杉目　恒志 （スギメ　ヒサシ）

コミュニケーション情報 byコメンテータガイド

• コメント

  化学工学の観点からナノ材料の合成と応用技術の開発を行っています。

研究者情報

学位

• 博士(工学)（2010年03月 東京大学）

ホームページURL

https://orcid.org/0000-0003-0247-3445

科研費研究者番号

• 60716398

ORCID ID

•  https://orcid.org/0000-0003-0247-3445

Researcher ID

• G-5678-2015

J-Global ID

• 201601019050275228

研究キーワード

• カーボンナノチューブ、マキシン、グラフェン、ナノカーボン、バイオセンサ、電気化学   

現在の研究分野（キーワード）

化学工学の観点からナノ材料の合成と応用技術の開発を行っています。

研究分野

• ナノテク・材料 / ナノ材料科学 / 化学気相成長，スパッタ，電気化学
• ナノテク・材料 / ナノ材料科学 / マキシン
• ナノテク・材料 / ナノバイオサイエンス / カーボンナノチューブ、グラフェン、バイオセンサー
• ものづくり技術（機械・電気電子・化学工学） / 反応工学、プロセスシステム工学

所属学協会

• 電気化学会   応用物理学会   フラーレン・ナノチューブ・グラフェン学会   化学工学会   

研究活動情報

論文

• Safe and damage-less dry-purification of carbon nanotubes using FeCl3 vapor

  Hideaki Tanaka; Takuma Goto; Kohki Hamada; Kei Ohashi; Toshio Osawa; Hisashi Sugime; Suguru Noda

  Carbon 212 118171 - 118171 2023年05月
• Near Infrared Light‐to‐Heat Conversion for Liquid‐Phase Oxidation Reactions by Antimony‐Doped Tin Oxide Nanocrystals

  Hiroaki Tada; Shin‐ichi Naya; Hisashi Sugime

  ChemPhysChem 2023年01月
• Formation mechanism of radial mesocrystals consisting of ZnO nanowires

  Yaozong Yan; Hiroaki Tada; Hisashi Sugime; Tetsuro Soejima

  CrystEngComm 2023年 

  Radial semiconductor mesocrystals (rad-SEM MCs), the so-called sea urchin-like microspheres, combining both the properties of nanoparticles and microparticles have widely attracted much interest. Elucidation of the detailed formation mechanism is...
• Catalyst Dynamics in the Growth of High-Density CNT Forests; Fine Control of the Mass Density of Forest by Colloidal Catalyst Nanoparticles

  Kento Tabata; Yuga Kono; Ryosuke Goto; Yuya Abe; Takayuki Nakano; Hisashi Sugime; Yoku Inoue

  The Journal of Physical Chemistry C 2022年12月
• Ag Nanoparticle-Based Aerogel-like Films for Interfacial Thermal Management

  Sebun Munakata; Shunji Kobayashi; Hisashi Sugime; Shota Konishi; Junichiro Shiomi; Suguru Noda

  ACS Applied Nano Materials 5 10 15755 - 15761 2022年10月 

  A Ag aerogel-like film (referred to as aerogel hereafter), used as a thermal interface material with enhanced performance and thermal stability, is reported. An aerogel/foil/aerogel "monocomposite"is created by rapidly forming and depositing Ag nanoparticles on both faces of a Ag foil by the gas-evaporation and particle-deposition method in a few minutes. The monocomposite, having an aerogel of a low packing ratio (<10%) with a clean surface, exhibits low thermal resistance (18 mm2 K W-1) when sandwiched with Cu rods. The monocomposite exhibits excellent thermal stability and significantly reduced thermal resistance (3.0 mm2 K W-1) at 246 °C, keeping its low thermal resistance (2.8 mm2 K W-1) after the temperature is decreased to 51 °C; further, the resistance reduces to 2.1 mm2 K W-1 after 10 cycles of heating and cooling (100-200 °C). The Ag monocomposite, having high performance comparable to that of the benchmark In sheet and excellent thermal stability at a temperature higher than the melting point of In, will enable high-power and high-temperature operation of computing and power devices.
• Photothermal Oxidation of Cinnamyl Alcohol with Hydrogen Peroxide Catalyzed by Gold Nanoparticle/Antimony-Doped Tin Oxide Nanocrystals

  Haruki Inoue; Shin ichi Naya; Atsunobu Akita; Hisashi Sugime; Hiroaki Tada

  Chemistry - A European Journal 28 46 2022年08月 

  Gold nanoparticles with different mean sizes were formed on antimony-doped tin oxide nanocrystals by the temperature-varied deposition-precipitation method (Au/ATO NCs). Au/ATO NCs possess strong absorption in the near-infrared region due to Drude excitation in addition to the localized surface plasmon resonance (LSPR) of AuNPs around 530 nm. Au/ATO NCs show thermally activated catalytic activity for the oxidation of cinnamyl alcohol to cinnamaldehyde by hydrogen peroxide. The catalytic activity increases with a decrease in the mean Au particle size (dAu) at 5.3 nm≤dAu≤8.2 nm. Light irradiation (λex >660 nm, ∼0.5 sun) of Au/ATO NCs increases the rate of reaction by more than twice with ∼95 % selectivity. Kinetic analyses indicated that the striking enhancement of the reaction stems from the rise in the temperature near the catalyst surface of ∼30 K due to the photothermal effect of the ATO NCs.
• Noble Metal-Free Inorganic Photocatalyst Consisting of Antimony-Doped Tin Oxide Nanorod and Titanium oxide for Two-Electron Oxygen Reduction Reaction

  Haruya Suzuki; Junpei Yamauchi; Shin ichi Naya; Hisashi Sugime; Hiroaki Tada

  ChemPhysChem 23 15 2022年08月 

  This study reports a noble metal-free robust inorganic photocatalyst for H2O2 synthesis via two-electron oxygen reduction reaction (ORR). Antimony-doped tin oxide nanorods were heteroepitaxially grown from rutile TiO2 seed crystals with an orientation of (001)ATO//(001)TiO2 (ATO−NR//TiO2,//denotes heteroepitaxial junction) by a hydrothermal method. UV-light irradiation of ATO−NR//TiO2 particles stably and continuously produces H2O2 from aerated aqueous solution of ethanol. Electrochemical measurements using rotating electrodes show that Sb-doping into SnO2 greatly enhances the electrocatalytic activity for two-electron ORR. The striking photocatalytic activity of ATO−NR//TiO2 stems from the effective charge separation, electrocatalytic activity for two-electron ORR, low catalytic activity for H2O2 decomposition, and extraordinary robustness.
• Systematic investigation of anode catalysts for liquid ammonia electrolysis

  Natsuho Akagi; Keisuke Hori; Hisashi Sugime; Suguru Noda; Nobuko Hanada

  Journal of Catalysis 406 222 - 230 2022年02月 

  Liquid ammonia is able to release hydrogen via electrolysis with a theoretical voltage of 0.077 V. However, the actual operation voltage is much higher (around 1–2 V) due to the large overpotential of the anodic reaction. We systematically investigated Pt, Ir, Ru, Ni, Co, Fe, Ta, and Ti as the anodic catalyst, and observed a volcano correlation when plotting the current density against the formation enthalpy of metal nitrides per nitrogen ΔfHMN (kJ/mol-N). ΔfHMN reflects the strength of metal-nitrogen bond, and Ru having a moderate ΔfHMN showed the highest catalytic activity. Then, the activity enhancement via microstructure control was examined. The sputtered Pt and Ni films having a columnar structure with a rough surface showed 7- and 13-times higher current density than the Pt and Ni plates, respectively. An anodic current density of 0.45 mA/cm2 was achieved for the sputtered Ni film at an anodic potential as low as 0.3 V vs H2/NH3.
• Fast and stable hydrogen storage in the porous composite of MgH2 with Nb2O5 catalyst and carbon nanotube

  Kosuke Kajiwara; Hisashi Sugime; Suguru Noda; Nobuko Hanada

  Journal of Alloys and Compounds 893 162206 - 162206 2022年02月 

  The MgH2-Nb2O5-carbon nanotube (CNT) composite was fabricated to accommodate the volume change of particles during the hydrogen storage cycles by holding the MgH2-Nb2O5 particles within the sponge-like matrix of the CNT. This allowed for preservation of the composite structure and led to more stable hydrogen sorption properties during 20 cycles, as compared to without CNT. To investigate this effect of CNT on the cyclic stability of MgH2-Nb2O5, CNT and expanded graphite (EG) were added to MgH2-Nb2O5 via ball milling. The MgH2-Nb2O5-CNT powder showed stable cyclic performance, similar to the MgH2-Nb2O5-CNT composite, whereas the MgH2-Nb2O5-EG powder exhibited cyclic degradation similar to MgH2-Nb2O5. From SEM-EDS, it was found that the C/Mg ratio of the surface of the MgH2-Nb2O5-CNT powder was higher than that of the MgH2-Nb2O5-EG powder. Thus, the fibrous CNT on the surface of the MgH2 particles could be responsible for the greater cyclic stability of the MgH2-Nb2O5-CNT composite.
• Switching of Electron Transport Direction from the Long Axis to Short Axis in a Radial SnO2(Head)–Rutile TiO2 Nanorod(Tail) Heteromesocrystal Photocatalyst

  Atsunobu Akita; Ryota Kojima; Hisashi Sugime; Hiroaki Tada

  The Journal of Physical Chemistry Letters 12 48 11717 - 11722 2021年12月 

  Heteroepitaxial growth of rutile TiO2 nanorods from SnO2 seeds yielded radial heteromesocrystals consisting of SnO2(head) and rutile TiO2 nanorod(tail) with the SnO2(head) oriented toward the center (TiO2-NR//SnO2 HEMCs). Iron oxide clusters were formed on the surface by the chemisorption-calcination technique. The FeOx-surface modification gives rise to drastic increases in the photocatalytic activity for aerobic oxidation of 2-naphthol under irradiation of UV and visible light. As a 2D-model for 3D-TiO2-NR//SnO2 HEMC, electrochemical measurements were performed for the rutile TiO2-NR array formed on a fluorine-doped tin oxide (SnO2:F) electrode. The results showed that the FeOx clusters possess electrocatalytic activity for a multielectron oxygen reduction reaction, and the high photocurrent of the electrode is remarkably reduced by the FeOx-surface modification. Consequently, the striking photocatalytic activity of FeOx/TiO2-NR//SnO2 HEMCs was ascribable to the switching of the electron transport direction necessary for the charge separation from the long axis of the TiO2 NR to the short axis.
• Thermocatalytic Activity of Gold Truncated Nanopyramids on Strontium Titanate Nanocube

  Kota Kurokawa; Hisashi Sugime; Shin Ichi Naya; Hiroaki Tada

  Chemistry Letters 50 12 1997 - 2000 2021年12月 

  Gold truncated nanopyramids smaller than 10nm with clean surfaces were formed on SrTiO3 naocubes (Au TNPy//SrTiO3 NCs, // denotes heteroepitaxial junction) by the deposition precipitation method without surface modifier, while the shape of Au nanoparticles (NPs) on irregular shaped SrTiO3 NPs was hemisphere-like (Au HS/SrTiO3 NPs). As a probe reaction, the oxidation of o-phenylenediamine (OPD) to 2,3-diaminophenazine (DAP) by H2O2 was carried out with the catalysts in the dark at 25 °C. Au TNPy//SrTiO3 NCs exhibit significantly higher catalytic activity for the oxidation reaction than Au HS/ SrTiO3 NPs. Kinetic analyses indicated that H2O2 can be more effectively activated to be utilized for the OPD oxidation in the former system than the latter system.
• Why shouldn’t double-layer capacitance (Cdl) be always trusted to justify Faradaic electrocatalytic activity differences?

