Suguru Noda

Millimeter-tall single-walled carbon nanotubes rapidly grown with and without water.

Millimeter-tall vertically aligned single-walled carbon nanotubes (SWCNTs) were grown in 10-15 min by chemical vapor deposition from C(2)H(2)/Ar with or without water addition using Fe catalyst supported on an Al-Si-O underlayer. Using combinatorial catalyst libraries coupled with the real-time monitoring of SWCNT growth, the catalyst and chemical vapor deposition conditions were systematically examined, and millimeter-tall SWCNTs were obtained even without water addition. The key for millimeter-scale growth of SWCNTs is to limit the C(2)H(2) supply to below a certain partial pressure to retain an active catalyst. Water prolongs the catalyst lifetime under excess C(2)H(2) supply, whereas it deactivates small catalyst particles and degrades the quality of SWCNTs at the same time. We also observed a gradual increase in the diameter of SWCNTs with growth because of the coarsening of catalyst particles and found that water had no effect on this phenomenon. We demonstrate millimeter-tall SWCNTs grown by simply using C(2)H(2)/Ar gas without water addition, which revealed the mysterious role of water, and we show a practical route for the large-scale production of SWCNTs.

Self-standing positive electrodes of oxidized few-walled carbon nanotubes for light-weight and high-power lithium batteries

Binder-free and self-standing carbon nanotube (CNT) electrodes of tens of microns in thickness have been assembled via a vacuum-filtration process of oxidized few-walled CNTs (FWNTs), with different amounts of oxygen functional groups on FWNTs. Sub-millimetre long FWNTs can provide high electrical conductivity and mechanical strength in self-standing porous networks by reducing the number of junctions among FWNTs. We show that the gravimetric capacity of FWNT electrodes in lithium cells can be enhanced by increasing oxygen functional groups on FWNTs, which results from Faradaic reactions between lithium ions and surface oxygen functional groups. These self-standing FWNT electrodes (free of binder/additive and current collector) can provide a high gravimetric energy of ∼200 W h kg−1 at a high power of ∼10 kW kg−1, showing promise as the positive electrode for light-weight, high-power lithium batteries.

Comprehensive perspective on the mechanism of preferred orientation in reactive-sputter-deposited nitrides

Texture control of sputter-deposited nitride films has provoked a great deal of interest due to its technological importance. Despite extensive research, however, the reported results are scattered and discussions about the origin of preferred orientation (PO) are sometimes conflicting, and therefore controversial. The aim of this study is to acquire a clear perspective in order to discuss the origin of PO of sputter-deposited nitrides. Among nitrides, we focus on titanium nitride (TiN), aluminum nitride (AlN), and tantalum nitride (TaN), which are three commonly used nitrides. First, we collected reported experimental results about the relation between operating conditions and PO, because PO is considered to be determined by film formation processes, such as surface diffusion or grain growth, which is affected by operating conditions. We also collected reported results about such PO-determining processes. Then, we categorized the PO-determining processes into an initial stage and a growth stage of film d...

Initial growth and texture formation during reactive magnetron sputtering of TiN on Si(111).

The initial growth and texture formation mechanism of titanium nitride (TiN) films were investigated by depositing TiN films on (111) silicon substrates by using reactive magnetron sputtering of a Ti metallic target under a N2/Ar atmosphere, and then analyzing the films in detail by using transmission electron microscopy (TEM) and x-ray diffraction (XRD). Two power sources for the sputtering, dc and rf, were compared. At the initial growth stage, a continuous amorphous film containing randomly oriented nuclei was observed when the film thickness was about 3 nm. The nuclei grew and formed a polycrystalline layer when the film thickness was about 6 nm. As the film grew further, its orientation changed depending on the deposition conditions. For dc sputtering, the appearance of (111) or (200)-preferred orientations depended on the N2 partial pressure, and the intensity of the preferred orientation increased with increasing film thickness. For rf sputtering, however, when the film thickness was small (for ins...

Electrochemical polymerization of pyrene derivatives on functionalized carbon nanotubes for pseudocapacitive electrodes

Electrochemical energy-storage devices have the potential to be clean and efficient, but their current cost and performance limit their use in numerous transportation and stationary applications. Many organic molecules are abundant, economical and electrochemically active; if selected correctly and rationally designed, these organic molecules offer a promising route to expand the applications of these energy-storage devices. In this study, polycyclic aromatic hydrocarbons are introduced within a functionalized few-walled carbon nanotube matrix to develop high-energy, high-power positive electrodes for pseudocapacitor applications. The reduction potential and capacity of various polycyclic aromatic hydrocarbons are correlated with their interaction with the functionalized few-walled carbon nanotube matrix, chemical configuration and electronic structure. These findings provide rational design criteria for nanostructured organic electrodes. When combined with lithium negative electrodes, these nanostructured organic electrodes exhibit energy densities of ∼350 Wh kg−1electrode at power densities of ∼10 kW kg−1electrode for over 10,000 cycles.

