Shigeo Maruyama | The University of Tokyo (original) (raw)

Papers by Shigeo Maruyama

Materials Express, Sep 1, 2012

We investigated the thermal and electrical conductivity of water seeded with single-walled carbon... more We investigated the thermal and electrical conductivity of water seeded with single-walled carbon nanotubes (SWCNT) synthesized using the alcohol catalytic chemical vapour deposition method. Sodium deoxycholate was used as the surfactant to prepare stable nanofluids, which we then thoroughly characterized by microscopic and spectroscopic methods. Electrical conductivity measurements showed power law dependence with respect to SWCNT loading, while the thermal conductivity increase showed a linear dependence on loading. The effective thermal conductivity of the nanofluid was also found to increase with increasing temperature. Viscosity of the nanofluids showed a threefold increase compared to the thermal conductivity increase, which may play a crucial role in utilizing this fluid for practical applications. We compare experimental results with existing analytical models and discuss the critical role of thermal boundary resistance, which limits the improvement in thermal conductivity. Influence of SWCNT aggregation in the increase of effective thermal conductivity is also discussed.

Nanotechnology, 2021

The thermal properties of individual single-walled carbon nanotubes (SWCNTs) have been well docum... more The thermal properties of individual single-walled carbon nanotubes (SWCNTs) have been well documented in the literature following decades of intensive study. However, when SWCNTs form a macroscale assembly, the thermal transport in these complex structures usually not only depends on the properties of the individual tubes, but also is affected and sometimes dominated by inner structural details, e.g. bundles and junctions. In this work, we first performed an experimental measurement of the thermal conductivities of individual SWCNT bundles of different sizes using a suspended micro-thermometer. The results, together with the data that we obtained from a previous work, give a complete experimental understanding of the effect of bundling on the thermal conductivity of SWCNTs. With these quantitative understandings, we propose a phenomenological model to describe the thermal transport in two-dimensional (2D) SWCNT films. The term ‘line density’ is defined to describe the effective the...

Science, 2020

Growing coaxial nanotubes Heterostructures of highly crystalline two-dimensional materials such a... more Growing coaxial nanotubes Heterostructures of highly crystalline two-dimensional materials such as graphene, hexagonal boron nitride (hBN), and molybdenum disulfide (MoS 2 ) are now routinely assembled from films or grown as layers. Xiang et al. report the growth of one-dimensional analogs of these heterostructures on single-walled carbon nanotubes (SWCNTs) through a chemical vapor deposition (see the Perspective by Gogotsi and Yakobson). Single-crystalline monolayers or multilayers of hBN or MoS 2 were grown that maintained the electrical conductivity of the SWCNT. A monolayer of MoS 2 was grown on a trilayer of hBN that encapsulated a SWCNT. Science , this issue p. 537 ; see also p. 506

Diamond and Related Materials, 2019

We report the structure-controlled growth of single-walled carbon nanotubes (SWCNTs) based on alc... more We report the structure-controlled growth of single-walled carbon nanotubes (SWCNTs) based on alcohol chemical vapor deposition with the addition of water vapor. The introduction of water vapor during the growth and pretreatment by water vapor were both systematically examined for the growth of SWCNTs. Raman spectroscopy analysis revealed that the addition of water vapor in both cases induced a decrease in the tube diameters, which indicates the importance of catalyst conditioning for the changes in chirality distribution. The selective growth of SWCNTs having small diameters and large chiral angles was achieved by water vapor pretreatment.

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Nanoscale, Jan 28, 2018

We present a systematic study on the fabrication, characterization and high temperature surface e... more We present a systematic study on the fabrication, characterization and high temperature surface enhanced Raman spectroscopy (SERS) performance of SiOcoated silver nanoparticles (Ag@SiO) on a flat substrate, aiming to obtain a thermally robust SERS substrate for monitoring high temperature reactions. We confirm that a 10-15 nm SiOcoating provides a structure stability up to 900 °C without significantly sacrificing the enhancement factor, while the uncoated particle cannot retain the SERS effect above 500 °C. The finite difference time domain (FDTD) simulation results supported that the SiOcoating almost has no influence on the distribution of the electric field but only physically trapped the most enhanced spot inside the coating layer. On this thermally robust substrate, we confirmed that the SERS of horizontally aligned single walled carbon nanotubes is stable at elevated temperatures, and demonstrate an in situ Raman monitoring of the atmosphere of the annealing process of nanodia...

