Simple Chemical Vapor Deposition Research Articles

Vertically rooting carbon nanotubes on cobalt-loaded hollow Titanium Dioxide spheres as conductive multifunctional sulfur hosts for superior lithium-sulfur performance

The rechargeable lithium-sulfur (Li–S) batteries have been regarded as the most promising alternatives for Li-ion batteries. However, the poor conductivity, the large volume expansion of sulfur, and the “shuttle effect” of polysulfides lead to the rapid capacity decay of sulfur cathodes, which impedes the practical application of Li–S batteries. Herein, a novel three-dimensional (3D) hierarchical structured high-efficiency sulfur host (Co-CNTs@TiO2), which was assembled by hollow TiO2 spheres and vertically rooted carbon nanotubes (CNTs) network framework, was developed by simple chemical vapor deposition (CVD) method. The 3D CNTs network promoted long-range conductivity and efficiently exposed the Co active sites. Remarkably, the Co particles acted as adsorptive and catalytic sites, which were effective for chemical fixation and conversion of polysulfides. Meanwhile, the hollow and porous structures of Co-CNTs@TiO2 microspheres were conducive to the buffering of volume change during the cycling process, and could physically encapsulate polysulfides. Consequently, the S/Co-CNTs@TiO2 cathode can deliver a high initial specific capacity of 1134.9 mAh g−1 at 0.2C, remarkable long-term cycling stability over 500 cycles with a low capacity fading rate of 0.072% per cycle at 1.0C, as well as excellent performance under high sulfur loading up to 5.9 mg cm−2.

SnO2-anchored carbon fibers chemical vapor deposition (CVD) synthesis: effects of growth parameters on morphologies and electrochemical behaviors

Morphological effects on the electrochemical behaviors of Tin Dioxide (SnO2) have recently been explored in several studies. Nevertheless, the preparations of SnO2 in those works are mostly based on wet-chemistry methods, while the usage of dry-chemistry methods is still lack of investigation. In this work, for the first time, we report the successful fabrication of SnO2 particles attached on carbon fibers via a simple two-step Chemical Vapor Deposition (CVD) approach. CVD growth parameters (temperature, growth time and gas inlet flow rate) were systematically varied to observe the changes in morphologies (in terms of particle density and size distribution) as well as the formation of core–shell Sn/SnO2 structures; and the electrochemical properties of the as-synthesized samples were studied. Our experiments indicate strong correlations among the synthesis conditions, morphologies and electrochemical behaviors. Overall, our findings provide new insights into CVD as a morphological tailoring approach for electrochemical applications—in addition to its simple apparatus and short synthesizing duration, the process is easily extendable for the preparation of other metal and metal oxide particles.

Carbon nanotubes/Ni and chain-like carbon nanospheres/Ni nanocomposites: selective production and their microwave absorption performances

It was well recognized that constructing the dielectric/magnetic nanocomposites was considered as an effective way to develop excellent microwave absorption materials (MAMs). Herein, we proposed a simple water-assisted chemical vapour deposition process to selectively produce carbon nanotubes (CNTs)/Ni and chain-like carbon nanospheres (CCNSs)/Ni nanocomposites in high yield by controlling the decomposition temperature. The ultrahigh yield of CCNSs could be achieved when C2H2 was catalytically decomposed at 515 °C, which was up to ca. 211.0. The results suggested that electromagnetic and microwave absorption properties of as-prepared samples were highly dependent on their microstructures and composition parameters, which could be regulated by the introduction of water vapour and decomposition temperature. It was worth mentioning that the obtained CCNSs/Ni nanocomposites could simultaneously present an optimal reflection loss of − 28.32 dB with a matching thickness of 1.68 mm, and an effective frequency bandwidth of 4.60 GHz with the matching thickness of 1.71 mm. Our results provided an effective and facile strategy to produce CCNSs/Ni in high yield, which provided a new idea for the designing and synthesis of lightweight and excellent MAMs.