Combinatorial method to prepare metal nanoparticles that catalyze the growth of single-walled carbon nanotubes

Enhanced surface diffusion at the growth temperature of single-walled carbon nanotubes (SWNTs) can cause coarsening of metal catalysts. By balancing the nominal thickness and surface diffusion length of metals, metal nanoparticles of desirable size are expected to form spontaneously under the SWNTs growth conditions. Our combinatorial method, using a library of nominally 0.001 to 1 nm thick sputter-deposited cobalt patterns, identified in a single experimental run that cobalt nanoparticles from submonolayers can catalyze the growth of high-quality SWNTs.

Self-organized metallic nanoparticle and nanowire arrays from ion-sputtered silicon templates

We demonstrate a production method for self-organized arrays of metal nanoparticles and aligned nanowires. Ion beam-sputtered Si∕SiO2 substrates are used as templates for metallic vapor deposition, forming aligned arrays of 5–20nm silver and cobalt nanoparticles with a period of 35nm. The 20nm diameter cobalt nanowires with lengths in excess of a micrometer are produced under appropriate conditions. All processing steps can be integrated into a single vacuum chamber and performed in a matter of minutes at mild temperatures. This inherently scalable technique can be extended to a range of substrate materials, array patterns, and nanoparticle materials.

Effect of interfacial interactions on the initial growth of Cu on clean SiO2 and 3-mercaptopropyltrimethoxysilane-modified SiO2 substrates

The effect of interfacial interactions on the initial growth of Cu on clean SiO2 and 3-mercaptopropyltrimethoxysilane (MPTMS)-modified SiO2 substrates by sputter deposition was studied using transmission electron microscopy, energy dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy. Plasma damage during sputter deposition makes surfaces of MPTMS-modified SiO2 substrates consist of small MPTMS islands several tens of nanometers in diameter and bare SiO2 areas. These MPTMS islands are composed of disordered multilayer MPTMS aggregates. The initial growth behavior of Cu on MPTMS-modified SiO2 substrates differs from that on clean SiO2 substrates, although Cu grows in three-dimensional-island mode on both of them. After a 2.5-monolayer Cu deposition on clean SiO2 substrates, spherical Cu particles were formed at a low number density of 1.3×1016 /m2 and at a long interparticle distance of 5 nm. In contrast, after the same amount of deposition on MPTMS-modified SiO2 substrates, Cu particles pre...

One-Step Sub-10 μm Patterning of Carbon-Nanotube Thin Films for Transparent Conductor Applications

We propose a technique for one-step micropatterning of as-grown carbon-nanotube films on a plastic substrate with sub-10 μm resolution on the basis of the dry transfer process. By utilizing this technique, we demonstrated the novel high-performance flexible carbon-nanotube transparent conductive film with a microgrid structure, which enabled improvement of the performance over the trade-off between the sheet resistance and transmittance of a conventional uniform carbon-nanotube film. The sheet resistance was reduced by 46% at its maximum by adding the microgrid, leading to a value of 53 Ω/sq at a transmittance of 80%. We also demonstrated easy fabrication of multitouch projected capacitive sensors with 12 × 12 electrodes. The technique is quite promising for energy-saving production of transparent conductor devices with 100% material utilization.

Influence of Deposition Temperature on the Microstructure of Pb-Ti-Nb-O Thin Films by Metallorganic Chemical Vapor Deposition

In the current study, we grew Pb-Ti-Nb-O (PTN) thin films on Pt/Ti/SiO 2 /Si substrate by metallorganic chemical vapor deposition (MOCVI) at temperatures ranging from 400 to 620°C. The thin films obtained were examined by X-ray diffraction and cross-sectional transmission electron microscopy. It was revealed that both the PTN film and its interface with the underlying Pt layer were quite sensitive to variations in the deposition temperature. The considerable change in surface morphology of PTN thin films with an enhanced deposition temperature is discussed in relation to the surface hillocks formed on the Pt layer by aggregation of the out-diffused Pt atoms during MOCVD.