Vertically Aligned Single-walled Carbon Nanotubes Research Articles

Effect of ion bombardment on the synthesis of vertically aligned single-walled carbonnanotubes by plasma-enhanced chemical vapor deposition

The synthesis of vertically aligned single-walled carbon nanotubes (VA-SWNTs)by plasma-enhanced chemical vapor deposition (PECVD) was achieved at500–600 °C, using ethylene as the carbon source and 1 nm Fe film as the catalyst. For growth ofhigh-quality VA-SWNTs in a plasma sheath, it is crucial to alleviate the undesirable ionbombardment etching effects by the optimization of plasma input power and gas pressure.The resistibility of synthesized VA-SWNTs against ion bombardment etching was foundto be closely related to the growth temperature. At relatively low temperature(500 °C), the VA-SWNTs were very susceptible to ion bombardments, which could inducestructural defects, and even resulted in a structural transition to few-walled nanotubes. Forcapacitively coupled radio frequency (rf) PECVD operating at moderate gas pressure(0.3–10 Torr), the ion bombardment etching effect is mainly dependent on the ion flux,which is related to the plasma input power and gas pressure.

Alcohol CVD Growth and Optical Characterization of Vertically-Aligned Single-Walled Carbon Nanotubes

not Available.

Thermal Degradation of Single-Walled Carbon Nanotubes

An optical absorbance technique was used to study the burning temperature and burning mechanism of vertically aligned single-walled carbon nanotube (VA-SWNT) films. The use of this simple optical method is shown to be consistent with the standard thermogravimetric analysis (TGA) method, but it can be applied to a very small amount of SWNTs. Experimental results indicate that burning of the VA-SWNTs is not localized, but occurs throughout the film. Furthermore, thick films have a slightly higher burning temperature than thin films synthesized under the same conditions. This is believed to be due to a higher bundle density and more uniform distribution of SWNTs within thicker films.

Growth dynamics of vertically aligned single-walled carbon nanotubes from in situ measurements

An in situ optical absorbance measurement was used to study the growth dynamics of vertically aligned single-walled carbon nanotubes (VA-SWCNTs) synthesized by chemical vapor deposition of ethanol. The growth rate of the VA-SWCNT film was found to decay exponentially from an initial maximum, resulting in an effective growth time of approximately 15 min. Investigation of various growth conditions revealed an optimum pressure at which growth is maximized, and this pressure depends on the growth temperature. Below this optimum pressure the synthesis reaction is first-order, and the rate-limiting step is the arrival of ethanol at the catalyst. We also present a novel method for determining the burning temperature of low-mass materials, which combines the in situ absorbance measurement with controlled oxidation.

Gecko‐Foot‐Mimetic Aligned Single‐Walled Carbon Nanotube Dry Adhesives with Unique Electrical and Thermal Properties

Vertically aligned single-walled carbon nanotube (VA-SWNT) arrays synthesized by a combined plasma-enhanced chemical vapor deposition and fast heating method show a maximum achievable macroscopic adhesive force of 29 N cm–2, which is the highest among all synthetic and natural gecko feet (10 N cm–2). This, together with the unique thermal and electric properties of SWNTs, represents a significant advance in developing new dry adhesives of electrical/thermal management capabilities for diverse potential applications, ranging from smart packaging to advanced electronic integration.

Revealing the Small-Bundle Internal Structure of Vertically Aligned Single-Walled Carbon Nanotube Films

Freestanding arrays of vertically aligned single-walled carbon nanotubes (VA-SWNTs) synthesized from alcohol were observed directly by transmission electron microscopy (TEM). These observations revealed that the films are comprised primarily of small bundles, containing 10 or fewer SWNTs per bundle. The absence of large, well-formed bundles is supported by electron diffraction spectra in which no bundle peak is observed. Furthermore, electron energy-loss spectroscopy shows an unusually low π plasmon energy, meaning dielectric screening from tube−tube interactions is insignificant. Not only does this suggest a prevalence of small bundles but it also indicates that the optical properties of the VA-SWNT array are determined by the one-dimensional nature of the component SWNTs, rather than the bulk dimensions of the entire SWNT film.

