapor deposition) approach. The optoelectronic properties of monolayer TMDCs are strongly influenced by their surroundings and can be used as a humidity sensor, which we demonstrate with photoluminescence measurements. Furthermore, we quantify the stability of metallic, monolayer TMDCs when it is converted from the semiconducting to the metallic phase and functionalized, where comparisons are made to few-layer TMDCs. By controlling these optoelectronic properties, we can better understand the catalytic performance for hydrogen evolution.

Batch synthesis of transfer-free graphene with wafer-scale uniformity

Scalable synthesis of transfer-free graphene over insulators offers exciting opportunity for next-generation electronics and optoelectronics. However, rational design of synthetic protocols to harvest wafer-scale production of directly grown graphene still remains a daunting challenge. Herein we explore a batch synthesis of large-area graphene with wafer-scale uniformity by virtue of direct chemical vapor deposition (CVD) on quartz. Such a controllable CVD approach allows to synthesize 30 pieces of 4-inch graphene wafers in one batch, affording a low fluctuation of optical and electrical properties. Computational fluid dynamics simulations reveal the mechanism of uniform growth, indicating thermal field and confined flow field play leading roles in attaining the batch uniformity. The resulting wafer-scale graphene enables the direct utilization as key components in optical elements. Our method is applicable to other types of insulating substrates (e.g., sapphire, SiO2/Si, Si3N4), which may open a new avenue for direct manufacture of graphene wafers in an economic fashion.

Covalently Connected Nb4N5-xOx-MoS2 Heterocatalysts with Desired Electron Density to Boost Hydrogen Evolution.

Rational design and controllable synthesis of efficient and robust electrocatalysts for hydrogen evolution reaction (HER) remain a critical challenge for the renewable energy economy. Herein, heterostructured Nb4N5-xOx-MoS2 (0 < x < 1) anchored on N-doped graphene (defined as Nb4N5-xOx-MoS2/NG) is synthesized by hydrothermal and chemical vapor deposition (CVD) approaches. During the CVD process, MoS2 nanosheets are etched into small pieces and covalently interconnected with Nb4N5-xOx to form fine Nb4N5-xOx-MoS2 heterostructures, which possess abundant interfaces and fully exposed edge active sites. The as-prepared Nb4N5-xOx-MoS2 heterostructures with Nb-(N,S)-Mo bridges provide desired electron density, which exhibit excellent chemisorption ability for both H and water, significantly improving the intrinsic HER activity. Meanwhile, the covalently connected Nb4N5-xOx-MoS2 heterostructures together with chemical coupling of Nb4N5-xOx-MoS2 and N-doped graphene improve the structural stability and ensure fast electron transfer in the Nb4N5-xOx-MoS2/NG nanocomposite, further supporting the H2 generation and stability.

Utilization of waste engine oil for carbon nanotube aerogel production using floating catalyst chemical vapor deposition

The floating catalyst chemical vapor deposition (FCCVD) approach has been successfully employed in offering a continuous single-step process to the synthesis of carbon nanotubes aerogel (CNT aerogel) in terms of the industrial scale. Industrial applications require selecting a carbon source that is abundant, cost-effective and environment-friendly. Thus, waste engine oil (WEO) is preferably employed as a carbon source involving the production of CNT aerogel. In this research study, the catalytic decomposition of the WEO was employed to synthesize CNT aerogel. First, fractional distillation of WEO was achieved resulted in five (5) fractions. As per analysis is performed via GC-MS, low molecular weight hydrocarbons could be efficiently separated, which is required for catalyst dissolving. As per CNS analysis, each fraction was found to contain >69% carbon, <0.1% sulfur and <0.3% nitrogen. The FCCVD method was employed to synthesize CNT aerogel via a WEO fraction 1 mixed along with ferrocene catalyst at a temperature of 1150 °C. It was found that the product’s MWCNTs were associated with 86.74% purity and 496% carbon deposition yield. The aerogel was found to possess a mesopore distribution of 142.9 m2 g−1 as its specific surface area, 39.079 nm as average pore diameter and 1.3964 cm3 g−1 as total pore volume. The CNTs tend to assemble randomly as well as get entangled to form a 3-D structure.

