Shigeo Maruyama - Profile on Academia.edu (original) (raw)

Papers by Shigeo Maruyama

Japanese Journal of Applied Physics, Mar 1, 2004

A newly developed technique of synthesizing single-walled carbon nanotubes (SWNTs) directly on th... more A newly developed technique of synthesizing single-walled carbon nanotubes (SWNTs) directly on the surface of Si and quartz substrates is introduced in this report. This technique adopted a liquid-based dip-coating method to mount a very small amount of catalyst metals on the surface of substrates using Mo/Co bimetallic acetate solution. The merits of this approach lie in its easy, costless, and geometry-flexible nature compared with conventional sputtering and deposition approaches. We used the alcohol catalytic chemical vapor deposition (ACCVD) method that can produce relatively high-quality SWNTs even at low temperatures down to 600°C. This low-temperature process contributes to the prevention of the agglomeration of catalytic metals on the surface and chemical reaction between catalytic metal and silicon, which helps us to eliminate any kind of intermediating support materials. Thereby synthesized SWNTs on Si and quartz substrates under various CVD conditions are characterized by means of SEM, TEM, Raman scattering, and optical absorbance measurements. The underlying reasons our experimental procedure and choice of catalyst worked for the synthesis of SWNTs are discussed through comparative studies. At the end of this report, some possible applications of this technique are stated.

Single-walled carbon nanotubes (SWNTs) with outstanding electronic, optical, mechanical and therm... more Single-walled carbon nanotubes (SWNTs) with outstanding electronic, optical, mechanical and thermal properties are expected to be the most promising materials for next-generation energy as well as optical and electronic devices. However, the structure-controlled assembling of SWNTs to macroscale for various devices is still challenging. This study focused on the SWNT assemblies for improving the performance of SWNT-Si heterojunction solar cells. A water vapor breath figure method to build up SWNTs into a self-assembled microhoneycomb network for the applications of solar cells has been developed. The micro-honeycomb network consists of vertical aggregated SWNT walls and a buckypaper bottom (quasi two-dimensional random network). The pristine micro-honeycomb structured SWNT-Si heterojunction solar cell shows a record-high fill factor of 72% as well as a stable power conversion efficiency (PCE) of 6.04%. The PCE increased to 10.02% in the dry state after the dilute nitric acid treatment. For comparison, the state-of-the-art randomly oriented SWNT films with high transparency and with low sheet resistance were also used for fabricating solar cells. The PCE and fill factor of the randomly oriented SWNT-Si solar cell are 10.12% and 61%, respectively. In addition, the relationship between the equivalent series resistance and the fill factor was investigated through the diode equation modeling. This study demonstrates that the micro-honeycomb structure formed by the condensation and evaporation of the water vapor is beneficial for improving the performance of solar cell, especially in terms of the fill factor.

Bulletin of the American Physical Society, Mar 2, 2015

Journal of Physical Chemistry C, Mar 14, 2012

We used both R-cut and R-face crystal quartz substrates for the growth of horizontally aligned si... more We used both R-cut and R-face crystal quartz substrates for the growth of horizontally aligned singlewalled carbon nanotubes (SWNTs). The R-plane (10-11) is one of the low-index crystallographic planes of crystal quartz. The surface cut from a synthetic quartz block parallel to the R-plane was used as R-cut substrates, and the exposed R-plane was used as R-face substrates. We elucidated that the atomic structure of the R-plane causes the alignment of the SWNTs. While a step-and-terrace structure clearly appeared on R-face substrates, SWNTs were aligned on the terraced area of the R-plane, regardless of the direction of the step edges. Comparison between R-face and ST-cut substrates suggests that the ST-cut surface can be considered as a collection of tiny r-plane (01-11) domains, which are very similar to the R-plane (10-11).

Chemical Physics Letters, Jun 1, 2003

High purity single-walled carbon nanotubes (SWNTs) were synthesized from ethanol by catalytic CVD... more High purity single-walled carbon nanotubes (SWNTs) were synthesized from ethanol by catalytic CVD method. The yield of SWNTs was determined based on TGA complemented by Raman and TEM analyses. The effects of CVD reaction time and pre-reduction of catalytic metal on the yield and quality of synthesized SWNTs were investigated. The SWNT yield of more than 40 % was achieved over the weight of zeolite support powder with Fe/Co catalyst, which corresponded to more than 800 % yield over the weight of the catalytic metal, within the CVD reaction time of 120 minutes assuring as-grown high quality.

