Thermal Chemical Vapor Deposition Technique Research Articles

Controlling the adsorption behavior of hydrogen at the interface of polycrystalline CVD graphene

Polycrystalline graphene films were synthesized from renewable biomaterials in ambient air using a facile and rapid thermal chemical vapour deposition technique. Characterization of the graphene reveals a large surface area, the presence of nanoscale domains and open edges, atomic-level stacking, and high electrical conductivity, which are favorable features for electrochemical hydrogen evolution reactions (HERs). The numerous boundaries and open edges accelerate the gas diffusion process and enlarge the effective reactive surface area for gas evolution, which is responsible for a significant improvement of HER performance and stability compared to a commercial graphene film. The hydrogen adhesion behavior in investigated for both bare Ni foil/foam and graphene grown on Ni foil/foam samples. The hydrogen gas bubbles adhere to the polycrystalline graphene for a long period of time before detaching, in contrast to their behavior on the pristine Ni foil surface. Post treatment of the graphene film using plasma treatment increases the desorption rate of hydrogen bubbles from the surface. The results indicate a wide range of possibilities for use of graphene-based catalysts in electrocatalytic gas evolution reactions.

UV-blue spectral down-shifting of titanium dioxide nano-structures doped with nitrogen on the glass substrate to study its anti-bacterial properties on the E. Coli bacteria

In this study, titanium dioxide (TiO2) nano-structures including nanoparticles and nano-wires are synthesized on the glass substrate at temperatures of 300, 400 and 500 °C using thermal chemical vapor deposition technique. Doping with nitrogen are done in three different temperatures including 300, 400, 500 °C to obtain optimum nitrogen doping content. To investigate the optical properties, crystalline structure, morphology, thickness and chemical components of the nano-structures, UV–Visible spectrometer, X-Ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy are used, respectively. Results show that the temperature and location of substrate play a significant impact on the morphology and structure of as-grown TiO2 nano-structures. The crystal structure of the obtained layers including TiO2 nano-structures on the glass are consisted anatase and rutile crystalline phases. The atomic percentage of nitrogen in TiO2 nano-structures at a doping temperature of 400 °C increase in comparison to the other two doping temperatures. In addition, observing the peak of TiN and Ti3.72 O8.00 N2.24 structures in the X-Ray pattern at doping temperature of 400 °C, refer to dope TiO2 nano-structures with a significant amount of nitrogen. Moreover, the reduction of band gap at about 0.4 eV, for N-TiO2 nano-structures grown at 400 °C, confirms the enhancement of photo-catalytic activity in the visible region. Antibacterial properties of pure titanium dioxide and doped with nitrogen were examined under dark, sunlight and UV light for E. Coli bacteria. The results show that growth of E. Coli bacteria significantly reduces in solution using N-TiO2/glass system treated at 400 °C in NH3/N2 ambient under sunlight due to down shifting of TiO2 band gap in compared with other samples.

Periodic chiral magnetic domains in single-crystal nickel nanowires

We report on experimental and computational investigations of the domain structure of ~0.2 x 0.2 x 8 {\mu}m single-crystal Ni nanowires (NWs). The Ni NWs were grown by a thermal chemical vapor deposition technique that results in highly-oriented single-crystal structures on amorphous SiOx coated Si substrates. Magnetoresistance measurements of the Ni NWs suggest the average magnetization points largely off the NW long axis at zero field. X-ray photoemission electron microscopy images show a well-defined periodic magnetization pattern along the surface of the nanowires with a period of {\lambda} = 250 nm. Finite element micromagnetic simulations reveal that an oscillatory magnetization configuration with a period closely matching experimental observation ({\lambda} = 240 nm) is obtainable at remanence. This magnetization configuration involves a periodic array of alternating chirality vortex domains distributed along the length of the NW. Vortex formation is attributable to the cubic anisotropy of the single crystal Ni NW system and its reduced structural dimensions. The periodic alternating chirality vortex state is a topologically protected metastable state, analogous to an array of 360{\deg} domain walls in a thin strip. Simulations show that other remanent states are also possible, depending on the field history. Effects of material properties and strain on the vortex pattern are investigated. It is shown that at reduced cubic anisotropy vortices are no longer stable, while negative uniaxial anisotropy and magnetoelastic effects in the presence of compressive biaxial strain contribute to vortex formation.