Single wall carbon nanotubes growth over cobalt-iron mesoporous MCM-41 bimetallic catalyst under methane chemical vapor deposition, an experimental and DFT evaluation

Cobalt and iron MCM-41 catalysts were synthesized through an in-situ incorporation process starting from commercial iron and cobalt nitrates. The incorporation was confirmed by diffuse reflectance UV spectroscopy (DRS-UV) inspecting the cobalt and iron silicate-like photon absorption features and comparing with pure MCM-41-Co and MCM-41-Fe catalysts. Additionally it was found that the incorporation of cobalt and iron does not compromise the mesoporous structure of MCM-41 as confirmed by N2 adsorption isotherms. All catalysts showed high surface areas (∼1100 m2g−1). Catalysts performance was conducted in a simple methane chemical vapor deposition (CVD) set up at 800 °C to produce single wall carbon nanotubes (SWCNT) under a constant flow of methane for 30 min. CVD products were characterized by thermogravimetric analysis (TGA) and Raman spectroscopy, finding that the iron content in the catalysts favors the selectivity and yield of graphitic-like structures, and confirming the presence of SWCNT by the appearance of a characteristic radial breathing mode (RBM) signals. These results were supported by Density Functional Theory (DFT) simulations of the methane dissociation (CH4 +TM → H3C –TMH) over Con (n = 1–5) and ComFe (m = 1–4), finding a different activation energy trend where ComFe (m = 1–4) clusters have the lower activation energy. The DFT study also revealed a charge difference (δC − δTM) higher in the case of dissociation over ComFe (m = 1–4) which may lead to an electrostatic stabilization of the transition metal, diminishing the activation energy of those clusters and leading to a faster carbon uptake.

Boosted photoelectrochemical performance of In2O3 nanowires via modulating oxygen vacancies on crystal facets

Introducing oxygen vacancies into faceted metal oxide nanostructures will largely boost photoelectrochemical water splitting ability, but currently remains a huge challenge. Herein, a simple one-step chemical vapor deposition method is developed to effectively introduce oxygen vacancies into In2O3 nanowires with the active {001} facets exposed. Theoretical calculations reveal that the introduction of oxygen vacancies produces a new defect level as shallow donor and increases the states of density, thereby enhancing the visible light absorption and promoting the separation and transportation of photogenerated carrier of faceted In2O3 nanowires. The In2O3 nanowires grown at optimal condition yield the maximal photocurrent density of 1 mA/cm2 at 0.22 V versus Ag/AgCl with unity Faradic efficiency. The results demonstrate that introducing oxygen vacancies into faceted photoelectrodes is feasible for further promoting the photoelectrochemical performance. Moreover, the methodology can be extended to other practical optoelectronic devices such as solar cell and photodetectors.

Novel NiCl2 Nanosheets Synthesized via Chemical Vapor Deposition with High Specific Energy for Thermal Battery.

Two-dimensional (2D) nanomaterials possessing a unique sheet structure, compared to correlative bulk materials, exhibit excellent properties, especially in the energy storage and energy conversion field. In this case, NiCl2 nanosheets with thicknesses of 2-8 nm are first prepared by a simple chemical vapor deposition method. For the Li-B/LiF-LiCl-LiBr/NiCl2 thermal battery, the specific energy of NiCl2 nanosheets increases from 510 W h kg-1 (NiCl2 rods) to 616 W h kg-1 at an operation temperature of 500 °C and a current density of 0.2 A cm-2. The 2D morphology and large numbers of defects not only improve the redox reaction rates and the lithium storage capacity, but also enhance the adsorption capacity with the flake-like binder MgO, which prolong the discharge time by suppressing the discharge product diffusion to the electrolyte. These results indicate that NiCl2 nanosheets have a great possibility to become a desirable candidate of cathode materials for assisting in the development of high energy output and provide a new way to restrain the immersion between the electrode and electrolyte.