Direct Growth of Graphene over Insulators by Gaseous‐Promotor‐Assisted CVD: Progress and Prospects

AbstractUtilizing a direct chemical vapor deposition (CVD) approach to allow transfer‐free synthesis of graphene on insulating substrates is appealing. Nevertheless, the quality and uniformity of thus‐grown graphene without the aid of any catalyst stay normally inferior to that of graphene formed on metals by far. This mainly stems from the catalytic inertness of the insulating surface with regard to the decomposition of carbon feedstock. In this respect, delicate methodologies have been devised to date to boost the quality of directly‐grown graphene. In this Minireview, recent advances in the direct CVD growth of graphene on insulators by introducing various gaseous promotors is covered. The effects and mechanisms of different types of promotors on the direct growth are discussed. At the end, existing challenges and future perspectives in this field are further highlighted.

Recent advances in carbon nanotube sponge–based sorption technologies for mitigation of marine oil spills

HypothesisOil spills stemming from supertankers, drilling, and natural events represent a serious problem worldwide due to the potential harms to marine ecosystems and aquatic life. To date, various functional absorbents have been developed to treat spilled oil. Among them, carbon nanotube (CNT)-based aerogels and sponges gained attention due to superior performance in uptake and recovery of various types of oil and organic solvents. CNT aerogel/sponge absorbents are demonstrated for a multitude of merits such as: rapid superhydrophobic/superoleophilic absorption (water contact angle > 150°), high capacity (≥100 mg g−1), large surface area (300–400 m2 g−1)), enhanced strength and flexibility (>95% volume reduction and restoration of pristine morphology at <0.25 MPa stress), mesoporous characteristics with high pore density (pore diameter = 80 nm and >99% porosity), recyclability, and easy surface modification. ExperimentsThis review compares CNT sponge–based absorbents with conventional techniques for remediation/recovery of spilled oil. Typically, synthesis of CNT sponges is performed using chemical vapor deposition (CVD) approach in the presence of a catalyst or using sacrificial removal of template. This work summarizes recent progress in strategies for oil-spill treatment based on CNT sponge techniques. The performance of CNT sponges for oil spill removal was evaluated in terms of their adsorption capacity, compressive stressability, and desorption methods (e.g., heat treatment, burning, or squeezing). FindingsCNT sponges were observed to have high performance for removal of oil spills in terms of key performance metrics. This review offers valuable insights into the current state of CNT-mediated oil-spill cleanup technologies and guidance for future research at the same time. This literature survey would help the stakeholders (researchers, scientists, entrepreneurs, and commercial houses) pursue contamination-free water.

The synthesis of 2D MoS2 flakes with tunable layer numbers via pulsed-Argon-flow assisted CVD approach

Modified chemical vapor deposition (CVD) is highly desirable to achieve versatile synthesis of two-dimensional (2D) molybdenum sulfide (MoS2) crystals with certain layer-number and configuration. In this study, we have demonstrated growth of MoS2 domains with diverse layer numbers through the pulsed-Ar-flow assisted CVD method utilizing Mo foil and Si/SiO2 substrate to construct confined reaction space. Layer number of obtained samples under varied time width of pulsed Ar flow is regulated from monolayer to multilayer (>3). Thickness evolution may be derived from the manipulation of on-time width of pulsed Ar gas. Our result provides an optional strategy to synthesize other transition metal dichalcogenides (TMDCs) crystals with desired configurations.

