Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Koji Takahashi Last modified date:2020.06.20

Professor / Thermophysics and Fluid Mechanics / Department of Aeronautics and Astronautics / Faculty of Engineering


Papers
1. Sota Hirokawa, Hideaki Teshima, Pablo Solís-Fernández, Hiroki Ago, Yoko Tomo, Qin-Yi Li, Koji Takahashi, Nanoscale Bubble Dynamics Induced by Damage of Graphene Liquid Cells, ACS Omega, 10.1021/acsomega.0c01207, 5, 19, 11180-11185, 2020.05, Graphene liquid cells provide the highest possible spatial resolution for liquid-phase transmission electron microscopy. Here, in graphene liquid cells (GLCs), we studied the nanoscale dynamics of bubbles induced by controllable damage in graphene. The extent of damage depended on the electron dose rate and the presence of bubbles in the cell. After graphene was damaged, air leaked from the bubbles into the water. We also observed the unexpected directional nucleation of new bubbles, which is beyond the explanation of conventional diffusion theory. We attributed this to the effect of nanoscale confinement. These findings provide new insights into complex fluid phenomena under nanoscale confinement..
2. Hideaki Teshima, Sirshendu Misra, Koji Takahashi, Sushanta K. Mitra, Precursor-Film-Mediated Thermocapillary Motion of Low-Surface-Tension Microdroplets, Langmuir : the ACS journal of surfaces and colloids, 10.1021/acs.langmuir.0c00148, 36, 19, 5096-5105, 2020.05, In contrast to microdroplet condensation with high contact angles, the one with low contact angles remains unclear. In this study, we investigated dynamics of microdroplet condensation of low-surface-tension liquids on two flat substrate surfaces by using reflection interference confocal microscopy. Spontaneous migration toward relatively larger droplets was first observed for the microdroplets nucleated on the hydrophilic quartz surface. The moving microdroplets showed a contact angle hysteresis of ∼0.5°, which is much lower than the values observed on typical flat substrates and is within the range observed on slippery lubricant-infused porous surfaces. Because the microdroplets on the hydrophobic polydimethylsiloxane surface did not move, we concluded that the ultrathin precursor film is formed only on the hydrophilic surface, which reduces a resistive force to migration. Also, reduced size of droplets promotes the thermocapillary motion, which is induced by a gradient in local temperature inside a small microdroplet arising due to the difference in size of adjacent droplets..
3. Biao Shen, Jiewei Liu, Gustav Amberg, Minh Do-Quang, Junichiro Shiomi, Koji Takahashi, Yasuyuki Takata, Contact-line behavior in boiling on a heterogeneous surface
Physical insights from diffuse-interface modeling, Physical Review Fluids, 10.1103/PhysRevFluids.5.033603, 5, 3, 2020.03, Enhancement of boiling heat transfer on biphilic (mixed-wettability) surfaces faces a sudden reversal at low pressures, which is brought about by excessive contact-line spreading across the wetting heterogeneities. We employ the diffuse-interface approach to numerically study bubble expansion on a heating surface that consists of opposing wettabilities. The results show a dramatic shift in the dynamics of a traversing contact line across the wettability divide under different gravities, which correspond to variable bubble growth rates. Specifically, it is found that the contact-line propagation tends to follow closely the rapidly expanding bubble at low gravity, with only a brief interruption at the border between the hydrophobic and hydrophilic sections of the surface. Only when the bubble growth becomes sufficiently weakened at high gravity does the contact line get slowed down drastically to the point of being nearly immobilized at the edge of the hydrophilic surface. The following bubble expansion, which faces strong limitations in the direction parallel to the surface, features a consistent apparent contact angle at around 66.4°, regardless of the wettability combination. A simple theoretical model based on the force-balance analysis is proposed to describe the physical mechanism behind such a dramatic transition in the contact-line behavior..
4. Qin Yi Li, Tianli Feng, Wakana Okita, Yohei Komori, Hiroo Suzuki, Toshiaki Kato, Toshiro Kaneko, Tatsuya Ikuta, Xiulin Ruan, Koji Takahashi, Enhanced Thermoelectric Performance of As-Grown Suspended Graphene Nanoribbons, ACS nano, 10.1021/acsnano.9b03521, 13, 8, 9182-9189, 2019.08, Conventionally, graphene is a poor thermoelectric material with a low figure of merit (ZT) of 10<sup>-4</sup>-10<sup>-3</sup>. Although nanostructuring was proposed to improve the thermoelectric performance of graphene, little experimental progress has been accomplished. Here, we carefully fabricated as-grown suspended graphene nanoribbons with quarter-micron length and â40 nm width. The ratio of electrical to thermal conductivity was enhanced by 1-2 orders of magnitude, and the Seebeck coefficient was several times larger than bulk graphene, which yielded record-high ZT values up to â0.1. Moreover, we observed a record-high electronic contribution of â20% to the total thermal conductivity in the nanoribbon. Concurrent phonon Boltzmann transport simulations reveal that the reduction of lattice thermal conductivity is mainly attributed to quasi-ballistic phonon transport. The record-high ratio of electrical to thermal conductivity was enabled by the disparate electron and phonon mean free paths as well as the clean samples, and the enhanced Seebeck coefficient was attributed to the band gap opening. Our work not only demonstrates that electron and phonon transport can be fundamentally tuned and decoupled in graphene but also indicates that graphene with appropriate nanostructures can be very promising thermoelectric materials..
5. Hideaki Teshima, Yasuyuki Takata, Koji Takahashi, Adsorbed gas layers limit the mobility of micropancakes, Applied Physics Letters, 10.1063/1.5113810, 115, 7, 2019.08, In contrast to surface nanobubbles, the properties of atomically flat gas phases such as micropancakes remain unclear. In this study, we investigated nanoscopic gas phases existing at the interface between highly ordered pyrolytic graphite and air-supersaturated pure water using high-sensitivity frequency-modulation atomic force microscopy (AFM). Micropancakes appeared on a disordered gas layer overlying an ordered gas layer and moved in the direction of AFM scanning. Their movement stopped at the edge of the disordered gas layers, whereas the two gas layers did not move at all. The limited mobility of micropancakes is explained by assuming that the disordered and ordered gas layers, which are composed of strongly adsorbed gas molecules, behave like solid surfaces, and that the surface heterogeneity between them results in a pinning effect..
6. Qin Yi Li, Ryo Matsushita, Yoko Tomo, Tatsuya Ikuta, Koji Takahashi, Water Confined in Hydrophobic Cup-Stacked Carbon Nanotubes beyond Surface-Tension Dominance, Journal of Physical Chemistry Letters, 10.1021/acs.jpclett.9b00718, 10, 13, 3744-3749, 2019.01, Water confined in carbon nanotubes (CNTs) can exhibit distinctly different behaviors from the bulk. We report transmission electron microscopy (TEM) observation of water phases inside hydrophobic cup-stacked CNTs exposed to high vacuum. Unexpectedly, we observed stable water morphologies beyond surface-tension dominance, including nanometer thin free water films, complex water-bubble structures, and zigzag-shaped liquid-gas interface. The menisci of the water phases are complex and inflected, where we measured the contact angles on the CNT inner wall to be 68-104°. The superstability of the suspended ultrathin water films is attributed to the strong hydrogen-bonded network among water molecules and adsorption of water molecules on the cup-structured inner wall. The complex water-bubble structure is a result of the stability of free water films and interfacial nanobubbles, and the zigzag edge of the liquid-gas interface is explained by the pinning effect. These experimental findings provide valuable knowledge for the research on fluids under nanoscale confinement..