Epitaxial growth of metal-semiconductor van der Waals heterostructures NbS2/MoS2 with enhanced performance of transistors and photodetectors

Two-dimensional (2D) heterostructures based on layered transition metal dichalcogenides (TMDs) have attracted increasing attention for the applications of the next-generation high-performance integrated electronics and optoelectronics. Although various TMD heterostructures have been successfully fabricated, epitaxial growth of such atomically thin metal-semiconductor heterostructures with a clean and sharp interface is still challenging. In addition, photodetectors based on such heterostructures have seldom been studied. Here, we report the synthesis of high-quality vertical NbS2/MoS2 metallic-semiconductor heterostructures. By using NbS2 as the contact electrodes, the field-effect mobility and current on-off ratio of MoS2 can be improved at least 6-fold and two orders of magnitude compared with the conventional Ti/Au contact, respectively. By using NbS2 as contact, the photodetector performance of MoS2 is much improved with higher responsivity and less response time. Such facile synthesis of atomically thin metal-semiconductor heterostructures by a simple chemical vapor deposition strategy and its effectiveness as ultrathin 2D metal contact open the door for the future application of electronics and optoelectronics.

Synthesis, characterization, and electrochemical properties of carbon nanotubes used as cathode materials for Al–air batteries from a renewable source of water hyacinth

AbstractWater hyacinth (WH) is a noxious weed. Its rapid growth can clog waterways, causing widespread ecological and environmental threats as well as power generation and irrigation issues. In the present study, water hyacinth was utilized as a precursor to synthesize multiwall carbon nanotubes (MWCNTs) using a simple chemical vapor deposition method. FESEM-EDS revealed that the synthesized MWCNTs had noodle-like, dense, and rough surfaces. TEM confirmed that MWCNTs had a bamboo-like structure with the diameter of 30–40 nm, and the wall thickness of approximately 7 nm. The interlayer distance was found to be approximately 0.34 by XRD. Raman spectra displayed three major bands of MWCNTS: D-band at 1,340 cm−1, G-band at 1,596 cm−1, and (D + G)-band between 2,783 and 2,953 cm−1. The ratio of the D-to-G band intensity was 0.94 ± 0.03, indicating that the synthesized MWCNTs had well degree of graphitization. Electrochemical measurement results of the prepared MWCNTs cathode for aluminum–air battery showed that MWCNTs exhibited higher energy capacity than commercial graphite. Collectively, this study shows that water hyacinth could be used effectively as a precursor for the production of MWCNTs, thus successfully converting the noxious weed into high value-added materials.

Fast Growth of Continuous Single-Crystal Graphene Film on Copper by Low-Pressure Chemical Vapor Deposition

In this study, continuous and single-crystal graphene films on copper (Cu) are synthesized by low-pressure chemical vapor deposition in a growth time of 40 min. Meticulous modulation of the oxygen and carbon supply in multistage synthesis processing and dependence of graphene properties on the oxygen and carbon supply has been investigated. It is found that double-oxygen passivation together with the optimal methane (CH4):hydrogen (H2) ratio leads to a balance between nucleation and graphene growth rate to accomplish continuous single-crystal bilayer graphene films in a short time. Moreover, the graphene-based field effect transistor reveals the superior hole mobility of 5565 cm2 V−1 s−1. Our study provides a simple chemical vapor deposition procedure to achieve high quality graphene film on Cu in a short time.

