Injection Chemical Vapor Deposition Research Articles

Compressive and interlaminar shear properties of carbon/carbon composite laminates reinforced with carbon nanotube-grafted carbon fibers produced by injection chemical vapor deposition

Carbon nanotubes (CNTs) were grown in situ on the surface of carbon fiber cloths by injection chemical vapor deposition using ethanol as a carbon source and ethylenediamine as a promoter. The nanotube-grown cloths were stacked to form multilayered preforms, and then densified by isothermal chemical vapor infiltration to prepare CNT reinforced carbon/carbon (CNT–C/C) composite laminates. The effect of CNTs on microstructure and mechanical properties of carbon/carbon (C/C) laminates were investigated. Results show that the existence of CNTs not only contributes to refine the pyrocarbon (PyC) grain size but also inhibits matrix cracking, resulting in high cohesion of PyC matrix. The grown CNTs possess high surface area thus modifying the fiber surface condition, which in turn improves the fiber/matrix (F/M) interface. Both the high matrix cohesion and strong F/M interface bonding give rise to the powerful interaction between adjacent layers in the CNT–C/C laminates. The measured out-of-plane, in-plane compressive strength and interlaminar shear strength of these laminates show a significant enhancement of 32%, 115% and 108%, respectively compared with the laminates without CNTs. Out-of-plane and in-plane compressive modulus of these laminates are also improved by 11% and 46%, respectively.

Comparative Study of Antibacterial Efficiency of M-TiO<sub>2</sub> (M = Ag, Cu) Thin Films Grown by CVD

M-TiO2 (M = Ag, Cu) nanocomposite layers were grown by pulsed direct liquid injection chemical vapor deposition (DLICVD) on various substrates to produce bactericidal surfaces with long term activity. Monodisperse Ag nanoparticles (NPs) with an average size of 5-10 nm are embedded in an anatase matrix. A bactericidal behavior determined by the JIS Z 2801 standard test was found for Ag-TiO2 films for Ag ≤ 1 at. % and above. Higher Ag content is not necessary since efficiency is already at its maximum (relative activity 100%). By contrast, using Cu as antibacterial agent, a larger size distribution of metal particles was found (20 to 400 nm). Cu-TiO2 films exhibit a bactericidal behavior if their thickness is higher than 100 nm and Cu content ≥ 3.5 at. %. These coatings are still antibacterial after 5 months of aging and their efficiency has decreased by only 35%.

Interesting Evidence for Template‐Induced Ferroelectric Behavior in Ultra‐Thin Titanium Dioxide Films Grown on (110) Neodymium Gallium Oxide Substrates

The first evidence for room‐temperature ferroelectric behavior in anatase‐phase titanium dioxide (a‐TiO2) is reported. Behavior strongly indicative of ferroelectric characteristics is induced in ultra‐thin (20 nm to 80 nm) biaxially‐strained epitaxial films of a‐TiO2 deposited by liquid injection chemical vapor deposition onto (110) neodymium gallium oxide (NGO) substrates. The films exhibit significant orthorhombic strain, as analyzed by X‐ray diffraction and high‐resolution transmission electron microscopy. The films on NGO show a switchable dielectric spontaneous polarization when probed by piezoresponse force microscopy (PFM), the ability to retain polarization information written into the film using the PFM tip for extended periods (several hours) and at elevated temperatures (up to 100 °C) without significant loss, and the disappearance of the polarization at a temperature between 180 and 200 °C, indicative of a Curie temperature within this range. This combination of effects constitutes strong experimental evidence for ferroelectric behavior, which has not hitherto been reported in a‐TiO2 and opens up the possibility for a range of new applications. A model is presented for the effects of large in‐plane strains on the crystal structure of anatase which provides a possible explanation for the experimental observations.