7. Masahiro Narasaki, Qin Yi Li, Tatsuya Ikuta, Jin Miyawaki, Koji Takahashi, Modification of thermal transport in an individual carbon nanofiber by focused ion beam irradiation, Carbon, 10.1016/j.carbon.2019.07.056, 153, 539-544, 2019.11, We report on the in situ thermal measurement of a carbon nanofiber (CNF) modified by focused ion beam (FIB) irradiation. The FIB irradiation led to local amorphization of the crystalline structure of the CNF. The in situ measurement was improved by correcting for the effect of the scattered ions on the sensor. The low effective thermal conductivity of the pristine CNF (∼39 W/mK) resulted from the anisotropic structure made of many individual graphitic fibers. The first FIB irradiation decreased the thermal conductivity by approximately 3.2%. This relatively small decrease is attributed to the structure of the CNF consisting of many individual fibers, with some fibers remaining pristine even after the FIB irradiation. Analysis using a thermal-circuit model suggested that the thermal transport in the CNF could include a ballistic feature of phonons in the micrometer range. Our proposed in situ thermal measurement method can be extended to the study of thermal transport in various structurally modified nanomaterials..
8. Qinyi Li, Koji Takahashi, Xing Zhang, Frequency-domain Raman method to measure thermal diffusivity of one-dimensional microfibers and nanowires, International Journal of Heat and Mass Transfer, 10.1016/j.ijheatmasstransfer.2019.01.057, 539-546, 2019.05, Thermal property measurement of individual micro- and nano-materials has been very challenging and the development of measurement methods is crucial for the experimental investigation of microscale and nanoscale heat transfer. Here we present a noncontact frequency-domain Raman method to measure thermal diffusivity of individual 1D microfibers and nanowires without the need of knowing laser absorptivity. Cosine-wave modulated laser is used to heat the sample, while the laser-intensity-weighted spatiotemporal average temperature is simultaneously detected from the sample's Raman band shift. Transient heat conduction models under periodic heating are established and analytically solved in the frequency domain with considerations of the Gaussian laser distribution and thermal contact resistance. By varying the laser modulation frequency as well as the laser spot size, we can eliminate the laser absorptivity by a normalization technique and extract the thermal diffusivity with high sensitivity. Typically, if the thermal diffusivity is on the order of 10 −4 m 2 /s, we need to use the modulation frequencies on the order of 10 Hz to measure millimeter long microfibers, and ∼MHz frequencies to measure micrometer long nanowires. We also demonstrate that any kind of periodic laser modulation can be decomposed to a series of cosine modes and readily analyzed by this frequency-domain approach, which can greatly broaden the applications of transient Raman techniques..
9. Biao Shen, Takeshi Hamazaki, Wei Ma, Naoki Iwata, Sumitomo Hidaka, Atsushi Takahara, Koji Takahashi, Yasuyuki Takata, Enhanced pool boiling of ethanol on wettability-patterned surfaces, Applied Thermal Engineering, 10.1016/j.applthermaleng.2018.12.049, 325-331, 2019.02, Due to the considerably reduced boiling point, organic fluids such as ethanol provide an attractive alternative to water as the working fluid in two-phase thermal management systems for high-heat-flux applications. The state-of-the-art enhancement methods for ethanol boiling normally involve surface structure engineering. Here we report, for the first time, enhancement of nucleate boiling of ethanol using wettability-patterned surfaces. By depositing onto a polished copper surface an array of circular spots of superamphiphobic coating of modified halloysite nanotubes (HNT) with fluoropolymer, which was shown to repel low-surface-tension fluids, we managed to create a meaningful biphilic pattern of alternating hydrophobicity (with ethanol contact angle exceeding 100°) and hydrophilicity (with contact angle close to 0°) on the surface. Boiling heat transfer was found to be improved dramatically on the coated surface. Specifically, the onset of nucleate boiling was found to drop by more than 35%. Moreover, at 20 K surface superheat (above the boiling point), a maximum heat transfer enhancement over 300% compared with a plain copper surface occurred on the surface with a pitch-to-spot ratio close to 2.5. The significantly increased heat transfer rate of the biphilic surfaces could be attributed to facilitated bubble nucleation and stronger agitation effect..
10. Qinyi Li, Koki Katakami, Tatsuya Ikuta, Masamichi Kohno, Xing Zhang, Koji Takahashi, Measurement of thermal contact resistance between individual carbon fibers using a laser-flash Raman mapping method, Carbon, 10.1016/j.carbon.2018.09.034, 141, 92-98, 2019.01, Thermal contact resistance (TCR) between individual carbon fibers (CFs) can dominate heat dissipation rates in CF-based composite materials. Here, we develop a totally non-contact “laser-flash Raman mapping” method to simultaneously measure the TCR at the CF-CF junction and their thermal conductivities. Laser power is used to heat the sample and the laser absorptivity is experimentally determined by a transient laser-flash Raman technique. The laser heating positions are changed along two connected CFs, and the change of temperature rise with varying positions is in-situ measured from the temperature dependent Raman band shifts. The high spatial resolution of the micro-Raman mapping allows direct observation of the abrupt jump of thermal resistance at the CF-CF junction, from which we extracted the TCR as well as the thermal conductivity. The laser absorptivity of the 11 μm-diameter CFs is measured to be 0.12 ± 0.03, the thermal conductivities of the individual CFs are around 200 W/mK, and the TCR of the CF-CF junction is (2.98 ± 0.92) × 105 K/W. This work provides indispensable knowledge for the design of CF-based composite for thermal management, and the novel non-contact measurement method can stimulate characterization and manipulation of contact/interface heat conduction between various micro- and nano-materials..
11. Yoko Tomo, Qinyi Li, Tatsuya Ikuta, Yasuyuki Takata, Koji Takahashi, Unexpected Homogeneous Bubble Nucleation near a Solid-Liquid Interface, Journal of Physical Chemistry C, 10.1021/acs.jpcc.8b09200, 122, 50, 28712-28716, 2018.12, We report a quasi-three-dimensional observation of electron-beam-induced nanobubbles inside a 1000 nm thick layer of water using the liquid cell electron microscopy. In the early stage of observation, heterogeneous bubble nucleation occurred, and small bubbles coalesced with the adjacent bubbles when they come in contact with each other. However, for the first time, we found that after prolonged electron beam irradiation heterogeneous nucleation did not occur more, and then homogeneous nucleation started even though a solid surface was available for heterogeneous nucleation. We conclude that the Ostwald ripening effect prevents heterogeneous nucleation from occurring and that the lower surface tension due to the generation of ions and radicals boosts the homogeneous nucleation. It was also discovered that the generation sites of homogeneous nucleation are beneath the three-phase contact lines of existing interfacial bubbles..
12. Biao Shen, Masayuki Yamada, Tomosuke Mine, Sumitomo Hidaka, Masamichi Kohno, Koji Takahashi, Yasuyuki Takata, Depinning of bubble contact line on a biphilic surface in subatmospheric boiling
Revisiting the theories of bubble departure, International Journal of Heat and Mass Transfer, 10.1016/j.ijheatmasstransfer.2018.06.030, 126, 715-720, 2018.11, Boiling suffers from inefficient intermittent cycles of bubble generation under subatmospheric conditions. Such deterioration in heat transfer rates can be alleviated but not completely eliminated by use of mixed-wettability (biphilic) surfaces. Here we study bubble dynamics on a single hydrophobic spot in low-pressure pool boiling. The results reveal an interesting transition in bubble departure behavior from the surface-driven mode to the drag-driven mode, which correlates closely with the dynamic state of the three-phase contact line on the surface. Based on the force-balance argument, a simple model is derived to map the contact-line mobility during bubble growth. It is found that below a certain threshold pressure, the bubble base expansion is increasingly likely to overcome the strong pinning of the contact line at the interface between the hydrophobic and hydrophilic regions. That could lead to total removal of vapor residues from the surface and cause deactivation of the nucleation site, which portends the eventual takeover of intermittent boiling on the biphilic surface..