Photothermal hierarchical carbon nanotube/reduced graphene oxide microspherical aerogels with radially orientated microchannels for efficient cleanup of crude oil spills

High viscosity and low fluidity of heavy crude oils usually hinder their rapid diffusion into porous adsorbents, causing a low efficiency of oil spill remediation. Photothermal effect is thus adopted to rapidly reduce the viscosity of heavy crude oil by in situ solar light heating. Photothermal carbon nanotube/reduced graphene oxide (CNT/RGO) microspherical aerogels are synthesized by fabrication of graphene oxide (GO)-based microspherical aerogels with numerous radially orientated microchannels, followed by growing CNTs inside the microchannels and high-temperature reduction of the GO components. Thanks to the efficient photothermal conversion effect and the rough and oleophilic surface of the microchannels with large surface area, such aerogels facilitate the solar light absorption and hence enhance the crude oil adsorption. Furthermore, the CNTs grown on the RGO skeleton by a chemical vapor deposition approach promote the photothermal conversion efficiency by trapping and absorbing broadband solar light. Under 1 sun irradiation, the surface temperature of the aerogel quickly rises to 83 °C in 1 min, resulting in a sharp decrease in crude oil viscosity. The optimal microspherical aerogels deliver an extraordinary adsorption capacity of heavy crude oil, up to 267 g g−1 within 10 min, superior to those of other oil adsorbents reported so far.

Color‐Tunable Photoluminescence and Whispering Gallery Mode Lasing of Alloyed CsPbCl3(1–x)Br3x Microstructures

AbstractBandgap engineering of perovskite micro/nanostructures is important in designing multifunctional optoelectronic circuits. Especially, wavelength tunable lasing and modes are essential to the practical applications of micro/nanoscale lasers. Here, for the first time, a sample source‐moving chemical vapor deposition approach for the spatial bandgap engineering of cesium lead halide perovskites (CsPbCl3(1–x)Br3x, X = 0–0.75) alloy microstructures on a single sapphire substrate is reported. Owing to temperature‐selected effort along the deposition zoon, cesium lead halide perovskites alloy CsPbCl3(1–x)Br3x microcrystals with engineerable bandgap from 2.39 to 2.91 eV are obtained. The emission light can be modulated gradually from blue (425 nm) to green (512 nm) under a 320 nm laser illumination. Furthermore, these alloyed perovskites structures grown on the sapphire substrate show stable emission with no measurable degradation after 24 h under a continuous wavelength 320 nm laser radiation. More importantly, high‐quality wavelength tunable whispering gallery mode lasing with emission peaks from 429 to 521 nm are first successfully fabricated based on these alloyed pervoskite crystals. These composition‐graded perovskite microcrystals demonstrated here may find applications in multicolor display and broad band light sources.

Highly Selective Gas Sensors Based on Graphene Nanoribbons Grown by Chemical Vapor Deposition.

Despite the recent advances in bottom-up synthesis of different kinds of atomically precise graphene nanoribbons (GNRs) with very diverse physical properties, the translation of these GNRs into electronic devices remains challenging. Among other factors, the electronic characterization of GNRs is hampered by their complex synthesis that often requires custom-made organic precursors and the need for their transfer to dielectric substrates compatible with the conventional device fabrication procedures. In this paper, we demonstrate that uniform electrically conductive GNR films can be grown on arbitrary high-temperature-resistant substrates, such as metals, Si/SiO2, or silica glasses, by a simple chemical vapor deposition (CVD) approach based on thermal decomposition of commercially available perylenetetracarboxylic dianhydride molecules. The results of spectroscopic and microscopic characterization of the CVD-grown films were consistent with the formation of oxygen-terminated N = 5 armchair GNRs. The CVD-grown nanoribbon films exhibited an ambipolar electric field effect and low on-off ratios, which were in agreement with the predicted metallic properties of N = 5 armchair GNRs, and remarkable gas sensing properties to a variety of volatile organic compounds (VOCs). We fabricated a GNR-based electronic nose system that could reliably recognize VOCs from different chemical classes including alcohols (methanol, ethanol, and isopropanol) and amines (n-butylamine, diethylamine, and triethylamine). The simplicity of the described CVD approach and its compatibility with the conventional device fabrication procedures, as well as the demonstrated sensitivity of the GNR devices to a variety of VOCs, warrant further investigation of CVD-grown nanoribbons for sensing applications.