Synthesis of multi-walled carbon nanotubes by thermal CVD technique on Pt–W–MgO catalyst

ABSTRACTBoth tungsten (W) and platinum (Pt) are materials of interest in modern science and technology. Here, in this paper, we report the growth of multi-walled carbon nanotubes (MWCNTs) by thermal chemical vapour deposition (CVD) on Pt–W catalyst with MgO as a support material. The XRD studies were used to determine the structural characteristic of the as-prepared catalyst. Raman spectroscopy studies confirm the growth of MWCNTs with less structural defects and non-crystalline carbonaceous products. The images of field scanning electron microscope (FESEM) show that the grown network of carbon nanotubes (CNTs) contains less impurities, whereas the high-resolution transmission electron microscope (HRTEM) images indicate that the grown MWCNTs have good crystallinity with no lateral carbon deposit. TGA of the unpurified CNT product shows the addition of catalyst particles with the sample. This study will pave way for the new research area in the synthesis of CNTs and their applications in the electronic industry. Moreover, the results were compared with the previously reported results in the literature.

Optical properties of tetrapod nanostructured zinc oxide by chemical vapour deposition

Tetrapod nanostructured zinc oxide (ZnO) thin films have been deposited onto indium tin oxide (ITO) coated glass substrate by thermal chemical vapor deposition (TCVD) technique. This work studies the effects of annealing temperature ranging from 100–500 oC towards its physical and optical properties. FESEM images showed that the structural properties of tetrapod nanostructured ZnO thin film were affected by the annealing temperature. The thickness of thin film is strongly support the FESEM analysis. The optical band gap energy (Eg) was evaluated at 2.78 – 3.06 eV, which the ZnO thin film was found to be influenced by the change of interatomic spacing of semiconductor. The result shows that the higher annealing temperature greatly affects the physical structure of tetrapod nanostructured ZnO thin film to become narrow and longer length. Keywords: tetrapod; TCVD; synthesizing; annealing; zinc oxide

Tuning vertical alignment and field emission properties of multi-walled carbon nanotube bundles

We report the growth of vertically aligned carbon nanotube bundles on Si substrate by thermal chemical vapor deposition technique. Vertical alignment was achieved without any carrier gas or lithography-assisted deposition. Growth has been carried out at 850 °C for different quantities of solution of xylene and ferrocene ranging from 2.25 to 3.00 ml in steps of 0.25 ml at a fixed concentration of 0.02 gm (ferrocene) per ml. To understand the growth mechanism, deposition was carried out for different concentrations of the solution by changing only the ferrocene quantity, ranging from 0.01 to 0.03 gm/ml. A tunable vertical alignment of multi-walled carbon nanotubes (CNTs) has been achieved by this process and examined by scanning and transmission electron microscopic techniques. Micro-crystalline structural analysis has been done using Raman spectroscopy. A systematic variation in field emission (FE) current density has been observed. The highest FE current density is seen for the film grown with 0.02 gm/ml concentration, which is attributed to the better alignment of CNTs, less structural disorder and less entanglement of CNTs on the surface. The alignment of CNTs has been qualitatively understood on the basis of self-assembled catalytic particles.

Manipulating Carbon Nanotubes for Efficient Removal of Both Cationic and Anionic Dyes from Wastewater

AbstractThis study explores the application of carbon nanotubes (CNTs) for efficient removal of a mixture of cationic and anionic dyes. The multi walled carbon nanotubes (MWCNT) have been synthesized using a thermal chemical vapor deposition technique and they have been functionalized via acid treatment (ACNT), heat treatment (HCNT) and have also been treated with amine (NH2CNT). Specific surface area, powder X‐ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infra‐red (FTIR) spectroscopy, zero point charge (pHzpc) of MWCNT, ACNT, HCNT and NH2CNT have been investigated in this study. The sorption studies have been done using rhodamine B (RhB), methylene blue (MB), malachite green (MG) and methyl orange (MO) dyes. The conditions for optimum adsorption of the dyes onto these CNTs have been determined by investigating the effect of the contact time, pH of solution, and initial solution concentration in batch adsorption process. MWCNT and ACNT showed greater affinity for cationic MB, MG and RhB dyes whereas NH2CNT exhibited better sorption of the anionic dye MO. For adsorption of MG by MWCNT, ACNT and HCNT and MO by NH2CNT, the Langmuir adsorption equilibrium isotherm data provides a better fit than the Freundlich isotherm. Furthermore, the separation factor, RL and the surface coverage, for Langmuir isotherm confirms that the proposed adsorption process is the most suitable for MWCNT, ACNT, HCNT and NH2CNT for these selected dyes. The reusability of the sorbents has also been tested and they have been found to retain their efficiency after three consecutive runs. The composites of NH2CNT with MWCNT/ACNT exhibits good sorption affinity for both cationic and anionic dyes which suggest that these could be effectively used for the removal of dye effluents from waste water.