  Sengeni Anantharaj; Hisashi Sugime; Suguru Noda

  Journal of Electroanalytical Chemistry 903 115842 - 115842 2021年12月 

  Electrocatalytic water splitting activity trend is mainly justified using two activity markers namely the electrochemical surface area measured in terms of double-layer capacitance (Cdl) and the charge transfer resistance (Rct). In general, a better active catalyst always tends to have higher Cdl and lower Rct. The non-Faradaic Cdl has so far been shown to match with the Faradaic catalytic activity trend. Nonetheless, emphasizing its non-Faradaic origin and the fact that all ion adsorption and desorption sites should not necessarily be electrocatalytically active sites, we show here a strong disagreement between non-Faradaic Cdl and Faradaic oxygen evolution reaction (OER) activity trend between stainless steel (SS) and bleached stainless steel (BSS). BSS apparently exhibited higher Cdl due to increased OER inactive iron oxide contents on the surface while significantly losing its OER activity. This study, therefore, questions the credibility of using non-Faradaic Cdl to justify the purely Faradaic electrocatalytic activity trend.
• Numerical simulation of heat supply and hydrogen desorption by hydrogen flow to porous MgH2 sheet

  Keisuke Yoshida; Kosuke Kajiwara; Hisashi Sugime; Suguru Noda; Nobuko Hanada

  Chemical Engineering Journal 421 129648 - 129648 2021年10月 [査読有り]
   

  We propose using hydrogen as a heat transfer medium to supply waste heat from hydrogen-driven devices to hydrogen storage tanks. In our model, MgH is used in the form of porous sheets, set in parallel in the tank, and heat is supplied via hot hydrogen flowed through the interspaces between the porous sheets. Feasibility of the hydrogen desorption reaction in this process was verified numerically. Hydrogen efficiently carried heat to the stack of porous MgH sheets via convective heat transfer and then carried heat into the porous MgH sheets via conductive heat transfer through the pores owing to its high thermal conductivity. We found that the hydrogen desorption is also fast enough to allow the supplied heat to be used efficiently to drive the endothermic hydrogen desorption reaction. It was understood that the thickness of the MgH sheet and hot hydrogen flow speed affected hydrogen desorption. These factors can be evaluated by using the dimensionless number of τ /τ which is the ratio of the space time to the time constant for heat transfer in the MgH sheet. Under τ /τ > 0.01 range, both the reaction and heat transfer are fast enough, the hydrogen desorption is limited by heat supply, and hydrogen desorption amount is proportional to the heat supplied to the reactor. The tank structure and operating conditions can be designed by using the dimensionless number of τ /τ . 2 2 2 2 s h 2 s h s h
• Enhanced CO2-assisted growth of single-wall carbon nanotube arrays using Fe/AlO catalyst annealed without CO2

  Mochen Li; Kotaro Yasui; Hisashi Sugime; Suguru Noda

  Carbon 185 264 - 271 2021年09月 

  Controlling catalyst-particle formation is essential for the growth of single-wall carbon nanotube (SWCNT) arrays with improved alignment, areal mass, and height. We have previously reported the positive effect of CO2 on SWCNT growth via chemical vapor deposition, and in this study, we found its negative effect on catalyst-particle formation during annealing. A Fe (1 nm)/AlOx (15 nm) catalyst that was sputter-deposited on SiO2/Si substrates demonstrated a prolonged lifetime and enabled the growth of SWCNT arrays with better alignment, twice the height, and three times higher areal mass when the catalyst was annealed under 10 vol% H2/Ar without CO2 than with 1 vol% CO2. Detailed analysis indicated that the Fe particles could remain partially oxidized during annealing in H2 with mildly oxidative CO2, resulting in the bulk diffusion of Fe into the AlOx layer. In contrast, Fe is reduced sufficiently in H2 in the absence of CO2, thereby remaining on the AlOx surface and active for SWCNT growth. The findings of this study emphasize the importance of maintaining a highly reductive atmosphere during annealing to achieve active catalyst particles with a higher number density and longer lifetime.
• Fluidized-bed production of 0.3 mm-long single-wall carbon nanotubes at 28% carbon yield with 0.1 mass% catalyst impurities using ethylene and carbon dioxide

  Mochen Li; Soichiro Hachiya; Zhongming Chen; Toshio Osawa; Hisashi Sugime; Suguru Noda

  Carbon 182 23 - 31 2021年09月 [査読有り]
   

  To produce carbon nanotubes (CNTs) practically, a high carbon source concentration and high carbon yield are essential. By feeding moderately active ethylene at 10–20 vol% with mildly oxidative carbon dioxide at 1 vol%, submillimeter-long single-wall CNT (SWCNT) arrays were synthesized via fluidized-bed chemical vapor deposition using an Fe/AlOx catalyst sputtered on ceramic beads. SWCNTs with an average diameter of 2.9 nm, long length (0.3 mm), low catalyst impurity (0.1 mass%), and high specific surface area (1178 m2/g) were obtained at a high carbon yield of 28%. This study thus introduces a route for more efficient and cleaner production of long and pure SWCNTs.
• Carbon nanotube/silicon heterojunction solar cell with an active area of 4 cm2 realized using a multifunctional molybdenum oxide layer

  Xiaoxu Huang; Emina Hara; Hisashi Sugime; Suguru Noda

  Carbon 185 215 - 223 2021年08月 [査読有り]
   

  Carbon nanotube (CNT)/silicon heterojunction solar cells have been extensively studied owing to the ease of junction fabrication. Encouraging power conversion efficiencies (PCEs) have been reported; however, many of them are limited to small cells (<1 cm2). Herein, we report MoOx as a multifunctional layer that enables the size and performance enhancement. A 4 cm2-sized MoOx–CNT/n-Si solar cell with a PCE of 10.0% was realized via simple processes: dispersion–filtration–transfer for the CNT layer, hot-wire oxidation–sublimation deposition for the MoOx layer, mask-deposition for the Ag grid electrodes, and spin-coating for the polymethyl methacrylate anti-reflective layer. The MoOx layer played an essential role as a blocking layer to prevent direct contact and current leakage between Ag and n-Si while allowing the electrical conduction between Ag and CNT. It also served as a p-type dopant for the CNTs, which enhanced the electrical conduction and separation of electron–hole pairs at the heterojunction, and as an enhancer for the anti-reflective effect of the MoOx–CNT layer. Post-thermal annealing of MoOx was found to be crucially important, and the role of MoOx was also evaluated. This combination of a multifunctional MoOx layer with a metal grid electrode provides a facile route for practical CNT/Si heterojunction solar cells.
• Ultra-long carbon nanotube forest via in situ supplements of iron and aluminum vapor sources

  Hisashi Sugime; Toshihiro Sato; Rei Nakagawa; Tatsuhiro Hayashi; Yoku Inoue; Suguru Noda

  Carbon 172 772 - 780 2021年02月 [査読有り]
   

  © 2020 Elsevier Ltd A carbon nanotube forest with a length of 14 cm grew with an average growth rate of 1.5 μm s−1 and a growth lifetime of 26 h. Several key factors to realize this unprecedented long growth such as catalyst conditions, growth conditions in chemical vapor deposition, and reactor system were clarified. It was found that the combination of the catalyst system of iron/gadolinium/aluminum oxide (Fe/Gd/Al2Ox) and the in situ supplements of Fe and Al vapor sources at very low concentration was crucially important. A cold-gas system, where only the substrate is heated while keeping the gas at room temperature, was employed to suppress unnecessary reactions and depositions. The long carbon nanotube forest enabled macroscopic measurements of the tensile and electrical properties of the carbon nanotube wires, and it gave several important insights for industrial applications of the carbon nanotubes in the future.
• Pushing the Limits of Rapid Anodic Growth of CuO/Cu(OH)2 Nanoneedles on Cu for the Methanol Oxidation Reaction: Anodization pH Is the Game Changer

  Sengeni Anantharaj; Hisashi Sugime; Shohei Yamaoka; Suguru Noda

  ACS Applied Energy Materials 4 1 899 - 912 2021年01月 [査読有り]
   

  We recently reported the fastest anodization method (just 80 s) of all for accessing a denser array of Cu(OH)2-CuO nanoneedles on a Cu foil substrate by applying a constant potential of 0.864 V vs a reversible hydrogen electrode in 1.0 M KOH that delivered a better activity for the methanol oxidation reaction (MOR). In this study, we show that the strength of the KOH solution used for anodization alters the size, morphology, surface chemistry, electrochemical accessibility of Cu sites, and the subsequent MOR activity trend. Intriguingly, an increase in KOH solution strength shortens the time of anodization from 80 s (1.0 M KOH) to 20 s with 3.0 M KOH, which in turn drastically reduces to just 6 s with 6.0 M KOH. As of now, this is the shortest time ever achieved for the anodic growth of Cu-OH/O nanoneedles on a Cu substrate. A set of detailed and comparative physical and electrochemical characterizations reveal positive relationships between anodization pH and anodization current, the size of Cu-OH/O nanoneedles grown, rate of growth, electrochemical accessibility of Cu sites, and electrocatalytic MOR activity. Thus, this study provides a universal approach to control the size of Cu-OH/O nanoneedles, electrochemical accessibility of Cu sites, and their subsequent MOR activity.
• High-performance solution-based silicon heterojunction solar cells using carbon nanotube with polymeric acid doping

  Xie, Rongbin; Sugime, Hisashi; Noda, Suguru

  Carbon 175 519 - 524 2021年 [査読有り]
   

  Carbon nanotube (CNT)/n-Si heterojunction solar cells were fabricated based on solution processes. CNT film with high transparency of 90% and low sheet resistance of ∼115 Ω/sq was fabricated from commercially available CNT powder via dispersion-filtration process using poly(p-styrene-sulfonic acid) (PSS) as both dispersant and dopant. Heterojunction was then fabricated by attaching the CNT-PSS film onto an n-Si wafer. The CNT/n-Si solar cell showed an enhanced efficiency of 11.7% with the PSS-doping compared with the device without doping (7.7%). The device showed further improvements in efficiency to 14.1% with an antireflective coating layer of sulfonated polytetrafluoroethylene (Nafion) and stability to 1000 h in ambient air without additional protection. The solution-based strategies using polymeric acids for efficiency and stability enhancement will open new avenues for the low-cost CNT/Si heterojunction solar cells.
• Surface amorphized nickel hydroxy sulphide for efficient hydrogen evolution reaction in alkaline medium

  Anantharaj, Sengeni; Sugime, Hisashi; Noda, Suguru

  Chemical Engineering Journal 408 2021年 [査読有り]
   

