One-step Chemical Vapor Deposition Method Research Articles

Direct Deposition of Amorphous Cobalt-Vanadium Mixed Oxide Films for Electrocatalytic Water Oxidation.

Efficiency of water oxidation catalysts in terms of overpotential, current density, and voltage stability over time with facile methods of their fabrication remains a key challenge in developing competent mechanisms of storing energy in the form of green hydrogen fuels. In this work, a rapid one-step aerosol-assisted chemical vapor deposition (AACVD) method is employed to synthesize amorphous and highly active cobalt–vanadium mixed oxide catalysts (CoVOx) directly over fluorine-doped tin oxide (FTO) substrates. Morphological and structural characterizations made by field emission scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy techniques revealed the formation of pure-phase amorphous films with a gradual variation of topography as a function of deposition time. Of these films, the most active film (CoVOx-20) was obtained in 20 min deposition, showing a spongy networking of interwoven nanofibers with a homogeneous distribution of 3–4 nm pores, achieving an overpotential of 308 mV at 10 mA/cm2 current density. A much higher current density of 175 mA/cm2 could be achieved just at 380 mV of overpotential with Tafel slope as low as 62 mV/dec for this whole range while exhibiting long-term stability. Mass activity, electrochemical impedance spectroscopy data, and the estimation of electrochemically active surface area all endorsed this high catalytic performance of CoVOx-20, which is unprecedented for a low-cost, upscalable, and relatively less conductive substrate such as FTO used here. Our findings, thus, not only highlight the benefits of using AACVD in preparing two-dimensional amorphous catalysts but also prove the high efficiency of CoVOx materials thus obtained, as outlined in a plausible reaction mechanism.

TiC/C core/shell nanowires arrays as advanced anode of sodium ion batteries

High-performance anodes of sodium ion batteries (SIBs) largely depends on rational architecture design and binder-free smart hybridization. Herein, we report TiC/C core/shell nanowires arrays prepared by a one-step chemical vapor deposition (CVD) method and apply it as the anode of SIBs for the first time. The conductive TiC core is intimately decorated with carbon shell. The as-obtained TiC/C nanowires are homogeneously grown on the substrate and show core/shell heterostructure and porous architecture with high electronic conductivity and reinforced stability. Owing to these merits, the TiC/C electrode displays good rate performance and outstanding cycling performance with a capacity of 135.3 mAh/g at 0.1 A/g and superior capacity retention of 90.14% after 1000 cycles at 2 A/g. The reported strategy would provide a promising way to construct binder-free arrays electrodes for sodium ion storage.

Role of copper grid mesh in the catalytic oxidation of CO over one-step synthesized Cu-Fe-Co ternary oxides thin film

The effective valuation of catalyst supports in the catalytic oxidation makes the contribution to understand the support effect of great interest. Here, the role of active substrate in the performance and stability of Cu-Fe-Co ternary oxides was studied towards the complete catalytic oxidation of CO. The Cu-Fe-Co oxide thin films were deposited on copper grid mesh (CUGM) using one-step pulsed-spray evaporation chemical vapor deposition method. Crystalline structure and morphology analyses revealed nano-crystallite sizes and dome-top-like morphology. Synergistic effects between Cu, Fe and Co, which affect the surface Cu2+, Fe3+, Co3+ and chemisorbed oxygen species (O2− and OH−) of thin films over the active support and thus result in better reducibility. The thin film catalysts supported on CUGM exhibited attractive catalytic activity compared to the ternary oxides supported on inert grid mesh at a high gas hourly space velocity. Moreover, the stability in time-on-stream of the ternary oxides on CUGM was evaluated in the CO oxidation for 30 h. The adopted deposition strategy of ternary oxides on CUGM presents an excessive amount of adsorbed active oxygen species that play an important role in the complete CO oxidation. The catalysts supported on CUGM showed better catalytic conversion than that on inert grid mesh and some literature-reported noble metal oxides as well as transition metal oxides counterparts, revealing the beneficial effect of the CUGM support in the improvement of the catalytic performance.

