Millimeter-Thick Single-Walled Carbon Nanotube Forests: Hidden Role of Catalyst Support

A parametric study of so-called "super growth" of single-walled carbon nanotubes(SWNTs) was done by using combinatorial libraries of iron/aluminum oxide catalysts. Millimeter-thick forests of nanotubes grew within 10 min, and those grown by using catalysts with a thin Fe layer (about 0.5 nm) were SWNTs. Although nanotube forests grew under a wide range of reaction conditions such as gas composition and temperature, the window for SWNT was narrow. Fe catalysts rapidly grew nanotubes only when supported on aluminum oxide. Aluminum oxide, which is a well-known catalyst in hydrocarbon reforming, plays an essential role in enhancing the nanotube growth rates.Comment: 11 pages, 3 figures. Jpn. J. Appl. Phys. (Express Letters) in pres

Growth of Continuous Monolayer Graphene with Millimeter-sized Domains Using Industrially Safe Conditions.

We demonstrate the growth of continuous monolayer graphene films with millimeter-sized domains on Cu foils under intrinsically safe, atmospheric pressure growth conditions, suitable for application in roll-to-roll reactors. Previous attempts to grow large domains in graphene have been limited to isolated graphene single crystals rather than as part of an industrially useable continuous film. With both appropriate pre-treatment of the Cu and optimization of the CH4 supply, we show that it is possible to grow continuous films of monolayer graphene with millimeter scale domains within 80 min by chemical vapour deposition. The films are grown under industrially safe conditions, i.e., the flammable gases (H2 and CH4) are diluted to well below their lower explosive limit. The high quality, spatial uniformity, and low density of domain boundaries are demonstrated by charge carrier mobility measurements, scanning electron microscope, electron diffraction study, and Raman mapping. The hole mobility reaches as high as ~5,7002 m(2) V(-1) s(-1) in ambient conditions. The growth process of such high-quality graphene with a low H2 concentration and short growth times widens the possibility of industrial mass production

Pyrene-Modified Cyclic Peptides Detect Cu2+ Ions by Fluorescence in Water

The detection of metal ions is an option for maintaining water quality and diagnosing metal ion-related diseases. In this study, we successfully detected metal ions using fluorescent peptides in water. First, we prepared seven linear (L1-L7) and seven cyclic (C1-C7) peptides containing two pyrenyl (Pyr) units and assessed the response to various metal ions by fluorescence. The results indicated that C1, which contains a hexameric cyclic peptide moiety consisting of Pyr and Gly units, did not show a fluorescent response to metal ions, while the linear L1 corresponding to C1 showed a response to Cu2+, but its selectivity was found to be poor through a competition assay for each metal ion. We then assessed C2-C7 and L2-L7, in which Gly was replaced by His units at various positions in the same manner. The results showed that C2-C7 responded to Cu2+ in a manner dependent on the His position. Additionally, superior selectivity was observed in C7 through a competition assay. These results demonstrate that the structural restriction of peptides and the sequence affect the selective detection of Cu2+ and reveal that peptides with an appropriate structure can accomplish the fluorescent detection of Cu2+ specifically

Growth of high quality, high density single-walled carbon nanotube forests on copper foils

We demonstrate the growth of high quality single-walled carbon nanotube (SWCNT) forests on commercial Cu foils by cold-wall chemical vapor deposition. Time-of-flight secondary ion mass spectrometry was employed to study the effect of annealing on the catalyst evolution with or without an AlOₓ barrier layer. X-ray photoelectron spectroscopy was used to investigate the chemical states of the catalyst and the barrier layer. SWCNT forests can be reproducibly grown on Cu foils sputter-coated with Al and Fe layers as thin as 6 nm and 0.4 nm, respectively. Al transforms into AlOₓ on exposure to air and during annealing. Most importantly, such a thin AlOₓ barrier layer ensures not only the growth of SWCNTs but also an Ohmic contact between the as grown SWCNTs and the Cu base as measured by a two-point probe station. The as-grown SWCNTs exhibit a bimodal distribution of diameters ranging from 0.6 to 4.5 nm, with two peaks centered at 0.8 nn and 2.6 nm, respectively.This work supported by Honda Research Institute USA Inc. Sugime H. acknowledges a research fellowship from the Japanese Society for the Promotion of Science (JSPS).This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.carbon.2015.11.04

Developmental Link between Sex and Nutrition; \u3ci\u3edoublesex\u3c/i\u3e Regulates Sex-Specific Mandible Growth via Juvenile Hormone Signaling in Stag Beetles