Epitaxial growth of spinel cobalt ferrite films on MgAl2O4 substrates by direct liquid injection chemical vapor deposition

The direct liquid injection chemical vapor deposition (DLI-CVD) technique has been used for the growth of cobalt ferrite (CFO) films on (100)-oriented MgAl2O4 (MAO) substrates. Smooth and highly epitaxial cobalt ferrite thin films, with the epitaxial relationship MAO(100)[001]∥CFO(100)[001], are obtained under optimized deposition conditions. The films exhibit bulk-like structural and magnetic properties with an out-of-plane lattice constant of 8.370Å and a saturation magnetization of 420kA/m at room temperature. The Raman spectra of films on MgAl2O4 support the fact that the Fe3+- and the Co2+-ions are distributed in an ordered fashion on the B-site of the inverse spinel structure. The DLI-CVD technique has been extended for the growth of smooth and highly oriented cobalt ferrite thin films on a variety of other substrates, including MgO, and piezoelectric lead magnesium niobate–lead titanate and lead zinc niobate–lead titanate substrates.

Interplay between exchange interaction and magnetic anisotropy for iron based nanoparticles in aligned carbon nanotube arrays

In this work, we investigate magnetic properties of iron based nanoparticles (NP) intercalated into carbon nanotube (CNT) aligned arrays synthesized by injection chemical vapor deposition. We have analyzed the temperature (T) and the ferrocene concentration (CF) dependences of the macroscopic magnetic parameters. From these experiments a weaker interaction between magnetic moments of NP was obtained for low CF values. The random anisotropy model for the experimental data analysis was applied and micromagnetic parameters were evaluated. The law of the approach to magnetic saturation (LAS) was analyzed using the general expression with the correlation function C(r=x/Ra) of magnetic axes, Ra being the magnetic anisotropy correlation length. We obtained that, while for CF=0.5% C(r) is a step-like (C(r<10)=1, C(r>10)=0), for CF⩾1% C(r) decays rapidly on a short range, (2-3)Ra. Such extended correlations for CF=0.5% could be associated with the dominant role of the coherent anisotropy, which is caused by the influence of the alignment of CNT. When the aligned CNTs for CF=0.5% are destroyed into powder, the LAS is changed to H−1/2, which means the dominant role of the exchange mechanism.

Dielectric properties and X-ray photoelectron spectroscopic studies of niobium oxide thin films prepared by direct liquid injection chemical vapor deposition method

Niobium oxide thin films were grown by direct liquid injection chemical vapor deposition using Nb(OC2H5)5 precursor. Influence of reactant's molar ratios [oxygen:Nb(OC2H5)5] and deposition temperatures on films properties such as growth rate, stoichiometry, crystal structure, morphology, dielectric constant and leakage current were studied. Films start crystallizing above 340°C in O2 atmosphere and become crystalline at 400°C. The surface roughness of weakly crystalline and crystalline films was significantly affected by deposition temperatures and reactant's molar ratios. It was found that decrease in surface roughness improved leakage current. X-ray photoelectron spectroscopic studies showed that films were in different oxidation states (Nb2+, Nb4+ and Nb5+). The dielectric constants of films were improved by increasing oxygen ratios. At ratio (150:1), the film showed high dielectric constant value (47) at 340°C and leakage current density of 2.0×10−5A/cm2 (at 3V).

Antibacterial properties of TiO2–Cu composite thin films grown by a one step DLICVD process

The correlations between microstructural features, chemical compositions and antibacterial properties of coatings containing metallic Cu particles embedded in a titanium dioxide matrix have been determined. A Direct Liquid Injection Chemical Vapor Deposition (DLICVD) process was used for the one step growth of TiO2–Cu composite coatings on various substrates. Titanium tetra-iso-propoxide (TTIP) and copper bis(2,2,6,6-tetramethyl-3,5-heptationate) (Cu(tmhd)2) were used as titanium and copper molecular sources, respectively. This growth process allows a good control of the quantity of metalorganic precursors injected into the CVD reactor and thus of the coating composition. The deposition occurs at 683K under low pressure (800Pa). The influence of the main features of the coatings on their antibacterial properties was investigated in order to produce bactericidal surfaces that are durable, non-toxic and containing a minimum amount of active agent. The antibacterial activity on Staphylococcus aureus without any photon activation was measured according to the JIS Z 2801:2000 standard method. An antibacterial activity was detected for a low metal content of ca. 1at.% Cu, and was found to increase with the Cu content. It was maximal for 3.5at.% Cu, i.e. TiO2–Cu composite coatings exhibit bactericidal behavior against S. aureus for this optimal composition (relative activity=100%). In order to better characterize the microbiological behavior of the coatings more discriminating methods derived from the literature were tested to assess the performances of these CVD coatings in terms of efficiency, release of antibacterial agent and accelerated aging.

