Thermal Chemical Vapor Deposition Technique Research Articles

Magnetism of amorphous carbon nanofibers

Amorphous carbon nanofibers (ACNFs) have been synthesized by a thermal chemical vapor deposition technique. The ACNFs grow as two branches perpendicular to {111} facets of a catalytic copper nanoparticle. The carbon nanofibers are composed of disordered localized nanofragments which in turn consist of several graphene layers. The ACNFs show a paramagnetic characteristics at 2, 5, and 10 K. The magnetic moments are suggested to originate from a large amount of defects in the graphene layers of the nanofragments.

Multi‐wall carbon nanotubes investigated by positron annihilation techniques and microscopies for further production handling

AbstractMulti‐wall carbon nanotube samples with various tube diameters produced by Thermal Chemical Vapor Deposition technique using various catalysts were studied by various microscopic methods and positron annihilation spectroscopy (PAS) with the aim of assessing the applicability of these methods for structural studies in these novel materials. Specifically, positron lifetime (LT) and Doppler broadening (DB) techniques, transmission electron microscopy (TEM) and atomic force microscopy (AFM) were employed, on iron‐containing samples Mössbauer spectroscopy was also utilized. The PAS measurements were carried out on densely packed powder samples and on samples pressed into pills in atmospheric pressure and in vacuum as well. The lifetime values could be interpreted by assuming trapping of positrons, the low contribution from longer‐living trapped positronium can be probably related to defects on walls of the tubes. Possibility of correlation of LT and DB data with the nanotube sizes and sample composition was also considered. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Selective growth of carbon nanotubes using catalyst poisoning and geometric trench

This work suggests catalyst poisoning and geometric patterned approaches to selectively grow multiwall carbon nanotubes. Ferromagnetic particles as a catalyst for CNTs growth vanish when they are deposited over an aluminum thin film. Additionally, geometric features, such as trenches or cavities, are revealed to be capable of selectively ceasing the growth of CNTs even though catalytic thin films were covered on entire samples by an atmospheric thermal chemical vapor deposition technique.

Catalyzed chemical vapor deposition of one-dimensional nanostructures and their applications

This article reviews progress in the growth of one-dimensional nanomaterials such as carbon nanotubes and inorganic nanowires. Catalyzed chemical vapor deposition has been the preferred method to grow these materials for various applications requiring controlled growth on patterned and unpatterned substrates. Both thermal and plasma chemical vapor deposition techniques have been widely used in the case of carbon nanotubes. In addition to the discussion on growth, a review of applications for one-dimensional nanostructures and future directions is provided.

Utilization of catalyst deactivation for the growth of aligned and random carbon nanotubes by a single-step process

We have synthesized hybrid carbon nanotubes (CNTs) i.e. random secondary carbon nanotubes, on top of the aligned primary CNTs grown on Fe deposited n-type (1 1 1) silicon substrate by thermal chemical vapor deposition technique utilizing the concept of catalyst deactivation. The transmission electron microscopy and Raman spectroscopy results reveal that the primary CNTs are highly pure and crystalline and the secondary CNTs contain defects and impurities with a low degree of crystallinity. It is observed that by providing Fe catalyst during deposition, vertically aligned primary CNTs are synthesized for a shorter duration of growth. Random and entangled secondary CNTs on top of primary tubes are found to grow if the duration of growth is increased. It is suggested that termination of primary CNTs after a short time duration is because of the deactivation of the Fe catalyst deposited on the substrate, whereas Fe catalyst provided in the precursor solution initiates secondary growth of CNTs. The present work also suggests that base and tip growth mechanisms are responsible for the growth of primary and secondary CNTs, respectively.

On the impact of silicon nitride technology on charge trap NAND memories

The aim of this work is to study the impact of silicon nitride deposition/treatment technologies on charge trap (CT) nonvolatile memory performances. The authors have found that the technology modifies the charge trapping behavior with a one to one correlation between write/erase and charge retention characteristics. In particular, they used rapid thermal chemical vapor deposition techniques to obtain films with different compositions, but they were not able to improve CT performances with respect to standard low pressure chemical vapor deposition (LPCVD). Besides, an in situ steam generated treatment applied to standard LPCVD silicon nitride modifies the film properties inducing a lower programming efficiency, but improving charge retention characteristics.

변화된 산소분압으로 증착된 SnO2박막의 표면과 계면에 관한 연구

This report examines the variations on structural properties of <TEX>$SnO_2$</TEX> thin films deposited by using thermal chemical vapor deposition techniques with different oxygen flow gas. TEM showed some of the interface to be atomically rough. The aspects of the boundary shape and growth behavior agree well with the theory of interface growth. The electron diffraction showed that the roughness was changed as the different oxygen flow gas increased. These measurement results suggested that the number of interface facet and abnormal grain growth were related oxygen flow gas.