Sexual dimorphisms in trait expression are widespread among animals and are especially pronounced in ornaments and weapons of sexual selection, which can attain exaggerated sizes. Expression of exaggerated traits is usually male-specific and nutrition sensitive. Consequently, the developmental mechanisms generating sexually dimorphic growth and nutritiondependent phenotypic plasticity are each likely to regulate the expression of extreme structures. Yet we know little about how either of these mechanisms work, much less how they might interact with each other. We investigated the developmental mechanisms of sex-specific mandible growth in the stag beetle Cyclommatus metallifer, focusing on doublesex gene function and its interaction with juvenile hormone (JH) signaling. doublesex genes encode transcription factors that orchestrate male and female specific trait development, and JH acts as a mediator between nutrition and mandible growth. We found that the Cmdsx gene regulates sex differentiation in the stag beetle. Knockdown of Cmdsx by RNA-interference in both males and females produced intersex phenotypes, indicating a role for Cmdsx in sex-specific trait growth. By combining knockdown of Cmdsx with JH treatment, we showed that female-specific splice variants of Cmdsx contribute to the insensitivity of female mandibles to JH: knockdown of Cmdsx reversed this pattern, so that mandibles in knockdown females were stimulated to grow by JH treatment. In contrast, mandibles in knockdown males retained some sensitivity to JH, though mandibles in these individuals did not attain the full sizes of wild type males. We suggest that moderate JH sensitivity of mandibular cells may be the default developmental state for both sexes, with sex-specific Dsx protein decreasing sensitivity in females, and increasing it in males. This study is the first to demonstrate a causal link between the sex determination and JH signaling pathways, which clearly interact to determine the developmental fates and final sizes of nutrition-dependent secondary-sexual characters

Stable, efficient p-type doping of graphene by nitric acid

We systematically dope monolayer graphene with different concentrations of nitric acid over a range of temperatures, and analyze the variation of sheet resistance under vacuum annealing up to 300 °C.</p

Growth of high-density carbon nanotube forests on conductive TiSiN supports

This is the accepted manuscript. The final version is available at http://scitation.aip.org/content/aip/journal/apl/106/8/10.1063/1.4913762.We grow vertically aligned carbon nanotube forests on refractory conductive films of TiSiN and achieve area densities of (5.1 ± 0.1) × 1012 tubes cm−2 and mass densities of about 0.3 g cm−3. The TiSiN films act as diffusion barriers limiting catalyst diffusion into the bulk of the support, and their low surface energy favours catalyst de-wetting, inducing forests to grow by the root growth mechanism. The nanotube area density is maximised by an additional discontinuous AlOx layer, which inhibits catalyst nanoparticle sintering by lateral surface diffusion. The forests and the TiSiN support show ohmic conduction. These results suggest that TiSiN is the favoured substrate for nanotube forest growth on conductors and liable of finding real applications in microelectronics.The authors acknowledge funding from European project Grafol. J.Y. thanks Sarah Fearn and David McPhail from Imperial College London for use of the SIMS instrument. A.W.R. is supported by EPSRC (Platform Grant Nos. EP/F048009/1 and EP/K032518/1) and Korean Institute for Energy Research. H.S. acknowledges a research fellowship from the Japanese Society for the Promotion of Science

Low-Temperature Growth of Carbon Nanotube Forests Consisting of Tubes with Narrow Inner Spacing Using Co/Al/Mo Catalyst on Conductive Supports.

We grow dense carbon nanotube forests at 450 °C on Cu support using Co/Al/Mo multilayer catalyst. As a partial barrier layer for the diffusion of Co into Mo, we apply very thin Al layer with the nominal thickness of 0.50 nm between Co and Mo. This Al layer plays an important role in the growth of dense CNT forests, partially preventing the Co-Mo interaction. The forests have an average height of ∼300 nm and a mass density of 1.2 g cm(-3) with tubes exhibiting extremely narrow inner spacing. An ohmic behavior is confirmed between the forest and Cu support with the lowest resistance of ∼8 kΩ. The forest shows a high thermal effusivity of 1840 J s(-0.5) m(-2) K(-1), and a thermal conductivity of 4.0 J s(-1) m(-1) K(-1), suggesting that these forests are useful for heat dissipation devices.This work has been funded by the European projects Technotubes and Grafol. H.S. acknowledges a research fellowship from the Japanese Society for the Promotion of Science (JSPS).This is the accepted manuscript. The final version is available at http://pubs.acs.org/doi/abs/10.1021/acsami.5b04846