Preparation of iridium metal films by spray chemical vapor deposition

AbstractMetal Ir films were prepared by spray chemical vapor deposition (CVD) in air from an Ir precursor, (1,3-cyclohexadiene)(ethylcyclopentadienyl)iridium, Ir(EtCp)(CHD). Film deposition was ascertained at 270–430°C on a SiO2/Si substrate and the deposition rate increased with the deposition temperature but was saturated above 330°C. The obtained films consisted of Ir metal without any iridium oxide impurity irrespective of the deposition temperature. Films tended to orient to (111) with increasing deposition temperature. Resistivity of these Ir films decreased with increasing film thickness and reached to values on the order of 10-6 Ω・cm, which was the same order of the values for bulk Ir metal. Good step coverage was observed for the Ir metal films deposited at 270°C and 330°C. This shows that the simple spray CVD process in air is a good candidate for depositing Ir metal films with good conductivity and step coverage.

Electron density modulation of GaN nanowires by manganese incorporation for highly high-rate Lithium-ion storage

Gallium nitride (GaN) has high theoretical capacity and low discharge platform. However, it still suffers from poor conductivity and unsatisfactory cycle performance in lithium-ion batteries (LIBs). In this work, the doped manganese (Mn) are realized in GaN nanowires through a simple and straight forward chemical vapor deposition (CVD) process. When the successful Mn doping was carefully examined in structural characterizations, it is discovered at the atomic level that the species of Mn dopants in GaN nanowires only exist in the feature of Mn+ rather than of metallic Mn, which can significantly promote the electrical conductivity and Li-ions transfer. The tested Mn doped GaN nanowire arrays electrode exhibit the capacity up to 780.3 mA h g−1 at 0.1 A g−1 after 100 cycles and 326.8 mA h g−1 at 5.0 A g−1 after 500 cycles, respectively. The tight and direct contact between Mn doped GaN nanowires and graphite layer provides ultrafast electronic transfer. Density functional theory (DFT) studies confirm that Mn covalent doping can generate the change of local atomic arrangement. Moreover, the electronic structure change significantly increase the electrical conductivity for the fast charge transfer efficiency. This covalent doping strategy for the electron densities regulation could boost the Li-ions storage performance for developing advanced electrode materials in energy storage and beyond.

Growth of aligned SnS nanowire arrays for near infrared photodetectors

Aligned SnS nanowires arrays were grown via a simple chemical vapor deposition method. As-synthesized SnS nanowires are single crystals grown along the [111] direction. The single SnS nanowire based device showed excellent response to near infrared lights with good responsivity of 267.9 A/W, high external quantum efficiency of 3.12 × 104 % and fast response time. Photodetectors were built on the aligned SnS nanowire arrays, exhibiting a light on/off ratio of 3.6, and the response and decay time of 4.5 and 0.7 s, respectively, to 1064 nm light illumination.

Construction and characterization of versatile flexible composite nanofibrous aerogels based on thermoplastic polymeric nanofibers

Poly(vinyl alcohol-co-ethylene) (PVA-co-PE) nanofibers (flexible and effective bonding together) were combined with stiff and flame-resistant sepiolite nanorods (SEP) to fabricate composite nanofibrous aerogels (NFAs) through a versatile and gelation-free freeze-drying method. The PVA-co-PE nanofibers prepared based on a high-yield Melt-Extrusion-Phase-Separation process could form a continuous fibrous structure, and the fibrous networks and surface wettability of composite NFAs could be tuned by the amount of SEP used. The introduction of an appropriate amount of SEP improved mechanical properties of composite aerogels, while excessive SEP would lead to a decrease in compression strength of them. The mechanical properties of composite NFAs are shown to be governed by a combination of stiffness of SEP and effective bonding of PVA-co-PE nanofibers. More importantly, the presence of SEP can substantially improve flame resistance of aerogels. After a simple thermal chemical vapor deposition treatment with methyltrichlorosilane, the surface of composite NFAs become rougher and siloxane nanoparticles became visible. With this deposition, hydrophilic NFAs became hydrophobic as a significant surface property modification. Furthermore, the maximum stress at 60% strain went up from 15.57 to 19.17 kPa and the resilience of composite aerogels improved. Thermal properties results confirmed silane coating can improve the thermal stability and insulation characteristics of polymeric aerogel. The manufactured NFAs are demonstrated as good thermal insulators (0.0274 W m−1 K−1), excellent refractories, efficient water/oil separators (45–108 g/g, 78.58–91.76%) and reusable absorbers. Consequently, the multifunctional silane-coated PVA-co-PE/SEP composite NFAs could be envisaged for several demanding applications.

