Single-step Chemical Vapor Deposition Research Articles

Graphene-ceramic hybrid nanofibers for ultrasensitive electrochemical determination of ascorbic acid

The authors describe the fabrication of a 3-dimensional interconnected edge-exposed graphene nanostructure. It was fabricated by single-step chemical vapor deposition of highly foliated graphene on a network of γ-alumina nanofibers having a single fiber diameter of around 7 nm. It is shown that a highly sensitive electrochemical sensor can be prepared for simultaneous detection of ascorbic acid, uric acid and dopamine from such graphene-coated nanofibers possessing different but controllable density of foliates. The study concentrates on the determination of ascorbic acid in a concentration range that extends from as low as 5 nM to 1 mM. The electrochemical properties of the materials were studied by cyclic voltammetry, chronoamperometry and differential pulse voltammetry using hexacyanoferrate as a redox probe. Response is linear in the 1 μM to 60 μM ascorbate concentration range, the sensitivity is 1.06 μA⋅μM−1⋅cm−2, and the detection limit is 117 nM at foliate density of 50 foliates μm−1. The sensor was successfully applied to the determination of ascorbic acid in spiked urine samples. These results demonstrate a method for controllable growth of graphene possessing tailored morphology. In our perception, the application of such graphene-decorated nanostructures paves the way to the design of ultrasensitive electrochemical sensors of high stability.

Superconductivity and magnetotransport of single-crystalline NbSe2 nanoplates grown by chemical vapour deposition.

NbSe2 is a typical transition metal dichalcogenide with a rich variety of electronic ground states existing in its nanostructures, including two-dimensional superconductivity and charge density wave. However, the direct growth of high-quality single-crystalline NbSe2 nanostructures is still challenging, which limits their applications in electronic devices. Here, we report the growth of high-quality NbSe2 nanoplates by a single-step chemical vapour deposition. Their temperature and magnetic-field dependent superconducting behaviors were investigated by four-terminal devices fabricated on individual nanostructures. The NbSe2 nanoplates show two-dimensional characteristics of superconducting transitions and strong anisotropy with magnetic field orientation, providing potential platforms for the exploration of new physics in nanoelectronic devices.

Chemical vapor deposition growth of single-crystalline cesium lead halide microplatelets and heterostructures for optoelectronic applications

Organic–inorganic hybrid halide perovskites, such as CH3NH3PbI3, have emerged as an exciting class of materials for solar photovoltaic applications; however, they are currently plagued by insufficient environmental stability. To solve this issue, all-inorganic halide perovskites have been developed and shown to exhibit significantly improved stability. Here, we report a single-step chemical vapor deposition growth of cesium lead halide (CsPbX3) microcrystals. Optical microscopy studies show that the resulting perovskite crystals predominantly adopt a square-platelet morphology. Powder X-ray diffraction (PXRD) studies of the resulting crystals demonstrate a highly crystalline nature, with CsPbCl3, CsPbBr3, and CsPbI3 showing tetragonal, monoclinic, and orthorhombic phases, respectively. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies show that the resulting platelets exhibit well-faceted structures with lateral dimensions of the order of 10–50 μm, thickness around 1 μm, and ultra-smooth surface, suggesting the absence of obvious grain boundaries and the single-crystalline nature of the individual microplatelets. Photoluminescence (PL) images and spectroscopic studies show a uniform and intense emission consistent with the expected band edge transition. Additionally, PL images show brighter emission around the edge of the platelets, demonstrating a wave-guiding effect in high-quality crystals. With a well-defined geometry and ultra-smooth surface, the square platelet structure can function as a whispering gallery mode cavity with a quality factor up to 2,863 to support laser emission at room temperature. Finally, we demonstrate that such microplatelets can be readily grown on a variety of substrates, including silicon, graphene, and other two-dimensional materials such as molybdenum disulfide, which can readily allow the construction of heterostructure optoelectronic devices, including a graphene/perovskite/graphene vertically-stacked photodetector with photoresponsivity > 105 A/W. The extraordinary optical properties of CsPbX3 platelets, combined with their ability to be grown on diverse materials to form functional heterostructures, can lead to exciting opportunities for broad optoelectronic applications.

