Catalytic Thermal Chemical Vapor Deposition Research Articles

Can a Procedure for the Growth of Single‐layer Graphene on Copper be used in Different Chemical Vapor Deposition Reactors?

In the last decade, catalytic chemical vapor deposition (CVD) has been intensively explored for the growth of single-layer graphene (SLG). Despite the scattering of guidelines and procedures, variables such as the surface texture/chemistry of catalyst metal foils, carbon feedstock, and growth process parameters have been well-scrutinized. Still, questions remain on how best to standardize the growth procedure. The possible correlation of procedures between different CVD setups is an example. Here, two thermal CVD reactors were explored to grow graphene on Cu foil. The design of these setups was entirely distinct, one being a "showerhead" cold-wall type, whereas the other represented the popular "tubular" hot-wall type. Upon standardizing the Cu foil surface, it was possible to develop a procedure for cm2 -scale SLG growth that differed only by the carrier gas flow rate used in the two reactors.

Electron microscopy study of surface-treated carbon fiber for interface modification in composites

Relatively poor adhesion of carbon fibers with matrix leads to various serious concerns in high performance composites. Interface debonding during loading is the most vulnerable among them particularly when polymer matrix is used. This paper presents the results of electron microscopy investigation of four different techniques that are beneficial for improving interfacial bonding. These techniques were based on modifying the fiber surface by way of both; coating a film on the fiber and ablating a layer from it. The former employed growth of nanostructures of carbon and zinc oxide by thermal catalytic chemical vapor deposition and magnetron sputtering respectively and depositing a layer of pyrolytic carbon by CVD while the latter involved ablation of an outer layer of fiber using femtosecond laser treatment. Both the approaches relied on introducing mechanical anchoring on the fiber surface by micro roughening anticipating an improved fiber- matrix interfacial bonding. Carbon fiber surface prior and post treatment was investigated microscopically using FESEM and TEM. CNTs growth formed network like structure around the fiber, while PyC coating showed continuous layer around the fiber. HRTEM images of ZnO nanostructures; both nanowires and nanowalls possessed crystalline structure revealed by the presence of Moiré fringes formed due to overlapping of two crystals with different orientation. Laser treated fiber surface showed formation of LIPSS with average periodicity of 147 ± 10 nm.

Urchin-like boron nitride hierarchical structure assembled by nanotubes-nanosheets for effective removal of heavy metal ions

Water pollution has become a serious global issue owing to the large amounts of contaminants generated from industrial and agricultural development. Recently, various boron nitride-based micro/nano-materials have exhibited efficient sorption capacity for contaminants from water. Herein, novel urchin-like boron nitride hierarchical structure assembled by free-growing boron nitride nanotubes and crapy boron nitride nanosheets is firstly fabricated via a sample two-step approach, including the synthesis of analogous "core-shell" structured boron-containing precursor and thermal catalytic chemical vapor deposition. A combined growth mechanism of vapor-liquid-solid and vapor-solid is proposed to control the formation of BN hierarchical structure. The unique structure exhibits superior removal capacity of 115.07 mg g−1 and 92.85 mg g−1 for Pb2+ and Cu2+ in water solution, respectively. The excellent adsorption performance of the product mainly derives from the vast lattice imperfections, the high-density edge active sites, the expanded interplanar spacing, as well as the unique structural characteristics. They are beneficial for structural stability and enough space for accommodating the adsorbed heavy metal ions. These results indicate that the urchin-like boron nitride hierarchical structure is a promising adsorption material for water treatment.

Optical reflectance of patterned frost column-like CNT forest for metamaterial applications

In this paper, the optical properties of a frost column-like carbon nanotube (CNT) forest, a hybrid structure of carbon film and a CNT forest, in which carbon films are supported by low-density, vertically-aligned CNT forests, are reported for the first time. The frost column-like CNT forest exhibits a significant interference reflectance, which is not typically observed in conventional CNT forests. Oscillating spectra in the visible (VIS) reflectance were analyzed by simple optical interference between the substrate and carbon films. Fishnet type metamaterial patterns of catalyst films were successfully fabricated by focused ion beam (FIB) pattern processing, followed by CNT growth using a thermal catalytic chemical vapor deposition (CVD) method. Optical properties of fishnet-type frost column-like CNT forest were also investigated. We also found that within the infrared region, optical absorption increased with fishnet type metamaterial CNT, frost column-like CNT forest, compared with non-patterned one. These results suggested that a metamaterial effect of fishnet patterns was observed.

