Thermal CVD Method Research Articles

Self-Sustained Three-Dimensional Macroporous TiO2-Graphene Photocatalyst for Sunlight Decolorization of Methyl Orange.

The development of highly efficient sunlight-driven photocatalysts has triggered increased attention due to their merit in effluent treatment through a chemically green approach. To this end, we present herein the synthesis and characterization of the TiO2/3D-GF/Ni hybrid emphasizing the main structural and morphological properties and the photodegradation process of a highly resistant aromatic azo dye, methyl orange, under both UV light and simulated sunlight. Three-dimensional (3D) graphene was grown by the thermal CVD method on the nickel foam and subsequently coated with thin films of anatase employing the sol-gel method. Thereafter, it was gratifyingly demonstrated that the hybrid nanomaterial, TiO2/3D-GF-Ni, was able to bring about more than 90% decolorization of methyl orange dye after 30 min under simulated sunlight irradiance. Moreover, the efficiency of the methyl orange decolorization was 99.5% after three successive cycles. This high-performance photocatalyst which can effectively decolorize methyl orange will most likely make a great contribution to reducing environmental pollution by employing renewable solar energy.

Low-energy Ar+ ion beam induced chemical vapor deposition of silicon carbide films using dimethylsilane

In this paper, a methodology for silicon carbide (SiC) film formation by ion beam induced chemical vapor deposition (IBICVD) using dimethylsilane (DMS) is presented. Both pure DMS gas and Ar+ ion beam were simultaneously injected to a Si substrate. The Ar+ ion energy was 100 eV. The Si substrate temperature was 400, 600, or 800 °C. The duration of each ion beam injection experiment was 10 h. When the substrate temperature was 400 °C, no film formation occurred by the IBICVD experiment. In the case of 600 °C, a film was found to be formed on the substrate by the injection of both DMS gas and Ar+ ion beam. Although Fourier transform infrared (FTIR) spectroscopy measurement of the film showed that the film consisted of SiC, the film thickness was not enough to analyze the film characteristics further. When the Si substrate was set at 800 °C, a film was formed on the substrate by IBICVD. FTIR, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS) measurements of the film showed the occurrence of SiC deposition. The XPS measurement also showed that the atomic concentration ratio of carbon to silicon (C/Si ratio) of the film was 1.36. Therefore, excessive C atoms were incorporated to the deposited films. On the contrary, the C/Si ratio of a SiC film prepared by the thermal CVD method using DMS was 1.88. These results suggest that the Ar+ ion beam induced chemical vapor deposition using DMS is useful for reducing of the amount of C atoms to be excessively included in the film.

Room temperature ferromagnetism and electrical properties of Mn-doped Zn2SnO4 nanorods

We have investigated the magnetic and electrical properties of Mn doped zinc stannate (Zn2SnO4; ZTO) nanorods synthesized via vapour transport method in a vacuum operated thermal CVD setup. Saturation magnetization up to 21.55 emu/cm3 has been observed for Mn doped ZTO samples. Room temperature resistivity, mobility and carrier concentration has been found to be Mn and oxygen content dependent in the sample arising during growth process. X-ray photoelectron spectroscopy confirms the role contributing O 1s in mediating room temperature ferromagnetism (RTFM) as well as RT electrical transport properties. These results indicate that, simple vapour transport thermal CVD method of obtaining metal doped complex ternary oxides is an effective technique to tailor magnetic and electrical properties.

Vertically aligned CNT arrays: structural integrity and surface properties

Purpose Carbon nanotube-based architectures have increased the scientific interest owning to their exceptional performance rendering them promising candidates for advanced industrial applications in the nanotechnology field. Despite individual CNTs being considered as one of the most known strong materials, much less is known about other CNT forms, such as CNT arrays, in terms of their mechanical performance. The paper aims to discuss these issues. Design/methodology/approach In this work, thermal CVD method is employed to produce VA-MWCNT carpets. Their structural properties were studied by means of SEM, XRD and Raman spectroscopy, while their hydrophobic behavior was investigated via contact angle measurements. The resistance to indentation deformation of VA-MWCNT carpets was investigated through nanoindentation technique. Findings The synthesized VA-MWCNTs carpets consisted of well-aligned MWCNTs. Static contact angle measurements were performed with water and glycerol, revealing a rather super-hydrophobic behavior. Originality/value The structural analysis, hydrophobic behavior and indentation response of VA-MWCNTs carpets synthesized via CVD method are clearly demonstrated.