The field emission of carbon-in-Al4O4C nanoneedles and its failure mechanism: high-field induced shell cracking and chemical decomposition

Although ceramic Al4O4C has recently been found to have interesting optical properties, its low conductivity makes it difficult to be used in fields related to electron transport. Here, we achieved carbon-in-Al4O4C core–shell nanoneedles via a one-step chemical vapor deposition method. The core with the form of few-layer graphene embedded in amorphous carbon improves the electron transport largely, as the I–V measurement is based on a single nanowire. Good field electron emission behavior was observed in these nanoneedles. Noticeably, when a large electric field was loaded, the nanoneedle failed in two manners, i.e. zippered dispassion between the core and shell, and chemical deposition of the Al4O4C shell into metastable δ-Al2O3. These results help to broaden the application field of Al4O4C and understand its physicochemical behavior under extreme conditions.

Design of g-C3N4/TiO2 nanotubes heterojunction for enhanced organic pollutants degradation in waste water

Heterojunction photocatalysts of g-C3N4/TiO2 nanotubes have been designed and prepared via a one-step chemical vapor deposition method by using urea as precursor. The characterizations demonstrate the composite structure does not change the original structure of g-C3N4 and TiO2 nanotubes. Benefiting from the synergistic effect between g-C3N4 and TiO2 nanotubes, 99.2% of Rhodamine B could be removed from waste water under simulate light, in which the degradation efficiency was greatly improved compared with TiO2 nanotubes and g-C3N4. Moreover, this heterojunction structure will be beneficial to improve the photocatalyst stability.

VSe2/carbon-nanotube compound for all solid-state flexible in-plane supercapacitor

Two-dimensional (2D) metallic transition-metal dichalcogenide (MTMD)/carbon-nanotube (CNT) compounds are competitive electrode materials for solid-state flexible in-plane supercapacitors, resulting from the synergistic effect of the large specific surface area of 2D MTMDs and the excellent mechanical properties of the CNT. In this paper, the high-quality VSe2/CNT electrode material is prepared by the one-step chemical vapor deposition (CVD) method. The CVD method offers a facile and safe way to synthesize a pure VSe2/CNT compound. The VSe2 nanosheets are vertically grown on the surface of the CNT cluster. The vertical configuration of the VSe2 nanosheets on the conductive CNT cluster takes full advantage of the large specific surface area of the VSe2 nanosheets to store charges. The ductile and conductive CNT cluster offers good mechanical and electrical connections to the VSe2 nanosheets. The VSe2/CNT compound is applied as the electrode material of a solid-state flexible in-plane supercapacitor which achieves a specific area capacitance of 1854 μF/cm2 and stable cycling stability, ∼7% degradation after 10 000 times of current cycling. The VSe2/CNT also presents a desirable mechanical stability, and ∼ 90% capacitance is retained after bending up to 40°. This work promotes the application of 2D MTMD compounds in the field of energy storage and wearable devices.

One-step synthesis of nitrogen-doped graphene from a sole aromatic precursor

A cheap aromatic precursor (1,10-phenanthroline) with heteroatom and planar-structure was designed to synthesize large-scale, continuous and mostly single-layer nitrogen-doped graphene (NG) films by one-step chemical vapor deposition method. The NG sheets can be obtained even at 600 °C. The results indicated that the content and type of doped N are intensely relied on the growth temperature. Our fabrication approach provides an economic synthetic route and potentially promotes the practical application of graphene-based materials.

Controllable epitaxial growth of MoSe2–MoS2 lateral heterostructures with tunable electrostatic properties

Recently, two-dimensional (2D) transition-metal dichalcogenides (TMDCs) have attracted much attention due to their promising applications in the fields of electronics and optoelectronics. Controllable growth of TMDC heterostructures stimulates new interest by tuning their optical and electronic properties. Herein, large-scale lateral MoSe2–MoS2 and MoSe2(1−x)S2x–MoS2 heterostructures have been synthesized through one-step epitaxial ambient-pressure chemical vapor deposition method and we found that the growth time plays an important role in the formation of lateral heterostructures. Lateral MoSe2–MoS2 heterostructures have been systematically characterized by using atomic force microscopy, Raman spectroscopy and photoluminescence spectroscopy. Corresponding surface potential and charge distributions of MoSe2–MoS2 heterostructures have been investigated by employing Kelvin probe force microscopy. We found that the electrostatic properties of MoSe2–MoS2 heterostructures can be effectively tuned by injecting charges through conductive atomic force microscopy. Our results pave a new route for constructing 2D lateral heterostructures toward electronic and optoelectronic applications.