Investigation on the Formation Mechanism of Double-Layer Vertically Aligned Carbon Nanotube Arrays via Single-Step Chemical Vapour Deposition

The mechanism for the formation of double-layer vertically aligned carbon nanotube arrays (VACNTs) through single-step CVD growth is investigated. The evolution of the structures and defect concentration of the VACNTs are tracked by scanning electron microscopy (SEM) and Raman spectroscopy. During the growth, the catalyst particles are stayed constantly on the substrate. The precipitation of the second CNT layer happens at around 30 min as proved by SEM. During the growth of the first layer, catalyst nanoparticles are deactivated with the accumulation of amorphous carbon coatings on their surfaces, which leads to the termination of the growth of the first layer CNTs. Then, the catalyst particles are reactivated by the hydrogen in the gas flow, leading to the precipitation of the second CNT layer. The growth of the second CNT layer lifts the amorphous carbon coatings on catalyst particles and substrates. The release of mechanical energy by CNTs provides big enough energy to lift up amorphous carbon flakes on catalyst particles and substrates which finally stay at the interfaces of the two layers simulated by finite element analysis. This study sheds light on the termination mechanism of CNTs during CVD process.Graphical The mechanism for the formation of double-layer vertically aligned carbon nanotube arrays (VACNTs) through single-step CVD growth was investigated. The growth of the second CNT layer lifts the amorphous carbon coatings on catalyst particles and substrates.

Aerosol Assisted Chemical Vapour Deposition Synthesis of Copper(I) Oxide Thin Films for CO<SUB>2</SUB> Reduction Photocatalysis

Copper(I) oxide thin films have been deposited on glass using a simple single-step chemical vapour deposition method, utilising commercially available Cu(acac)₂ (acac = acetylacetonato) dissolved in toluene and deposited at 350 °C, which when exposed to air on cooling forms a native protective layer of CuO <10 nm thick. These films are demonstrated to be active for photoelectrochemical reduction of carbon dioxide at −0.6 V versus Ag/AgCl, a potential route for conversion of waste CO₂ to useful organic chemicals, and stable to photocorrosion.

Preparation of silica-graphene nanohybrid as a stabilizer of emulsions

In the present study, a novel silica-graphene nanohybrid was synthesized through a facile and single step chemical vapor deposition of acetylene on silica aerogel in the presence of hydrogen as a reducing agent at atmospheric pressure and 600°C. The physiochemical properties of the nanohybrid were thoroughly characterized by XRD, TGA, Raman, BET, DLS, FT-IR, SEM, and TEM. The amount of graphene in the silica-graphene nanohybrid was found to be 16wt% while a remarkable specific surface area about 843.64m2/g has been accomplished. The as-prepared nanohybrid was employed for stabilization of decalin/water emulsion. In addition, the effective factors on the droplets size and condition of stabilization for emulsion preparation were investigated through Taguchi L16 statistical design. Ultimately, the Wilhemy plate method shows that by dispersion of nanohybrid in water/decalin emulsion the interfacial tension (IFT) can be considerably declined from 55 to 30.12mN/m.