Functional Metal Oxide Coatings by Molecule-Based Thermal and Plasma Chemical Vapor Deposition Techniques

Deposition of thin films through vaccum processes plays an important role in industrial processing of decorative and functional coatings. Many metal oxides have been prepared as thin films using different techniques, however obtaining compositionally uniform phases with a control over grain size and distribution remains an enduring challenge. The difficulties are largely related to complex compositions of functional oxide materials, which makes a control over kinetics of nucleation and growth processes rather difficult to control thus resulting in non-uniform material and inhomogeneous grain size distribution. Application of tailor-made molecular precursors in low pressure or plasma-enhanced chemical vapor deposition (CVD) techniques offers a viable solution for overcoming thermodynamic impediments involved in thin film growth. In this paper molecule-based CVD of functional coatings is demonstrated for iron oxide (Fe2O3, Fe3O4), vanadium oxide (V2O5, VO2) and hafnium oxide (HfO2) phases followed by the characterization of their microstructural, compositional and functional properties which support the advantages of chemical design in simplifying deposition processes and optimizing functional behavior.

Regrowth of Carbon Nanotube Array by Microwave Plasma-Enhanced Thermal Chemical Vapor Deposition

A repeated growth process (regrowth process) has been carried out to fabricate a carbon nanotube (CNT) array without additional catalyst by a custom-made plasma-enhanced thermal chemical vapor deposition (PE-thermal CVD) technique. An Fe film with a thickness of 3 nm is coated as a catalyst before the first growth on the SiO2/Si by arc plasma deposition. Two types of treatments, lift-off and thermal annealing, are used to remove the CNTs away for the next growth. Thermal annealing is also used to remove amorphous carbon, which covers the catalytic nanoparticles and to activate the catalyst. The CNT array is regrown without coating additional catalyst through the regrowth process. After certain cycles, high-purity single-walled carbon nanotubes (SWNTs) are synthesized and the ID/IG ratio of the Raman spectrum reaches a low value of 0.41. The crystallization of CNTs is improved after each growth cycle of thermal annealing treatment.

Self Catalyzing Behavior of Kanthal Wire for Coating of Carbon Nanotubes

Carbon nanotubes (CNTs) were coated on kanthal wire without using any external transition metal catalyst. It was synthesized through thermal chemical vapour deposition technique at 800°C and in a flow of gas mixtures, that is, 100 sccm nitrogen, 25 sccm hydrogen and 20 sccm acetylene. Iron and chromium oxides from the surface of kanthal wire activate in hydrogen environment to form Fe‐Cr particles. These Fe‐Cr bimetallic catalyst particles then catalyze to grow CNTs on the surface of kanthal wire. It was characterized through scanning electron microscopy, energy dispersive X‐ray analysis and atomic force microscopy.

Synthesis and Optimization of MWCNTs on Co-Ni/MgO by Thermal CVD

Multiwalled carbon nanotubes (MWCNTs) were prepared by the thermal chemical vapor deposition (CVD) technique. Monometallic and bimetallic Co and Ni combinations were used as a catalyst on MgO support. The mixer ofH2/C2H2was used as a carbon source. The prepared CNTs were found to possess different shapes, morphologies, and sizes. Maximum yield was found for 50% Co (MgO: 50% and Ni: 0%) catalyst at 600°C. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) techniques were used for structural analysis. Raman spectra were taken to investigate the quality and crystalline perfection of the prepared CNTs. The ratio of D- and G-bands (ID/IG) was measured from these spectra.

Effects of the restructuring of Fe catalyst films on chemical vapor deposition of carbon nanotubes

We investigated the restructuring of Fe catalyst films during high temperature processing and its effects on the morphologies of carbon nanotubes (CNTs) arrays synthesized using the thermal chemical vapor deposition (CVD) techniques. Results show that annealing time and gas environment deeply influence the particle size distribution, which determines the morphologies of the corresponding CNT arrays. Fe particles with narrow size distribution were obtained after proper high temperature processing in NH 3, from which higher purity CNT arrays with better-alignment and uniform diameter distribution have been grown.

Electron field emission from semiconducting nanowires

In this paper we report on investigations of field emission (FE) properties of semiconducting (SiC, ZnO) one-dimensional (1D) nanostructures – nanowire/nanorod arrays, and fabrication of low-voltage field emission display (FED) devices based on these 1D nanomaterials. SiC nanowires were grown on Ni-coated Si substrates using a thermal metal-organic chemical vapor deposition (MOCVD) technique, and ZnO nanostructures were grown on gold-coated Si substrates by a thermal CVD method. Electron field emission properties of SiC and ZnO nanostructures were examined in plane geometry using a flat phosphor screen. The interrelation between the FE characteristics (emission thresholds, current density, surface uniformity, etc.) and microstructure and surface morphology of the produced 1D nanostructures was established. Diode-type FED devices (flat vacuum lamps) with SiC-nanowire-based cathodes were developed and fabricated. The FEDs are characterized by low threshold and operating electric fields – lower 2 V/μm and 5 V/μm, respectively, high current density and brightness, and stable performance of the nanowire-based cathodes.