Carbon Dioxide Promotes Dehydrogenation in the Equimolar C2 H2 -CO2 Reaction to Synthesize Carbon Nanotubes.

The equimolar C2 H2 -CO2 reaction has shown promise for carbon nanotube (CNT) production at low temperatures and on diverse functional substrate materials; however, the electron-pushing mechanism of this reaction is not well demonstrated. Here, the role of CO2 is explored experimentally and theoretically. In particular, 13 C labeling of CO2 demonstrates that CO2 is not an important C source in CNT growth by thermal catalytic chemical vapor deposition. Consistent with this experimental finding, the adsorption behaviors of C2 H2 and CO2 on a graphene-like lattice via density functional theory calculations reveal that the binding energies of C2 H2 are markedly higher than that of CO2 , suggesting the former is more likely to incorporate into CNT structure. Further, H-abstraction by CO2 from the active CNT growth edge would be favored, ultimately forming CO and H2 O. These results support that the commonly observed, promoting role of CO2 in CNT growth is due to a CO2 -assisted dehydrogenation mechanism.

Growth, structure, and luminescence properties of novel silica nanowires and interconnected nanorings

Novel silica nanowires and interconnected nanorings were firstly synthesized on a graphite paper by typical thermal catalytic chemical vapor deposition method, using silicon and carbon black powders as raw materials. The field emission scanning electron microscopy, energy dispersive x-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy were used to investigate the composition and structure characterization, which indicates that the silica nanowires and interconnected nanorings were amorphous. The growth of the as-prepared silica nanowires and interconnected nanorings was related to the vapor-liquid-solid mechanism, but the nanowire-ring structure may be due to the polycentric nucleation and periodic stable growth with gradual direction changes. The room temperature photoluminescence emission spectrum showed that the silica nanostructures emitted strong blue light at 460 nm, resulting from the combination of neutral oxygen vacancy (≡Si-Si≡) and selftrapped excitons. The as-synthesized novel silica nanowires and interconnected nanorings could be a potential candidate for applications in future light-emitting diodes and optoelectronic nanodevices.

Fabrication of Ti Porous body with Improved Specific Surface Area by Synthesis of CNTs

이 논문은 2015년도 정부 (미래창조과학부)의 재원으로 한국 연구 재단의 지원을 받아 수행된 연구임(No.2012R1A2A2A02046179). 본 연구는 2015년도 산업통상자원부의 재원으로 한국에너지기술평가원(KETEP)의 지원을 받아 수행한 연구 과제입니다(No. 20154030200900).

Vertically aligned carbon nanotube field emitter arrays with Ohmic base contact to silicon by Fe-catalyzed chemical vapor deposition

In this study, dense arrays of aligned carbon nanotubes are obtained by thermal catalytic chemical vapor deposition, using Fe catalyst dispersed on a thin Ta layer. Alignment of the carbon nanotubes depends on the original Fe layer thickness from which the catalyst dispersion is obtained by thermal treatment prior to the synthesis step, as well as on the synthesis temperature, which in this study was varied between 680 and 740°C. For the intended application of the nanotubes as field emitters, it is essential that electrical conductivity between the tubes and the substrate is guaranteed. In a novel approach, a noble metal layer, of 100nm Pt or Au, was applied between the Ta layer and the support, which ensures an Ohmic contact throughout the metal multilayer which connects the silicon substrate with the CNT fibers, because oxidation of Ta at its interface with Si is prevented. For optimized dense arrays of aligned nanotubes with low Ohmic resistance, field emission in nitrogen atmosphere is demonstrated, with field enhancement factors of up to ca. 2000 for nanotubes grown using Fe/Ta catalyst deposited on Au and Pt.