Large-area epitaxial growth of curvature-stabilized ABC trilayer graphene

The properties of van der Waals (vdW) materials often vary dramatically with the atomic stacking order between layers, but this order can be difficult to control. Trilayer graphene (TLG) stacks in either a semimetallic ABA or a semiconducting ABC configuration with a gate-tunable band gap, but the latter has only been produced by exfoliation. Here we present a chemical vapor deposition approach to TLG growth that yields greatly enhanced fraction and size of ABC domains. The key insight is that substrate curvature can stabilize ABC domains. Controllable ABC yields ~59% were achieved by tailoring substrate curvature levels. ABC fractions remained high after transfer to device substrates, as confirmed by transport measurements revealing the expected tunable ABC band gap. Substrate topography engineering provides a path to large-scale synthesis of epitaxial ABC-TLG and other vdW materials.

Ultrafast growth of large single crystals of monolayer WS2 and WSe2.

Monolayer transition metal dichalcogenides (TMDs) have attracted considerable attention as atomically thin semiconductors for the ultimate transistor scaling. For practical applications in integrated electronics, large monolayer single crystals are essential for ensuring consistent electronic properties and high device yield. The TMDs available today are generally obtained by mechanical exfoliation or chemical vapor deposition (CVD) growth, but are often of mixed layer thickness, limited single crystal domain size or have very slow growth rate. Scalable and rapid growth of large single crystals of monolayer TMDs requires maximization of lateral growth rate while completely suppressing the vertical growth, which represents a fundamental synthetic challenge and has motivated considerable efforts. Herein we report a modified CVD approach with controllable reverse flow for rapid growth of large domain single crystals of monolayer TMDs. With the use of reverse flow to precisely control the chemical vapor supply in the thermal CVD process, we can effectively prevent undesired nucleation before reaching optimum growth temperature and enable rapid nucleation and growth of monolayer TMD single crystals at a high temperature that is difficult to attain with use of a typical thermal CVD process. We show that monolayer single crystals of 450 μm lateral size can be prepared in 10 s, with the highest lateral growth rate up to 45 μm/s. Electronic characterization shows that the resulting monolayer WSe2 material exhibits excellent electronic properties with carrier mobility up to 90 cm2 V−1 s−1, comparable to that of the best exfoliated monolayers. Our study provides a robust pathway for rapid growth of high-quality TMD single crystals.

Facile Au-assisted epitaxy of nearly strain-free GaN films on sapphire substrates.

The nearly strain-free GaN films were epitaxially grown successfully on the Au-coated c-plane sapphire substrate by a convenient chemical vapor deposition approach. The growth of GaN single crystalline epitaxial films is a self-patterned process. The morphology, structure, compositions and optical properties of as-synthesized GaN materials were characterized through field-emission scanning electron microscopy, atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive spectroscopy mapping, Raman spectroscopy and photoluminescence spectroscopy. The characterization results confirm that the epitaxial GaN films grown on Au-coated c-plane sapphire substrates have a single-crystalline and nearly strain-free structure, and exhibit strong UV emission. A possible growth mechanism of the GaN film is proposed: Au-assisted vapor deposition initiates the nucleation of the GaN seeds, and then these seeds grow into inclined inverted hexagonal GaN pyramids with a threefold azimuthal symmetry and vertical inverted hexagonal pyramids; and subsequently, the vertical inverted hexagonal pyramids expand laterally and annihilate the inclined inverted hexagonal pyramids; eventually these vertical pyramids coalesced to form nearly strain-free GaN films. This synthesis strategy provides a new idea for the simple self-patterned growth of nearly strain-free GaN epitaxial films on Au-coated sapphire substrates, and will promote broader applications in GaN-based electronic and optoelectronic devices.

Metal-Free Synthesis of Boron-Doped Graphene Glass by Hot-Filament Chemical Vapor Deposition for Wave Energy Harvesting.