Improvement of silicon nanowire solar cells made by metal catalyzed electroless etching and nano imprint lithography

Silicon nanowires were fabricated by metal catalyzed electroless etching (MCEE) and nano imprint lithography (NIL), then a shell p-type layer was grown by thermal chemical vapor deposition (CVD) techniques. To reduce back surface recombination and also to activate the dopant, we used two techniques, back surface field (BSF) treatment and rapid thermal annealing (RTA), to improve device performance. In this study, we investigated BSF and RTA treatments in silicon nanowire solar cells, and improved the device performance and efficiency from 4.1 to 7.4% (MCEE device) and from 1.1 to 6.6% (NIL device) after introducing BSF and RTA treatments. Moreover, to achieve better metal contact without sacrificing the reflectance after the shell formation, the selective-area etching method was investigated. Finally, after combining all processes, silicon nanowire solar cells fabricated via the MCEE process exhibited 8.7% efficiency.

Synthesis of boron nitride nanostructures from catalyst of iron compounds via thermal chemical vapor deposition technique

For the first time, patterned growth of boron nitride nanostructures (BNNs) is achieved by thermal chemical vapor deposition (TCVD) technique at 1150°C using a mixture of FeS/Fe2O3 catalyst supported in alumina nanostructured, boron amorphous and ammonia (NH3) as reagent gas. This innovative catalyst was synthesized in our laboratory and systematically characterized. The materials were characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The X-ray diffraction profile of the synthesized catalyst indicates the coexistence of three different crystal structures showing the presence of a cubic structure of iron oxide and iron sulfide besides the gamma alumina (γ) phase. The results show that boron nitride bamboo-like nanotubes (BNNTs) and hexagonal boron nitride (h-BN) nanosheets were successfully synthesized. Furthermore, the important contribution of this work is the manufacture of BNNs from FeS/Fe2O3 mixture.

SWCNT-TiO2 Nanocomposite Photo-Anode for Improved Thermal Performances of Dye-Sensitized Solar Cells

In this study, we report a novel single-wall carbon nanotube (SWCNT)-TiO2 composite photoanode with enhanced thermal conductivity for photovoltaic applications. Thermal chemical vapor deposition technique was used for the growth of high quality SWCNTs. Structural and morphological properties of as synthesized SWCNT and SWCNT-TiO2 composites were inspected using ultra-high resolution transmission electron microscope (UHRTEM) and Raman spectroscopy. Thermal conductivity of pure titania (TiO2) and SWCNT-TiO2 composites were estimated by an optothermal method. Photovoltaic performance of Dye-sensitized solar cell (DSSC) containing composite photoanodes was studied at various temperatures (ranging from room temperature-323K). We observed a notable decline in the overall photovoltaic performance of the DSSC containing pure TiO2 photoanode at elevated temperatures. Whereas, DSSC with composite photoanodes showed a significant improvement in overall photovoltaic performance consistently at room temperature as well as at elevated temperatures that is believed to be due to the existence of SWCNT and provides a conducting pathway to electrons in trap states and which are released at higher temperature and thus, quench recombination more effectively.

Formation of Al2O3-graphite core shells versus growth time by using thermal chemical vapor deposition

Al2O3-graphite core shells were synthesized on Al2O3 nanopowders by using a thermal chemical vapor deposition technique with C2H2, H2, and Ar gases, and the effects of the growth time on the formation of the core shells were investigated. The crystalline quality of the Al2O3-graphite core shells increased with increasing growth time. The C-Al chemical bonding at 283 eV was confirmed by using X-ray photoelectron spectroscopy (XPS), and thus the thin Al layers on Al2O3 cores, which formed through a reduction process, played an important role in the fabrication of the graphene shells. The characteristics of an electrode composed of Al2O3-graphite core-shell ink on a glass substrate were investigated. This study demonstrated a very effective and simple method for the synthesis of Al2O3-graphite core shells, and the technique developed in this study may be applicable to the synthesis of various metal-graphite core shells.