Photovoltaic response of Cu2O/In2S3 hetero-structure grown on Cu substrate

A thin layer of p-type Cu2O was grown over flexible 30μm thick copper substrates. Using Injection Chemical Vapor Deposition technique, n-type In2S3 thin films were grown over the Cu2O layer. A p–n junction was thus realized. The Cu2O/In2S3 hetero-structure showed photovoltaic behavior. A solar cell with the structure Cu/Cu2O/In2S3/Ag could be fabricated. An acidic texturization sequence was developed which increased the photo-sensitivity of the In2S3 window layer. The Cu/Cu2O/In2S3/Ag hetero-structure with the textured window layer had an open circuit voltage of 377mV, short circuit current density of 0.118mA/cm2 and fill factor of 33.34%. It was found that the efficiency of the solar cell depended upon the photo-sensitivity of the In2S3 window layer. The work demonstrates the use of copper substrate for thin film solar cell fabrication.

Structural and Compositional Regulation of Nitrogen-Doped Carbon Nanotubes with Nitrogen-Containing Aromatic Precursors

Nitrogen-doped carbon nanotubes (NCNTs) have been catalytically synthesized from five different nitrogen-containing aromatic precursors by injection chemical vapor deposition (CVD) in the temperature range of 550–850 °C. The doped nitrogen mainly exists as pyridinic or graphitic nitrogen with the total content of 2–9 at. % depending on the precursor and preparation condition. Over 60% carbon and nitrogen atoms could be converted to NCNTs products for all the precursors, indicating the high efficiency and potential for scale-up of the injection CVD method. The oxidation processes of the NCNTs products have been illustrated in detail with the in-situ thermogravimetry–differential scanning calorimetry–mass spectrum coupling technique, and the results clearly indicate the successful incorporation of nitrogen into the nanotubes as supported by X-ray photoelectron spectroscopy. There is a dependent correlation between the pre-existing C–N bond in the precursor and the N incorporation in the corresponding NCNTs ...

The development of a ‘process map’ for the growth of carbon nanomaterials from ferrocene by injection CVD

Ferrocene was used as a catalyst in a hydrocarbon solution to carry out injection chemical vapour deposition (CVD) growth of carbon nanomaterials in a horizontal tube furnace. The presence and quality of various carbon materials was determined using Raman spectroscopy, thermogravimetric analysis, and electron microscopy. Products ranged from amorphous carbon (a-C), multi walled carbon nanotubes (MWNTs) and vapour grown fibers (VGFs). Catalyst concentration, growth temperature, injection rate, carrier gas flow rate, and the choice of hydrocarbon were found to influence the product outcome. Slower injection rates gave higher isolated yield. High catalyst concentrations were found to produce less pure carbon materials with iron oxides impurities. Higher temperatures were favourable to nanotube formation. The use of benzene was found to increase yield compared with the other hydrocarbons. In this work we developed a process map to chart the various carbon nanomaterial allotropes that were created according to reaction parameters.

Bi-Functional N-Doped CNT/Graphene Composite as Highly Active and Durable Electrocatalyst for Metal Air Battery Applications

Ethylene diamine-based nitrogen doped carbon nanotube (NCNT) was successfully synthesized on thermally reduced graphene oxide (TRGO) by an injection chemical vapor deposition method and its electrocatalytic activities for oxygen reduction and evolution reactions (ORR and OER, respectively) were investigated for metal air battery applications. The TRGO/NCNT composite with a novel bridged planes morphology does not only exhibits ORR performance similar to that of commercial Pt/C catalyst, but also demonstrates a superior OER activity. Furthermore, the composite exhibits an excellent electrochemical durability confirmed by full range cyclic voltammetry (CV) cycling. This study highlights an approach to prepare highly active and durable metal free catalysts as a highly efficient electrode material for rechargeable metal air battery applications.