13. Biao Shen, Jiewei Liu, Junichiro Shiomi, Gustav Amberg, Minh Do-Quang, Masamichi Kohno, Koji Takahashi, Yasuyuki Takata, Effect of dissolved gas on bubble growth on a biphilic surface
A diffuse-interface simulation approach, International Journal of Heat and Mass Transfer, 10.1016/j.ijheatmasstransfer.2018.06.043, 126, 816-829, 2018.11, In this paper, we numerically study pool boiling of a binary (water and nitrogen) mixture on a surface endowed with a combination of hydrophobicity and hydrophilicity (i.e., the so called biphilic surface). Here we adopt a numerical approach based on the phase field theory, where the vapor-liquid interface is assumed to be of a finite thickness (hence diffusive in nature) and requires no explicit tracking schemes. The theoretical modeling of two-phase heat and mass transfer in water diluted with nitrogen demonstrates the significant impact of impurities on bubble dynamics. The simulations show that locally high concentrations of nitrogen gas within the vapor bubble is essential to weakening the condensation effect, which results in sustained bubble growth and ultimately (partial) departure from the surface under the artificially enlarged gravity. Simply increasing the solubility of nitrogen in water, however, turns out to be counterproductive because possible re-dissolution of the aggregated nitrogen by the bulk water could deprive the bubble of vital gas contents, leading instead to continuous bubble shrinkage and collapse. Additionally, it is found that with the significant accumulation of nitrogen, the bubble interface is increasingly dominated by a strong interfacial thermocapillary flow due to the Marangoni effect..
14. Yutaka Yamada, Kanoko Taguchi, Tatsuya Ikuta, Akihiko Horibe, Koji Takahashi, Meniscus Motion and Void Generation Inside Carbon Nanotubes, Journal of Physical Chemistry C, 10.1021/acs.jpcc.8b06406, 122, 38, 21910-21918, 2018.09, The hollow inside of a carbon nanotube (CNT) has great potential not only for flow rate enhancement of nanocapillary, but also for a material container which can be applied for drug delivery and nanoparticle infusion. However, these applications focus on after liquid infusion into CNTs, whereas the understanding of the filling process is still limited. We conducted capillary filling experiments using individual open-ended CNTs, which were stuck into an ionic liquid and visualized by scanning transmission electron microscopy. The results showed that the meniscus stopped inside the CNT, which is not predicted by the Lucas-Washburn equation. To explain this discrepancy, the intermolecular force between the liquid and CNT inner wall was proposed to provide an additional friction force. In addition, voids were observed in the liquid inside the CNT. The generation mechanism of voids was proposed to be induced by the instability of the thin liquid layer along the CNT inner surface caused by the advance of the three-phase contact line. The results of the present study increase our understanding of nanoscale capillary action..
15. Koji Takahashi, Bubbles and droplets at the initial stage of nucleation
Recent advances in experimental techniques, 16th International Heat Transfer Conference, IHTC 2018 International Heat Transfer Conference, 2018-August, 359-367, 2018.01, Recent microfabrication techniques have exhibited tremendous opportunities to improve the phase-change heat transfer by tailoring the surface structure and wettability, which indicates that microscopic understanding of liquid-gas phase change is vital for further improvement of heat transfer devices. Boiling and condensation have been studied by numerous researchers for more than a half century and are known to be a successive process of nucleation, growth and departure of bubbles and droplets. Fluid dynamical modeling has been extensively developed for their growth and departure but the nucleation is still incompletely understood because of the lack of imaging techniques of two-phase phenomena smaller than the resolution limit of optical microscopy. This paper introduces new trends to investigate nanoscale bubbles and droplets experimentally, using AFM, SEM and TEM. AFM is of the highest spatial resolution and its feedback control of tip tapping enables us to obtain the accurate shape of nanobubbles at the solid-liquid interface. A new mode of AFM gives force data of approaching and retracting tips, which unveils the strong interaction between nanobubble and AFM tip. Environmental SEM is a useful tool for observing water condensation with droplets of micrometer-order diameter but there are several concerns including the contamination due to the electron beam irradiation. TEM requires ultra-high vacuum environment but utilization of nano liquid cell enables us to image the liquid-gas interface in nanoscale. By using these techniques, some key issues for generation and stability of interfacial nanobubbles and condensed nanodroplets have been understood, which should result in novel techniques to control the initial stage of phase change heat transfer..
16. Satoshi Takeichi, Takashi Nishiyama, Mitsuru Tabara, Shuichi Kawawaki, Masamichi Kohno, Koji Takahashi, Tsuyoshi Yoshitake, Effects of hydrogenation on thermal conductivity of ultrananocrystalline diamond/amorphous carbon composite films prepared via coaxial arc plasma deposition, Applied Physics Express, 10.7567/APEX.11.065101, 11, 6, 2018.06, Ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite (UNCD/a-C:H) and UNCD/non-hydrogenated amorphous carbon (a-C) composite (UNCD/a-C) films were prepared via coaxial arc plasma deposition, and their thermal conductivity and interfacial conductance in grain boundaries were measured using a time-domain thermoreflectance method. The interfacial conductance was estimated to be 1,010 and 4,892MW/(m
2
&K) for UNCD/a-C:H and UNCD/a-C films, respectively. The reasons for the hydrogenated film having lower interfacial conductance than the non-hydrogenated film are 1) the reduced number of carriers that contribute to heat transport and 2) the hydrogen atoms, which are preferentially located at the grain boundaries and enhance phonon scattering..
17. Yoko Tomo, Alexandros Askounis, Tatsuya Ikuta, Yasuyuki Takata, Khellil Sefiane, Koji Takahashi, Superstable Ultrathin Water Film Confined in a Hydrophilized Carbon Nanotube, Nano Letters, 10.1021/acs.nanolett.7b05169, 18, 3, 1869-1874, 2018.03, Fluids confined in a nanoscale space behave differently than in the bulk due to strong interactions between fluid molecules and solid atoms. Here, we observed water confined inside “open” hydrophilized carbon nanotubes (CNT), with diameter of tens of nanometers, using transmission electron microscopy (TEM). A 1−7 nm water film adhering to most of the inner wall surface was observed and remained stable in the high vacuum (order of 10−5 Pa) of the TEM. The superstability of this film was attributed to a combination of curvature, nanoroughness, and confinement resulting in a lower vapor pressure for water and hence inhibiting its vaporization. Occasional, suspended ultrathin water film with thickness of 3−20 nm were found and remained stable inside the CNT. This film thickness is 1 order of magnitude smaller than the critical film thickness (about 40nm) reported by the Derjaguin−Landau−Verwey−Overbeek theory and previous experimental investigations. The stability of the suspended ultrathin water film is attributed to the additional molecular interactions due to the extended water meniscus, which balances the rest of the disjoining pressures..
18. Hideaki Teshima, Koji Takahashi, Yasuyuki Takata, Takashi Nishiyama, Wettability of AFM tip influences the profile of interfacial nanobubbles, Journal of Applied Physics, 10.1063/1.5010131, 123, 5, 2018.02.
19. Hongbin He, Biao Shen, Liangyu Chen, Sumitomo Hidaka, Koji Takahashi, Masamichi Kohno, Yasuyuki Takata, Heat transfer enhancement of a loop thermosyphon with a hydrophobic spot-coated surface, Journal of Thermal Science and Technology, 10.1299/jtst.2018jtst0011, 13, 1, 2018.01.