Electrical and Optical Properties of Carbon Nanotube Hybrid Zinc Oxide Nanocomposites Prepared by Ball Mill Technique

The electrical and optical properties of carbon nanotubes hybrid zinc oxide (ZnO-CNTs) nanocomposites synthesized by ball mill technique have been investigated. The nanocomposites were prepared using zinc oxide (ZnO) powder and carbon nanotube (CNT) synthesized by catalytic thermal chemical vapor deposition (CVD). The diameters and lengths of the CNTs were respectively determined to be 20–30 nm and about 3–5 µm. DC conductivity measurements reveal that the nanocomposites are good conductive material. The room temperature DC electrical conductivity σdc of the un-doped ZnO and ZnO-CNT nanocomposites with 0.1% CNT, 0.5% CNT, and 1% CNT were found to be 6.55 × 10−5, 5.46 × 10−4, 1.49 × 10−3, and 4.01 × 10−3 S/cm, respectively. This indicates that there is a remarkable improvement of the electrical conductivity as the CNTs' content increases. The optical band gaps of the composites were determined by Kubelka-Munk theory based on the analysis of diffuse reflectance. The band gap (Eg) values of the composites decreased with increasing CNT contents. The obtained results indicate that the electrical and optical properties of ZnO semiconductor can be improved by incorporation of CNT.

Impact behavior and fractographic study of carbon nanotubes grafted carbon fiber-reinforced epoxy matrix multi-scale hybrid composites

Carbon nanotubes are the most promising reinforcement for high performance composites. Multiwall carbon nanotubes were directly grown onto the carbon fiber surface by catalytic thermal chemical vapor deposition technique. Multi-scale hybrid composites were fabricated using the carbon nanotubes grown fibers with epoxy matrix. Morphology of the grown carbon nanotubes was investigated using field emission scanning electron microscopy and transmission electron microscopy. The fabricated composites were subjected to impact tests which showed 48.7% and 42.2% higher energy absorption in Charpy and Izod impact tests respectively. Fractographic analysis of the impact tested specimens revealed the presence of carbon nanotubes both at the fiber surface and within the matrix which explained the reason for improved energy absorption capability of these composites. Carbon nanotubes presence at various cracks formed during loading provided a direct evidence of micro crack bridging. Thus the enhanced fracture strength of these composites is attributed to stronger fiber–matrix interfacial bonding and simultaneous matrix strengthening due to the grown carbon nanotubes.

Influence of thin film nickel pretreatment on catalytic thermal chemical vapor deposition of carbon nanofibers

Nickel and other metal nanoparticles are known to be active as catalysts in the synthesis of carbon nanofibers. In this paper we investigate how dewetting and break-up of nickel thin films depends on film thickness, film–substrate interaction and pretreatment conditions. This is evaluated for films evaporated on oxidized silicon and fused silica substrates with or without tantalum coating, which were subsequently exposed to different pretreatment atmospheres (vacuum, nitrogen, air and hydrogen; 1h, 650°C). Atomic force microscopy, scanning electron microscopy and energy dispersive X-ray analysis were used to characterize the films. Pretreated Ni films were subjected to a thermal catalytic chemical vapor deposition procedure with brief ethylene exposures (0.5–3min, 635°C). It was found that only on the spherical nanoparticles originating from a hydrogen pretreatment of a Ni film with Ta adhesion layer, homogeneously distributed, randomly-oriented, well-attached, and semi-crystalline carbon nanofibers be synthesized.

3 Dimensional Carbon Nanostructures for Li-ion Battery Anode

ABSTRACTCarbon nanofibers (CNFs) have been thoroughly investigated as potential anode materials in Li-ion battery owing to their exceptional properties such as the higher surface area to mass ratio, electrical conductivity and mechanical toughness. However, one of the major limitations of nano carbon materials is lower mass loading density. To address this issue, we have developed a novel anode system composed of CNFs directly grown on 3D Cu mesh current collector (hereafter mentioned as 3D CNFs) using a thermal catalytic chemical vapor deposition (CVD) method. Compared to CNF-based anodes on 2D Cu current collector, active The active material loading amount of the 3D CNFs has been found to be 400 % higher while comparing with 2D CNF. Owing to an increase of the active surface area, 3D CNFs demonstrated enhanced electrochemical performance of Li-ion battery in terms of charge capacity (50% improvement), rate capability and cycling life. Interfacial contact between the CNFs and Cu could play a crucial role in promoting the electrochemical properties. The intermediate TiC thin layer, formed at high temperature 750°C, could function as an efficient electric conducting pathway and a strong bonding bridge between the CNFs and Cu. In order to improve the pristine 3D CNF redox reactions, the amorphous Si (a-Si)/3D CNF has been sputter deposited to produce Si wrapped 3D CNF hybrid anode material. It has been found that the electrochemical properties of the a-Si/3D CNF yields superior specific capacity (Cdis 549 mAhg-1, LiC4.1) and cycling stability than that of pristine 3D CNF (461 mAhg-1, LiC4.8).