Investigating the Growth Process of Vertically Aligned Single-Walled Carbon Nanotubes Synthesized from Alcohol

ABSTRACTWe have performed a systematic investigation of the influence of the growth parameters on the synthesis of vertically aligned single-walled carbon nanotubes (VA-SWNTs) by the alcohol catalytic chemical vapor deposition (ACCVD) method. The growth process of the VA-SWNTs was monitored using an in situ optical absorbance technique and the effects of CVD temperature and ethanol pressure on the initial growth rate and the catalyst lifetime were investigated. We found that for a given CVD temperature, there is an optimum pressure at which the VA-SWNT film height is maximized, and this pressure increases with temperature. Below this optimum pressure the growth reaction is first-order, with the arrival of ethanol to the catalyst being the rate-limiting step. The activation energy of the growth was also determined to be approximately 1.5 eV.The root-growth mechanism of VA-SWNTs by the alcohol CVD method was also confirmed by a two-stage growth process. Following a short growth period using normal ethanol, isotope labeled 13C ethanol was introduced to continue the growth. The location of the 13C was confirmed by resonance Raman spectroscopy, confirming the root-growth mechanism.

Direct growth of three-dimensional multicomponent micropatterns of vertically aligned single-walled carbon nanotubes interposed with their multi-walled counterparts on Al-activated iron substrates

Vertically aligned single-walled carbon nanotubes (VA-SWNTs) have been synthesized by an Al-activated plasma-enhanced chemical vapor deposition (PECVD) method. On this basis, we have developed a facile but effective method for direct growth of multicomponent micropatterns of VA-SWNTs interposed within the patterned areas surrounded by vertically aligned multi-walled carbon nanotubes (VA-MWNTs) onto an Al-activated iron substrate. The Al-activated iron substrate was prepared by region-selectively depositing an Al thin layer on either an Fe-coated substrate or a commercially available iron foil. This simple approach allows for an effective integration of various aligned carbon nanotubes with different electronic characteristics into multifunctional materials and devices.

High-Yield Synthesis of Vertically Aligned Single-Walled Carbon Nanotubes in Ion-Damage and Radical-Damage Free Atmospheric Pressure PECVD

ABSTRACTPlasma-enhanced chemical vapor deposition (PECVD) is recognized as one of the viable fabrication techniques of carbon nanotubes (CNTs). However, “CNTs” synthesized in low-pressure PECVD is overwhelmingly carbon nanofibers or multi-walled carbon nanotubes because catalyst and CNTs receive severe damage from ion bombardment: single-walled carbon nanotubes (SWCNTs) has been exclusively synthesized in the thermal CVD regime except few examples. We present atmospheric pressure plasma enhanced chemical vapor deposition (AP-PECVD) for high-purity vertically-aligned SWCNT synthesis, because both ion-damage and radical-damage are preferentially avoided in atmospheric pressure. Tentative reaction mechanism is also discussed based gas phase chemistry analyzed by quadrupole mass spectrometer.

Synthesis of Vertically-Aligned Single-Walled Carbon Nanotubes in Micro Structure of Atmospheric Pressure Non-Equilibrium Plasma

Synthesis of Vertically-Aligned Single-Walled Carbon Nanotubes in Micro Structure of Atmospheric Pressure Non-Equilibrium Plasma

Field emission from a composite structure consisting of vertically aligned single-walledcarbon nanotubes and carbon nanocones

Vertically aligned single-walled carbon nanotubes (VA-SWCNTs) have been fabricated oncarbon nanocones (CNCs) in a gravity-assisted chemical vapour deposition (CVD) process. TheCNCs with nanoscale Co particles at the top were first grown on the Co/Si(100) substrate biasedat 350 V in a plasma enhanced chemical vapour deposition process. The CNCs typically are∼200 nm in height, andtheir diameters are ∼100 nmnear the bottom and ∼10 nm at the top. The nanoscale Co particles∼10 nm in diameter act as catalysts which favour the growth of VA-SWCNTs out of CNCs at850 °C in the gravity-assisted CVD process. The average length and the growth time of VA-SWCNTs are∼150 nm and 1.5 min, equivalent to a growth rate of∼6 µm h−1. The diameters of VA-SWCNTs are estimated to be 1.2–2.1 nm. WhenVA-SWCNTs are fabricated on CNCs, the turn-on voltage is reduced from 3.9 to0.7 V µm−1 and the emission current density at the electric field of5 V µm−1 is enhanced by a factor of more than 200. The composite VA-SWCNT/CNC structure ispotentially an excellent field emitter. The emission stability of the VA-SWCNT/CNC fieldemitter is discussed.