20. Qinyi Li, Xing Zhang, Koji Takahashi, Variable-spot-size laser-flash Raman method to measure in-plane and interfacial thermal properties of 2D van der Waals heterostructures, International Journal of Heat and Mass Transfer, 10.1016/j.ijheatmasstransfer.2018.05.011, 125, 1230-1239, 2018, Stacked layers of different atomically thin 2D materials is called the van der Waals (vdW) heterostructure, which has become a rapidly developing research field due to its extraordinary and tunable properties. In this paper, we develop a variable-spot-size laser-flash Raman method to in-situ measure the thermal properties as well as the laser absorption in the supported 2D vdW heterostructure with arbitrary layers. The extracted thermal properties include the in-plane thermal conductivity and diffusivity of each layer, and interfacial thermal conductance between every two adjacent layers. A three-dimensional transient heat conduction model is developed and analytically solved to describe the process of pulsed Gaussian laser heating supported n-layer heterostructure. The temperature of each atomic layer can be simultaneously non-contact detected from their distinct Raman peaks whose positions are temperature dependent. The laser spot sizes and pulse durations are varied to generate multiple temperature curves. The multiple thermal properties as well as the laser absorption can be extracted by simultaneously fitting these temperature curves into the analytical solutions at multiple spot sizes or/and pulse durations. We also establish the approach of sensitivity and uncertainty analysis for the multi-response multi-parameter least-square fitting in our proposed measurement methods. Case studies show that the transient temperature curves are generally more sensitive to the thermal properties than the steady-state temperatures at variable spot sizes. All the unknown thermal properties and laser absorption can be extracted with sufficiently high accuracy if multiple transient temperature curves at multiple spot sizes are simultaneously fitted into the analytical solution. The measurement method and uncertainty analysis approach presented here are useful for investigating the thermal transport in the emerging 2D materials and vdW heterostructures..
21. Biao Shen, Masayuki Yamada, Sumitomo Hidaka, Jiewei Liu, Junichiro Shiomi, Gustav Amberg, Minh Do-Quang, Masamichi Kohno, Koji Takahashi, Yasuyuki Takata, Early Onset of Nucleate Boiling on Gas-covered Biphilic Surfaces, Scientific Reports, 10.1038/s41598-017-02163-8, 7, 1, 2017.12.
22. Daniel Orejon, Orest Shardt, Naga Siva Kumar Gunda, Tatsuya Ikuta, Koji Takahashi, Yasuyuki Takata, Sushanta K. Mitra, Simultaneous dropwise and filmwise condensation on hydrophilic microstructured surfaces, INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, 10.1016/j.ijheatmasstransfer.2017.06.023, 114, 187-197, 2017.11.
23. Qinyi Li, Koji Takahashi, Xing Zhang, Comment on "divergent and Ultrahigh Thermal Conductivity in Millimeter-Long Nanotubes", Physical Review Letters, 10.1103/PhysRevLett.119.179601, 119, 17, 2017.10.
24. Masahiro Narasaki, Haidong Wang, Takashi Nishiyama, Tatsuya Ikuta, Koji Takahashi, Experimental study on thermal conductivity of free-standing fluorinated single-layer graphene, Applied Physics Letters, 10.1063/1.5001169, 111, 9, 2017.08.
25. Qin-Yi Li, Kailun Xia, Ji Zhang, Yingying Zhang, Qunyang Li, Koji Takahashi, Xing Zhang, Measurement of specific heat and thermal conductivity of supported and suspended graphene by a comprehensive Raman optothermal method, NANOSCALE, 10.1039/c7nr01695f, 9, 30, 10784-10793, 2017.08.
26. Haidong Wang, Shiqian Hu, Koji Takahashi, Xing Zhang, Hiroshi Takamatsu, Jie Chen, Experimental study of thermal rectification in suspended monolayer graphene, Nature Communications, 10.1038/ncomms15843, 8, 2017.06.
27. Yoko Tomo, Koji Takahashi, Takashi Nishiyama, Tatsuya Ikuta, Yasuyuki Takata, Nanobubble nucleation studied using Fresnel fringes in liquid cell electron microscopy, International Journal of Heat and Mass Transfer, 10.1016/j.ijheatmasstransfer.2017.01.013, 108, 1460-1465, 2017.05.
28. Yutaka Yamada, ASKOUNIS ALEXANDROS, Tatsuya Ikuta, Koji Takahashi, Yasuyuki Takata, SEFIANE KHELLIL, Thermal Conductivity of Liquid/CNT Core-Shell Nanocomposites, J. Appl. Phys., 10.1063/1.4973488, 121, 015104, 2017.01.
29. Hideaki Teshima, Takashi Nishiyama, Koji Takahashi, Nanoscale pinning effect evaluated from deformed nanobubbles, JOURNAL OF CHEMICAL PHYSICS, 10.1063/1.4973385, 146, 1, 2017.01.
30. Biao Shen, Bambang Joko Suroto, Sana Hirabayashi, Masayuki Yamada, Sumitomo Hidaka, Masamichi Kohno, Koji Takahashi, Yasuyuki Takata, Bubble activation from a hydrophobic spot at “negative“ surface superheats in subcooled boiling, Applied Thermal Engineering, 10.1016/j.applthermaleng.2014.10.054, 88, 2017.01.
31. Hongbin He, Kento Furusato, Masayuki Yamada, Biao Shen, Sumitomo Hidaka, Masamichi Kohno, Koji Takahashi, Yasuyuki Takata, Efficiency enhancement of a loop thermosyphon on a mixed-wettability evaporator surface, Applied Thermal Engineering, 10.1016/j.applthermaleng.2017.05.145, 123, 1245-1254, 2017.01.
32. M. Yamada, B. Shen, T. Imamura, S. Hidaka, Masamichi Kohno, Koji Takahashi, Yasuyuki Takata, Enhancement of boiling heat transfer under sub-atmospheric pressures using biphilic surfaces, International Journal of Heat and Mass Transfer, 10.1016/j.ijheatmasstransfer.2017.08.078, 115, 753-762, 2017.01.
33. Takashi Nishiyama, Masamichi Kohno, Koji Takahashi, Tsuyoshi Yoshitake, Thermal Conductivity of Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films Prepared by Coaxial Arc Plasma Deposition, ECS Transactions, 75, 25, 27-32, 2017.
34. Qinyi Li, Koji Takahashi, Zhang Xing, Measurement of specific heat and thermal conductivity of supported and suspended graphene by a comprehensive Raman optothermal method, Nanoscale, 9, 10784-10793, 2017.
35. Masahiro Narasaki, DONG HAI WANG, Yasuyuki Takata, Koji Takahashi, Influence of ion beam scattering on the electrical resistivity of platinum hot films, MICROELECTRONIC ENGINEERING, 10.1016/j.mee.2016.09.008, 166, 15-18, 2016.12.
36. ASKOUNIS ALEXANDROS, 山田 寛, Tatsuya Ikuta, Koji Takahashi, Yasuyuki Takata, SEFIANE KHELLIL, On the linear dependence of a carbon nanofiber thermal conductivity on wall thickness, AIP ADVANCES, 10.1063/1.4968831, 6, 11, 2016.11.
37. Tingting Miao, Shaoyi Shi, Shen Yan, Weigang Ma, Xing Zhang, Koji Takahashi, Tatsuya Ikuta, Integrative characterization of the thermoelectric performance of an individual multiwalled carbon nanotube, JOURNAL OF APPLIED PHYSICS, 10.1063/1.4962942, 120, 12, 2016.09.