Selective Growth of Stacking Fault Free ⟨100⟩ Nanowires on a Polycrystalline Substrate for Energy Conversion Application.

Cubic semiconductor nanowires grown along ⟨100⟩ directions have been reported to be promising for optoelectronics and energy conversion applications, owing to their pure zinc-blende structure without any stacking fault. But, until date, only limited success has been achieved in growing ⟨100⟩ oriented nanowires. Here we report the selective growth of stacking fault free ⟨100⟩ nanowires on a commercial transparent conductive polycrystalline fluorine-doped SnO2 (FTO) glass substrate via a simple and cost-effective chemical vapor deposition (CVD) method. By means of crystallographic analysis and density functional theory calculation, we prove that the orientation relationship between the Au catalyst and the FTO substrate play a vital role in inducing the selective growth of ⟨100⟩ nanowires, which opens a new pathway for controlling the growth directions of nanowires via the elaborate selection of the catalyst and substrate couples during the vapor-solid-liquid (VLS) growth process. The ZnSe nanowires grown on the FTO substrate are further applied as a photoanode in photoelectrochemical (PEC) water splitting. It exhibits a higher photocurrent than the ZnSe nanowires do without preferential orientations on a Sn-doped In2O3 (ITO) glass substrate, which we believe to be correlated with the smooth transport of charge carriers in ZnSe ⟨100⟩ nanowires with pure zinc-blende structures, in distinct contrast with the severe electron scattering happened at the stacking faults in ZnSe nanowires on the ITO substrate, as well as the efficient charge transfer across the intensively interacting nanowire-substrate interfaces.

Ultralight and Hydrophobic Palygorskite-based Aerogels with Prominent Thermal Insulation and Flame Retardancy.

Clay-based aerogel is a promising material in the field of thermal insulation and flame retardant, but obtaining clay-based aerogel with high fire resistance, low thermal conductivity, hydrophobicity, and mechanical robustness remains a challenge. In this work, palygorskite-based aerogel was successfully fabricated via combining with a very small proportion of alginate to form a distinctive hierarchically meso-microporous structure. By employing ethanol solution (EA) replacement method and freeze-drying process, the resultant aerogel exhibited ultralow density (0.035-0.052 g/cm3), practical mechanical strengths (0.7-2.1 MPa), and low thermal conductivity of 0.0332-0.165 W/mK (25-1000 °C). The hydrophobicity of aerogel was achieved by simple chemical vapor deposition of methyltrimethoxysilane (MTMS). The Pal-based aerogel showed good performance in both fire resistance with high limiting oxygen index up to 90%, and heat resistance with tolerance of flame up to 1000 °C for 10 min. This renewable Pal-based aerogel with a 3D framework is a promising material to be applied in fields of construction and aerospace for thermal insulation and high fire resistance.

Novel self-supported MoS2/FeS2 nanocomposite as an excellent electrocatalyst for hydrogen evolution