Chemical Physics Letters, Aug 1, 2003

A new technique of synthesizing high-quality single-walled carbon nanotubes (SWNTs) directly on t... more A new technique of synthesizing high-quality single-walled carbon nanotubes (SWNTs) directly on the surface of silicon and quartz substrates has been developed by means of the low-temperature catalytic CVD method using ethanol. The proposed method does not employ conventional deposition/sputtering for the mounting of catalytic metals on the substrates, but it adopts an easy and costless liquid-based dip-coat approach without need of support/underlayer materials that were often used in previous studies. The substrate surface is blackened with a uniform layer of SWNTs after the CVD at an optimum condition. The optical absorption of 'as-grown' SWNTs has first been measured using thereby prepared SWNT-synthesized quartz substrate.

Physical Review Letters, Jun 15, 2010

Direct measurements of the diffusion length of excitons in air-suspended single-walled carbon nan... more Direct measurements of the diffusion length of excitons in air-suspended single-walled carbon nanotubes are reported. Photoluminescence microscopy is used to identify individual nanotubes and to determine their lengths and chiral indices. Exciton diffusion length is obtained by comparing the dependence of photoluminescence intensity on the nanotube length to numerical solutions of diffusion equations. We find that the diffusion length in these clean, as-grown nanotubes is significantly longer than those reported for micelle-encapsulated nanotubes.

Chemical Physics Letters, Jul 1, 2003

Single-walled carbon nanotubes with narrow diameter-distributions were synthesized by the catalyt... more Single-walled carbon nanotubes with narrow diameter-distributions were synthesized by the catalytic CVD technique using fullerene, C 60 or C 70 , as the carbon source. Fe/Co bimetal particles supported with zeolite powder were exposed to fullerene vapor in a heated quartz tube furnace. With a precise control of fullerene vapor pressure, macroscopic amounts of SWNTs with relatively high quality were generated. The diameter distributions of SWNTs, estimated by an analysis of resonance Raman scattering using excitation wavelengths of 633, 514.5 and 488 nm, ranged between 0.8 to 1.1 nm. The narrowness of this distribution is ascribed to the formation of nanotube caps due to fullerene collisions.

Thermal science and engineering, Jul 1, 2005

ACS Nano, Apr 21, 2021

Single-and multi-walled molybdenum disulfide (MoS2) nanotubes have been coaxially grown on small ... more Single-and multi-walled molybdenum disulfide (MoS2) nanotubes have been coaxially grown on small diameter boron nitride nanotubes (BNNTs) which were synthesized from heteronanotubes by removing single-walled carbon nanotubes (SWCNTs), and systematically investigated by optical spectroscopy. The strong photoluminescence (PL) from single-walled MoS2 nanotubes supported by core BNNTs is observed in this work, which evidences a direct band gap structure for single-walled MoS2 nanotubes with around 6 -7 nm in diameter. The observation is consistent with our DFT results that the single-walled MoS2 nanotube changes from an indirect-gap to a direct-gap semiconductor when the diameter of a nanotube is more than around 5 nm. On the other hand, when there are SWCNTs inside the heteronanotubes of BNNTs and MoS2 nanotubes, the PL signal is considerably quenched. The charge transfer and energy transfer between SWCNTs and single-walled MoS2 nanotubes were examined through characterizations by PL, XPS, and Raman spectroscopy. Unlike the single-walled MoS2 nanotubes, multi-walled MoS2 nanotubes do not emit light. Single-and multi-walled MoS2 nanotubes exhibit different Raman features in both resonant and non-resonant Raman spectra. The method of assembling heteronanotubes using BNNTs as templates provides an efficient approach for exploring the electronic and optical properties of other transition metal dichalcogenide nanotubes.