38. Haidong Wang, Kosaku Kurata, Takanobu Fukunaga, Hiroki Ago, Hiroshi Takamatsu, Xing Zhang, Tatsuya Ikuta, Koji Takahashi, Takashi Nishiyama, Yasuyuki Takata, A general method of fabricating free-standing, monolayer graphene electronic device and its property characterization, Sensors and Actuators, A: Physical, 10.1016/j.sna.2016.05.002, 247, 24-29, 2016.08, We demonstrate a general process for fabricating graphene nanoelectronic devices that have next several features: free-standing, micrometer-sized monolayer graphene with high quality, arbitrarily-shaped metallic electrodes or sensors. In contrast to the normal routes, a gas etching process is used to create a deep trench in silicon for suspending the whole graphene device in a much larger area. User-designed electrodes or sensors are fabricated on the suspended graphene at the same time for realizing multiple functions. In this work, a suspended gold nanofilm sensor is designed to measure the intrinsic electrical and thermal properties of graphene on site. The sensor serves as both electrode and precise resistance thermometer at the same time. By simply changing the metallic electrode shape and electrical circuit, the free-standing graphene can be made into different devices, such as single-molecule detector or nano-resonator. In order to test the robustness of graphene device, a high electrical current is applied to heat the graphene in vacuum until it breaks. The breakdown current density is measured to be 1.86 mA/μm. More importantly, this method is not only limited to graphene, but also can be applied to any other two-dimensional materials..
39. Koji Takahashi, Takashi Nishiyama, 山田 寛, Yasuyuki Takata, Experimental Study of Nanobubbles and Nanodroplets on Hydrophilic/Hydrophobic Combined Surfaces, 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics (HEFAT2016), 11 to 13 July 2016, Costa del Sol, Spain, 655-662, 2016.07.
40. 山田 寛, Koji Takahashi, Yasuyuki Takata, SEFIANE KHELLIL, Wettability on Inner and Outer Surface of Single Carbon Nanotubes, LANGMUIR, 10.1021/acs.langmuir.6b01366, 32, 28, 7064-7069, 2016.07.
41. Qin-yi Li, Masahiro Narasaki, Koji Takahashi, Temperature-dependent specific heat of suspended platinum nanofilms at 80-380 K, Chinese Physics B, 10.1088/1674-1056/25/11/114401, 25, 11, 2016.07.
42. DONG HAI WANG, Kosaku Kurata, Takanobu Fukunaga, Hiroki Ago, Hiroshi Takamatsu, Xing Zhang, Tatsuya Ikuta, Koji Takahashi, Takashi Nishiyama, Yasuyuki Takata, Simultaneous measurement of electrical and thermal conductivities of suspended monolayer graphene, JOURNAL OF APPLIED PHYSICS, DOI: 10.1063/1.4954677, 119, 244306, 2016.06.
43. Haidong Wang, Kosaku Kurata, Takanobu Fukunaga, Hiroki Ago, Hiroshi Takamatsu, Xing Zhang, Tatsuya Ikuta, Koji Takahashi, Takashi Nishiyama, Yasuyuki Takata, Simultaneous measurement of electrical and thermal conductivities of suspended monolayer graphene, Journal of Applied Physics, 10.1063/1.4954677, 119, 24, 2016.06, We measured both in-plane electrical and thermal properties of the same suspended monolayer graphene using a novel T-type sensor method. At room temperature, the values are about 240 000 Ω-1 m-1 and 2100 W m-1 K-1 for the electrical and thermal conductivities, respectively. Based on the Wiedemann-Franz law, the electrons have negligible contribution to the thermal conductivity of graphene, while the in-plane LA and TA modes phonons are the dominant heat carriers. In monolayer graphene, the absence of layer-layer and layer-substrate interactions enhances the contribution of long wave-length phonons to the heat transport and increases the thermal conductivity accordingly. The reported method and experimental data of suspended monolayer graphene are useful for understanding the basic physics and designing the future graphene electronic devices..
44. Haidong Wang, Kosaku Kurata, Takanobu Fukunaga, Hiroshi Takamatsu, Xing Zhang, Tatsuya Ikuta, Koji Takahashi, Takashi Nishiyama, Hiroki Ago, Yasuyuki Takata, A simple method for fabricating free-standing large area fluorinated single-layer graphene with size-tunable nanopores, Carbon, 10.1016/j.carbon.2015.12.070, 99, 564-570, 2016.04, As a solid-state membrane with only one-atom thickness, nano-porous graphene has attracted intense attention in many critical applications. Here, the key challenge is to suspend a single-layer graphene (SLG) and drill nanopores with precise dimensions. Here, we report a simple and reliable route for making suspended fluorinated SLG with size-tunable nanopores. Our method consists of two steps: 1. a free-standing SLG ribbon was created between two gold pads after deep dry etching of silicon substrate by xenon difluoride. The SLG was fluorinated by 5-13%. Superior to the normal wet etching method, the dry etching process is much simpler and results in less hole-defect and edge deformation. A large area fluorinated SLG can be suspended due to the sufficient etch depth. 2. a focused ion beam was introduced to drill nanopores in graphene with an initial diameter around 20 nm. Followed by an electron beam induced carbon deposition, the diameter of nanopore was gradually decreased to sub-10 nm. By changing the deposition time, the size of nanopore can be precisely controlled. High-cost transmission electron microscope is no longer needed. Our method provides a simple and effective way for preparing free-standing fluorinated SLG ribbon suitable for single-molecule detection..
45. Weigang Ma, Tingting Miao, Xing Zhang, Koji Takahashi, Tatsuya Ikuta, Boping Zhang, Zhenhua Ge, A T-type method for characterization of the thermoelectric performance of an individual free-standing single crystal Bi2S3 nanowire , Nanoscale, 10.1039/C5NR05946A , 8, 2704-2710, 2016.02.
46. DONG HAI WANG, Kosaku Kurata, Takanobu Fukunaga, Hiroshi Takamatsu, Xing Zhang, Tatsuya Ikuta, Koji Takahashi, Takashi Nishiyama, Hiroki Ago, Yasuyuki Takata, In-situ measurement of the heat transport in defect-engineered free-standing single-layer graphene, Scientific Reports, DOI: 10.1038/srep21823, 6, 21823, 2016.02.
47. Takashi Nishiyama, Koji Takahashi, Taysuya Ikuta, Yutaka Yamada, Yasuyuki Takata, Hydrophilic Domains Enhance Nanobubble Stability, ChemPhysChem, 10.1002/cphc.201501181, 2016.02.
48. Weigang Ma, Tingting Miao, Xing Zhang, Koji Takahashi, Tatsuya Ikuta, Boping Zhang, Zhenhua Ge, A T-type method for characterization of the thermoelectric performance of an individual free-standing single crystal Bi2S3 nanowire, Nanoscale, 10.1039/c5nr05946a, 8, 5, 2704-2710, 2016.02, A comprehensive method to evaluate the thermoelectric performance of one-dimensional nanostructures, called the T-type method, has been first developed. The thermoelectric properties, including the Seebeck coefficient, thermal conductivity and electrical conductivity, of an individual free-standing single crystal Bi2S3 nanowire have been first characterized by applying the T-type method. The determined figure of merit is far less than the reported values of nanostructured bulk Bi2S3 samples, and the mechanism is that the Seebeck coefficient is nearly zero in the temperature range of 300-420 K and changes its sign at 320 K..