Towards convective heat transfer enhancement: surface modification, characterization and measurement techniques

In this work, heat transfer surface modification and heat transfer measurement technique is developed. Heat transfer investigation was aimed to study the effect of carbon nano fibers (extremely high thermal conductive material) on the enhancement level in heat transfer. Synthesis of these carbon nano structures is achieved using thermal catalytic chemical vapor deposition process (TCCVD) on a 50 μm pure nickel (Ni270) wire. The micro wire samples covered with CNF layers were subjected to a uniform flow from a nozzle. Heat transfer measurement was achieved by a controlled heat dissipation through the micro wire to attain a constant temperature during the flow. This measurement technique is adopted from hot wire anemometry calibration method. Synthesis of carbon nano structures, heat transfer surface characterization and measurement technique are evaluated. Preliminary results indicate that an average enhancement in Nusselt Number of 17% is achieved.

Evidence of wettability variation on carbon nanofiber layers grown on oxidized silicon substrates

This paper describes how layers of carbon nanofibers (CNFs) with a controllable wettability can be synthesized by means of thermal catalytic chemical vapor deposition on nickel-based thin films on oxidized silicon supports. In order to achieve well-adhesive CNF-layers with a uniform surface coverage and tunable wettability without the necessity of post-synthesis treatments, a series of synthesis parameters is investigated: the pretreatment atmosphere (hydrogen or oxygen; 2h, 500°C), the use of ethylene (C2H4) or an ethylene/hydrogen (C2H4/H2) mixture as hydrocarbon source, and the growth time (in the range 5–60min).Fast and uniform CNF-growth is found on reduced Ni-based thin films using C2H4/H2 at a synthesis temperature of 635°C. The CNF-layers on Ni are superhydrophobic or highly hydrophobic for all growth times, but their adhesion to the support is poor for growth times >30min. In contrast, the adhesion of CNF-layers on Ni/Ta is excellent. Moreover, the wettability of these as-synthesized CNF-layers can be controlled by variation of the growth time: from superhydrophobic (⩽10min) to hydrophilic (⩾50min). CNF-layers with such tunable wettability can be easily integrated in flow channels of silicon-based microfluidic systems, thereby offering numerous applications.

Enhanced growth of crystalline-amorphous core-shell silicon nanowires by catalytic thermal CVD using in situ generated tin catalyst

In this work, we prepared silicon nanowires (Si NWs) on both fluorine-doped SnO2 (FTO) coated glass substrate and common glass substrate by catalytic thermal chemical vapor deposition (CVD) using indium film as the catalyst. It is confirmed that indium can catalyze the growth of Si NWs. More importantly, we found that tin generated in situ from the reduction of SnO2 by indium can act as catalyst, which greatly enhances the growth of Si NWs on FTO substrate. The obtained Si NWs have a uniform crystalline-amorphous core-shell structure that is formed via vapor-liquid-solid and vapor-solid growth of silicon sequentially. This work provides a strategy to prepare Si NWs in high yield by catalytic thermal CVD using the low melting point metal catalysts.

Integration of Hexagonal Boron Nitride with Quasi-freestanding Epitaxial Graphene: Toward Wafer-Scale, High-Performance Devices

Hexagonal boron nitride (h-BN) is a promising dielectric material for graphene-based electronic devices. Here we investigate the potential of h-BN gate dielectrics, grown by chemical vapor deposition (CVD), for integration with quasi-freestanding epitaxial graphene (QFEG). We discuss the large scale growth of h-BN on copper foil via a catalytic thermal CVD process and the subsequent transfer of h-BN to a 75 mm QFEG wafer. X-ray photoelectron spectroscopy (XPS) measurements confirm the absence of h-BN/graphitic domains and indicate that the film is chemically stable throughout the transfer process, while Raman spectroscopy indicates a 42% relaxation of compressive stress following removal of the copper substrate and subsequent transfer of h-BN to QFEG. Despite stress-induced wrinkling observed in the films, Hall effect measurements show little degradation (<10%) in carrier mobility for h-BN coated QFEG. Temperature dependent Hall measurements indicate little contribution from remote surface optical phonon scattering and suggest that, compared to HfO(2) based dielectrics, h-BN can be an excellent material for preserving electrical transport properties. Graphene transistors utilizing h-BN gates exhibit peak intrinsic cutoff frequencies >30 GHz (2.4× that of HfO(2)-based devices).