ACS Nano, Mar 1, 2021

The synthesis of one-dimensional van der Waals heterostructures was realized recently, which open... more The synthesis of one-dimensional van der Waals heterostructures was realized recently, which opens up new possibilities for prospective applications in electronics and optoelectronics. The even reduced dimension will enable novel properties and further miniaturization beyond the capabilities of its two-dimensional counterparts have revealed. The natural doping results in p-type electrical characteristics for semiconducting singlewalled carbon nanotubes, while n-type for molybdenum disulfide with conventional noble metal contacts. Therefore, we demonstrate here a one-dimensional heterostructure nanotube of 11-nm-wide, with the coaxial assembly of semiconducting single-walled carbon nanotube, insulating boron nitride nanotube, and semiconducting molybdenum disulfide nanotube which induces a radial semiconductor-insulator-semiconductor heterojunction. When SWCNT BNNT MoS 2 NT -2 0 2 0 5 [110 -7 ] + -Forward bias p-type SWCNT BNNT n-type MoS 2 NT Voltage (V) Current (μA) Diode ON Diode OFF 0.4 0.2 0.6 0.8 0 opposite potential polarity was applied on semiconducting single-walled carbon nanotube and molybdenum disulfide nanotube, respectively, the rectifying effect was materialized. KEYWORDS single-walled carbon nanotubes, one-dimensional heterostructure, heterojunction diode, boron nitride nanotubes, molybdenum disulfide, van der Waals

ACS Nano, Mar 22, 2022

Single-walled carbon nanotubes have been a candidate for outperforming silicon in ultrascaled tra... more Single-walled carbon nanotubes have been a candidate for outperforming silicon in ultrascaled transistors, but the realization of nanotube-based integrated circuits requires dense arrays of purely semiconducting species. Control over kinetics and thermodynamics in tube-catalyst systems plays a key role for direct growth of such nanotube arrays, and further progress requires the comprehensive understanding of seemingly contradictory reports on the growth kinetics. Here, we propose a universal kinetic model and provide its quantitative verification by ethanol-based isotope labeling experiments. While the removal of carbon from catalysts dominates the growth kinetics under a low supply of precursors, our kinetic model and experiments demonstrate that chirality-dependent growth rates emerge when sufficient amounts of carbon and etching agents are co-supplied. As the model can be extended to create kinetic maps as a function of gas compositions, our findings resolve discrepancies in literature and offer rational strategies for chirality selective growth for practical applications.

Scientific Reports, 2021

Second sound and heat diffusion in single-walled carbon nanotubes (SWCNT) are well-known phenomen... more Second sound and heat diffusion in single-walled carbon nanotubes (SWCNT) are well-known phenomena which is related to the high thermal conductivity of this material. In this paper, we have shown that the heat diffusion along the tube axis affects the macroscopic motion of SWCNT and adapting this phenomena to coarse-grained (CG) model can improve the precision of the coarse-grained molecular dynamics (CGMD) exceptionally. The nonlinear macroscopic motion of SWCNT in the free thermal vibration condition in adiabatic environment is demonstrated in the most simplified version of CG modeling as maintaining finite temperature and total energy with suggested dissipation process derived from internal heat diffusion. The internal heat diffusion related to the cross correlated momentum from different potential energy functions is considered, and it can reproduce the nonlinear dynamic nature of SWCNTs without external thermostatting in CG model. Memory effect and thermostat with random noise ...

The nonlinear macroscopic motion of single walled carbon nanotubes (SWCNT) is depicted precisely ... more The nonlinear macroscopic motion of single walled carbon nanotubes (SWCNT) is depicted precisely using simple beads system. The motion is in the free thermal vibration condition so that it is supposed to be in the reversible state as which has been published in 2015 [Koh et al., PRB 92 (2015) 024306]. The nonlinear dynamic characteristics from the various scale of simple beads systems are examined with expanding its time step and node length simultaneously. The internal heat diffusion related to the cross correlated momentum from different potential energy functions is considered, and it stabilizes the motion of coarse-grained molecular dynamics (CGMD) simulation with a good one-side compatibility from the MD simulation. We demonstrate that even the most simplified version of molecular modeling can maintain finite temperature with well-defined random potential energy function and it can reproduce the nonlinear dynamic nature of SWCNTs. Good precision of this CG modeling indicates th...