49. Haidong Wang, Kosaku Kurata, Takanobu Fukunaga, Hiroshi Takamatsu, Xing Zhang, Tatsuya Ikuta, Koji Takahashi, Takashi Nishiyama, Hiroki Ago, Yasuyuki Takata, In-situ measurement of the heat transport in defect-engineered free-standing single-layer graphene, Scientific reports, 10.1038/srep21823, 6, 2016.02, Utilizing nanomachining technologies, it is possible to manipulate the heat transport in graphene by introducing different defects. However, due to the difficulty in suspending large-area single-layer graphene (SLG) and limited temperature sensitivity of the present probing methods, the correlation between the defects and thermal conductivity of SLG is still unclear. In this work, we developed a new method for fabricating micro-sized suspended SLG. Subsequently, a focused ion beam (FIB) was used to create nanohole defects in SLG and tune the heat transport. The thermal conductivity of the same SLG before and after FIB radiation was measured using a novel T-type sensor method on site in a dual-beam system. The nanohole defects decreased the thermal conductivity by about 42%. It was found that the smaller width and edge scrolling also had significant restriction on the thermal conductivity of SLG. Based on the calculation results through a lattice dynamics theory, the increase of edge roughness and stronger scattering on long-wavelength acoustic phonons are the main reasons for the reduction in thermal conductivity. This work provides reliable data for understanding the heat transport in a defective SLG membrane, which could help on the future design of graphene-based electrothermal devices..
50. Yamada, Yutaka; Takahashi, Koji; Ikuta, Tatsuya; Nishiyama, Takashi; Takata, Yasuyuki; Ma, Wei; Takahara, Atsushi, Tuning Surface Wettability at the Submicron-Scale: Effect of Focused Ion Beam Irradiation on a Self-Assembled Monolayer, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/acs.jpcc.5b09019, 120, 1, 14532-14537, 2016.01, 撥水の性質を有する薄膜にGaイオンビームを照射することで50nmの精度で濡れ性を超撥水から親水へ変化させることができることを見出し、そのメカニズムを調査した論文である。この研究は熱工学分野において重要な相変化現象を薄膜というナノ材料を用いて高度に制御可能とするもので、熱エネルギーの有効利用や機器の温度管理技術の向上に寄与する研究成果である。.
51. DONG HAI WANG, Kosaku Kurata, Takanobu Fukunaga, Hiroshi Takamatsu, Xing Zhang, Tatsuya Ikuta, Koji Takahashi, Takashi Nishiyama, Hiroki Ago, Yasuyuki Takata, A simple method for fabricating free-standing large area fluorinated single-layer graphene with size-tunable nanopores, Carbon, http://dx.doi.org/10.1016/j.carbon.2015.12.070, 99, 564-570, 2016.01.
52. Koji Takahashi, Yusuke Kuwada, Tatsuya Ikuta, MEASURING THE THERAL CONTACT RESISTANCE WITHOUT SURFACE ROUGHNESS, Proceedings of the 26th International Symposium on Transport Phenomena, 27 Sep. - 1 Oct. 2015, Leoben, Austria, PaperID=16, 2015.09.
53. Daio, Takeshi; Bayer, Thomas; Ikuta, Tatsuya; Nishiyama, Takashi; Takahashi, Koji; Takata, Yasuyuki; Sasaki, Kazunari; Lyth, Stephen Matthew, In-Situ ESEM and EELS Observation of Water Uptake and Ice Formation in Multilayer Graphene Oxide, SCIENTIFIC REPORTS, 10.1038/srep11807, 5, 2015.07.
54. Koji Takahashi, Kazuma Nomoto, Tatsuya Ikuta, Temperature Mapping on a Suspended Carbon Nanotube Using Electron Thermal Microscopy, Proceedings of IEEE NANO 2015, 15th INTERNATIONAL CONFERENCE ON NANOTECHNOLOGY, 27-30 JULY 2015, ROME, ITALY, PaperID=264, 2015.07.
55. Qin-Yi Li, Koji Takahashi, Hiroki Ago, Xing Zhang, Taysuya Ikuta, Takashi Nishiyama, Kenji Kawahara, Temperature dependent thermal conductivity of a suspended submicron graphene ribbon, JOURNAL OF APPLIED PHYSICS, 10.1063/1.4907699, 117, 6, 065102, 2015.02.
56. Takashi Nishiyama, Yutaka Yamada, Taysuya Ikuta, Koji Takahashi, Yasuyuki Takata, Metastable Nanobubbles at the Solid-Liquid Interface Due to Contact Angle Hysteresis, LANGMUIR, 10.1021/la5036322, 31, 3, 982-986, 2015.01.
57. Biao Shen, Bambang Joko Suroto, Sana Hirabayashi, Masayuki Yamada, Sumitomo Hidaka, Masamichi Kohno, Koji Takahashi, Yasuyuki Takata, Bubble activation from a hydrophobic spot at “negative” surface superheats in subcooled boiling, Applied Thermal Engineering, 10.1016/j.applthermaleng.2014.10.054, 88, 230-236, 2015.01.
58. Yutaka Yamada, Koji Takahashi, Taysuya Ikuta, Takashi Nishiyama, Yasuyuki Takata, Droplet Nucleation on a Well-Defined Hydrophilic-Hydrophobic Surface of 10 nm Order Resolution, Langmuir, 10.1021/la503615a, 30, 14532-14537, 2014.11.
59. Hiroyuki Hayashi, Koji Takahashi, Taysuya Ikuta, Takashi Nishiyama, Yasuyuki Takata, Xing Zhang, Direct evaluation of ballistic phonon transport in a multi-walled carbon nanotube, APPLIED PHYSICS LETTERS, 10.1063/1.4869470, 104, 11, 014301, 2014.03.
60. Jun Hirotani, Taysuya Ikuta, Koji Takahashi, Experimental Study on Thermal Contact Resistance at the End of a Carbon Nanotube, International Journal of Thermophysics, 10.1007/s10765-011-1137-1, 34, 12, 025301, 2013.12.
61. Qin-Yi Li, Jin-Hui Liu, Hai-Dong Wang, Xing Zhang, Koji Takahashi, Optical absorptance measurement of an individual multiwall carbon nanotube using a T type thermal probe method, REVIEW OF SCIENTIFIC INSTRUMENTS, 10.1063/1.4824494, 84, 10, 014301, 2013.10.
62. Jun Hirotani, Juo Amano, Taysuya Ikuta, Takashi Nishiyama, Koji Takahashi, Carbon nanotube thermal probe for quantitative temperature sensing, Sensors and Actuators A: Physical, doi:10.1016/j.sna.2013.04.038, 199, 1-8, 2013.09.
63. Jun Hirotani, Juo Amano, Tatsuya Ikuta, Takashi Nishiyama, Koji Takahashi, Carbon nanotube thermal probe for quantitative temperature sensing, Sensors and Actuators, A: Physical, 10.1016/j.sna.2013.04.038, 199, 1-8, 2013.06, Quantitative temperature sensing at the nanoscale point contact is developed using a platinum hot film sensor with a carbon nanotube (CNT) as a thermal probe. High spatial resolution and robustness is achieved because of the small tip radius and high stiffness of the CNT. The quantitative local temperature at the CNT probe contact point is determined by bringing the probe in and out of contact and controlling the amount of heat of the Pt hot film in high vacuum environment. Using this method, we overcome the problems of thermal contact resistance (TCR) between the CNT and sample surface. Sensor sensitivity for TCR and thermal conductivity measurement of a CNT is analyzed and the sensor configuration is optimized..
64. Haidong Wang, Jinhui Liu, Xing Zhang, Koji Takahashi, Breakdown of Wiedemann-Franz law in individual suspended polycrystalline gold nanofilms down to 3 K, International Journal of Heat and Mass Transfer, 10.1016/j.ijheatmasstransfer.2013.07.066, 66, 585-591, 2013.08, Metallic nanofilms are of great importance in integrated circuit design and electronic devices. Understanding energy dissipation and transport in metallic nanofilms is essential to practical thermal management. The Wiedemann-Franz (WF) law states a precisely fixed ratio by which the electrons transport heat and charge, providing a basic rule to determine the thermal properties. Hitherto no bulk material has been known to violate the WF law. We report compelling evidence for the breakdown of the WF law in polycrystalline gold nanofilms at low temperatures, the Lorenz number increases notably with decreasing temperature. Our results show that the electrons dominate in heat transport at high temperatures, leading to a constant Lorenz number. While below 40 K, inelastic electron scattering at grain boundaries becomes significant and part of the electron energy is transferred to phonons. Correspondingly, the phonon thermal conductivity is increased and the WF law is violated. A detailed kinetic theoretical model has been developed to investigate several phonon scattering mechanisms in depth and matches well with the experimental results..