The Effect of Catalyst on Carbon Nanotubes (CNTs) Synthesized by Catalytic Chemical Vapor Deposition (CVD) Technique

Catalyst plays a crucial role in determining the characteristics of carbon nanotubes (CNTs) produced by using thermal catalytic chemical vapor deposition (CVD). It is essential to investigate how the catalyst preparation affects the characteristics of CNTs because certain application demands specific size for optimum performance. This study reports the effect of the types of catalyst and the duration of the catalyst pre-treatment (wet etching time, dry etching time and ball milling) on the diameter of CNTs. The synthesized CNTs samples were characterized by scanning and transmission electron microscopy and Raman spectroscopy. Wet etching (2M hydrofluoric acid) time was varied from 1 to 2.5 hrs and the diameter range was found to be in the range of 23 to 52 nm. The diameter range for CNTs produced for 3 hrs and 5 hrs of dry etching treatment (with ammonia gas) are 38 to 51 nm and 23 to 48 nm, respectively. The diameter size of CNTs produced using Ni (14 to 25 nm) was found to be smaller than Fe (38 to 51 nm). There is a significant decrease in the diameter of CNTs by prolonging the wet etching period. Shorter and curly shaped CNTs can also be obtained by using Ni as the catalyst. Keywords: chemical vapor deposition, carbon nanotubes, catalyst pretreatment

First-principles based kinetic modeling of effect of hydrogen on growth of carbon nanotubes

We investigate the influence of hydrogen on carbon nanotube (CNT) growth in thermal catalytic chemical vapor deposition. Kinetic calculations of gas-phase transformations of hydrocarbons show that hydrogen interacts with gaseous carbon precursors, resulting in modification of the carbon supply rate to the catalyst particle. A surface-kinetic model of CNT growth is developed to study adsorption and decomposition kinetics of precursors on Ni catalyst particles. The detailed surface kinetics of carbon precursors and transport of carbon atoms through the catalyst particle are described in the framework of the surface/bulk site formalism, with the parameters of the reactions determined on the basis of first-principles calculations for Ni (1 1 1) and (1 1 3) surfaces. Using this model, different regimes of CNT growth, with and without hydrogen in the system, are analyzed. Hydrogen is shown to enhance desorption of hydrocarbons, leading to a decrease of the surface coverage and effective carbon supply rate.

Effect of Gas Pressure on Electron Field Emission from Carbon Nanotube Forests

This article quantifies the effect of the operating pressure of the H2 + C2H4 gas mixture on the current density and threshold voltage of the electron emission from dense forests of multiwalled carbon nanotubes synthesized using thermal catalytic Chemical Vapor Deposition under near atmospheric pressure process conditions. The results suggest that in the pressure range of interest 400-700 Torr the field emission properties can be substantially improved by operating the process at lower gas pressures when the nanostructure aspect ratios are higher. The obtained threshold voltage approximately 1.75 V/microm and the emission current densities approximately 10 mA/cm2 offer competitive advantages compared with the results reported by other authors.

A cone-shaped 3D carbon nanotube probe for neural recording

A novel cone-shaped 3D carbon nanotube (CNT) probe is proposed as an electrode for applications in neural recording. The electrode consists of CNTs synthesized on the cone-shaped Si (cs-Si) tip by catalytic thermal chemical vapor deposition (CVD). This probe exhibits a larger CNT surface area with the same footprint area and higher spatial resolution of neural recording compared to planar-type CNT electrodes. An approach to improve CNT characteristics by O 2 plasma treatment to modify the CNT surface will be also presented. Electrochemical characterization of O 2 plasma-treated 3D CNT (OT-CNT) probes revealed low impedance per unit area (∼64.5 Ω mm −2) at 1 kHz and high specific capacitance per unit area (∼2.5 mF cm −2). Furthermore, the OT-CNT probes were employed to record the neural signals of a crayfish nerve cord. Our findings suggest that OT-CNT probes have potential advantages as high spatial resolution and superb electrochemical properties which are suitable for neural recording applications.