ACS Nano, 2019

In order to achieve the chirality-specific growth of single-walled carbon nanotubes (SWCNTs), it ... more In order to achieve the chirality-specific growth of single-walled carbon nanotubes (SWCNTs), it is crucial to understand the growth mechanism. Even though many molecular dynamics (MD) simulations have been employed to analyze the SWCNT growth mechanism, it has been difficult to discuss the chirality determining kinetics because of the defects remaining on the SWCNTs grown in simulations. In this study, we demonstrate MD simulations of defect-free SWCNTs, i.e. chirality definable SWCNTs, under the optimized carbon supply rate and temperature. The chiralities of the SWCNTs were assigned as (14,1), (15,2), and (9,0), indicating the preference of near-zigzag and pure-zigzag SWCNTs. The SWCNTs contained at least one complete row of defect-free walls consisting of only hexagons. The near-zigzag SWCNTs grew via a kink-running process, in which bond formation between a carbon atom at a kink and a neighboring carbon chain led formation of a hexagon with a new kink at the SWCNT edge. Defects including pentagons and heptagons were sometimes formed but effectively healed into hexagons on metal surface. The purezigzag SWCNTs grew by the kink-running and the hexagon nucleation processes. In addition, chirality change events along SWCNT with incorporation of pentagon-heptagon pair defects were observed in the MD simulations. Here, pentagons and heptagons were frequently observed as adjacent pairs, resulting in (n,m) chirality changes by (±1,0), (0,±1), (1,-1), or (-1,1).

Journal of Nanoscience and Nanotechnology, 2015

We proposed a water vapor treatment to build up SWNTs to a self-assembled microhoneycomb network ... more We proposed a water vapor treatment to build up SWNTs to a self-assembled microhoneycomb network for the application of solar cells . The micro-honeycomb network consists of vertically aggregated SWNT walls and a buckypaper bottom. This hierarchical structure is very efficient to collect holes from the interface of Si. The heterojunction solar cell was fabricated by dry depositing the SWNT film to the 3 mm by 3 mm n-type silicon substrate. The pristine SWNT-Si heterojunction solar cell shows a record-high fill factor of 72 % as well as a power conversion efficiency (PCE) of 6 % without tuning the diameter or height of original vertically aligned SWNTs. A recent record of highest PCE was about 8.9 % without doping. The PCE remains stable for months in ambient condition. A PCE exceeding 10 % is achieved in the dry state after dilute nitric acid treatment. Coating with PMMA also is found to be efficient to increase the PCE up to 11%. On the other hand, heterojunction solar cells using highly transparent-conductive SWNT films from controlled bundle-diameter and long bundle length are also promising . Here, SWNTs were synthesized by the thermal decomposition of ferrocene vapor in a carbon monoxide atmosphere, with the average diameter of approx. 2 nm. Our preliminary test result shows the highest PCE of 11 % among such CNT-Si design without chemical doping. These solar cells are stable after 10 months . Finally, millimeter scale single crystal graphene is probed to be a very useful hole collector in the same configuration as SWNT film. The preliminary test of 5 mm graphene with PMMA exhibits more than 11% PCE. Growth control of graphene by alcohol CVD [3] is also discussed.

Microelectronics Journal, 2008

We report that entirely end-bonded multiwalled carbon nanotubes (MWNTs) can exhibit superconducti... more We report that entirely end-bonded multiwalled carbon nanotubes (MWNTs) can exhibit superconductivity with a transition temperature (T c ) as high as 12 K, which is approximately 30 times greater than T c reported for ropes of single-walled nanotubes. We find that the emergence of this superconductivity is very sensitive to the junction structures of the Au electrode/MWNTs. This reveals that only MWNTs with optimal numbers of electrically activated shells, which are realized by end bonding, can allow superconductivity due to intershell effects.

Microelectronic Engineering, 2011

We propose a method of patterning vertically aligned single-walled carbon nanotubes (VA-SWNTs) wi... more We propose a method of patterning vertically aligned single-walled carbon nanotubes (VA-SWNTs) with the aim of increasing the emission current. We patterned regular arrays of VA-SWNTs by pressing a microstructured Si mold with 2.5 Â 2.5 Â 2.5 lm 3 cubic holes and a pitch of 5 lm on a VA-SWNT film. We observed that the substrate exhibited field-emission properties, and we determined the effectiveness of the substrate as an electron field-emission array.