Fabrication of vertically aligned single-walled carbon nanotubes in atmospheric pressure non-thermal plasma CVD

A fabrication technique of high-purity vertically aligned single-walled carbon nanotubes (VA-SWCNTs) using atmospheric pressure plasma enhanced chemical vapor deposition is presented. Although densely mono-dispersed Fe–Co catalysts of a few nanometers is primarily responsible for VA-SWCNT growth, carbon precipitation was virtually absent in the thermal CVD regime at 700 °C. On the other hand, high-purity VA-SWCNTs without measurable defects were grown at 4 μm min −1 by applying atmospheric pressure radio-frequency discharge (APRFD) which has been previously developed for this purpose. The results proved that cathodic ion sheath adjacent to the substrates, where a large potential drop exists, also plays an essential role for the controlled growth of SWCNTs, while ion damage to the VA-SWCNTs is inherently avoided due to high collision frequency among molecules in atmospheric pressure. Operation regime of APRFD and tentative reaction mechanisms for VA-SWCNT growth are discussed along with optical emission spectroscopy of near substrate region.

Effects of atomic hydrogen and active carbon species in 1mm vertically aligned single-walled carbon nanotube growth

A hot filament chemical vapor deposition (HFCVD) method has been used to investigate the effects of atomic hydrogen and active carbon species on the growth of 1mm vertically aligned single-walled carbon nanotubes (VA-SWNTs). Isotopic shifts of the tangential phonon mode of SWNTs indicate that SWNT growth occurs primarily via reactions of acetylene and ethylene. The authors find that the presence of atomic hydrogen and active carbon species such as ethylene and acetylene appears to be essential for both nucleation and growth of VA-SWNTs in this HFCVD.

Production and Applications of Vertically Aligned Single-Walled Carbon Nanotubes *

Synthesis of vertically aligned single-walled carbon nanotube (VA-SWNT) thin films by alcohol catalytic chemical vapor deposition has been clarified using an in situ optical absorbance measurement technique, which makes it possible to control the final film thickness. These VA-SWNT films can be detached from the substrates on which they are grown and reattached onto arbitrary solid surfaces by a simple hot water-assisted process. This will allow many new areas of SWNT applications to be investigated.

Detachment of vertically aligned single-walled carbon nanotube films from substrates and their re-attachment to arbitrary surfaces

A method for detachment of vertically aligned single-walled carbon nanotube (VA-SWNT) films from substrates simply using hot water has been developed. The VA-SWNT films were peeled off spontaneously by submersing the substrate into heated (larger than 60 °C) distilled water, and the detached films floated on the water surface. The detached films could readily be re-attached onto arbitrary solid surfaces, and conservation of the vertically aligned morphology after the re-attachment was confirmed based on measurements by field-emission scanning electron microscopy, resonant Raman scattering, and optical absorption spectroscopy. A possible mechanism for the process of film detachment is discussed.

A213 垂直配向単層カーボンナノチューブのCVD成長制御(マイクロ・ナノスケール6)

Vertically aligned single-walled carbon nanotubes (VA-SWNTs) are a new material expected to be used in various applications, such as field emission displays, or optical devices. We have developed the alcohol catalytic chemical vapor deposition (ACCVD) method to produce high-purity VA-SWNT films from alcohol. However, ACCVD growth control is not well-established because the SWNT synthesis mechanism has not yet been clarified. In this research, we attempt to better understand the SWNT growth mechanism, with the aim of improving the uniformity in length, diameter and chirality of the VA-SWNT films.

Imperfect surface order and functionalization in vertical carbon nanotube arrays probed by near edge X-ray absorption fine structure spectroscopy (NEXAFS)

Probing surface order as well as the degree of structural modification in carbon nanotube systems is of fundamental importance for incorporation of these materials into practical functional devices. The current study pertains to the analysis of the surface order of vertically-aligned single-walled and multi-walled carbon nanotube arrays of varying length and composition by means of near-edge X-ray fine structure spectroscopy (NEXAFS). Both NEXAFS and scanning electron microscopy (SEM) studies concluded that the nanotubes in these samples were oriented vertically to the plane of the surface. However, NEXAFS polarization analysis provided a more quantitative and nuanced description of the surface structure, indicative of far less localized surface order, an observation partially attributed to misalignment and bending of the tubes. Moreover, it was demonstrated by NEXAFS that the surface order of the arrays was imperfect and relatively independent of the height of the nanotube arrays. In addition, we have shown that NEXAFS can be used to correlate the extent of chemical functionalization and oxygenation with disruption of the electronic and physical structure of nanotubes embedded in array motifs.