Branched CdO/ZnO Core/Shell Heterogeneous Structure and Its Enhanced Photoelectrocatalytic Performance.

Branched nanostructures of semiconductors based on one-dimensional heterostructures have many promising applications in optoelectronics, supercapacitors, photocatalysts, etc. Here, we report a novel branched core/shell CdO/ZnO hetero-nanostructure that resembles a Crimson bottlebrush (Callistemon Citrinus) but with intriguing hexagonal symmetry. The nanomaterials were fabricated via an improved one-step chemical vapor deposition method and consist of a CdO wire as the core and ZnO as the shell. With cadmium acting as a catalyst, ZnO nanowires grow as perpendicular branches from the CdO/ZnO one-dimensional core/shell structure. The nanostructures were characterized with X-ray diffraction scanning and transmission electron microscopy. A homogeneous epitaxial growth mechanism has been postulated for the formation of the nanostructure. The materials show a broad and strong absorption ranging from visible to ultraviolet and a better photoelectrocatalytic properties in comparison to pure ZnO or CdO. Our synthetic strategy may open up a new way for controlled preparation of one-dimensional nanomaterials with core/shell heterostructure, which could find potential applications in solar cells and opto-electrochemical water-splitting devices.

Band Alignment Engineering in Two-Dimensional Lateral Heterostructures.

Two-dimensional (2D) heterostructures have aroused widespread attentions due to the fascinating properties originating from the interfaces and the derived potential applications in modern electronics and optoelectronics. The interfacial band alignment engineering of 2D heterostructures would open up promising routes toward the flexible design and optimization of the electronic and optoelectronic properties. Herein, we report a one-step chemical vapor deposition method for the growth of band alignment continuously modulated WS2-WS2(1- x)Se2 x (0 < x ≤ 1) monolayer lateral heterostructures, with atomically sharp interfaces at the junction area. Local photoluminescence (PL) and Raman measurements demonstrate the position-dependent composition and band gap information on the as-grown nanosheets. Kelvin probe force microscopy (KPFM) investigations further confirm the tunable band alignments in the heterostructures, where a continuously decreased Fermi level difference between the core and the shell regions is observed with the x value varied from 1 to 0. The direct growth of high-quality atomic-level junctions with controllable band alignment marks an important step toward the potential applications of 2D semiconductors in integrated electronic and optoelectronic devices.

Improved corrosion resistance and biocompatibility of biodegradable magnesium alloy by coating graphite carbon nitride (g-C3N4)

In this study, one-step chemical vapor deposition method (OS-CVD) using urea as a precursor was used to deposit carbon nitride (g-C3N4) film on the magnesium alloy. The material composition and characteristic functional groups of the as-prepared films were characterized by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The surface morphology of the carbon nitride film on the magnesium alloy was observed by using a scanning electron microscope (SEM) and an atomic force microscope (AFM). The corrosion resistance of magnesium alloy was investigated via an electrochemical method and an immersion test. The biocompatibility and hemolysis rate of graphitic carbon nitride films were studied via in vitro cellular experiments and in vivo animal experiments. The results indicated that the corrosion resistance and biocompatibility of AZ31B Mg alloy was significantly improved by g-C3N4 coating.

AlxGa1-xN -GaN core-shell nanorods: Synthesis and field emission properties

Quasi-aligned AlxGa1-xN-GaN core-shell nanorods have been synthesized on Si (100) substrate by a one-step and catalyst-free chemical vapor deposition method. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray analysis, Raman spectroscopy, and cathodoluminescence analyses reveal that the core/shell nanorods consist of AlxGa1-xN core and GaN shell. Field-emission measurements show that the AlxGa1-xN-GaN core-shell nanorod arrays present a turn-on field of ∼3.6 V/μm, threshold field of ∼4.8 V/μm, and a field-enhancement factor of ∼1197, which is much better than most AlN or GaN nanostructures. The excellent field-emission characteristics are originated from the low electron affinity of AlxGa1-xN and narrow band gap of GaN, resulting in good electron transport from AlxGa1-xN to GaN as evident from the band diagram of the core-shell material. Such AlxGa1-xN-GaN core-shell nanorods are envisaged to be one of decent candidates for advanced electronic and optoelectronic nanodevices.