Large area chemical vapor deposition growth of monolayer MoSe2 and its controlled sulfurization to MoS2

Abstract

Nitrogen-doped carbon nanofibers on expanded graphite as oxygen reduction electrocatalysts

A single-step chemical vapor deposition method using simple gaseous precursors was employed to grow nitrogen-doped carbon nanofibers from Fe and Ni particles on the surface of expanded graphite (N-CNF/EG). Due to the high electronic conductivity of the expanded graphite the N-CNF/EG could be used as electrocatalysts without the need for harsh purification procedures. Electrochemical testing showed that the N-CNFs grown from Fe exhibited a notable activity for the oxygen reduction in both acidic and alkaline electrolyte, in addition to demonstrating a high durability with a well-preserved catalytic activity after 1600 cycles in O2-saturated 0.5 M H2SO4. Physicochemical characterization revealed the formation of N-CNFs with a bamboo-like structure, encapsulated Fe particles and high pyridinic nitrogen content. The combination of high ORR-activity, an easily scalable synthesis approach and a highly conductive support material makes N-CNF/EG a promising oxygen reduction catalyst for low temperature fuel cells.

Viscoelastic properties of coil carbon nanotube-coated carbon fiber-reinforced polymer nanocomposites

Strong interfacial bonding is necessary between carbon fiber and polymer matrix to take advantage of carbon fiber-reinforced polymer composites in structural applications. An attempt has been made to improve the interfacial bonding by coating coiled carbon nanotubes on carbon fiber surface through a single-step chemical vapor deposition process. Coiled structures were synthesized on nickel-coated carbon fiber by using thiophene as a sulphur impurity and acetylene as a carbon precursor. The coiled carbon nanotube-coated carbon fiber and epoxy were used, respectively, as the reinforcement and the matrix to form carbon fiber-reinforced polymer composites. The role of coiled carbon nanotubes on thermo-mechanical properties of carbon fiber-reinforced polymer composites was investigated using dynamic mechanical thermal analysis in three different modes of deformation. Unsized carbon fiber (carbon fiber heat-treated to remove sizing agents)/epoxy composites were used as the reference to evaluate the enhancement due to coiled carbon nanotubes. Substantial improvements in viscoelastic properties of coiled carbon nanotube/carbon fiber/polymer composites over unsized carbon fiber/polymer composites were observed in all of the deformation modes. Coiled Carbon nanotube composites in shear mode exhibit highest enhancements in both storage as well as loss moduli due to superior mechanical interlocking between coiled carbon nanotubes and polymer matrix.

Simple Growth of Faceted Au-ZnO Hetero-nanostructures on Silicon Substrates (Nanowires and Triangular Nanoflakes): A Shape and Defect Driven Enhanced Photocatalytic Performance under Visible Light.

A simple single-step chemical vapor deposition (CVD) method has been used to grow the faceted Au-ZnO hetero-nanostructures (HNs) either with nanowires (NWs) or with triangular nanoflakes (TNFs) on crystalline silicon wafers with varying oxygen defect density in ZnO nanostructures. This work reports on the use of these nanostructures on substrates for photodegradation of rhodamine B (RhB) dyes and phenol under the visible light illumination. The photoluminescence measurements showed a substantial enhancement in the ratio of defect emission to band-edge emission for TNF (ratio ≈ 7) compared to NW structures (ratio ≤ 0.4), attributed to the presence of more oxygen defects in TNF sample. The TNF structures showed 1 order of magnitude enhancement in photocurrent density and an order of magnitude less charge-transfer resistance (R(ct)) compared to NWs resulting high-performance photocatalytic activity. The TNFs show enhanced photocatalytic performance compared to NWs. The observed rate constant for RhB degradation with TNF samples is 0.0305 min(-1), which is ≈5.3 times higher compared to NWs case with 0.0058 min(-1). A comparison has been made with bulk ZnO powders and ZnO nanostructures without Au to deduce the effect of plasmonic nanoparticles (Au) and the shape of ZnO in photocatalytic performance. The results reveal the enhanced photocatalytic capability for the triangular nanoflakes of ZnO toward RhB degradation with good reusability that can be attracted for practical applications.