Effect of treatment temperature on surface wettability of methylcyclosiloxane layer formed by chemical vapor deposition

The surface wettability of the native Si oxide surfaces were tuned by chemical adsorption of 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS) molecules through thermal CVD method at different temperature. Water contact angle measurements revealed that the water contact angles of the TMCTS-modified Si oxide surfaces at the temperature of 333–373K were found to be in the range of 92±2–102±2°. The advancing and receding water contact angle of the surface prepared at 333K were found to be 97±2/92±2°, showing low contact angle hysteresis surface. The water contact angles of the surfaces prepared at the temperature of 373–413K increased with an increase in the treatment temperature. When the treatment temperature was more than 423K, the water contact angles of TMCTS-modified surfaces were found to become more than 150°, showing superhydrophobic surface. AFM study revealed that the surface roughness of the TMCTS-modified surface increased with an increase in the treatment temperature. This geometric morphology enhanced the surface hydrophobicity. The surface roughness could be fabricated due to the hydrolysis/condensation reactions in the gas phase during CVD process. The effect of the treatment temperature on the reactivity of the TMCTS molecules were also investigated using a thermogravimetric analyzer.

Precise control over physical characteristics of Carbon Nanotubes by differential variation of Argon flow rate during Chemical Vapor Deposition processing: A systematic study on growth kinetics

In this paper, we report a systematic work on growth analysis of carbon nanotubes (CNTs) using thermal CVD method where fine tuning of CNTs׳ physical characteristics, i.e. length(height of carpet), diameter, number of walls and orientation have been greatly achieved by simply varying the Argon(Ar) gas flow rate in the Ar and Acetylene gas mixture. Ar flow rate was varied from 0 to 100sccm with 20sccm interval and the growth evolution was monitored by FESEM, HRTEM, and Raman spectrometer. A gradual change was observed in the reduction of diameter, increase in height, decrease in defect density, and change in orientation from horizontal to vertical of the CNTs grown over the prescribed flow rate range. Growth mechanism is discussed at every step of Ar flow rate in consideration of the analysis done on the image from electron microscopes and Raman spectra.

Fabrication of Fe nanowires on yittrium-stabilized zirconia single crystal substrates by thermal CVD methods

Magnetic nanowires (NWs) are promising as material for use in spintronics and as the precursor of permanent magnets because they have unique properties due to their high aspect ratio. The growth of magnetic Fe whiskers was reported in the 1960s, but the diameter was not on a nanoscale level and the growth mechanism was not fully elucidated. In the present paper, we report the almost vertical growth of Fe NWs on a single crystal yttrium-stabilized zirconia (Y0.15Zr0.85O2) by a thermal CVD method. The NWs show a characteristic taper part on the bottom growing from a trigonal pyramidal nucleus. The taper angle and length can be controlled by changing the growth condition in two steps, which will lead to obtaining uniformly distributed thin Fe NWs for applications.

Preparation of rutile TiO(2) coating by thermal chemical vapor deposition for anticoking applications.

To inhibit the metal catalytic coking and improve the oxidation resistance of TiN coating, rutile TiO2 coating has been directly designed as an efficient anticoking coating for n-hexane pyrolysis. TiO2 coatings were prepared on the inner surface of SS304 tubes by a thermal CVD method under varied temperatures from 650 to 900 °C. The rutile TiO2 coating was obtained by annealing the as-deposited TiO2 coating, which is an alternative route for the deposition of rutile TiO2 coating. The morphology, elemental and phase composition of TiO2 coatings were characterized by SEM, EDX and XRD, respectively. The results show that deposition temperature of TiO2 coatings has a strong effect on the morphology and thickness of as-deposited TiO2 coatings. Fe, Cr and Ni at.% of the substrate gradually changes to 0 when the temperature is increased to 800 °C. The thickness of TiO2 coating is more than 6 μm and uniform by metalloscopy, and the films have a nonstoichiometric composition of Ti3O8 when the deposition temperature is above 800 °C. The anticoking tests show that the TiO2 coating at a deposition temperature of 800 °C is sufficiently thick to cover the cracks and gaps on the surface of blank substrate and cut off the catalytic coke growth effect of the metal substrate. The anticoking ratio of TiO2 coating corresponding to each 5 cm segments is above 65% and the average anticoking ratio of TiO2 coating is up to 76%. Thus, the TiO2 coating can provide a very good protective layer to prevent the substrate from severe coking efficiently.

Efficient mixed metal oxide routed synthesis of boron nitride nanotubes

In this work, the oxidizing efficiency of V2O5 is investigated in the B/Fe2O3 and B/Ni2O3 systems for the synthesis of boron nitride nanotubes via a thermal CVD method.