Enhanced exciton emission behavior and tunable band gap of ternary W(SxSe1-x)2 monolayer: temperature dependent optical evidence and first-principles calculations.

Up to date, the electronic and optical properties of WS2 and WSe2 have been widely explored. However, the synthesis and characterization of their ternary alloy nanosheets have been rarely reported. Here, we fabricated single layer W(SxSe1-x)2 nanosheets by a one-step chemical vapor deposition (CVD) method. It is demonstrated that exciton emission behavior of single layer W(SxSe1-x)2 nanosheets (0 ≤ x ≤ 1) can be remarkably tuned by changing the sulfur content. The theoretical calculations proved that single layer W(SxSe1-x)2 alloy has a direct gap, and the band gap can be tuned by the sulfur content, which is in accordance with the spectral experiments. Moreover, we present temperature-dependent photoluminescence (PL) measurements in monolayers of W(SxSe1-x)2 alloys from 80 K to 320 K. The neutral exciton (X) and charged exciton (trion, T) can be observed at all measured temperatures. In sulfur-rich ternary W(SxSe1-x)2 alloys, the trion dominates the PL spectra at low temperatures while the exciton dominates the PL spectra at higher temperatures. In selenium-rich ternary alloys, however, the exciton is dominant in PL spectra at all measured temperatures. As the sulfur content gradually increases, the intensity ratio of the trion to exciton becomes dramatically larger. There is an obvious upward trend of the trion intensity in W(SxSe1-x)2 monolayers, which results from the significant growth of the two-dimensional electron gas (2DEG) concentration. On the other hand, the strong exciton-trion coupling mediated by an optical phonon also contributes to this improvement. These results indicate that exciton emission behavior of W(SxSe1-x)2 monolayers is controllable with the sulfur content. It highlights the importance of further detailed characterization on exciton features in ternary alloy nanosheets, and can enable spectral tunability for potential optoelectronic applications.

Strain-Gradient Effect in Gas Sensors Based on Three-Dimensional Hollow Molybdenum Disulfide Nanoflakes.

A novel three-dimensional transition metal dichalcogenide (TMD) structure consisting of seamless hollow nanoflakes on two-dimensional basal layers was synthesized by a one-step chemical vapor deposition method. Here, we demonstrate that the as-grown nanoflakes are formed on an organic promoter layer which served as a positive template and are swollen at the grain boundaries by the bubbling effect. TMD nanosheets with hollow nanoflakes are successfully applied as chemical sensors, and it was found that their gas adsorption property is strongly related to the internal strain gradient resulting from the variation in the lattice parameter. This result is consistent with the theoretical prediction in previous studies. Our chemical vapor deposition-based approach is an efficient way to generate TMD-based nanostructures over a large surface area for various practical applications such as chemical sensors.

Wavelength-Tunable Electroluminescent Light Sources from Individual Ga-Doped ZnO Microwires.

Electrically driven wavelength-tunable light emission from biased individual Ga-doped ZnO microwires (ZnO:Ga MWs) is demonstrated. Single crystalline ZnO:Ga MWs with different Ga-doping concentrations have been synthesized using a one-step chemical vapor deposition method. Strong electrically driven light emission from individual ZnO:Ga MW based devices is realized with tunable colors, and the emission region is localized toward the center of the wires. Increasing Ga-doping concentration in the MWs can lead to the redshift of electroluminescent emissions in the visible range. Interestingly, owing to the lack of rectification characteristics, relevant electrical measurement results show that the alternating current-driven light emission functions excellently on the ZnO:Ga MWs. Consequently, individual ZnO:Ga MWs, which can be analogous to incandescent sources, offer unique possibilities for future electroluminescence light sources. This typical multicolor emitter can be used to rival and complement other conventional semiconductor devices in displays and lighting.