  © 2020 Elsevier B.V. Non-oxide/hydroxide hydrogen evolution reaction (HER) catalysts undergo hydroxylation to a significant extent even under reductive condition when exposed to alkali. Actual role of such hydroxylation in alkaline HER electrocatalysis is not previously given any significance. In this study, we report an intriguing finding that nickel sulfide a well-known HER electrocatalyst when subjected to anodic potential cycling covering Ni2+and Ni3+redox couple led to accelerated hydroxylation accompanying surface amorphization. As a result, improved electrochemical surface, better HER kinetics, and better charge transfer were achieved that lowering the HER overpotential by 110 mV at 100 mA cm2. This surface amorphized and hydroxylated nickel sulfide exhibited excellent stability upon both galvanostatic and potentiostatic electrolysis for over 50 h. Besides, it also showed a lower Tafel slope (120 mV dec-1), higher relative ECSA in terms of 2Cdl (3.85 µF cm−2), and higher electrochemical accessibility for Ni sites (3.7 × 1017 cm−2) which further advocate the superiority of our way of improving HER activity of a non-oxide/hydroxide catalyst. Thus, this study open up new avenues for re-examining other non-oxide/hydroxide catalysts in alkaline HER for benefiting the energy and cost-efficient hydrogen generation.
• Performance enhancement of carbon nanotube/silicon solar cell by solution processable MoOx

  Huang, Xiaoxu; Xie, Rongbin; Sugime, Hisashi; Noda, Suguru

  Applied Surface Science 542 2021年 [査読有り]
   

  © 2020 Elsevier B.V. Carbon nanotube/silicon solar cells have increasingly attracted attention owing to their high efficiency and cost-effectiveness. Herein, we demonstrated a significant improvement in the performance of the carbon nanotube/silicon solar cell by applying solution-processable MoOx. The MoOx acts as both an efficient chemical dopant and an anti-reflection coating, resulting in a reduction in the series resistance and an enhancement of the short-circuit current density of the cell. As a result, the power conversion efficiencies increased to 10.0%, which is a 39% increase from the pristine value (7.2%). The device showed considerable stability, maintaining the power conversion efficiency at 80% of its original value for two months in the air without any protective layer. The simple solution process at room-temperature in this study can lower the preparation cost and pave a way for the practical application of carbon nanotube/silicon solar cells.
• Chemical Leaching of Inactive Cr and Subsequent Electrochemical Resurfacing of Catalytically Active Sites in Stainless Steel for High-Rate Alkaline Hydrogen Evolution Reaction

  Sengeni Anantharaj; Hisashi Sugime; Suguru Noda

  ACS Applied Energy Materials 3 12 12596 - 12606 2020年12月 [査読有り]
   

  © 2020 American Chemical Society. In this study, we show a simple two-step surface engineering method that uses chemical oxidation (using KOH and NaClO in 1:2 M ratio)-assisted leaching of metals (Cr, Mn, and Ni) from the surface and an electrochemical potentiostatic activation enabled resurfacing of only catalytically active Ni and Mn of the alloy. Such surface-engineered stainless steel 304 (SS-304-Ox-ECA) foils rich in Ni(OH)2 and multivalent Mn oxides were found to have a coarse texture with uniform nanostructures. As a result of leached Cr, resurfaced catalytically active sites improved roughness with nanotexturing and enhanced the charge-transfer ability. The SS-304-Ox-ECA foil has become a high-performance HER electrocatalyst that delivered 400 mA cm-2 higher current density at -0.8 V versus RHE and demanded 210 mV lower overpotential for a current density of 100 mA cm-2 than pristine SS-304 foils in 1.0 M KOH. A smaller Tafel slope (90 mV dec-1) and a higher double-layer capacitance (2Cdl = 0.784 μF cm-2) further justified that the activity enhancement is also due to the improved HER kinetics and increased electrochemical surface area. This catalytic electrode of high abundance and low cost is a promising candidate for cost-efficient hydrogen production from water.
• Boosting the oxygen evolution activity of copper foam containing trace Ni by intentionally supplementing Fe and forming nanowires in anodization

  Anantharaj, Sengeni; Sugime, Hisashi; Chen, Bozhi; Akagi, Natsuho; Noda, Suguru

  Electrochimica Acta 364 2020年 [査読有り]
   

  © 2020 Elsevier Ltd Oxygen evolution reaction (OER) is the bottleneck for realizing energy-efficient hydrogen production through water electrolysis in both acid and alkali. Alkaline OER electrocatalyzed by Ni and Co hydroxides are well known which showed unexpected enhancement with the addition of Fe. We found that the commercially procured Cu foam containing trace amount of Ni (~1.5 wt.%) upon anodization formed Cu(OH)2–CuO nanowires with conceivable formation of Ni(OH)2 and experienced a notable enhancement in its OER activity. When sufficient amount of Fe was intentionally supplemented during anodization, OER activity of the same was further improved. Specifically, as a combined result of anodization in KOH and in Fe supplemented KOH, overpotential at 50 mA cm−2 was lowered by 153 mV. Such an activation also improved the kinetics of OER by lowering the Tafel slope by 100 mV dec−1. With these, it has been shown here that a moderately active OER catalyst i.e., Cu(OH)2–CuO/Cu formed upon the anodization of Cu foam can be turned into a highly active catalyst just by utilizing the trace Ni that it already contains and intentionally supplementing sufficient amount of Fe.
• Ultrafast Growth of a Cu(OH)2-CuO Nanoneedle Array on Cu Foil for Methanol Oxidation Electrocatalysis

  Anantharaj, S.; Sugime, H.; Noda, S.; Noda, S.

  ACS Applied Materials and Interfaces 12 24 27327 - 27338 2020年 [査読有り]
   

  Copyright © 2020 American Chemical Society. A swift potentiostatic anodization method for growing a 5-7 μm tall nanoneedle array of Cu(OH)2-CuO on Cu foil within 100 s has been developed. This catalytic electrode when screened for methanol oxidation electrocatalysis in 1 M KOH with 0.5 M methanol, delivered a current density as high as 70 ± 10 mA cm-2 at 0.65 V versus Hg/HgO which is superior to the performance of many related catalysts reported earlier. The observed activity enhancement is attributed to the formation of both Cu(OH)2-CuO nanoneedle arrays of high active surface area over the metallic Cu foil. In addition, the Cu(OH)2-CuO/Cu electrode had also exhibited excellent stability upon prolonged potentiostatic electrocatalytic oxidation of methanol while retaining the charge-transfer characteristics. Growth of such highly ordered assembly of Cu(OH)2-CuO nanoneedles within a minute has never been achieved before. When compared to its oxygen evolution reaction activity, the addition of 0.5 M methanol has lowered the overpotential at 10 mA cm-2 by 334 mV, which is significant. This encourages the use of methanol as a sacrificial anolyte for energy-saving production of H2 from water electrolysis.
• Facile catalyst deposition using mist for fluidized-bed production of sub-millimeter-long carbon nanotubes

  Li, M.; Risa, M.; Osawa, T.; Sugime, H.; Noda, S.

  Carbon 167 256 - 263 2020年 [査読有り]
   

  © 2020 Elsevier Ltd We developed a facile mist deposition method that yields nanometer-thick catalyst films on ceramic beads using aqueous solution of metal nitrates as a low cost catalyst precursor through two different strategies: (a) using a monolayer of a mixture of Fe(NO3)3 and Al(NO3)3 (Fe + Al) and (b) using a bilayer of Fe(NO3)3 on top of the mixture of Fe(NO3)3 and Al(NO3)3 (Fe/(Fe + Al)). In the fluidized bed, the catalyst precursor films were converted into Fe nanoparticles on an AlOx layer by thermal annealing and CNTs were synthesized by chemical vapor deposition. The yield and specific surface area of the resulting CNTs were strongly influenced by the deposition methods. The bilayer deposition strategy showed an improved controllability in acquiring small catalyst particles at a high density, which obtained high yields of CNTs with large specific surface area. As a result, CNTs of 7.5 nm in diameter, triple-wall on average, and 0.6 mm in length were synthesized by employing the fluidized bed chemical vaper deposition technique, suggesting a new way for the high-yield production of long few-wall CNTs at reasonable cost.
• Achieving Increased Electrochemical Accessibility and Lowered Oxygen Evolution Reaction Activation Energy for Co²⁺ Sites with a Simple Anion Preoxidation

  Anantharaj, S.; Sugime, H.; Chen, B.; Akagi, N.; Noda, S.

  Journal of Physical Chemistry C 124 18 9673 - 9684 2020年 [査読有り]
   

  Copyright © 2020 American Chemical Society. Cobalt chalcogenides are excellent oxygen evolution reaction (OER) precatalysts in alkaline medium as they readily form O2-evolving CoOOH entities in electrochemically accessible Co2+ sites when subjected to anodic potential. A key factor that determines the efficiency of OER in cobalt chalcogenides is the number of electrochemically accessible Co2+ sites. Here, an easy way of increasing the electrochemical accessibility of Co2+ sites in CoSe2 has been identified, which is the simple preoxidation of selenide to selenite. When screened for OER in alkali, it was found that the electrochemical accessibility of Co2+ after preoxidation of Se in CoSe2 was increased by 7.8 ± 2 times in the first cycle and 2-3 times after activation by potential sweeping and redox cycling. The corresponding OER activation energy lowered to ∼1/2 at overpotentials 450 mV or higher due to such preoxidation of Se. Irrespective of the lowering in the electrochemical accessibility of Co2+ sites from the 1st cycle to the 100th cycle, the overall OER activity was maintained to be the same. This is quite relatable as a major portion of Co2+ oxidized in the first cycle is shuttling between 3+ and 4+ states while evolving O2. Altogether, preoxidation of Se in CoSe2 benefitted the realization of increased electrochemical accessibility for Co2+ sites, improved ECSA, improved charge transfer at catalytic turnover conditions, and lowered OER activation energy.
• Dispersing and doping carbon nanotubes by poly(p-styrene-sulfonic acid) for high-performance and stable transparent conductive films

  Xie, R.; Sugime, H.; Noda, S.

  Carbon 164 150 - 156 2020年 [査読有り]
   

  © 2020 Elsevier Ltd Carbon nanotubes (CNTs) have been integrated into many electronic and energy devices due to their high conductivity and flexibility. Here, we report the discovery of poly (p-styrene-sulfonic acid) (PSS) as an efficient dispersant and stable dopant for CNTs. PSS showed an excellent dispersion performance; CNTs were partially dispersed by just stirring and well dispersed by sonication for only 3 min in PSS aqueous solution. PSS also showed an excellent doping performance; the as-filtrated CNT films, which had CNT bundles wrapped with a few nm-thick PSS layer, showed low sheet resistances of 115 and 49 Ω/sq at optical transmittances of 90% and 79%, respectively. Moreover, the CNT films showed long-term stability (>1000 h) and high-temperature stability (250 °C) in ambient air without any passivation layer. The simple dispersion and stable doping for CNTs is a promising way to achieve superior transparent conductive films for fundamental and industrial applications.
• Electrolysis of ammonia in aqueous solution by platinum nanoparticles supported on carbon nanotube film electrode

  Hanada, N.; Kohase, Y.; Hori, K.; Sugime, H.; Noda, S.