The density factor in the synthesis of carbon nanotube forest by injection chemical vapor deposition

Beneath the seeming straight-forwardness of growing carbon nanotube (CNT) forests by the injection chemical vapor deposition (CVD) method, control of the forest morphology on various substrates is yet to be achieved. Using ferrocene dissolved in xylene as the precursor, we demonstrate that the concentration of ferrocene and the injection rate of the precursor dictate the CNT density of these forests. However, CNT density will also be affected by the substrates and the growth temperature which determine the diffusion of the catalyst adatoms. The CNT growth rate is controlled by the temperature and chemical composition of the gases in the CVD reactor. We show that the final height of the forest is diffusion limited, at least in the conditions of our experiments. Because of the proximity and entanglement of the CNTs in a forest, the growing CNTs can lift-up the inactive CNTs resulting in reduced density toward the base of the forest unless the nucleation rate of the new catalyst particles is sufficiently high to replenish the inactive catalyst particles. Significant loss of CNT attachment by the lift-up effect reduces the adhesion of the forest to the substrate. Optimizing the ferrocene concentration in the precursor, precursor injection rate, gas mixture, substrate, and temperature is necessary to achieve desired forest morphology for specific applications.

Microstructural and ferromagnetic resonance properties of epitaxial nickel ferrite films grown by chemical vapor deposition

Microstructural and ferromagnetic resonance properties of epitaxial nickel ferrite (NiFe2O4) films grown by direct liquid injection chemical vapor deposition are reported. While high-quality epitaxial growth of NiFe2O4 films on (100)-oriented MgAl2O4 substrate is confirmed by high resolution transmission electron microscopy, bright field (diffraction contrast) TEM studies reveal the presence of dislocations and also dark diffused contrast areas, which originate from antiphase domains. Angle and frequency-dependent ferromagnetic resonance (FMR) experiments are conducted to determine the magnetic anisotropy and the magnetic relaxation. A low out-of-plane FMR linewidth of ∼160 Oe has been observed at a frequency of 10 GHz.

Electronic properties of crystalline Ge1-xSbxTey thin films

Ge1-xSbxTey thin films, grown by metalorganic and hot-wire liquid injection chemical vapor deposition in different crystalline phases, are investigated to determine resistivity, carrier density, and carrier mobility in the 4.2–300 K temperature range. It is found that all these chalcogenides exhibit p-type conduction, high carrier density (&amp;gt;2 · 1020 cm−3), and no carrier freeze-out, regardless of composition. Low-temperature mobility data show that both chemical composition and growth technique affect the defect density and, in turn, the carrier scattering mechanisms. In this regard, charge carrier mobility is analyzed according to semi-empirical scattering models and an interpretation is provided.

Chemical Vapor Deposition Synthesis of Carbon Nanotube-Graphene Nanosheet Hybrids and Their Application in Polymer Composites

Both carbon nanotubes (CNTs) and graphene nanosheets (GNs) have potential applications in polymer composites. Combining them may induce a synergistic effect on enhancing the properties of composites. Herein, CNT-GN 3D hybrids were prepared by liquid injection chemical vapor deposition through a spray containing both carbon feedstocks and catalyst precursors. Vertically aligned CNTs were self-organized on the GNs. The morphology of hybrids could be well controlled as a function of the synthesis parameters. The unique 3D geometry of the CNT-GN hybrids provided composites with a higher electrical conductivity as compared to composites solely reinforced by CNTs or GNs. However, the thermal stability of the neat poly(vinylidene fluoride) matrix was found to decrease upon the addition of these hybrid fillers.

