Jun Okawa

Temperature-Dependent Phonon Conduction and Nanotube Engagement in Metalized Single Wall Carbon Nanotube Films

Interfaces dominate the thermal resistances in aligned carbon nanotube arrays. This work uses nanosecond thermoreflectance thermometry to separate interface and volume resistances for 10 microm thick aligned SWNT films coated with Al, Ti, Pd, Pt, and Ni. We interpret the data by defining the nanotube-metal engagement factor, which governs the interface resistance and is extracted using the measured film heat capacity. The metal-SWNT and SWNT-substrate resistances range between 3.8 and 9.2 mm(2)K/W and 33-46 mm(2)K/W, respectively. The temperature dependency of the heat capacity data, measured between 125 and 300 K, is in good agreement with theoretical predictions. The temperature dependence demonstrated by the metal-SWNT interface resistance data suggests inelastic phonon transmission.

Vertically Aligned 13C Single-Walled Carbon Nanotubes Synthesized by No-Flow Alcohol Chemical Vapor Deposition and their Root Growth Mechanism

We present the successful synthesis of aligned 13C labeled single-walled carbon nanotube (SWNT) arrays from alcohol by a modified no-flow chemical vapor deposition (CVD) method that makes efficient growth possible using a small amount of carbon source. The synthesis of high-quality SWNTs by this alternative method was confirmed by resonance Raman spectroscopy, which also showed that the quality of the grown SWNTs is uniform in growth direction. The synthesis of 13C labeled SWNTs provides solid evidence for the root growth mechanism in alcohol catalytic CVD, which agrees well with the transmission electron microscopy (TEM) observations.

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.

Carbon Nanotube Stationary Phase in a Microfabricated Column for High-Performance Gas Chromatography

We report a microfabricated gas chromatography (GC) column that uses a thin layer of high‐quality single‐walled carbon nanotubes (SWNTs) as a stationary phase. This 1.0‐m‐long, 160‐μm‐wide, 250‐μm‐deep column has the highest separation efficiency reported to date for microfabricated columns having an SWNT stationary phase. Separation efficiency was evaluated with a Golay plot, in which the minimum of the height equivalent to a theoretical plate was 0.062 cm. The microfabricated column was able to separate n‐alkanes having high boiling points under temperature‐programmed conditions. Use of SWNTs as a stationary phase will be potentially useful for high‐performance micro‐GC.

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

We have performed a systematic investigation of the influence of 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 VA-SWNT film growth 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 reaction was determined to be approximately 1.5 eV. The root-growth mechanism of VA-SWNTs synthesized by the alcohol CVD method was also confirmed by a two-stage growth process. Following a short growth period using normal ethanol, C -labeled ethanol was introduced to continue the growth. The location of the C was determined from resonance Raman spectra, confirming the root-growth mechanism.