  Electrochimica Acta 341 2020年 [査読有り]
   

  © 2020 Electrolysis of ammonia in an aqueous solution can generate hydrogen gas at room temperature. An anode reaction of nitrogen gas desorption on ammonia electrolysis has a much larger overvoltage than that of a cathode reaction, and one of the useful electrode catalysts for the anode reaction is platinum (Pt). In this study, in order to increase the surface area of Pt three-dimensionally, Pt nanoparticles are held on a sponge-like film of carbon nanotubes (CNTs) that has a large surface area of 5000–10000 cm2 per 1 cm2 of the CNT film. The electrodes were adapted to the ammonia electrolysis to increase the current density with a low overvoltage. The Pt nanoparticles were deposited on the CNTs by a polyol method at various temperatures, and the Pt nanoparticles supported on the CNT (Pt-CNT) electrodes were fabricated by vacuum filtration of the Pt-CNT dispersion. The size of the deposited Pt nanoparticles was approximately 2–3 nm. The maximum electrochemical surface area of the Pt nanoparticles was more than 250 cm2 per unit electrode area of 1 cm2. The Pt-CNT film electrode with a large surface area of the Pt catalyst increased the current density of the anode reaction compared with the Pt plate or the Pt-black electrodes. The Pt-CNT decreased both the activation overvoltage corresponding to the high Pt surface area and the concentration overvoltage corresponding to the three-dimensional structure of the CNT films. Moreover, it is clarified that the deactivation of the catalysts by the anode reaction does not occur below −0.2 V (vs Hg|HgO) for the Pt-CNT electrodes.
• Direct formation of continuous multilayer graphene films with controllable thickness on dielectric substrates

  Sachie Akiba; Masaki Kosaka; Kei Ohashi; Kei Hasegawa; Hisashi Sugime; Suguru Noda

  Thin Solid Films 675 136 - 142 2019年04月 [査読有り]
   

  © 2019 Elsevier B.V. Direct formation of graphene films on dielectric substrates is investigated by the “etching-precipitation” method which converts metal-carbon mixed films to graphene films by etching metal away by Cl 2 at 600–650 °C. Here we report a new approach for improved control of the layer number and continuity of the graphene films. Reactive sputtering of Fe in C 2 H 4 /Ar enabled fine control of the carbon concentrations and thicknesses of the initial Fe-C films, which yielded continuous multilayer graphene films of controllable average layer numbers of ~10–40, low resistivity down to ~240 μΩ cm, and high Raman G-band to D-band intensity ratio up to 16 directly on SiO 2 substrates. We also show that the carbon concentration of the initial Fe-C films determines the film continuity and crystallinity of the graphene.
• 1.5 Minute-synthesis of continuous graphene films by chemical vapor deposition on Cu foils rolled in three dimensions

  Nagai, Y.; Sugime, H.; Noda, S.

  Chemical Engineering Science 201 319 - 324 2019年 [査読有り]
   

  © 2019 Elsevier Ltd We report a high-productivity chemical vapor deposition (CVD) process of graphene by extending the reaction field to three dimensions (3D) and shortening the CVD time to a few minutes. A large Cu foil (5 × 30 cm2) is rolled up and set in a small reactor (3.4 cm in diameter), and a continuous graphene film is obtained uniformly in a short time (1.5 min) by using C2H4 as a more reactive carbon source than the popular CH4. The graphene transferred onto a quartz glass showed optical transmittances of 94.8–96.7% (550 nm) with sheet resistances of 0.78–1.68 kΩ sq−1 (without doping) and 0.3 kΩ sq−1 (with doping by HNO3 vapor). Compared with the previous reports for fast and/or large-scale CVD, our method realized similarly high productivity of 100 cm2 min−1 based on the CVD time despite of the small reactor, and higher productivity of 0.03 cm2-graphene per cm3-reactor per minute based on the reactor volume and total time for high temperature processing (15 min for heating, 1 min for annealing, and 1.5 min for CVD). The knowledge obtained here on the CVD conditions and packing ratio of Cu foils (0.55 cm2 per cm3-reactor) is reusable for designing large-scale graphene production processes.
• Enhancing the photovoltaic performance of hybrid heterojunction solar cells by passivation of silicon surface via a simple 1-min annealing process

  Xie, R.; Ishijima, N.; Sugime, H.; Noda, S.

  Scientific Reports 9 1 12051  2019年 [査読有り]
   

  © 2019, The Author(s). Solution-based heterojunction technology is emerging for facile fabrication of silicon (Si)-based solar cells. Surface passivation of Si substrate has been well established to improve the photovoltaic (PV) performance for the conventional bulk Si cells. However, the impact is still not seen for the heterojunction cells. Here, we developed a facile and repeatable method to passivate the Si surface by a simple 1-min annealing process in vacuum, and integrated it into the heterojunction cells with poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) or carbon nanotube (CNT). A thin and dense oxide layer was introduced on the Si surface to provide a high-quality hole transport layer and passivation layer. The layer enhanced the power conversion efficiency from 9.34% to 12.87% (1.38-times enhancement) for the PEDOT:PSS/n-Si cells and from 6.61% to 8.52% (1.29-times enhancement) for the CNT/n-Si cells. The simple passivation is a promising way to enhance the PV performance of the Si cells with various solution-based heterojunctions.
• Gd-Enhanced Growth of Multi-Millimeter-Tall Forests of Single-Wall Carbon Nanotubes

  Sugime, H.; Sato, T.; Nakagawa, R.; Cepek, C.; Noda, S.

  ACS Nano 13 11 13208 - 13216 2019年 [査読有り]
   

  © 2019 American Chemical Society. Multi-millimeter-tall vertically aligned single-wall carbon nanotube (VA-SWCNT) forests were grown using Fe/Gd/Al2Ox catalyst with high initial growth rate of ∼2 μm s-1 and long catalyst lifetime of ∼70 min at 800 °C. The addition of Gd with a nominal thickness of 0.3 nm drastically prolonged the catalyst lifetime. The analysis of the VA-SWCNT forests by a transmission electron microscope showed that the average diameter of the SWCNTs grown with Gd is constant from the top to the bottom of the forests, while it monotonically increased without Gd. This indicated that Gd suppresses the structure change of the Fe nanoparticles in the lateral direction during the CNT growth. By X-ray photoelectron spectroscopy, it was found that the longer catalyst lifetime with Gd stems from the suppression of the interaction between Fe and C resulting in the smaller structure change of the Fe nanoparticles.
• Flame-assisted chemical vapor deposition for continuous gas-phase synthesis of 1-nm-diameter single-wall carbon nanotubes

  Shohei Okada; Hisashi Sugime; Kei Hasegawa; Toshio Osawa; Shohei Kataoka; Hiroki Sugiura; Suguru Noda

  Carbon 138 1 - 7 2018年11月 [査読有り]
   

  © 2018 The Authors Flame synthesis enables the mass-production of carbon black and fullerene but not of carbon nanotubes (CNTs) due to the narrow window for producing CNTs while preventing tar generation. We report a flame-assisted chemical vapor deposition method, in which a premixed flame is used for the instantaneous generation of floating catalysts, the heating of the gas, and the growth of single-wall CNTs (SWCNTs) using a furnace at the downstream of the flame. This method yields high quality SWCNTs with a small average diameter of 0.96 nm, a small diameter deviation of 0.21 nm, and a high carbon purity of ∼90 wt%. Multiple parameters affect the SWCNT production significantly, which are investigated systematically and optimized carefully. The effects and possible mechanisms of the key parameters are discussed.
• CO2-assisted growth of millimeter-tall single-wall carbon nanotube arrays and its advantage against H2O for large-scale and uniform synthesis

  Toshihiro Sato; Hisashi Sugime; Suguru Noda

  Carbon 136 143 - 149 2018年09月 [査読有り]
   

  © 2018 The Authors The CO2-assisted chemical vapor deposition (CVD) is reported as a versatile method for millimeter-tall vertically-aligned single-wall carbon nanotube (VA-SWCNT) arrays when compared with the famous H2O-assisted one. The mild oxidant CO2 enabled the VA-SWCNT growth with mostly equivalent structures and yield when it was added at a much higher concentration (0.3–1 vol%) than H2O (50 ppmv). Furthermore, CO2 showed a clear advantage for the uniform growth when 18 substrates (10 × 10 mm2) were loaded in one batch. The areal yield of VA-SWCNTs decreased drastically from 1.6 to 0.4 mg cm−2 for the first 4 substrates with 50 ppmv H2O because of its depletion whereas it decreased more mildly from 1.6 to 0.8 mg cm−2 for the whole 18 substrates with 1.0 vol% CO2. The gradual decrease in the SWCNT yield with 1.0 vol% CO2 was caused by the change in the carbon source depending on its position. The mixed feed of 0.30 vol% C2H2 (being converted to SWCNTs gradually) and 3.0 vol% C2H4 (yielding C2H2 gradually) realizes the uniform growth of VA-SWCNTs for the whole 18 substrates. The CO2-assisted CVD with optimized carbon feed is promising for the uniform growth of millimeter-tall SWCNTs in large areas.
• An interdigitated electrode with dense carbon nanotube forests on conductive supports for electrochemical biosensors

  Hisashi Sugime; Takuya Ushiyama; Keita Nishimura; Yutaka Ohno; Sugur Noda

  Analyst 143 15 3635 - 3642 2018年08月 [査読有り]
   

  © 2018 The Royal Society of Chemistry. A highly sensitive interdigitated electrode (IDE) with vertically aligned dense carbon nanotube forests directly grown on conductive supports was demonstrated by combining UV lithography and a low temperature chemical vapor deposition process (470 °C). The cyclic voltammetry (CV) measurements of K4[Fe(CN)6] showed that the redox current of the IDE with CNT forests (CNTF-IDE) reached the steady state much more quickly compared to that of conventional gold IDE (Au-IDE). The performance of the CNTF-IDE largely depended on the geometry of the electrodes (e.g. width and gap). With the optimum three-dimensional electrode structure, the anodic current was amplified by a factor of ∼18 and ∼67 in the CV and the chronoamperometry measurements, respectively. The collection efficiency, defined as the ratio of the cathodic current to the anodic current at steady state, was improved up to 97.3%. The selective detection of dopamine (DA) under the coexistence of l-ascorbic acid with high concentration (100 μM) was achieved with a linear range of 100 nM-100 μM, a sensitivity of 14.3 mA mol-1 L, and a limit of detection (LOD, S/N = 3) of 42 nM. Compared to the conventional carbon electrodes, the CNTF-IDE showed superior anti-fouling property, which is of significant importance for practical applications, with a negligible shift of the half-wave potential (ΔE1/2 < 1.4 mV) for repeated CV measurements of DA at high concentration (100 μM).
• Corrigendum to “Millimeter-tall carbon nanotube arrays grown on aluminum substrates” [Carbon 130 (2018) 834–842] (S0008622318300848) (10.1016/j.carbon.2018.01.075))

  Shota Miura; Yu Yoshihara; Mayu Asaka; Kei Hasegawa; Hisashi Sugime; Aun Ota; Hisayoshi Oshima; Suguru Noda

  Carbon 133 77 - 77 2018年07月 [査読有り]
   

  © 2018 Elsevier Ltd The authors regret that the incorrect version of the Graphical Abstract was included with this article. The figures within the article are correct. The correct Graphical Abstract appears below: [Figure presented] The authors would like to apologise for any inconvenience caused.
• Carbon nanotube isolation layer enhancing in-liquid quality-factors of thin film bulk acoustic wave resonators for gravimetric sensing

  Girish Rughoobur; Hisashi Sugime; Mario DeMiguel-Ramos; Teona Mirea; Shan Zheng; John Robertson; Enrique Iborra; Andrew John Flewitt

  Sensors and Actuators, B: Chemical 261 398 - 407 2018年05月 [査読有り]
   