SWCNT-TiO2 Nanocomposite Photo-Anode for Improved Thermal Performances of Dye-Sensitized Solar Cells

In this study, we report a novel single-wall carbon nanotube (SWCNT)-TiO2 composite photoanode with enhanced thermal conductivity for photovoltaic applications. Thermal chemical vapor deposition technique was used for the growth of high quality SWCNTs. Structural and morphological properties of as synthesized SWCNT and SWCNT-TiO2 composites were inspected using ultra-high resolution transmission electron microscope (UHRTEM) and Raman spectrosctopy. Thermal conductivity of pure titania (TiO2) and SWCNT-TiO2 composites were estimated by an optothermal method. Photovoltaic performance of Dye-sensitized solar cell (DSSC) containing composite photoanodes was studied at various temperatures (ranging from room temperature-323K). We observed a notable decline in the overall photovoltaic performance of the DSSC containing pure TiO2 photoanode at elevated temperatures. Whereas, DSSC with composite photoanodes showed a significant improvement in overall photovoltaic performance consistently at room temperature as well as at elevated temperatures that is believed to be due to the existence of SWCNT and provides a conducting pathway to electrons in trap states and which are released at higher temperature and thus, quench recombination more effectively.

Role of growth temperature in CVD synthesis of Carbon nanotubes from Ni-Co bimetallic catalysts

The effect of temperature variation on the growth of Carbon Nanotubes (CNTs) using Thermal Chemical Vapor Deposition (TCVD) is presented. Nickel and Cobalt (Ni-Co) thin films on Silicon (Si) substrates were used as catalysts in TCVD technique. Acetylene gas was used in CNTs growth process at the controlled temperature ranges from 850-1000 C. Catalysts and CNTs characterization was carried out using Atomic Force Microscopy (AFM), Energy Dispersive X-ray (EDX), Field Emission Scanning Electron Microscopy (FESEM) and Raman spectroscopy. It was found that the CNTs diameters increased with the temperature. The CNTs diameters were continually increased from 70 nm to 180 nm in the temperature range. In addition, the degree of crystallinity of the grown CNTs decreased.

On the nature of interface of carbon nanotube coated carbon fibers with different polymers

Experimental investigations are carried out to analyse the wetting behaviour of carbon nanotube (CNT) coated carbon fiber to determine their suitability to process carbon nanotube coated carbon fiber/polymer multiscale composites for structural applications. To overcome the problem of agglomeration, CNTs are grown directly on the surface of carbon fibers as well as fabric using thermal chemical vapour deposition (CVD) technique. The term multiscale is used because different reinforcement mechanisms operate at the scale of long fibers and CNTs which are of few micrometers in length. The load carrying capacity of these multiscale composites critically depends on the efficiency and extent of load transfer from low strength matrix to high strength fiber which in turn depends on the interfacial strength between CNT coated carbon fiber and polymer matrix. A systematic analysis of wetting behaviour of CNT coated carbon fiber with epoxy and polyester matrix is carried out in this study. It is shown that CNT coated carbon fibers as well as fabric show better wettability with epoxy matrix as compared to polyester matrix. This results in stronger interface of CNT coated carbon fiber with epoxy as compared to polyester in multiscale composite system. A similar observation is made in nanoindentation testing of single fiber multiscale composites processed with epoxy and polyester matrix. In addition, it is observed that wettability, interfacial strength and average properties of CNT coated carbon fiber/polymer composites are a function of CNT density on the surface of carbon fibers.

Studies of n-SiCN/p-Si diode for low cost and high temperature ultraviolet light sensing applications

In this paper, we study of n-SiCN/p-Si heterojunction for low cost and high temperature ultraviolet (UV) detecting applications in details. The cubic crystalline SiCN film was deposited on p-Si (100) substrate using C3H8 for carbon source by rapid thermal chemical vapor deposition (RTCVD) technique. The developed device has a high photo/dark current ratio (PDCR) of 32.7 under room temperature (25°C) with and without an irradiation of 254nm, 0.5mW/cm2 power UV light source. Even up to 175°C, the PDCR can keep at 3.03. Although, these results are less than the reported n-SiCN/PS/p-Si diode with a porous Si (PS) as buffer layer; however, it still better than the reported ZnO on GaAs substrate or ZnO nanowires on p-silicon substrate UV detectors. Without the PS layer, one can simplify preparing process and thus improving yield. More important, it immunizes some interface reliability issues, due to the absorption of ambient gases by the higher reactive PS surface. Therefore, the new developed n-SiCN/p-Si heterojunction has a better potential for the low cost and high temperature UV sensing applications.