Property modulation of graphene glass by heteroatom doping such as boron (B) and nitrogen (N) is important to extend its practical applications. However, unlike N doping, research studies about the metal-free synthesis of B-doped graphene on glass through the chemical vapor deposition (CVD) method are rarely reported. Herein, we report a hot-filament CVD approach to prepare B-doped graphene glass using diborane (B2H6) as the B dopant. The synthesized B-doped graphene was uniform on a large-scale and composed of nanocrystalline graphene grains. By raising the B2H6 flow from 0 to 15 sccm, the B content of graphene was facilely modulated from 0 to 5.3 at. %, accompanied with the improvement of both transparency and conductivity. The B-doped graphene prepared on glass at 15 sccm B2H6 flow presented the optimal transparent conductive performance superior to those of most reported graphene glass fabricated by other state-of-the-art approaches. Furthermore, for the first time, the performance of graphene glass for wave energy harvesting has been elaborated. It was found that the output power produced by inserting graphene glass into 0.6 M sodium chloride (NaCl) solution could be improved by more than 6 times through B doping. The significant enhancement resulted from the higher waving voltage and smaller resistance of B-doped graphene on glass than the pristine ones. In addition, the waving voltage inversed the polarity after B doping, which was due to the opposite variation of surface potential of pristine and B-doped graphene after NaCl immersion. This work would pave ways for the metal-free preparation and expand the energy-harvesting applications of B-doped graphene materials.

Dual‐channel type tunable field‐effect transistors based on vertical bilayer WS2(1 − x)Se2x/SnS2 heterostructures

AbstractLayered semiconductor heterostructures are essential elements in modern electronic and optoelectronic devices. Dynamically engineering the composition of these heterostructures may enable the flexible design of the properties of heterostructure‐based electronics and optoelectronics as well as their optimization. Here, we report for the first time a two‐step chemical vapor deposition approach for a series of WS2(1 − x)Se2x/SnS2 vertical heterostructures with high‐quality and large areas. The steady‐state photoluminescence results exhibit an obvious composition‐related quenching ratio, revealing a strong coherence between the band offset and the charge transfer efficiency at the junction interface. Based on the achieved heterostructures, dual‐channel back‐gate field‐effect transistors were successfully designed and exhibited typical composition‐dependent transport behaviors, and pure n‐type unipolar transistors to ambipolar transistors were realized in such systems. The direct vapor growth of these novel vertical WS2(1 − x)Se2x/SnS2 heterostructures could offer an interesting system for probing new physical properties and provide a series of layered heterostructures for high‐quality devices.image

Synthesis of bamboo-like SiC nanowires with controllable densities of bamboo nodes

Herein, bamboo-like SiC nanowires were synthesized via the atmospheric pressure chemical vapor deposition (APCVD) approach. The mixed powders of polycarbosilane (PCS) and activated carbon (AC) were used as the raw materials. Particularly, the pyrolysis rate of the raw materials were controlled by adjusting the proportion of activated carbon. The reaction gas was periodically changed by placing raw materials in two different temperature zones. Subsequently, bamboo-like SiC nanowires with different densities of bamboo nodes were obtained in the way of adjusting the time of periodic change in the concentration of the reaction gas. The morphologies and microstructure of the bamboo-like nanowires were investigated by x-ray diffraction, scanning electron microscope, and high resolution transmission electron microscopy as well as selected area electron diffraction. Finally, the growth process of the bamboo-like SiC nanowires was investigated from the perspective of the root vapor-liquid-solid (VLS) mechanism as well as the periodic change in concentration.

Comparative Study of Photocarrier Dynamics in CVD-deposited CuWO4, CuO, and WO3 Thin Films for Photoelectrocatalysis

Abstract The temporal evolution of photogenerated carriers in CuWO4, CuO and WO3 thin films deposited via a direct chemical vapor deposition approach was studied using time-resolved microwave conductivity and terahertz spectroscopy to obtain the photocarrier lifetime, mobility and diffusion length. The carrier transport properties of the films prepared by varying the copper-to-tungsten stoichiometry were compared and the results related to the performance of the compositions built into respective photoelectrochemical cells. Superior carrier mobility was observed for CuWO4 under frontside illumination.