  © 2018 Elsevier B.V. A thickness longitudinal mode (TLM) thin film bulk acoustic resonator biosensor is demonstrated to operate in water with a high quality-factor, Q. This is achieved using a layer of carbon nanotubes (CNTs) on top of the resonator which has a significantly different acoustic impedance to either the resonator or liquid whilst being susceptible to the binding of biological molecules. This allows the resonance to be decoupled from direct energy loss into the liquid, although still retaining mass sensitivity. AlN solidly mounted resonators (SMRs) having a thickness shear mode (TSM) at 1.1 GHz and TLM at 1.9 GHz are fabricated. CNTs with different forest densities are grown by chemical vapor deposition on the active area with Fe as the catalyst and resulting devices are compared. High forest density CNTs are shown to acoustically decouple the SMRs from the water and in-liquid TLM Q values higher than 150 are recorded even exceeding TSM SMRs without CNTs. The TLM Q in water is remarkably improved from 3 to 160 for the first time by dense CNT forests, rendering the large-scale fabrication of TLM SMRs for liquid-phase sensing applications possible. Despite this partial isolation, SMRs with CNT forests ∼15 μm tall can still detect binding of bovine serum albumin.
• Millimeter-tall carbon nanotube arrays grown on aluminum substrates

  Shota Miura; Yu Yoshihara; Mayu Asaka; Kei Hasegawa; Hisashi Sugime; Aun Ota; Hisayoshi Oshima; Suguru Noda

  Carbon 130 834 - 842 2018年04月 [査読有り]
   

  © 2018 Elsevier Ltd Millimeter-tall vertically aligned carbon nanotubes (VA-CNTs) were grown directly on Al substrates. Atmospheric pressure chemical vapor deposition is performed at 600 °C, which is well below the melting point of Al (660 °C), using Fe catalyst and C2H2 as a highly reactive carbon feedstock. The CNT height was sensitive to the C2H2 concentration and 0.06 vol% was optimum for balanced growth rate and catalyst lifetime, yielding 0.06 mm-tall VA-CNTs in 2 h. The CO2 addition at 1.8 vol% to the C2H2/Ar gas significantly enhanced the CNT growth, yielding 1.1 mm-tall VA-CNTs in 12 h. CO2 shows this remarkable effect when added in large excess to C2H2, differently from the well-known method of “small addition of water.” Moreover, the resulting VA-CNTs showed electrical contact with the Al sheets with resistance of ≤0.7 Ω cm−2. The effect of CO2 is systematically studied and discussed.
• Catalyst nucleation and carbon nanotube growth from flame-synthesized Co-Al-O nanopowders at ten-second time scale

  Shirae, H.; Hasegawa, K.; Sugime, H.; Yi, E.; Laine, R.M.; Noda, S.

  Carbon 114 31 - 38 2017年 [査読有り]
   

  Flame-synthesized (CoO)(x)(Al2O3)(1-x) spinel nanopowders with primary particles of similar to 20 nm were used to grow small diameter carbon nanotubes (CNTs). The nanopowders with x <= 035 grew few CNTs whereas that with x = 0.65 grew CNTs efficiently. Low crystalline and large-diameter multi-wall CNTs grew by annealing and chemical vapor deposition (CVD) at 800 degrees C for similar to 10 min, whereas single-wall CNTs with high crystallinity (G-band to D-band intensity ratio of 20-100 by Raman spectroscopy) grew by annealing and CVD at >= 1000 degrees C for similar to 10 s. The excess Co in the spinel reduced and segregated to form multiple Co nanoparticles on the surface of the single primary alumina nanoparticles in similar to 10 s, yielding SWCNTs in similar to 10 s. Such flame synthesized nanopowders, reduced and activated by H-2, provide CNTs from C2H2, all in ten-second time scale, and as such are promising for practical, high-through-put production of small-diameter CNTs. (C) 2016 Elsevier Ltd. All rights reserved.
• Ten-Second Epitaxy of Cu on Repeatedly Used Sapphire for Practical Production of High-Quality Graphene

  Nagai, Y.; Okawa, A.; Minamide, T.; Hasegawa, K.; Sugime, H.; Noda, S.

  ACS Omega 2 7 3354 - 3362 2017年 [査読有り]
   

  Epitaxial copper (Cu) films yield graphene with superior quality but at high cost. We report 1-3 μm thick epitaxial Cu films prepared on c plane sapphire substrates in 10-30 s, which is much faster than that of the typical sputtering method. Such rapid deposition is realized by vapor deposition using a Cu source heated to 1700-1800 °C, which is much higher than its melting point of 1085 °C. Continuous graphene films, either bilayer or single-layer, are obtained on the epitaxial Cu by chemical vapor deposition and transferred to carrier substrates. The sapphire substrates can be reused five to six times maintaining the quality of the epitaxial Cu films and graphene. The mechanisms and requirements are discussed for such quick epitaxy of Cu on reused sapphire, which will enable high-quality graphene production at lower cost.
• From Growth Surface to Device Interface: Preserving Metallic Fe under Monolayer Hexagonal Boron Nitride

  Caneva, S.; Martin, M.-B.; D'Arsié, L.; Aria, A.I.; Sezen, H.; Amati, M.; Gregoratti, L.; Sugime, H.; Esconjauregui, S.; Robertson, J.; Hofmann, S.; Weatherup, R.S.

  ACS Applied Materials and Interfaces 9 35 29973 - 29981 2017年 [査読有り]
   

  We investigate the interfacial chemistry between Fe catalyst foils and monolayer hexagonal boron nitride (h-BN) following chemical vapor deposition and during subsequent atmospheric exposure, using scanning electron microscopy, X-ray photoemission spectroscopy, and scanning photoelectron microscopy. We show that regions of the Fe surface covered by h-BN remain in a metallic state during exposure to moist air for similar to 40 h at room temperature. This protection is attributed to the strong interfacial interaction between h-BN and Fe, which prevents the rapid intercalation of oxidizing species. Local Fe oxidation is observed on bare Fe regions and dose to defects in the h-BN film (e.g., domain boundaries, wrinkles, and edges), which over the longer-term provide pathways for slow bulk oxidation of Fe. We further confirm that the interface between h-BN and metallic Fe can be recovered by vacuum annealing at similar to 600 degrees C, although this is accompanied by the creation of defects within the h-BN film. We discuss the importance of these findings in the context of integrated manufacturing and transfer-free device integration of h-BN, particularly for technologically important applications where h-BN has potential as a tunnel barrier such as magnetic tunnel junctions.
• Low temperature growth of fully covered single-layer graphene using a CoCu catalyst

  Sugime, H.; D'Arsié, L.; Esconjauregui, S.; Zhong, G.; Wu, X.; Hildebrandt, E.; Sezen, H.; Amati, M.; Gregoratti, L.; Weatherup, R.S.; Robertson, J.

  Nanoscale 9 38 14467 - 14475 2017年 [査読有り]
   

  A bimetallic CoCu alloy thin-film catalyst is developed that enables the growth of uniform, high-quality graphene at 750 degrees C in 3 min by chemical vapour deposition. The growth outcome is found to vary significantly as the Cu concentration is varied, with similar to 1 at% Cu added to Co yielding complete coverage single-layer graphene growth for the conditions used. The suppression of multilayer formation is attributable to Cu decoration of high reactivity sites on the Co surface which otherwise serve as preferential nucleation sites for multilayer graphene. X-ray photoemission spectroscopy shows that Co and Cu form an alloy at high temperatures, which has a drastically lower carbon solubility, as determined by using the calculated Co-Cu-C ternary phase diagram. Raman spectroscopy confirms the high quality (I-D/I-G < 0.05) and spatial uniformity of the single-layer graphene. The rational design of a bimetallic catalyst highlights the potential of catalyst alloying for producing two-dimensional materials with tailored properties.
• Growth of high quality, high density single-walled carbon nanotube forests on copper foils

  Zhong, G.; Yang, J.; Sugime, H.; Rao, R.; Zhao, J.; Liu, D.; Harutyunyan, A.; Robertson, J.

  Carbon 98 624 - 632 2016年 [査読有り]
   

  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. (C) 2015 Elsevier Ltd. All rights reserved.
• Growth of Continuous Monolayer Graphene with Millimeter-sized Domains Using Industrially Safe Conditions

  Wu, X.; Zhong, G.; D'Arsié, L.; Sugime, H.; Esconjauregui, S.; Robertson, A.W.; Robertson, J.

  Scientific Reports 6 21152  2016年 [査読有り]
   

  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 (H-2 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 similar to 5,700 cm(2) V-1 s(-1) in ambient conditions. The growth process of such high-quality graphene with a low H-2 concentration and short growth times widens the possibility of industrial mass production.
• Stable, efficient p-type doping of graphene by nitric acid

  D'Arsie, Lorenzo; D'Arsie, Lorenzo; Esconjauregui, Santiago; Esconjauregui, Santiago; Weatherup, Robert S.; Weatherup, Robert S.; Wu, Xingyi; Wu, Xingyi; Arter, William E.; Arter, William E.; Sugime, Hisashi; Sugime, Hisashi; Cepek, Cinzia; Cepek, Cinzia; Robertson, John; Robertson, John

  RSC Advances 6 114 113185 - 113192 2016年 [査読有り]
   

  We systematically dope monolayer graphene with different concentrations of nitric acid over a range of temperatures, and analyze the variation of sheet resistance after vacuum annealing up to 300 degrees C. The optimized HNO3 doping conditions yield sheet resistances as low as 180 Omega sq.(-1), which is significantly more stable under vacuum annealing than previously reported values. Raman and photoemission spectroscopy suggest that this stable graphene doping occurs by a bi-modal mechanism. Under mild conditions the dopants are weakly bonded to graphene, but at high acid temperatures and concentrations, the doping is higher and more stable upon post-doping annealing, without causing significant lattice damage. This work shows that large, stable hole concentrations can be induced by transfer doping in graphene.
• Spatial Variability in Large Area Single and Few-layer CVD Graphene

  Clara F. Moldovan; Krzysztof Gajewski; Michele Tamagnone; Robert S. Weatherup; Hisashi Sugime; Anna Szumska; Wolfgang A. Vitale; John Robertson; Adrian M. Ionescu

  2015 JOINT INTERNATIONAL EUROSOI WORKSHOP AND INTERNATIONAL CONFERENCE ON ULTIMATE INTEGRATION ON SILICON (EUROSOI-ULIS) 85 - 88 2015年 [査読有り]
   

  Variability in graphene can result from the material synthesis or post-processing steps as well as the surrounding environment. This is a critical issue for the performance of large area devices as well as for the large-scale production of micro-and nano-scale graphene devices, leading to low yield and reliability. The aim of this study is to investigate variability of single and few-layer graphene structures, on different substrates, and the effects it has on its electronic properties. We demonstrate a combination of Kelvin probe force microscopy (KPFM) and non-contact Fourier transform infrared spectroscopy (FTIR) measurements for centimeter-scale quantitative mapping of the electrical variability of large-area chemical vapor deposited graphene films. KPFM provides statistical insight into the influence of micro-scale defects on the surface potential, while FTIR gives the spatially averaged chemical potential of the graphene structures. Test structures consisting of single-, bi- and few-layer graphene on SiO2 and Al2O3 were fabricated and analyzed.
• Growth of high-density carbon nanotube forests on conductive TiSiN supports

  Yang, J.; Esconjauregui, S.; Robertson, A.W.; Guo, Y.; Hallam, T.; Sugime, H.; Zhong, G.; Duesberg, G.S.; Robertson, J.