Growth of Nitrogen‐Containing Carbon Nanotubes by Thermal Chemical Vapor Deposition

We report the formation of well‐aligned high concentration nitrogen‐containing carbon nanotube (N‐CNT) bundles on quartz using thermal chemical vapor deposition technique. The N‐CNTs were deposited by pyrolysis of ferrocene, xylene and acetonitrile mixture at 900°C in an Ar environment. The average length of these N‐CNTs, as estimated from scanning electron microscopy images, was around 60–80 µm. Energy dispersive X‐ray analysis showed that the concentration of nitrogen in the CNTs was 12–13%. Transmission electron microscopy of these N‐CNTs exhibited a bamboo‐like structure. X‐ray diffraction revealed the structure of N‐CNTs as C3N4.

Aligned carbon nanotubes for through-wafer interconnects

Through-wafer interconnects by aligned carbon nanotube for three-dimensional stack integrated chip packaging applications have been reported in this letter. Two silicon wafers are bonded together by tetra-ethyl-ortho-silicate. The top wafer (100μm thick) with patterned through-holes allows carbon nanotubes to grow vertically from the catalyst layer (Fe) on the bottom wafer. By using thermal chemical vapor deposition technique, the authors have demonstrated the capability of growing aligned carbon nanotube bundles with an average length of 140μm and a diameter of 30μm from the through holes. The resistivity of the bundles is measured to be 0.0097Ωcm by using a nanomanipulator.

Stable Field Emission Property of Patterned MgO Coated Carbon Nanotube Arrays

Aligned carbon nanotubes (CNTs) in a specific pattern were synthesized by catalytic thermal chemical vapor deposition (CVD) technique. The carbon nanotubes were then coated with MgO layer of different thicknesses to improve the field emission property. Field emission with high stability and low turn-on voltage of about 116 V was observed for the aligned nanotubes coated with a MgO layer of thickness 10 nm compared to that of uncoated CNTs. The current fluctuation for 8 h was found to be as low as 9% for MgO (10 nm) coated nanotubes. The field emission image indicated a very uniform emission from the whole area of the deposited CNTs on the substrate for the 10-nm-MgO-coated CNTs.

Opto-electrical properties of amorphous carbon thin film deposited from natural precursor camphor

A simple thermal chemical vapor deposition technique is employed for the pyrolysis of a natural precursor “camphor” and deposition of carbon films on alumina substrate at higher temperatures (600–900 °C). X-ray diffraction measurement reveals the amorphous structure of these films. The carbon films properties are found to significantly vary with the deposition temperatures. At higher deposition temperature, films have shown predominately sp 2-bonded carbon and therefore, higher conductivity and lower optical band gap (Tauc gap). These amorphous carbon (a-C) films are also characterized with Raman and X-ray photoelectron spectroscopy. In addition, electrical and optical properties are measured. The thermoelectric measurement shows these as-grown a-C films are p-type in nature.

Number of Walls Controlled Synthesis of Millimeter-Long Vertically Aligned Brushlike Carbon Nanotubes

Millimeter (mm) long vertically aligned carbon nanotubes (CNTs) were grown by the catalyst assisted thermal chemical vapor deposition (CVD) technique. The continuous growth of CNTs as long as 7 mm was observed after 12 h of deposition by adjusting the growth parameters for making the catalyst active for a long time. The direct dependence of the number of walls of mm-long CNTs on the Fe catalyst thickness was observed. The successful syntheses of single-walled nanotubes (SWNTs), double-walled nanotubes (DWNTs), and multiwalled nanotubes (MWNTs) with high percentages (∼80%) were achieved by varying the catalyst layer thickness. The effect of Al2O3 buffer layer was found to be critical for this controlled synthesis, which has been discussed in detail. The possible growth mechanism is also discussed to better understand this phenomenon.

Electrical measurement on individual multi-walled carbon nanotubes

The characterization of electrical property of multi-walled carbon nanotubes (MWCNTs) on a nanometer scale is essential for their potential application in nano-electronic devices. The MWCNTs were synthesized on Fe 2O 3/SiO 2/Si substrate and Pt plate substrate by simple thermal chemical vapor deposition (STCVD) technique and the electrical measurements of individual MWCNT grown on silicon substrate and Pt plate substrate were performed by home-made ‘nano-manipulator’, respectively. According to current-voltage curves obtained in the experiments the current density that the MWCNTs can carry is calculated to be about 10 7 A/cm 2, which is much larger than that of normal metals.

Electrical properties of carbon nanofibers synthesized using carbon disulfide as precursor

Abstract Electrical characterization of carbon nanofibers synthesized by a thermal chemical vapor deposition technique using carbon disulfide as the source of carbon is reported. Electrical resistance of mats and thin films samples of carbon nanofibers has been measured in the range of temperatures of 100–430 K. The electrical behavior of the mats can be explained within the Luttinger liquid model, but thin films show an anomaly around 273 K that may be related to charge trapping enhanced by the presence of water molecules.