The proceedings of the JSME annual meeting, 2002

We have demonstrated the high-quality and low-temperature generation of single-walled carbon nano... more We have demonstrated the high-quality and low-temperature generation of single-walled carbon nanotubes (SWNTs) by utilizing gas phase alcohols (methanol and ethanol) over iron and cobalt catalytic metal particles supported with zeolite. SWNTs were observed by SEM and TEM, and analyzed by Raman spectroscopy. Raman spectra revealed that the diameter of SWNTs had the dependency on the generation temperature and gas flow rate. In order to create nanotube devices, we tried to generate SWNTs on a silicon wafer. Very small amount of Fe/Co supported with zeolite particles was located on a silicon wafer, and SWNTs were generated by catalyst chemical vapor deposition (CCVD) technique from ethanol at 900°C. SWNTs on a silicon wafer were generated from the surface of zeolite particles and the bundles of SWNTs were running on the silicon surface.

The Proceedings of the Symposium on Micro-Nano Science and Technology, 2009

Extended Abstracts of the 2010 International Conference on Solid State Devices and Materials, 2010

ASME 2012 Third International Conference on Micro/Nanoscale Heat and Mass Transfer, 2012

Extended Abstracts of the 2011 International Conference on Solid State Devices and Materials, 2011

2010 14th International Heat Transfer Conference, Volume 6, 2010

Controlling the detailed structures of single-walled carbon nanotubes (SWNTs) is imperative for r... more Controlling the detailed structures of single-walled carbon nanotubes (SWNTs) is imperative for realizing many SWNT applications, and understanding the SWNT growth mechanism is important to improve the growth techniques. In the present study, we performed SWNT growth by a catalytic chemical vapor deposition (CVD) method in wide temperature and pressure ranges, using a high-vacuum CVD chamber. We focused on low CVD gas pressure and low temperature conditions and investigated the SWNT growth mechanism. SWNTs were synthesized by using ethanol gas as the carbon source. As the catalyst, Co and Mo metal nano-particles deposited onto silicon substrates were used. SWNTs were grown via the reaction between ethanol gas and the catalytic metal nano-particles at high temperature. The ethanol gas pressure ranged from 10−3 Pa to 102 Pa, and the CVD temperature ranged from 400 to 900 °C. The yield of SWNTs was assumed to be proportional to the G-band intensity, which was measured by Raman scatteri...

Physical Review B, 2011

Gate-voltage effects on photoluminescence spectra of suspended single-walled carbon nanotubes are... more Gate-voltage effects on photoluminescence spectra of suspended single-walled carbon nanotubes are investigated. Photoluminescence microscopy and excitation spectroscopy are used to identify individual nanotubes and to determine their chiralities. Under an application of gate voltage, we observe slight blueshifts in the emission energy and strong quenching of photoluminescence. The blueshifts are similar for different chiralities investigated, suggesting extrinsic mechanisms. In addition, we find that the photoluminescence intensity quenches exponentially with gate voltage.

Physical Review B, 2005

We present experimental evidence of drastic changes in low-frequency Raman scattering spectra dep... more We present experimental evidence of drastic changes in low-frequency Raman scattering spectra depending on the polarization of the incident laser with respect to the single-walled carbon nanotube ͑SWNT͒ axis. Employing recently developed vertically aligned SWNT films, which have a high density ͑1.0ϫ 10 17 m −2 ͒ and a thickness of 5 m, enabled us to obtain sufficient Raman scattering intensity from the film cross section where bundles of SWNTs are aligned along the same direction, in addition to from the top surface of the film. The measured peaks of the radial breathing mode ͑RBM͒ by 1.96, 2.41, and 2.54 eV incident lasers are clearly distinguished into 2 groups. One group of peaks is dominant for perpendicular polarization while the other group of peaks is dominant in the case of light polarized parallel to the SWNT axis. The selective vanishing of the perpendicular peaks by adsorption of molecules to the SWNTs along with the resultant change in optical absorption spectrum evidences that the parallel and perpendicular peaks originate from ⌬ = 0 and ⌬ = ±1 excitations of electrons, respectively. The grouping behavior of RBM peaks also causes the drastic spectral variation caused by a change in incident laser power. The unambiguous classification of each RBM peak's nature presented in this study will allow sounder characterization of SWNTs by the resonant Raman scattering analysis.