  Applied Physics Letters 106 8 83108  2015年 [査読有り]
   

  We grow vertically aligned carbon nanotube forests on refractory conductive films of TiSiN and achieve area densities of (5.1 +/- 0.1) x 10(12) 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. (C) 2015 AIP Publishing LLC.
• Low-Temperature Growth of Carbon Nanotube Forests Consisting of Tubes with Narrow Inner Spacing Using Co/Al/Mo Catalyst on Conductive Supports

  Sugime, H.; Esconjauregui, S.; D'Arsié, L.; Yang, J.; Robertson, A.W.; Oliver, R.A.; Bhardwaj, S.; Cepek, C.; Robertson, J.

  ACS Applied Materials and Interfaces 7 30 16819 - 16827 2015年 [査読有り]
   

  We grow dense carbon nanotube forests at 450 degrees 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 CoMo interaction. The forests have an average height of similar to 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 similar to 8 k Omega. The forest shows a high thermal effusivity of 1840 J s0.5 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.
• Efficient Transfer Doping of Carbon Nanotube Forests by MoO3

  Esconjauregui, S.; D'Arsié, L.; Guo, Y.; Yang, J.; Sugime, H.; Caneva, S.; Cepek, C.; Robertson, J.

  ACS Nano 9 10 10422 - 10430 2015年 [査読有り]
   

  We dope nanotube forests using evaporated MoO3 and observe the forest resistivity to decrease by 2 orders of magnitude, reaching values as low as similar to 5 x 10(-5) Omega cm, thus approaching that of copper. Using in situ photoemission spectroscopy, we determine the minimum necessary MoO3 thickness to dope a forest and study the underlying doping mechanism. Homogenous coating and tube compaction emerge as key factors for decreasing the forest resistivity. When all nanotubes are fully coated with MoO3 and packed, conduction channels are created both inside the nanotubes and on the outside oxide layer. This is supported by density functional theory calculations, which show a shift of the Fermi energy of the nanotubes and the conversion of the oxide into a layer of metallic character. MoO3 doping removes the need for chirality control during nanotube growth and represents a step forward toward the use of forests in next-generation electronics and in power cables or conductive polymers.
• Carbon nanotube forests as top electrode in electroacoustic resonators

  Esconjauregui, S.; Makaryan, T.; Mirea, T.; DeMiguel-Ramos, M.; Olivares, J.; Guo, Y.; Sugime, H.; D'Arsié, L.; Yang, J.; Bhardwaj, S.; Cepek, C.; Robertson, J.; Iborra, E.

  Applied Physics Letters 107 13 133106  2015年 [査読有り]
   

  We grow carbon nanotube forests on piezoelectric AlN films and fabricate and characterize nanotube-based solidly mounted bulk acoustic wave resonators employing the forests as the top electrode material. The devices show values for quality factor at anti-resonance of similar to 430, and at resonance of similar to 100. The effective coupling coefficient is of similar to 6%, and the resonant frequencies are up to similar to 800 MHz above those observed with metallic top electrodes. AlN promotes a strong catalyst-support interaction, which reduces Fe catalyst mobility, and thus enforces the growth of forests by the base growth mechanism. (C) 2015 AIP Publishing LLC.
• Carbon nanotube growth on conductors: Influence of the support structure and catalyst thickness

  Esconjauregui, S.; Bhardwaj, S.; Yang, J.; Castellarin-Cudia, C.; Xie, R.; D'Arsié, L.; Makaryan, T.; Sugime, H.; Fernandez, S.E.; Cepek, C.; Robertson, J.

  Carbon 73 13 - 24 2014年 [査読有り]
   

  We investigate the formation and stability of Fe nanoparticles on TiN and poly-crystalline PtSi films, and their ability to grow carbon nanotubes forests. Using different-microstructure films, coated with or without their native oxides, we show that, upon purely-thermal catalyst pretreatment, PtSi favours the formation of homogenously sized nanoparticles and forest growth, partly due to its low surface energy. TiN, in contrast, leads to much less controllable processes and only when coated with its native oxide, or with thick catalyst films, yields large diameter nanotube forests. The microstructure of the material can dramatically limit catalyst diffusion into the bulk of the support during nanotube growth. These results allow us to establish the general behaviour expected for nanotube growth on any conductive materials. (C) 2014 Elsevier Ltd. All rights reserved.
• Co-catalytic absorption layers for controlled laser-induced chemical vapor deposition of carbon nanotubes

  Michaelis, F.B.; Weatherup, R.S.; Bayer, B.C.; Bock, M.C.D.; Sugime, H.; Caneva, S.; Robertson, J.; Baumberg, J.J.; Hofmann, S.

  ACS Applied Materials and Interfaces 6 6 4025 - 4032 2014年 [査読有り]
   

  The concept of co-catalytic layer structures for controlled laser-induced chemical vapor deposition of carbon nanotubes is established, in which a thin Ta support layer chemically aids the initial Fe catalyst reduction. This enables a significant reduction in laser power, preventing detrimental positive optical feedback and allowing improved growth control. Systematic study of experimental parameters combined with simple thermostatic modeling establishes general guidelines for the effective design of such catalyst/absorption layer combinations. Local growth of vertically aligned carbon nanotube forests directly on flexible polyimide substrates is demonstrated, opening up new routes for nanodevice design and fabrication.
• Hybrids of carbon nanotube forests and gold nanoparticles for improved surface plasmon manipulation

  Makaryan, T.; Esconjauregui, S.; Gonçalves, M.; Yang, J.; Sugime, H.; Nille, D.; Renganathan, P.R.; Goldberg-Oppenheimer, P.; Robertson, J.

  ACS Applied Materials and Interfaces 6 8 5344 - 5349 2014年 [査読有り]
   

  We report the fabrication and characterization of hybrids of vertically-aligned carbon nanotube forests and gold nanoparticles for improved manipulation of their plasmonic properties. Raman spectroscopy of nanotube forests performed at the separation area of nanotube-nanoparticles ;shows a scattering enhancement factor of the order of 1 x 10(6). The enhancement is related to the plasmonic coupling of the nanoparticles and is potentially applicable in high-resolution scanning near-field optical microscopy, plasmonics, and photovoltaics.
• Effect of oxygen plasma alumina treatment on growth of carbon nanotube forests

  Yang, J.; Esconjauregui, S.; Xie, R.; Sugime, H.; Makaryan, T.; D'Arsié, L.; Gonzalez Arellano, D.L.; Bhardwaj, S.; Cepek, C.; Robertson, J.

  Journal of Physical Chemistry C 118 32 18683 - 18692 2014年 [査読有り]
   

  We use oxygen plasma to increase the height of forests from similar to 0.2 to >2 mm. The effectiveness of treating alumina by oxygen plasma, prior to iron nanoparticle formation, is studied using cycles of nanotube growth, nanotube burning, and regrowth. This demonstrates that plasma-treated alumina is more resistant to iron bulk diffusion than an untreated one. Secondary ion mass spectroscopy shows there is negligible iron diffusion into the bulk of treated alumina. Plasma treatment of catalyst supports is potentially useful for growth of ultra-high-density nanotube forests for applications such as interconnects in integrated circuits and heat sinks.
• Growth kinetics and growth mechanism of ultrahigh mass density carbon nanotube forests on conductive Ti/Cu supports

  Sugime, H.; Esconjauregui, S.; D'Arsié, L.; Yang, J.; Makaryan, T.; Robertson, J.

  ACS Applied Materials and Interfaces 6 17 15440 - 15447 2014年 [査読有り]
   

  We evaluate the growth kinetics and growth mechanism of ultrahigh mass density carbon nanotube forests. They are synthesized by chemical vapor deposition at 450 degrees C using a conductive Ti/Cu support and Co-Mo catalyst system. We find that Mo stabilizes Co particles preventing lift off during the initial growth stage, thus promoting the growth of ultrahigh mass density nanotube forests by the base growth mechanism. The morphology of the forest gradually changes with growth time, mostly because of a structural change of the catalyst particles. After 100 min growth, toward the bottom of the forest, the area density decreases from similar to 3-6 x 10(11) cm(-2) to similar to 5 x 10(10) cm(-2) and the mass density decreases from 1.6 to 0.38 g cm(-3). We also observe part of catalyst particles detached and embedded within nanotubes. The progressive detachment of catalyst particles results in the depletion of the catalyst metals on the substrate surfaces. This is one of the crucial reasons for growth termination and may apply to other catalyst systems where the same features are observed. Using the packed forest morphology, we demonstrate patterned forest growth with a pitch of similar to 300 nm and a line width of similar to 150 nm. This is one of the smallest patterning of the carbon nanotube forests to date.
• Comparison of carbon nanotube forest growth using AlSi, TiSiN, and TiN as conductive catalyst supports

  Yang, J.; Esconjauregui, S.; Sugime, H.; Makaryan, T.; Hallam, T.; Duesberg, G.S.; Robertson, J.

  Physica Status Solidi (B) Basic Research 251 12 2389 - 2393 2014年 [査読有り]
   

  We evaluate carbon nanotube growth by employing AlSi, TiSiN and TiN as conductive catalyst supports. Using a wide range of chemical vapour deposition conditions, we find that only AlSi and TiSiN yield homogeneously-sized nanoparticles, which are stable throughout both catalyst preparation and nanotube synthesis processes. This favours the growth of forests with area densities of the order of 1012 nanotubes cm(-2). TiN, in contrast, yield lower density forests in a very narrow window process. The forests and the three screened catalyst supports show ohmic conductivity. TiSiN, however, is the only conductor that leads to the very robust growth process. This suggests TiSiN is useful for applications requiring forest growth on conductors and thus warrants further assessment for reducing nanotube diameter and improving area density of the forests. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
• Low temperature growth of ultra-high mass density carbon nanotube forests on conductive supports

  H. Sugime; S. Esconjauregui; J. Yang; L. D'Arsié; R.A. Oliver; S. Bhardwaj; C. Cepek; J. Robertson

  Appl. Phys. Lett. 103 7 73116  2013年 [査読有り]
  
• Erratum: Low temperature growth of ultra-high mass density carbon nanotube forests on conductive supports (Applied Physics Letters (2013) 103 (073116))

  Sugime, H.; Esconjauregui, S.; Yang, J.; D'Arsié, L.; Oliver, R.A.; Bhardwaj, S.; Cepek, C.; Robertson, J.

  Applied Physics Letters 103 10 73116  2013年 [査読有り]
  
• Evaluation of bimetallic catalysts for the growth of carbon nanotube forests

  Tornatzky, H.; Hardeman, D.; Esconjauregui, S.; D'Arsié, L.; Xie, R.; Sugime, H.; Yang, J.; Makaryan, T.; Thomsen, C.; Robertson, J.

  Physica Status Solidi (B) Basic Research 250 12 2605 - 2610 2013年 [査読有り]
   

  We systematically study the growth of carbon nanotube forests by chemical vapor deposition using evaporated monometallic or bimetallic Ni, Co, or Fe films supported on alumina. Our results show two regimes of catalytic activity. When the total thickness of catalyst is larger than nominally 1nm, bimetallic catalysts tend to outperform the equivalent layers of a single metal, yielding taller forests of multi-walled carbon nanotubes (CNTs). In contrast, for layers thinner than approximate to 1nm, bimetallic catalysts are notably less active than individually. However, the amount of small diameter and single-walled CNTs is significantly increased. This possible transition at approximate to 1nm might be related to different catalyst composition after annealing, depending whether or not the films overlap during evaporation and alloy during catalyst formation. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
• Fluidized-bed synthesis of sub-millimeter-long single walled carbon nanotube arrays

  Kim, D.Y.; Sugime, H.; Hasegawa, K.; Osawa, T.; Noda, S.