A Study on the Tribological Characteristics of Surface Modification by TiC,N of the Thermal CVD Method use to the Automotive Poppet Valve

A Study on the Tribological Characteristics of Surface Modification by TiC,N of the Thermal CVD Method use to the Automotive Poppet Valve

Effect of Nickel Catalyst on Carbon Nanotubes by Using Palm Oil as a Starting Material

Carbon nanotubes (CNTs) were produced on silicon (Si) substrate prepared by Thermal-CVD method using C55H96O6 (Palm Oil) as a starting material. Catalyst has been prepared by dissolving Nickel (II) nitrate, Ni (NO3) 2.6H2O and ethyl alcohol, C2H5OH. The CNTs was deposited on nickel coated silicon where the nickel acts as catalyst .Various parameters such as amount of catalyst, amount of palm oil, deposition time, deposition temperature, flow rate of gas and carrier gas have been studied. By using Thermal-CVD, samples were penetrated using NH3 (argon) gas at a temperature 700-900oC for catalyst and 450oC for Palm Oil. Surface morphology and uniformity of CNTs were characterized using FESEM at different deposition temperature. Chemical functional groups of CNTs were characterized using FTIR. The surface morphology and uniformity of CNTs are dependents on parameters used.

Carbon Nanotubes Prepared by Thermal-CVD of from Palm Oil

Carbon nanotubes (CNTs) were produced on silicon (Si) substrate prepared by Thermal-CVD method using C55H96O6 (Palm Oil) as a starting material. Catalyst has been prepared by dissolving Nickel (II) nitrate, Ni (NO3)2.6H2O and ethyl alcohol, C2H5OH. Before the deposition process, silicon was coated with Nickel using spin coater. Various parameters such as amount of catalyst, amount of palm oil, deposition time, deposition temperature, flow rate of gas and carrier gas have been studied. By using Thermal-CVD, samples were penetrated using NH3 (argon) gas at a temperature 700 - 900oC for catalyst and 450oC for palm oil. Surface morphology and uniformity of CNTs were characterized using FESEM at different deposition temperature. Chemical functional groups of CNTs were characterized using FTIR. The surface morphology and uniformity of CNTs are dependents on parameters used.

Floating Catalyst Method for Preparation of Carbon Nanotubes Using Fe/Co/Al Catalyst by Thermal-CVD

Carbon nanotubes (Cnts) produced using single furnace thermal CVD method by the floating catalyst method, at low temperature condition; 650oC. Carbon nanotubes were produced from natural source of camphor oil, using Fe/Co/Al as catalyst source, yielding a thickened submicron vapor grown of multi-wall Cnts. Carbon nanotubes are observed to form by different weight composition of catalyst. For the production of carbon nanotubes, natural precursor was used as the carbon feedstock, and the catalysts were added in a precursor compound. FESEM analysis confirms that this type of stacked-cup Cnts is produced by vaporize catalyst and mixing with the hydrocarbon source. In fact, few Cnts have either a particle tip at the end or trapped metal particle inside the wide hollow core of this type of produced carbon material. Chemical properties carried out by FTIR and Raman spectroscopy.

BET Analysis on Carbon Nanotubes: Comparison between Single and Double Stage Thermal CVD Method

Carbon nanotubes have many applications and therefore widely produced. However, it is limited due to the high production cost. In this paper, by preparing the CNTs using the Thermal Chemical Vapor Deposition method, CNTs were synthesized with a low cost method since palm oil is used as the precursor which is a biodegradable and cheap source. The aerosol or spray pyrolysis method is used for single stage and double stage TCVD method. Then, the samples were both collected at deposition temperature of 750°C and were characterized using Brunauer, Emmett and Teller (BET) method. Since CNTs are said to have high surface area therefore BET method is used to prove this fact. Results showed that by using double stage TCVD method, more CNTs were synthesized compared to single stage TCVD method which produced more impurities namely amorphous carbon. CNTs also have higher surface area compared to amorphous carbon. To support this result, the images of the CNTs produced by same method but different parameters were characterized with field emission scanning electron microscope (FE-SEM) and the raman spectra was determined by the raman spectroscopy characterization.

A narrow process window for the preparation of polytypes of microcrystalline silicon carbide thin films by hot-wire CVD method

Effects of deposition conditions on the structure of microcrystalline silicon carbide (μc-SiC) films prepared by hot-wire chemical vapor deposition (hot-wire CVD) method have been investigated. It is found from X-ray diffraction patterns of the film that a diffraction peak from crystallites from hexagonal polytypes of SiC is observed in addition to those of 3C-SiC crystallites. This result is obtained in the film under a narrow deposition conditions of SiH3CH3 gas pressure of 8Pa, the H2 gas pressure of 80–300Pa and the total gas pressure of 40–300Pa under fixed substrate and filament temperatures employed in this study. Furthermore, the grain size of hexagonal crystallites (about 20nm) on c-Si substrates becomes larger than that of 3C-SiC crystallites (about 10nm) for the films deposited under the total gas pressure of 36–88Pa. The fact that microcrystalline hexagonal SiC can be deposited under limited deposition conditions could be interpreted in the context of a result for c-SiC polytypes prepared by thermal CVD method.