Nano Research, 2011

We present a systematic study of the effects of surfactants in the separation of single-walled ca... more We present a systematic study of the effects of surfactants in the separation of single-walled carbon nanotubes (SWNTs) by density gradient ultracentrifugation (DGU). Through analysis of the buoyant densities, layer positions, and optical absorbance spectra of SWNT separations using the bile salt sodium deoxycholate (DOC) and the anionic salt sodium dodecyl sulfate (SDS), we clarify the roles and interactions of these two surfactants in yielding different DGU outcomes. The separation mechanism described here can also help in designing new DGU experiments by qualitatively predicting outcomes of different starting recipes, improving the efficacy of DGU and simplifying post-DGU fractionation.

Japanese Journal of Applied Physics, 2011

In this study, we investigated carbon feedstock decomposition conditions on the synthesis of sing... more In this study, we investigated carbon feedstock decomposition conditions on the synthesis of single-walled carbon nanotubes (SWNTs) by chemical vapour deposition. We simulated gas-phase thermal decomposition of ethanol and dimethyl ether (DME) at typical SWNT growth conditions using the chemical kinetic model, and confirmed the reaction trends and primary products using Fourier transform infrared (FT-IR) spectroscopy. Molar fractions were correlated against residence time in the reactor by adjusting the volumetric gas flow rate, and concentration profiles of reaction species were compared to the predicted decomposition mechanism. Signature peak intensities indicated concentrations of both ethanol and DME.

Chemical Physics Letters, 2006

Fe, Co, and Ni are catalytically effective for growing single-walled carbon nanotubes (SWNTs). On... more Fe, Co, and Ni are catalytically effective for growing single-walled carbon nanotubes (SWNTs). On substrates, however, Ni tends to yield only multi-walled carbon nanotubes. Because enhanced surface diffusion at the elevated growth temperature required for deposition might cause coarsening of Ni catalyst nanoparticles, adjusting the nominal Ni thickness should be crucial for controlling the particle size. Using our previously developed combinatorial method, we prepared a thickness profile of Ni on a quartz glass (SiO 2) substrate and found that Ni nanoparticles catalyzed the growth of SWNTs by chemical vapor deposition only when nominal thickness of Ni was in the monolayer range.

Applied Physics Letters, 2012

We fabricated polymer-laminated, transparent, all-carbon-nanotube field-effect transistors (CNT-F... more We fabricated polymer-laminated, transparent, all-carbon-nanotube field-effect transistors (CNT-FETs), making use of the flexible yet robust nature of single-walled carbon nanotubes (SWNTs). All components of the FET (active channel, electrodes, dielectric layer, and substrate) consist of carbon-based materials. The use of a plastic substrate that is considerably thinner than those used in other flexible CNT-FETs allowed our devices to be highly deformable without degradation of electrical properties. Using this approach, flexible, transparent CNT-FET devices able to withstand a 1 mm bending radius were realized.

Applied Physics Letters, 2011

Isotope-induced scattering of optical phonons in individual single-walled carbon nanotubes (SWNTs... more Isotope-induced scattering of optical phonons in individual single-walled carbon nanotubes (SWNTs) was investigated by resonance Raman scattering measurements of more than 600 suspended, isotope-mixed SWNTs. The G+ and G− features in the SWNT G-band exhibit broadening of up to 80% and 25%, respectively, indicating a reduced lifetime of the corresponding longitudinal and transverse optical (LO and TO) phonons. We propose that this reduced lifetime is due to a combination of enhanced phonon scattering by isotopic inhomogeneity and overbending in the LO phonon branch, both of which increase the scattering rate.