Review of carbon nanotubes production by thermal chemical vapor deposition technique

ABSTRACTWe have reviewed carbon nanotubes (CNTs) production on a silicon wafer by thermal chemical vapor deposition (TCVD) using acetylene as a carbon source, cobalt as a catalyst and ammonia as a reactive gas. The DC-sputtering system was used to prepare cobalt thin films on Si substrates. Energy Dispersive X-ray (EDX) measurements were used to investigate the elemental composition of the Co nanocatalyst deposited on Si substrates. Atomic Force Microscopy (AFM) was used to characterize the surface topography of the Co nanocatalyst deposited on Si substrates. The as-grown CNTs were characterized under Field Emission Scanning Electron Microscopy (FESEM) to study the morphological properties of CNTs.

Properties of multi-walled carbon nanotubes synthesis on porous silicon by double furnace thermal-CVD technique

Multi-walled carbon nanotubes (MWCNs) were synthesised using double-furnace thermal chemical vapour deposition technique at 700-900°C on porous silicon nanostructure (PSiNs). Palm oil was used as a carbon natural source, ferrocene as a catalyst and nitrogen gas as a carrier gas. The precursor were vaporised at 475°C carried by nitrogen gas which flow at constant rate of 150 sccm/min. Carbon nanotubes (CNTs) were characterised by using Raman spectroscopy and field emission scanning electron microscopy (FESEM) to check its structure and crystallites before being tested with I-V probe. Au contact was used as a metal contact deposited on CNTs layer. CNTs with uniform diameter were found grown on porous silicon for each temperature used. Based on micro-Raman spectroscopy result, the peak of NTs (around 1,300 to 1,600 nm) was detected. The I-V characteristic of CNTs deposited had different profile when deposited at different temperatures.

Coaxial carbon@boron nitride nanotube arrays with enhanced thermal stability and compressive mechanical properties.

Vertically aligned carbon nanotube (CNT) arrays have aroused considerable interest because of their remarkable mechanical properties. However, the mechanical behaviour of as-synthesized CNT arrays could vary drastically at a macro-scale depending on their morphologies, dimensions and array density, which are determined by the synthesis method. Here, we demonstrate a coaxial carbon@boron nitride nanotube (C@BNNT) array with enhanced compressive strength and shape recoverability. CNT arrays are grown using a commercially available thermal chemical vapor deposition (TCVD) technique and an outer BNNT with a wall thickness up to 1.37 nm is introduced by a post-growth TCVD treatment. Importantly, compared to the as-grown CNT arrays which deform almost plastically upon compression, the coaxial C@BNNT arrays exhibit an impressive ∼4-fold increase in compressive strength with nearly full recovery after the first compression cycle at a 50% strain (76% recovery maintained after 10 cycles), as well as a significantly high and persistent energy dissipation ratio (∼60% at a 50% strain after 100 cycles), attributed to the synergistic effect between the CNT and outer BNNT. Additionally, the as-prepared C@BNNT arrays show an improved structural stability in air at elevated temperatures, attributing to the outstanding thermal stability of the outer BNNT. This work provides new insights into tailoring the mechanical and thermal behaviours of arbitrary CNT arrays which enables a broader range of applications.

High electromagnetic wave absorbing performance of activated hollow carbon fibers decorated with CNTs and Ni nanoparticles

Activated hollow carbon fibers (ACHFs) decorated with carbon nanotubes (CNTs) and nickel nanoparticles (CNTs–Ni–ACHFs) were prepared by thermal reduction and chemical vapor deposition technique. Microwave reflection loss, permittivity and permeability of CNTs–Ni–ACHFs composites as novel electromagnetic wave absorbents were studied in the frequency range of 2–18GHz. It was demonstrated that CNTs–Ni–ACHFs absorbents possessed the best microwave absorbing performances whose minimum reflection loss was −43.457dB at 13.10GHz with a thickness of 2.0mm, which is much better than those of Ni–ACHFs and ACHFs samples. The dielectric polarizations and magnetic loss derived from the effect of the porous structures, Ni nanoparticles, and defects in the CNTs–Ni–ACHFs composites are playing an important role for the excellent microwave absorbing performances.

High-purity cobalt thin films with perpendicular magnetic anisotropy prepared by chemical vapor deposition

A study of the chemical vapor deposition (CVD) of high-purity cobalt thin films is described. The Co layer prepared by a thermal CVD technique with a Pt/Ta underlayer and a Pt cap layer shows a saturation magnetization (Ms) of ∼1.8 T and perpendicular magnetic anisotropy (PMA) with an anisotropy energy (Ku) of ∼105 J/m3. The cobalt thickness dependence of Ku reveals that the interfacial anisotropy at the Pt/Co interface is most likely the origin of the obtained PMA.