Low temperature growth mechanisms of vertically aligned carbon nanofibers and nanotubes by radio frequency-plasma enhanced chemical vapor deposition

Using radio frequency-plasma enhanced chemical vapor deposition (RF-PECVD), carbon nanofibers (CNFs) and carbon nanotubes (CNTs) were synthesized at low temperature. Base growth vertical turbostratic CNFs were grown using a sputtered 8 nm Ni thin film catalyst on Si substrates at 140 °C. Tip growth vertical platelet nanofibers were grown using a Ni nanocatalyst in 8 nm Ni films on TiN/Si at 180 °C. Using a Ni catalyst on glass substrate at 180 °C a transformation of the structure from CNFs to CNTs was observed. By adding hydrogen, tip growth vertical multi-walled carbon nanotubes were produced at 180 °C using FeNi nanocatalyst in 8 nm FeNi films on glass substrates. Compared to the most widely used thermal CVD method, in which the synthesis temperature was 400–850 °C, RF-PECVD had a huge advantage in low temperature growth and control of other deposition parameters. Despite significant progress in CNT synthesis by PECVD, the low temperature growth mechanisms are not clearly understood. Here, low temperature growth mechanisms of CNFs and CNTs in RF-PECVD are discussed based on plasma physics and chemistry, catalyst, substrate characteristics, temperature, and type of gas.

Investigation of CNT Growth by Substrate Temperature Control Using Thermal CVD Method

Influence of metal catalyst (Fe) surface condition was investigated for the growth of carbon nanotubes (CNTs). Surface condition of 5 nm thick Fe coated on Si substrate was changed by varying substrate temperature during the CNTs synthesis in a thermal CVD method. Acetylene and argon were used as precursor and carrier gas, respectively, for the synthesis of CNTs. After the growth, the CNTs were removed from the substrate and the post-growth condition of the substrate surface was studied by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Unlike the case of untreated Fe-coated Si substrate, XPS analysis shows Si peaks from the thermal treated substrate/samples, which indicates the formation of Fe nanoparticles. AFM results indicate that 750 degrees C is optimum temperature for the nanoparticle formation. Moreover, SEM results show that 700 degrees C is optimum temperature for the CNTs synthesis. The results of this study clarify that the optimum temperature for nanoparticle formation and CNT synthesis are different.

Hot filament CVD of Fe–Cr catalyst for thermal CVD carbon nanotube growth from liquid petroleum gas

A hot filament chemical vapor deposition (HFCVD) method was used to prepare Fe–Cr thin film on Si substrate. The produced layers were used as catalysts for growing carbon nanotubes (CNTs) from liquid petroleum gas (LPG) at 825 °C by thermal CVD (TCVD) method. To characterize the obtained catalysts or CNTs, X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Raman spectroscopy were used. CNTs were grown on HFCVD derived Fe–Cr catalyst with the LPG as carbon source successfully. It was found that an annealing process on catalysts enhances the surface concentration of Cr atoms and reduces the sizes of catalyst particles. The grown CNTs on annealed sample were morphologically denser with smaller diameters compared to the as deposited one. In addition, the effect of filament temperature on CNTs was investigated. By increasing the filament temperature from 850 to 1050 °C the surface density and diameters of CNTs were improved.

Hardness effect of stainless steel substrates on tribological properties of water-lubricated DLC films against AISI 440C ball

Diamond-like carbon (DLC) films were deposited on stainless steel substrates with different hardness by thermal electron excited plasma CVD method, and their tribological properties in water-lubricated conditions were investigated. EDS was used to estimate the wear of the films. The results show that the hardness of the substrates has little effect on the friction and, the wear loss of the films is much smaller than that measured by an optical interferometer. The deep wear track is mainly due to the plastic deformation of the substrates and the films but not due to wear. However, the failure of the films is closely related to the hardness of their substrates. The harder the substrate, the higher the failure-resistant capability. The film deposited on a soft substrate is easy to crack and fail due to the low deformation resistance of the substrate and rubbing at a high contact-pressure. On the other hand, the wear of the counter balls increases with the hardness of the substrates.

Effect of laser irradiation on carbon nanotube films for NOx gas sensor

A carbon nanotube (CNT) thin film prepared by the thermal CVD method was flashed by second harmonic light of a pulsed Nd:YAG laser (λ=532 nm) under various laser fluences. A part of the defective CNTs and amorphous carbon in the film was removed by 10 shots of laser irradiation at Ef=600 mJ/cm2. Raman spectra of the laser irradiated CNT thin film showed the increase of IG/ID ratio, which indicated that the CNTs thin film was purified by laser irradiation. A multi-walled CNTs (MWCNTs) based gas sensor treated by laser irradiation showed good sensor response to NO gas.