65. Hiroyuki Hayashi, Taysuya Ikuta, Takashi Nishiyama, Koji Takahashi, Enhanced anisotropic heat conduction in multi-walled carbon nanotubes, J. Appl. Phys., DOI: 10.1063/1.4772612, 113, 014301, 2013.03.
66. Jun Hirotani, Taysuya Ikuta, Takashi Nishiyama, Koji Takahashi, Measuring the Thermal Boundary Resistance of van der Waals Contacts Using an Individual Carbon Nanotube, Journal of Physics: Condensed Matter, doi:10.1088/0953-8984/25/2/025301, 25, 025301, 2013.01.
67. Hiroyuki Hayashi, Tatsuya Ikuta, Takashi Nishiyama, Koji Takahashi, Enhanced anisotropic heat conduction in multi-walled carbon nanotubes, Journal of Applied Physics, 10.1063/1.4772612, 113, 1, 2013.01, Anisotropy of heat conduction in multi-walled carbon nanotubes (MWNTs) is investigated by measuring heat flows in a pristine MWNT and in a MWNT with defects. The in- and out-of-shell thermal conductivities of each MWNT graphite shell are determined, and differences of more than four orders of magnitude are obtained because of the inter-shell gaps. This enhanced anisotropy reduces the conductance by 74% compared with that of the pristine MWNT because of the presence of outer shell defects, which comprise only 2.8% volume ratio. Furthermore, the anisotropy-assisted length dependence of thermal conductivity is demonstrated, even though there is no ballistic phonon transport..
68. Jun Hirotani, Tatsuya Ikuta, Takashi Nishiyama, Koji Takahashi, Measuring the thermal boundary resistance of van der Waals contacts using an individual carbon nanotube, Journal of Physics Condensed Matter, 10.1088/0953-8984/25/2/025301, 25, 2, 2013.01, Interfacial thermal transport via van der Waals interaction is quantitatively evaluated using an individual multi-walled carbon nanotube bonded on a platinum hot-film sensor. The thermal boundary resistance per unit contact area was obtained at the interface between the closed end or sidewall of the nanotube and platinum, gold, or a silicon dioxide surface. When taking into consideration the surface roughness, the thermal boundary resistance at the sidewall is found to coincide with that at the closed end. A new finding is that the thermal boundary resistance between a carbon nanotube and a solid surface is independent of the materials within the experimental errors, which is inconsistent with a traditional phonon mismatch model, which shows a clear material dependence of the thermal boundary resistance. Our data indicate the inapplicability of existing phonon models when weak van der Waals forces are dominant at the interfaces..
69. Wang H. D., Liu J. H., Guo Z. Y., Koji Takahashi, Non-fourier heat conduction study for steady states in metallic nanofilms, Chin. Sci. Bull., doi: 10.1007/s11434-012-5288-7, 57, 24, 3239-3243, 2012.08.
70. Masanari Kimura, Takafumi Matsuzaki, Koji Takahashi, EDGE EFFECT ON PHONON TRANSPORT IN SUSPENDED AND SUPPORTED GRAPHENE NANORIBBONS, Computational Thermal Sciences, DOI: 10.1615/ComputThermalScien.2012004393, 4, 3, 193-199, 2012.04.
71. Koji Takahashi, Jun Hirotani, Takashi Nishiyama, Tatsuya Ikuta, Hiroshi Takamatsu, APPLICATIONS OF NANO HOT-FILM SENSOR FOR MICRO/NANOSCALE THERMAL MEASURMENT, Proceedings of the ASME 2012 3rd Micro/Nanoscale Heat & Mass Transfer International Conference, March 3-6, 2012, Atlanta, Georgia, USA, MNHMT2012-75030, 2012.03.
72. Yutaka Yamada, Takashi Nishiyama, Takahiro Yasuhara, Koji Takahashi, Thermal Boundary Conductance between Multi-walled Carbon Nanotubes, Journal of Thermal Science and Technology, DOI: 10.1299/jtst.7.190, 7, 1, 190-198, 2012.01.
73. Yutaka Yamada, Takashi Nishiyama, Takahiro Yasuhara, Koji Takahashi, Thermal boundary conductance between multi-walled carbon nanotubes, Journal of Thermal Science and Technology, 10.1299/jtst.7.190, 7, 1, 190-198, 2012.01, Interfacial thermal transport of multi-walled carbon nanotubes (MWNTs) is investigated by using bulk pellet specimens. Steady-state conduction method gives thermal conductivity of 1 to 4 W/mK for the pellets with mass density from 0.2 to 0.35 g/cm3. This low thermal conductivity is due to the thermal boundary conductance between the nanotubes. Computational analysis is conducted for the pellet modeled as a random network of spherocylinders (SCs) and calculated dependency of thermal conductivity on pellet density shows good agreement with experimental data when we treat non-uniform SCs. By comparing the experimental and computational results, the thermal boundary conductance between two MWNTs can be taken as 1.5×10-8 W/K. This result agrees well with the reported data obtained by individual measurement, which suggests this simple method is applicable to probe the interfacial thermal phenomena of nanomaterials. An improved scaling law, k ∝ ρ2.14, for thermal conductivity of MWNTs aggregations is also proposed and discussed..
74. Masanari Kimura, Takafumi Matsuzaki, Koji Takahashi, Edge effect on phonon transport in suspended and supported graphene nanoribbons, Computational Thermal Sciences, 10.1615/ComputThermalScien.2012004393, 4, 3, 193-199, 2012, Heat conduction in a graphene nanoribbon (GNR) is investigated using nonequilibrium molecular dynamics simulation. GNR shows an intriguing dependence of thermal conductivity on its width, length, and edge shape. For example, thermal conductivity of thin armchair GNR is about three times lower than that of zigzag GNR due to the strong phonon scattering at the armchair edge. The substrate interaction is another critical issue for phonon transport. GNR supported on a substrate is analyzed by using the Lennard-Jones potential, and the thermal conductivity of a zigzag ribbon is found to decrease significantly due to phonon scattering by the substrate. However, under the same conditions, that of armchair ribbon is not affected by the substrate or even increases. This phenomenon is caused by the suppression of edge-localized flexural phonons of armchair GNR, which triggers their smaller thermal conductivity than the zigzag one. This anomalous edge-substrate combined effect on thermal transport in supported GNR is discussed..
75. Wang, H.-D. , Liu, J.-H. , Zhang, X. , Guo, Z.-Y., Takahashi, K., Experimental study on the influences of grain boundary scattering on the charge and heat transport in gold and platinum nanofilms, Heat and Mass Transfer/Waerme- und Stoffuebertragung, 47, 893-898, 2011.08.
76. Jun Hirotani, Tatsuya Ikuta, Takashi Nishiyama, Koji Takahashi, Thermal boundary resistance between the end of an individual carbon nanotube and a Au surface, Nanotechnology, 10.1088/0957-4484/22/31/315702, 22, 31, 2011.08, The thermal boundary resistance between an individual carbon nanotube and a Au surface was measured using a microfabricated hot-film sensor. We used both closed and open-ended multi-walled carbon nanotubes and obtained thermal boundary resistance values of 0.947-1.22 × 107KW- 1 and 1.43-1.76 × 107KW- 1, respectively. Considering all uncertainties, including the contact area, the thermal boundary conductances per unit area were calculated to be 8.6 × 107-2.2 × 108Wm- 2K- 1 for c-axis orientation and 4.2 × 108-1.2 × 109Wm- 2K- 1 for the a-axis. The trend in these values agrees with the predicted conductance dependence on the interface orientation of anisotropic carbon-based materials. However, the measured thermal boundary conductances are found to be much larger than the reported results..