Transformation of carbon black into carbon nano-beads and nanotubes: the effect of catalysts

Structural transformation of carbon black (CB) into carbon nano-beads and nanotubes was achieved at 1000 °C using ferrocene and nickelocene as catalyst precursors using a simple and single step chemical vapor deposition method. The samples were characterized by XRD, SEM, TEM, HR-TEM and Raman spectroscopy. Results indicate that different morphological and high quality nano carbon structures were obtained using different weight ratios of catalyst to precursor. The use of bimetallic catalysts provides many different morphologies and a higher degree of crystal order of the carbon nanostructures than the use of mono-metallic catalysts. The nanotubes were mostly filled with metal nanoparticles and the degree of metal-filling is dependent on the weight ratio of catalyst precursor to CB. Metal–filled multi-walled carbon nano-bead structures with a high degree of crystalline order are also obtained at weight ratios of CB: ferrocene: nickelocene of 1:2:2.

Comparing graphene growth on Cu(111) versus oxidized Cu(111).

The epitaxial growth of graphene on catalytically active metallic surfaces via chemical vapor deposition (CVD) is known to be one of the most reliable routes toward high-quality large-area graphene. This CVD-grown graphene is generally coupled to its metallic support resulting in a modification of its intrinsic properties. Growth on oxides is a promising alternative that might lead to a decoupled graphene layer. Here, we compare graphene on a pure metallic to graphene on an oxidized copper surface in both cases grown by a single step CVD process under similar conditions. Remarkably, the growth on copper oxide, a high-k dielectric material, preserves the intrinsic properties of graphene; it is not doped and a linear dispersion is observed close to the Fermi energy. Density functional theory calculations give additional insight into the reaction processes and help explaining the catalytic activity of the copper oxide surface.

One-step synthesis of Pt-decorated graphene–carbon nanotubes for the electrochemical sensing of dopamine, uric acid and ascorbic acid

Platinum nanoparticle-decorated graphene and carbon nanotube (Pt-Gr-CNT) nanocomposites synthesized by a single step chemical vapor deposition process, serve as a promising platform for the simultaneous electrochemical sensing of dopamine, uric acid and ascorbic acid.

Single-step synthesis of carbon nanotubes/iron/iron oxide composite films through inert-ambient CVD using ferric acetylacetonate as a precursor

Fe–Fe3O4–CNT composite thin film was obtained by single step chemical vapor deposition process using Fe(acac)3 as the sole precursor. By changing the deposition pressure, the form of carbon deposited could be changed from amorphous to CNTs.

Coaxial Zn2GeO4@carbon nanowires directly grown on Cu foils as high-performance anodes for lithium ion batteries.

A single-step chemical vapor deposition method is utilized to prepare a novel electrode structure composed of coaxial Zn2GeO4@carbon nanowires directly grown on a Cu foil current-collector (ZGO@C/Cu), and the obtained ZGO@C/Cu hybrid electrode is employed as additive-free anode in lithium ion battery studies. The ZGO@C/Cu electrode exhibits a high reversible capacity of 1162 mA h g(-1) between 0.01 and 3.0 V at a current density of 0.2 A g(-1). It also shows a remarkable cycling stability and an excellent high-rate capability. At a current density of 2.0 A g(-1), a stable capacity of 790 mA h g(-1) is obtained without any noticeable decay over 100 cycles. Even at a high current density of 10 A g(-1), a reversible capacity of 465 mA h g(-1) is still obtained. The synthesis approach developed here could be utilized for the fabrication of other high-performance heterogeneous electrode structures for lithium ion battery applications.

Single-step CVD growth of high-density carbon nanotube forests on metallic Ti coatings through catalyst engineering

We demonstrate the direct growth of carbon nanotube (CNT) forests on metallic titanium (Ti) coatings by single-step chemical vapor deposition. This was achieved by catalyst engineering, which involves a novel design of Fe/Ti/Fe nanostructure sputtering coated on SiO2/Si wafers. The Fe sublayer, an additional catalyst added to the conventional catalyst/support design, plays a key role in the growth of well aligned and highly dense CNT forests. Depth profile analysis of substrates by secondary ion mass spectroscopy shows that the Fe sublayer is thermally unstable at the Ti/SiO2 interface under the growth conditions. Catalyst diffusion back to the surface from the Fe sublayer is much more significant than down towards the SiO2/Si substrate from the surface Fe layer. This makes it possible to minimize the thickness of surface catalyst layer, and ensures the growth of well aligned and high-density CNT forests on Ti coatings. The filling factor of nanotubes on the substrate after liquid-induced compaction can be dramatically increased up to 57%, leading to an estimation of the areal density of around 1012 cm−2.