Modeling Synthesis of Carbon Nanotubes by Using Injection Chemical Vapor Deposition Reactor

Modeling Synthesis of Carbon Nanotubes by Using Injection Chemical Vapor Deposition Reactor

Nanoscale engineered electrochemically active silicon–CNT heterostructures-novel anodes for Li-ion application

Heterostructures of vertically aligned carbon nanotubes (CNTs) and nanostructured silicon were synthesized on quartz substrates using a simple 2 step liquid injection chemical vapor deposition (CVD) approach. The CVD conditions and the process parameters were modified to engineer droplets and thin film morphologies of silicon on the CNTs. The combined influence of these Si morphologies on the electrochemical performance was then studied. Structural analyses conducted on the heterostructures using XRD and Raman spectroscopy indicated the existence of nanocrystalline and amorphous phases of silicon. Cycling performance of these heterostructures exhibit very high specific discharge capacities in excess of 2300mAh/g accompanied by a low irreversible loss (10%) for a loading density of ∼2–3mg/cm2 demonstrating the use of these heterostructures as next generation lithium-ion anodes.

Vertically aligned carbon nanotubes grown on carbon fabric with high rate capability for super-capacitors

Vertically aligned carbon nanotubes (VACNTs) were directly grown on carbon fabric (CF) using the controllable injection chemical vapor deposition without the pretreatment of the surface of CF. Electrochemical characterization indicated that VACNT/CF electrodes achieved a relative high specific capacitance of 75Fg−1 at a current density of 1Ag−1 due to large specific surface area and low contact resistance. The specific capacitance still remained 63Fg−1 at a high current density of 100Ag−1 with the retention of 84%, which far exceeded other carbonaceous materials. This excellent rate capability of VACNT/CF electrodes was attributed to large mesopore size, three-dimensional hierarchical architecture and aligned pathway, facilitating the diffusion of electrolyte ions. In addition, the area-normalized capacitance of VACNT/CF electrodes was improved remarkably by prolonging the growth time of CNT.

The influence of reagent stoichiometry on the yield and aspect ratio of acid-oxidised injection CVD-grown multi-walled carbon nanotubes

Injection chemical vapour deposition (ICVD) was used for the preparation of multi-walled carbon nanotubes (MWCNTs) with varying lengths and diameters. The concentration of iron injected with the feedstock is related to the resulting average MWCNT dimensions, mass yield, packing density, crystallinity, and iron content. An optimum set of conditions is identified that maintains a constant diameter during growth; higher iron injection concentrations lead to an increasing MWCNT diameter as growth proceeds. Carbon nanotubes are frequently oxidised in mixtures of concentrated nitric and sulphuric acids in order to purify, functionalise, and shorten as-synthesised materials. Here, the carbon:acid stoichiometry is systematically varied, and shown to control the yield and dimensions of the resulting oxidised MWCNTs in a predictable manner, for the various ICVD starting materials. With increasing acid content, the yield of nanotubes decreases, the fraction of oxidised debris increases, and the initial, defect-driven, cutting reaction saturates, whilst thinning reactions continue. The results provide insight into both ICVD synthesis and acid oxidation of MWCNTs, as well as a means to prepare well-dispersed samples with controlled dimensions.

Nonlinear viscoelasticity of freestanding and polymer-anchored vertically aligned carbon nanotube foams

Vertical arrays of carbon nanotubes (VACNTs) show unique mechanical behavior in compression, with a highly nonlinear response similar to that of open cell foams and the ability to recover large deformations. Here, we study the viscoelastic response of both freestanding VACNT arrays and sandwich structures composed of a VACNT array partially embedded between two layers of poly(dimethylsiloxane) (PDMS) and bucky paper. The VACNTs tested are ∼2 mm thick foams grown via an injection chemical vapor deposition method. Both freestanding and sandwich structures exhibit a time-dependent behavior under compression. A power-law function of time is used to describe the main features observed in creep and stress-relaxation tests. The power-law exponents show nonlinear viscoelastic behavior in which the rate of creep is dependent upon the stress level and the rate of stress relaxation is dependent upon the strain level. The results show a marginal effect of the thin PDMS/bucky paper layers on the viscoelastic responses. At high strain levels (ɛ = 0.8), the peak stress for the anchored CNTs reaches ∼45 MPa, whereas it is only ∼15 MPa for freestanding CNTs, suggesting a large effect of PDMS on the structural response of the sandwich structures.