  Carbon 50 4 1538 - 1545 2012年 [査読有り]
   

  The rapid growth method for vertically aligned, single walled carbon nanotube (SWCNT) arrays on flat substrates was applied to a fluidized-bed, using ceramic beads as catalyst supports as a means to mass produce sub-millimeter-long SWCNT arrays. Fe/Al2Ox catalysts were deposited on the surface of Al2O3 beads by sputtering and SWCNTs were grown on the beads by chemical vapor deposition (CVD) using C2H2 as a feedstock. Scanning electron microscopy and transmission electron microscopy showed that SWCNTs of 2-4 nm in diameter grew and formed vertically aligned arrays of 0.5 mm in height. Thermogravimetric analysis showed that the SWCNTs had a catalyst impurity level below 1 wt.%. Furthermore, they were synthesized at a carbon yield as high as 65 at.% with a gas residence time as short as <0.2 s. Our fluidized-bed CVD, which efficiently utilizes the three-dimensional space of the reactor volume while retaining the characteristics of SWCNTs on substrates, is a promising option for mass-production of high-purity, sub-millimeter-long SWCNT arrays. (C) 2011 Elsevier Ltd. All rights reserved.
• Cold-gas chemical vapor deposition to identify the key precursor for rapidly growing vertically-aligned single-wall and few-wall carbon nanotubes from pyrolyzed ethanol

  Sugime, H.; Noda, S.

  Carbon 50 8 2953 - 2960 2012年 [査読有り]
   

  Vertically-aligned carbon nanotubes (VA-CNTs) were rapidly grown from ethanol and their chemistry has been studied using a "cold-gas" chemical vapor deposition (CVD) method. Ethanol vapor was preheated in a furnace, cooled down and then flowed over cobalt catalysts upon ribbon-shaped substrates at 800 degrees C, while keeping the gas unheated. CNTs were obtained from ethanol on a sub-micrometer scale without preheating, but on a millimeter scale with preheating at 1000 degrees C. Acetylene was predicted to be the direct precursor by gas chromatography and gas-phase kinetic simulation, and actually led to millimeter-tall VA-CNTs without preheating when fed with hydrogen and water. There was, however a difference in CNT structure, i.e. mainly few-wall tubes from pyrolyzed ethanol and mainly single-wall tubes for unheated acetylene, and the by-products from ethanol pyrolysis possibly caused this difference. The "cold-gas" CVD, in which the gas-phase and catalytic reactions are separately controlled, allowed us to further understand CNT growth. (C) 2012 Elsevier Ltd. All rights reserved.
• Sub-millimeter-long carbon nanotubes repeatedly grown on and separated from ceramic beads in a single fluidized bed reactor

  Kim, D.Y.; Sugime, H.; Hasegawa, K.; Osawa, T.; Noda, S.

  Carbon 49 6 1972 - 1979 2011年 [査読有り]
   

  A semi-continuous fluidized-bed process is reported which rapidly converts acetylene into carbon nanotubes (CNTs). Catalysts are first immobilized on ceramic beads and CNTs are then grown on the beads and then separated from them in a repetitive process accomplished within a single reactor simply by switching gases at a fixed temperature. CNTs of 6-10 nm diameter, three walls on average, 0.4 mm length and 99 wt.% purity were synthesized at an yield of over 70% in a reactor residence time shorter than 0.3 s. The easy and efficient production of such CNTs with in situ separation from the catalysts may accelerate the development of CNT-based nanotechnology industries. (C) 2011 Elsevier Ltd. All rights reserved.
• Tailoring the morphology of carbon nanotube assemblies using microgradients in the catalyst thickness

  Shiratori, Y.; Furuichi, K.; Tsuji, Y.; Sugime, H.; Noda, S.

  Japanese Journal of Applied Physics 50 9 PART 1 095101-1-7  2011年 [査読有り]
   

  In addition to the structural control of individual carbon nanotubes (CNTs), the morphological control of their assemblies is crucial to realize miniaturized CNT devices. Microgradients in the thickness of catalyst are used to enrich the variety of available self-organized morphologies of CNTs. Microtrenches were fabricated in gate/spacer/cathode trilayers using a conventional self-aligned top-down process and catalyst exhibiting a microgradient in its thickness was formed on the cathode by sputter deposition through gate slits. CNTs, including single-walled CNTs, of up to 1 mu m in length were grown within 5-15 s by chemical vapor deposition. The tendency of thin CNTs to aggregate caused interactions between CNTs with different growth rates, yielding various morphologies dependent on the thickness of the catalyst. The field emission properties of several types of CNT assemblies were evaluated. The ability to produce CNTs with tailored morphologies by engineering the spatial distribution of catalysts will enhance their performance in devices. (C) 2011 The Japan Society of Applied Physics
• Microstructures and transparent conducting properties of self-organized networks of single-walled carbon nanotubes

  Ketpreechasawat Suarpa; 杉目 恒志; 白鳥 洋介; 野田 優

  化学工学会 研究発表講演要旨集 2010 549 - 549 公益社団法人 化学工学会 2010年
• A simple combinatorial method aiding research on single-walled carbon nanotube growth on substrates

  Noda, S.; Sugime, H.; Hasegawa, K.; Kakehi, K.; Shiratori, Y.

  Japanese Journal of Applied Physics 49 2 PART 2 02BA02  2010年 [査読有り]
   

  Establishing fabrication methods of carbon nanotubes (CNTs) is essential to realize many applications expected for CNTs. Catalytic growth of CNTs on substrates by chemical vapor deposition (CVD) is promising for direct fabrication of CNT devices, and catalyst nanoparticles play a crucial role in such growth. We have developed a simple method called "combinatorial masked deposition (CMD)'', in which catalyst particles of a given series of sizes and compositions are formed on a single substrate by annealing gradient catalyst layers formed by sputtering through a mask. CMD enables preparation of hundreds of catalysts on a wafer, growth of single-walled CNTs (SWCNTs), and evaluation of SWCNT diameter distributions by automated Raman mapping in a single day. CMD helps determinations of the CVD and catalyst windows realizing millimeter-tall SWCNT forest growth in 10 min, and of growth curves for a series of catalysts in a single measurement when combined with real-time monitoring. A catalyst library prepared using CMD yields various CNTs, ranging from individuals, networks, spikes, and to forests of both SWCNTs and multi-walled CNTs, and thus can be used to efficiently evaluate self-organized CNT field emitters, for example. The CMD method is simple yet effective for research of CNT growth methods. (C) 2010 The Japan Society of Applied Physics
• Millimeter-tall single-walled carbon nanotube forests grown from ethanol

  Sugime, H.; Noda, S.

  Carbon 48 8 2203 - 2211 2010年 [査読有り]
   

  Millimeter-tall vertically-aligned carbon nanotubes (VA-CNTs) were grown from ethanol under ambient pressure by Co-catalyzed chemical vapor deposition (CVD), with systematic optimization of the CVD temperature and catalytic conditions using combinatorial catalyst libraries. We investigated the use of both aluminum oxide and silicon oxide as underlayers for the Co catalyst and found that VA-CNTs grew to millimeter heights in 15-30 min when the pyrolysis of ethanol was carried out at high temperatures (2-850 degrees C) and long residence times (>= 10 s). Thick Co catalytic layers (>= 1.3 nm) produced (sub)millimeter-tall multi-walled VA-CNTs on both the aluminum oxide and silicon oxide underlayers. However, thin Co catalytic layers (0.62-1.0 nm) produced (sub)millimeter-tall VA-CNTs, which consisted mainly of single-walled CNTs, only on the aluminum oxide underlayers. Stripe patterns were found in the VA-CNTs near the substrate on both aluminum oxide and silicon oxide, indicating some instability prior to growth termination. The possible roles of aluminum oxide in growing millimeter-tall single-walled VA-CNTs were discussed. (C) 2010 Elsevier Ltd. All rights reserved.
• 流動層による単層カーボンナノチューブの合成

  金 東榮; 深井 尋史; 杉目 恒志; 長谷川 馨; 大沢 利男; 野田 優

  化学工学会 研究発表講演要旨集 2009 12 - 12 公益社団法人 化学工学会 2009年
• 1-Second Implementation of CNT-Emitter Arrays on Glasses for BLUs

  Koji Furuichi; Yosuke Shiratori; Kotaro Sekiguchi; Hisashi Sugime; Suguru Noda

  2009 SID INTERNATIONAL SYMPOSIUM DIGEST OF TECHNICAL PAPERS, VOL XL, BOOKS I - III 139 - + 2009年 [査読有り]
   

  We realized simple fabrication of carbon nanotube field emitters for backlight units. Carbon nanotubes were directly grown on cathode lines patterned on low-strain glasses by atmospheric pressure CVD with pulse electrical heating of cathodes for I second. Field emission current density was as high as 5.6 mA/cm(2) at 3.3 V/mu m.
• Multiple "optimum" conditions for Co-Mo catalyzed growth of vertically aligned single-walled carbon nanotube forests

  Sugime, H.; Noda, S.; Maruyama, S.; Yamaguchi, Y.

  Carbon 47 1 234 - 241 2009年 [査読有り]
   

  Carbon nanotubes (CNTs) were grown directly on substrates by alcohol catalytic chemical vapor deposition using a Co-Mo binary catalyst. Optimum catalytic and reaction conditions were investigated using a combinatorial catalyst library. High catalytic activity areas on the substrate were identified by mapping the CNT yield against the orthogonal gradient thickness profiles of Co and Mo. The location of these areas shifted with changes in reaction temperature, ethanol pressure and ethanol flow rate. Vertically aligned single-walled CNT (SWCNT) forests grew in several areas to a maximum height of ca. 30 mu m in 10 min. A pure Co catalyst yielded a vertically aligned SWCNT forest with a bimodal diameter distribution. The effects of Mo on the formation of catalyst nanoparticles and on the diameter distribution of SWCNTs are discussed and Mo as thin as a monolayer or thinner was found to suppress the broadening of SWCNT diameter distributions. (C) 2008 Elsevier Ltd. All rights reserved.
• Combinatorial surface-enhanced raman spectroscopy and spectroscopic ellipsometry of silver Island films

  Oates, T.W.H.; Sugime, H.; Noda, S.

  Journal of Physical Chemistry C 113 12 4820 - 4828 2009年 [査読有り]
   

  Utilizing a combinatorial method, we used spectroscopic ellipsometry to determine the dielectric functions of silver island films over a large range of sizes and morphologies from the percolation threshold down to average particle size smaller than 5 nm. We measured films on silicon substrates with 2 and 20 nm oxide layers and compared the surface-enhanced Raman scattering properties of the films. As expected, the films on 20-nm-thick oxide substrates showed increased Raman counts due to reduced damping of the plasmon resonance; however, the optical absorption was greater in the films on 2 nm oxide. The maximum Raman scattering was observed for average particle diameters of 13.6 and 25 nm and interparticle spacings of 3.3 and 4.1 nm for the 2 and 20 nm oxide substrates, respectively. The use of a combinatorial method resulted in significantly reduced uncertainties by avoiding multiple sample preparations and allowed unambiguous identification of optimal film parameters for the different substrates.
• Efficient field emission from triode-type 1D arrays of carbon nanotubes

  Shiratori, Y.; Furuichi, K.; Tsuji, Y.; Sugime, H.; Noda, S.