Spatially Sequential Growth of Various WSi2 Networked Nanostructures and Mechanisms

Various WSi2 nanostructures including networked nanorods (NNWs), networked nanoribbons (NNRs), and nanosheets (NSs) were sequentially (spatial) synthesized in a controlled manner via a single-step chemical vapor deposition method. Their morphology, structure, and composition were characterized by scanning and transmission electron microscopes and X-ray diffraction. The nanostructures are 6–10 nm in thickness and several micrometers in length. The results reveal that the formation of WSi2 nanostructures is governed by a vapor solid mechanism and the concentration of reactive species plays a crucial role in controlling the formation of the various morphologies of the synthesized nanostructures. The time-dependent growth study shows that the nanostructures feature two-dimensional growth of WSi2, resulting in nanonets and nanosheets. Cyclic voltammetry measurements of these nanostructures demonstrate the chemical capacitance characteristics of WSi2 nanosheets and nanoribbons. Not only has this study paved a new route for preparing various nanostructures, but also these nanostructures are of great interest for nanodevices and electrochemical applications.

A facile approach for shape selective synthesis of rhodium nanostructures and conductivity studies

Shape selective synthesis of Rh nanostructures has been demonstrated with the help of a single step chemical vapor deposition, where different shapes like cubes at 500 °C, pyramids and hexagons at 500 °C, 700 °C and 900 °C respectively have been obtained as a function of temperature. Scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and four probe conductivity measurements were used to study the morphology, crystallinity and phase purity of the structures. The conductivity values for as synthesised nanostructures have been obtained in the range of 2-7 kS/cm2. On the basis of the experimental results, from TGA and XPS studies possible mechanistic pathway for the evolution of Rh nanostructures was discussed.

Aerographite: Ultra Lightweight, Flexible Nanowall, Carbon Microtube Material with Outstanding Mechanical Performance

An ultra lightweight carbon microtube material called Aerographite is synthesized by a novel single-step chemical vapor deposition synthesis based on ZnO networks, which is presently the lightest known material with a density smaller than μg/cm(3). Despite its low density, the hierarchical design leads to remarkable mechanical, electrical, and optical properties. The first experiments with Aerographite electrodes confirm its applicability.

Raman Spectroscopy and Field Emission Scanning Electron Microscopic Studies on Carbon Nanomaterials

Raman analysis is one of the main methods use to investigate type of graphitized carbon nanomaterials. It provides information on the vibration of crystal lattice, electron structure and regularity of crystal structure of the graphitized carbon materials. In this work the single step chemical vapour deposition (CVD) method was introduced for the direct growth of all as-synthesized carbon nanomaterials; carbon nanotubes (CNTs), carbon nanofiber (CNF), carbon nanosphere chain (CNSC) and CNT heterojunctions (HJCNTs). Series of metal catalysts were formulated from Ni, Fe, Cr and Cu, and were used in the synthesis of the respected carbon nanomaterials (CNMs). By introducing the right combination of the reaction conditions consisting of the formulated catalyst, reaction temperature and flow rate as well as type of carbon source resulted in the formation of different types of carbon nanomaterials. Raman spectra analysis revealed that the used of acetylene and ethanol as the carbon precursors are proficient to produce different form of carbon nanomaterials as depicted by the evolution of the G-band and D-band intensities. The FESEM micrographs obtained confirmed the morphology and types of the respected carbon nanomaterials synthesized in this study.