Large-scale template-free synthesis of N-doped graphene nanotubes and N-doped SiO 2 -coated graphene nanotubes: Growth mechanism and field-emission property

Abstract The use of dopants and other functional materials has been proven to be an effective approach in tailoring the electronic properties of the composition of graphene nanosheets. However, investigations into doping and compositing of tubular graphene are still at an early stage. Herein, the first large-scale synthesis of N-doped graphene nanotubes (GNTs) and the N-doped graphene coaxial nanotubes with amorphous SiO 2 coating layer (GNTs@SiO 2 ) have been performed in a facile free-template, one-step chemical vapor deposition method, and the growth mechanism was investigated in detail. This approach both simplifies the synthetic process and protects the nanotubes from destruction caused by template removal. Moreover, a high ratio of graphitic-N to pyridinic-N doping (∼6.5:1) was achieved, which is an important factor required to improve the various properties of graphene. The N-doped GNTs and GNTs@SiO 2 displayed excellent field emission properties, with E to of 1.2 and 0.5 V/μm and E thr of 3.4 and 4 V/μm, respectively, and a synergistic effect mechanism has been proposed to interpret the enhanced FE properties. This present research not only offers a new route for large-scale synthesis of N-doped tubular graphene and its nanocomposite, along with excellent field emission properties and electroconductivity, but also establishes a foundation for their application in various fields.

Facile fabrication of antifogging, antireflective, and self-cleaning transparent silica thin coatings

We have fabricated a multifunctional coating with properties of superhydrophilicity, high transparency, antireflection and self-clean via a low-cost one-step chemical vapor deposition method without any further chemical modification. We have investigated influence of the surface topography of the silica nanoparticles to the antifogging and antireflection. The results have indicated that the excellent antifogging and transparency properties are due to the amplification of the well-ordered nipple silica nanoparticles to the hydrophilicity and suppression of the reflection, respectively. Moreover, the superhydrophilicity have endowed the coating with self-cleaning property.

Growth and composition-dependent optoelectronic properties of AlxGa1−xN alloy nanowires arrays across the entire composition range on carbon cloth

Composition-tunable ternary AlxGa1−xN (0 ≤ x ≤ 1) alloy nanowires have been grown on flexible carbon cloth in large scale through a one-step and catalyst-free chemical vapor deposition method. Field emission scanning electron microscopy, x-ray diffraction analysis, transmission electron microscopy and x-ray energy-dispersive spectroscopy were employed to characterize the morphology, crystal structure, composition properties. All AlxGa1−xN samples exhibit hexagonal wurtzite single-phase structure and a preferred orientation along [0001] direction. The progressively evolutions in structural, Raman and field emission properties of AlxGa1−xN nanowires demonstrate the continuous composition tunability across the entire composition range. The enhancement in the field emission characteristic of AlxGa1−xN nanowires on carbon cloth is ascribed to the combined effect of the nanostructures and the excellent electron transport path of the conductive carbon cloth. The successful synthesis of AlxGa1−xN nanowires on carbon cloth provides the new possibility for the further development of flexible nano- and opto-electronic devices.

Microwave Plasma Chemical Vapor Deposition of SbxOy/C negative electrodes and their compatibility with lithium and sodium Hückel salts—based, tailored electrolytes

A synthesis of new types of SbxOy/C composite negative electrodes for lithium and sodium-ion batteries is reported. Thin layers of graphitic carbon decorated in 3D with Sb nanoparticles were produced from organic precursors triphenylantimony (III) using a one-step microwave plasma chemical vapor deposition (MPCVD) method. Thin-film SbxOy/C electrodes were electrochemically tested in lithium and sodium half cells with Li and NaTDI (2-trifluoromethyl-4,5-dicyanoimidazole lithium and sodium salts) 0.75M electrolytes and delivered capacity of 425mAhg−1 at C/10 discharge rate.

Synthesis and characterization of ultra-long straight carbon wires

Ultra-long straight carbon wires with few microns in diameter and centimeters in length were synthesized in large scale through a controllable one-step chemical vapor deposition (CVD) method. The ratio of axial length to diameter more than 1000:1. The scanning electron microscope (SEM) and high-resolution transmission electron microscopy (HRTEM) images prove the layered structure surrounding the wire center, and the energy dispersive spectra (EDS) confirm the main component of the as-obtained carbon wires is carbon. Room temperature Raman spectrum presents two distinct Raman peaks of 1351cm−1 (D band) and 1586cm−1(G band), which is consistent with carbon crystalline structures. I-V curves exhibit typical resistance characteristic, which can be used as electronic polar or mechanic probe to operate nanostructures.