  Nanotechnology 20 47 475707-1-7  2009年 [査読有り]
   

  Carbon nanotube (CNT) emitters were formed on line-patterned cathodes in microtrenches through a thermal CVD process. Single-walled carbon nanotubes (SWCNTs) self-organized along the trench lines with a submicron inter-CNT spacing. Excellent field emission (FE) properties were obtained: current densities at the anode (J(a)) of 1 mu A cm(-2), 10mA cm(-2) and 100 mA cm(-2) were recorded at gate voltages (V(g)) of 16, 25 and 36 V, respectively. The required voltage difference to gain a 1: 10 000 contrast of the anode current was as low as 9 V, indicating that a very low operating voltage is possible for these devices. Not only a large number of emission sites but also the optimal combination of trench structure and emitter morphology are crucial to achieve the full FE potential of thin CNTs with a practical lifetime. The FE properties of 1D arrays of CNT emitters and their optimal design are discussed. Self-organization of thin CNTs is an attractive prospect to tailor preferable emitter designs in FE devices.
• 自己組織化を利用した単層CNTフィールドエミッタの高密度集積

  野田 優; 古市 考次; 白鳥 洋介; 辻 佳子; 杉目 恒志; 山口 由岐夫

  化学工学会 研究発表講演要旨集 2008 791 - 791 公益社団法人 化学工学会 2008年
• 触媒CVD法における単層カーボンナノチューブ垂直配向成長の前駆体

  杉目 恒志; 野田 優; 山口 由岐夫

  化学工学会 研究発表講演要旨集 2008 783 - 783 公益社団法人 化学工学会 2008年
• 電子エミッタ応用を目的とした単層カーボンナノチューブの形態制御とコンビナトリアル特性評価

  白鳥 洋介; 古市 考次; 野田 優; 辻 佳子; 杉目 恒志; 張 正宜; 丸山 茂夫; 山口 由岐夫

  化学工学会 研究発表講演要旨集 2008 790 - 790 公益社団法人 化学工学会 2008年
• Field emission properties of single-walled carbon nanotubes with a variety of emitter morphologies

  Shiratori, Y.; Furuichi, K.; Noda, S.; Sugime, H.; Tsuji, Y.; Zhang, Z.; Maruyama, S.; Yamaguchi, Y.

  Japanese Journal of Applied Physics 47 6 PART 1 4780 - 4787 2008年 [査読有り]
   

  Field emission properties of single-walled carbon nanotubes (SWCNTs), which were prepared through alcohol catalytic chemical vapor deposition for 10-60s, were characterized in a diode configuration. Protrusive bundles at the top surface of samples act selectively as emission sites. The number of emission sites was controlled by emitter morphologies combined with texturing of Si substrates. SWCNTs grown on a textured Si substrate exhibited a turn-on field as low as 2.4 V/mu m at a field emission current density of 1 mu A/cm(2). Uniform spatial luminescence (0.5 cm(2)) from the rear surface of the anode was revealed for SWCNTs prepared on the textured Si substrate. Deterioration of field emission properties through repetitive measurements was reduced for the textured samples in comparison with vertically aligned SWCNTs and a random network of SWCNTs prepared on flat Si substrates. Emitter morphology resulting in improved field emission properties is a crucial factor for the fabrication of SWCNT-electron sources. Morphologically controlled SWCNTs with promising emitter performance are expected to be practical electron sources.
• Growth window and possible mechanism of millimeter-thick single-walled carbon nanotube forests

  Hasegawa, K.; Noda, S.; Sugime, H.; Kakehi, K.; Maruyama, S.; Yamaguchi, Y.

  Journal of Nanoscience and Nanotechnology 8 11 6123 - 6128 2008年 [査読有り]
   

  Our group recently reproduced the water-assisted growth method, so-called "SuperGrowth," of millimeter-thick single-walled carbon nanotube (SWNT) forests by using C2H4/H-2/H2O/Ar reactant gas and Fe/Al2O3 catalyst. In this current work, a parametric study was carried out on both reaction and catalyst conditions. Results revealed that a thin Fe catalyst layer (about 0.5 nm) yielded rapid growth of SWNTs only when supported on Al2O3, and that Al2O3 support enhanced the activity of Fe, Co, and Ni catalysts. The growth window for the rapid SWNT growth was narrow, however. Optimum amount of added H2O increased the SWNT growth rate but further addition of H2O degraded both the SWNT growth rate and quality Addition of H-2 was also essential for rapid SWNT growth, but again, further addition decreased both the SWNT growth rate and quality. Because Al2O3 catalyzes hydrocarbon reforming, Al2O3 support possibly enhances the SWNT growth rate by supplying the carbon source to the catalyst nanoparticles. The origin of the narrow window for rapid SWNT growth is also discussed.
• Combinatorial evaluation for field emission properties of carbon nanotubes

  Shiratori, Y.; Sugime, H.; Noda, S.

  Journal of Physical Chemistry C 112 46 17974 - 17982 2008年 [査読有り]
   

  Field emission properties of carbon nanotubes (CNTs) were comparatively evaluated by using combinatorial CNT libraries. The libraries were prepared by combinatorial masked deposition of a Co catalytic layer on Al2O3/Si substrates and subsequent CNT growth by chemical vapor deposition from ethanol. Each library reproduced various types of single- and multiwalled carbon nanotubes with different morphologies and a variety of field emission properties. Combinatorial evaluations immediately identified the CNTs preferable as field emitters. The results obtained from individual field emission evaluations for samples with a constant nominal Co thickness agreed well with the results obtained from comparative evaluations for combinatorial CNT libraries. The results revealed that protrusive single-walled carbon nanotubes with a moderate interspacing showed the best field emission properties.
• Fe/Al2O3触媒でのC2H4からのカーボンナノチューブ高速成長の条件とメカニズム

  長谷川 馨; 諸隈 慎吾; 伊藤 龍平; 杉目 恒志; 筧 和憲; 大沢 利男; 野田 優; 丸山 茂夫; 山口 由岐夫

  化学工学会 研究発表講演要旨集 2007 2 - 2 公益社団法人 化学工学会 2007年
• Millimeter-thick single-walled carbon nanotube forests: Hidden role of catalyst support

  Noda, S.; Hasegawa, K.; Sugime, H.; Kakehi, K.; Zhang, Z.; Maruyama, S.; Yamaguchi, Y.

  Japanese Journal of Applied Physics, Part 2: Letters 46 17-19 L399 - L401 2007年 [査読有り]
   

  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. Milli meter-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.
• A simple combinatorial method to discover Co-Mo binary catalysts that grow vertically aligned single-walled carbon nanotubes

  Noda, S.; Sugime, H.; Osawa, T.; Tsuji, Y.; Chiashi, S.; Murakami, Y.; Maruyama, S.

  Carbon 44 8 1414 - 1419 2006年 [査読有り]
   

  A simple yet versatile combinatorial method to discover binary metal nanoparticle catalysts was developed. In this method, the nominal thickness of component metals can be independently screened for a wide range by simply setting a mask with a slit above a substrate during sputter-deposition. Using this method, we prepared a catalyst library with Mo (0.2-4 nm) and Co (0.2-8 nm) thickness profiles on a SiO(2)/Si wafer and discovered active catalysts that grow vertically aligned single-walled carbon nanotubes by alcohol catalytic chemical vapor deposition. (C) 2005 Elsevier Ltd. All rights reserved.

MISC

• Combinatorial Control of Catalyst Nanoparticles for Customized Production of Single- and Multi-Walled Carbon Nanotubes

  NODA Suguru; HASEGAWA Kei; SUGIME Hisashi; KAKEHI Kazunori; MARUYAMA Shigeo; YAMAGUCHI Yukio Extended abstracts of the ... Conference on Solid State Devices and Materials 2007 1180 -1181 2007年09月
• C113 一酸化炭素からの単層カーボンナノチューブ合成に与えるCo/Mo比の影響(OS-11 ナノスケール伝熱I)

  西井 俊明; 村上 陽一; 野田 優; 杉目 恒志; 桝山 直人; 丸山 茂夫 熱工学コンファレンス講演論文集 2005 97 -98 2005年11月

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  杉目 恒志, 野田 優

受賞

• 2018年12月 早稲田大学リサーチアワード（国際研究発信力）
  
• 2017年09月 化学工学会CVD反応分科会・若手奨励賞
  

共同研究・競争的資金等の研究課題

• ファンデルワールス材料のキャリア制御によるアクティブ熱輸送制御

  日本学術振興会：科学研究費助成事業

  研究期間 : 2020年10月 -2024年03月 

  代表者 : 廣谷 潤; 大町 遼; 杉目 恒志; 劉 麗君; 山中 真仁

   

  本研究では、電子工学・化学・機械工学に特徴を持つ国際異分野若手研究者を結集して、原子層材料の熱物性をキャリア量や欠陥密度を厳密に把握したうえで明らかにすることを研究目的とする。ラマン分光計測やナノデバイスによる熱・電気計測で実績のある研究代表者に加え、材料組成制御、表面化学修飾、シミュレーションなどの強力な分担者のサポートの下、高感度熱計測の1つであるサーモリフレクタンス計測やナノ界面熱輸送に関して実績のある国際共同研究者がタッグを組むことで、層状物質に関する熱輸送の国際共同研究を推進する
• 成長停止の制御による長尺カーボンナノチューブフォレスト合成法の開発

  研究期間 : 2019年06月 -2021年03月 

  カーボンナノチューブ(CNT)は、高い機械的強度や電気・熱伝導性など極めて優れた特性を有し、幅広い産業での応用が期待されている。一方で、用途に応じた合成制御ができていないことが実用化を妨げており、例えばフォレストの成長停止が長尺化を妨げている。現在までの最長のCNTフォレストは約2cmであり、導電性ワイヤなどの応用において本来の引張強度や導電性を示さない。 本研究では、新規触媒の開発と反応系の設計を行い、成長停止しない数十cmのフォレスト(既存の10倍以上)の合成技術を開発し数十cmのCNTフォレストの合成を目指す。
• 導電性基板上での高密度カーボンナノチューブフォレストの構造制御と電子デバイス応用

  日本学術振興会：科学研究費助成事業

  研究期間 : 2017年04月 -2019年03月 

  代表者 : 杉目 恒志

   

  高密度カーボンナノチューブフォレストを用いた高感度・高耐久性な立体型櫛型電極(IDE)の開発とバイオセンサへの応用を行った。サイクリックボルタンメトリによるK4[Fe(CN)6]の電気化学的な測定の結果，Au電極IDEと比較してCNTフォレストIDEでは酸化還元電流が定常状態に早く到達した。アスコルビン酸共存下におけるドーパミンの測定の結果，線形領域が100 nM - 100 μM，検出感度が14.3 mA mol－1 L，検出限界(LOD, S/N=3)が42 nMとCNTF-IDEは高い特性を示した。また繰り返し測定において汚染による性能劣化が少なく、高い耐久性を持つことが分かった。電気化学センサに用いる電極材料として、カーボン電極は従来の金属電極と比較して高感度が得られることが期待される。中でも高い導電性と表面積を持つカーボンナノチューブを用いることでより高感度になることが期待できる。一方で従来の成長方法では電極応用するための適した構造を作製することが難しかった。本研究ではオリジナルの触媒と成長技術を用いて微細構造を作製し、実際に分析物を高感度に測定可能であることを示した。今後さらに技術開発を行うことで、小型かつ高感度なバイオセンサや医療技術などへの応用が期待できる

その他のリンク

researchmap

https://researchmap.jp/sugime