The development of earth-abundant electrocatalysts to replace high-cost precious metal Pt for water splitting to generate H2 is a hot topic in the researches on clean energy. Among them, MoS2 nanostructures have intrigued great interest for its low cost and potential high performance. However, due to the intrinsically low conductivity, its H2 evolution activity is not satisfactory as an applicable electrocatalyst. Herein we report a novel MoS2/FeS2 nanocomposite grown directly on carbon cloth by a facile method based on simple one-step chemical vapor deposition, which has significantly improved H2 evolution performance compared to its pure MoS2 nanosheets counterpart. Such self-supported MoS2/FeS2 nanocomposite electrode exhibits a relatively low overpotential of 134 mV at a current of 10 mA cm−2, a quite small Tafel slope of 76.8 mV⋅dec−1 and excellent electrocatalytic durability in 0.5 mol L−1 H2SO4. The remarkably high H2 evolution activity could be ascribed to the fully exposed and increased number of active sites, enhanced charge transfer rate between MoS2 nanosheets and FeS2 nanoparticles in the composite, and the 3D self-supported structure. This strategy to prepare MoS2/FeS2 nanocomposite with controllable morphology and highly active microstructure would provide a new way for the improvement of the electrocatalytic H2 evolution activity and durability of MoS2.

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.

Growth of Large-Scale Praseodymium Hexaborides (PrB6) Nanowires and Enhanced Field-Emission Performance

Large-scale PrB6 nanowires were fabricated by an effective, catalyst-free, and a simple low-pressure chemical vapor deposition (LPCVD) process. These nanowires, characterized in detail by various analytical instruments, demonstrated the large aspect ratio and high single-crystalline grown along the [001] crystal direction perpendicular to the (001) crystal plane. The field electron emission equipment tests manifest that the asgrown PrB6 products have a low turn-on field (Eto, 2.32 V/μm), a threshold field (Ethr, 4.28 V/μm), a high field enhancement factor (β, 2336), as well as a stable current-density (J) of field-emission. The relationships of the field electron emission parameters, such as J, Eto, and β versus cathode gap (d), have been established when d is increased from 500 μm to 800 μm. The outstanding properties suggest that the PrB6 products may be promising emitters in the cold-field-emission cathode application.

Synthesis of Monolayer MoS2 Films and Tuning Its Photoelectric Properties via Interface Engineering

Two-dimensional (2D) materials have received considerable attention for their applications in nextgeneration optoelectronics but are limited by the synthesis of large-area films and the challenges in device optimization. In this study, a uniform MoS2 monolayer film was synthesized by a simple chemical vapor deposition (CVD) method. Phototransistors based on the resulting MoS2 films were fabricated and their photoelectric properties were compared with that of a device with synthesized triangular MoS2 sheets. The results show that the photoresponsivity of the film-based phototransistor is 1180 mA/W at a power density of 1 mW/cm2, far exceeding (15 times) that of the sheet-based phototransistor. Furthermore, with mild vacuum annealing, the photoresponsivity and photoresponse speed in the film-based phototransistor demonstrated a simultaneous increase, in which the photoresponsivity reached up to 105 A/W with a decreased photoresponse/recovery time from 9 s/22 s to 5 s/8 s under illumination. This satisfactory improvement after vacuum annealing can be attributed to the removal of oxygen atoms from sulfur vacancies and a reduced inherent van der Waals gap at the MoS2/Au interface, which facilitates the trapping of photogenerated electrons and promotes carrier separation. Our work provides a promising strategy for high-performance 2D photodetectors via rational synthesis and interface engineering.

Synthesis of SiC nanowires by a simple chemical vapour deposition route in the presence of ZrB2

The SiC nanowires (NWs) were fabricated by a simple chemical vapour deposition (CVD) method at high temperature using Si, phenolic resin, and ZrB2 powder. The morphologies of the fabricated SiC NWs included SiC/SiO2 chain-beads and straight wires with core-shell structures. The fabricated SiC NWs were micrometre-to-millimetre in length, with chains 100–300 nm in diameter and beads with diameters of less than 1 μm. The core-shell-structured SiC NWs consisted of crystalline SiC cores and thin amorphous SiO2 shells. SiC crystals grew in the [111] direction governed by a vapour-solid (VS) mechanism. The added ZrB2 promotes the generation of gaseous species at higher gas pressures, which contributes to the formation of SiC NWs by CVD. The fabricated SiC NWs exhibited good photoluminescence properties due to many stacking faults and the presence of amorphous SiO2.