77. Jun Hirotani, Tatsuya Ikuta, Takashi Nishiyama and Koji Takahashi, Thermal boundary resistance between the end of an individual carbon nanotube and a Au surface, Nanotechnology, 22, 315702, 2011.05.
78. Satoshi Kai, Koji Takahashi, Hilmi Norsyazwan, Tatsuya Ikuta, Takashi Nishiyama and Kunihito Nagayama, Deposition rate and movement effect of paraffin-based EBID, Electronics and Communications in Japan, 94, 39, 2011.05.
79. Hiroyuki Hayashi, Yohei Ito and Koji Takahashi , Thermal rectification of asymmetrically-defective materials
, Journal of Mechanical Science and Technology, 25, 1, 27-32, 2011.01.
80. Koji Takahashi, Masato Inoue, Yohei Ito, Defective carbon nanotube for use as a thermal rectifier, Japanese journal of applied physics, 10.1143/JJAP.49.02BD12, 49, 2 PART 2, 2010.12, We investigated the thermal properties of a single-walled carbon nanotube with vacancy defects to determine its applicability to solid-state thermal rectification. Nonequilibrium molecular dynamics simulation of a nanotube with randomly located defects only along half the length revealed asymmetric heat conduction at room temperature. The direction of rectification is in good agreement with that obtained in a past experiment in which C9H16Pt was asymmetrically deposited on a nanotube, as far as the local deposition is supposed to cause defects in the nanotube lattice. The mechanism underlying the current thermal rectification effect is discussed considering the temperature dependence of the local thermal conductivity and the phonon filtering effect. The calculated phonon density of states shows larger overlapping when heat flows from the defective part to the pristine part and intermediate-frequency phonons are mainly responsible for rectification..
81. Weigang Ma, Xing Zhang, Koji Takahashi, Electrical properties and reduced Debye temperature of polycrystalline thin gold films, Journal Physics D: Applied Physics, 10.1088/0022-3727/43/46/465301, 43, 46, 2010.11, The temperature-dependent electrical properties of four suspended polycrystalline thin gold films with thicknesses of 20.0, 23.0, 36.0 and 54.0 nm have been measured in the temperature range 100-310 K. The measured results show that the electrical resistivity of the films significantly increases while the corresponding temperature dependence decreases compared with bulk gold. The significantly increased electrical resistivity indicates that grain boundary scattering dominates over surface scattering in the studied films. However, fixing the Debye temperature to the bulk value will lead to an erroneous temperature dependence of resistivity. Taking into account the reduced characteristic Debye temperature along with the surface and grain boundary scattering, the electrical properties of the films can be well described in the whole temperature range. The extracted grain boundary reflection coefficient is 0.3 ± 0.03, within the range of the previous reported values, 0.1-0.45. The films' characteristic Debye temperatures decrease from the bulk value of 165 K to between 83 and 121K and tend to increase with increasing film thickness. This tendency coincides with the previous studies on thin gold, copper, platinum, silver films or wires, and cobalt/nickel superlattices. The possible mechanism responsible for the reduced Debye temperature is phonon softening at the surfaces, grain boundaries, disorder, defects and impurities, part of which has been demonstrated in other studies..
82. Yohei Ito, Taku Higuchi, Koji Takahashi, Submicroscale flow sensor employing suspended hot film with carbon nanotube fins, Journal of Thermal Science and Technology, 10.1299/jtst.5.51, 5, 1, 51-60, 2010.10, A submicroscale flow sensor has been developed that consists of a suspended hot film and carbon nanotube (CNT) fins. Flow measurement experiments, together with a theoretical model, revealed the advantages of the use of CNT fins. The suspended metal film reduces heat loss and the CNT fins enhance the heat transfer to the fluid flow. Herein, the working principle of the CNT fins is presented in detail, together with a description of the micro electro mechanical systems (MEMS)/nano electro mechanical systems (NEMS) techniques used to fabricate the sensor. The CNTs were deposited by a manipulation method that is based on dielectrophoresis..
83. Koji Takahashi, Yohei Ito, Tatsuya Ikuta, A GRAPHENE CHAIN ACTS AS A LONG-DISTANCE BALLISTIC HEAT CONDUCTOR, Proceedings of the International Heat Transfer Conference IHTC14, August 8-13, 2010, Washington, DC, USA,, IHTC14-22289, 2010.08.
84. Hiroki Ago, Tetsushi Nishi, Kenta Imamoto, Naoki Ishigami, Masaharu Tsuji, Tatsuya Ikuta, Koji Takahashi, Orthogonal growth of horizontally aligned single-walled carbon nanotube arrays, Journal of Physical Chemistry C, 10.1021/jp1032993, 114, 30, 12925-12930, 2010.08, Direction-controlled growth of horizontally aligned single-walled carbon nanotubes (SWNTs) on r-plane sapphire substrates and their alignment mechanisms are demonstrated. On a flat r-plane substrate, anisotropic nanotube-substrate interaction is known to align SWNTs parallel to the [11̄01̄] direction of the sapphire. We find that the introduction of a slight miscut (-1° inclined to the [11̄01̄] direction) on the substrate changed the SWNT growth direction by 90°, aligning perpendicular to the [11̄01̄] direction. This dramatic change of the growth direction is explained by the contribution of newly proposed one-dimensional surface atomic rows and/or atomic steps appeared on the r-plane. Annealing the substrate in hydrogen atmosphere prior to SWNT growth recovers the original nanotube growth direction, while annealing in air deteriorates the alignment. The direct growth of an orthogonally aligned SWNT array is achieved through optimized surface treatment. Site-selective directional control of aligned SWNTs is also demonstrated by applying hydrogen annealing to the miscut substrate whose surface is partially covered with SiO2. Our study gives insights into the alignment mechanism on single crystal substrates and offers a new means to assemble SWNTs for advanced integrated structures..
85. Koji Takahashi, Masato Inoue, and Yohei Ito, Defective Carbon Nanotube for Use as a Thermal Rectifier, Japanese Journal of Applied Physics, 49, 02BD12, 2010.04.
86. Yohei Ito, Masato Inoue, and Koji Takahashi, One-dimensionality of phonon transport in cup-stacked carbon nanofiber , J. Phys.: Condens. Matter , 22, 065403, 2010.03.
87. Yohei Ito, Taku Higuchi and Koji Takahashi, Submicroscale Flow Sensor Employing Suspended Hot Film with Carbon Nanotube Fins, Journal of Thermal Science and Technology, Vol. 5, No. 1, pp.51-60, 2010.01.
88. Y. Ito, M. Inoue, Koji Takahashi, One-dimensionality of phonon transport in cup-stacked carbon nanofibers, Journal of Physics Condensed Matter, 10.1088/0953-8984/22/6/065403, 22, 6, 2010, We treat the ballistic heat conduction of cup-stacked carbon nanofibers (CSCNF) by a nonequilibrium molecular dynamics simulation. The CSCNF consist of numerous tiny graphene cups linked in line by weak intermolecular forces. The simulation results show that the thermal conductivity varies with the fiber length in a power law fashion with an exponent as large as 0.7. The calculated phonon density of states revealed that a low frequency oscillation in the radial and axial directions dominates the heat conduction in CSCNF. The atomic motions indicate that these low frequency oscillations are quasi-one-dimensional (1D) where each cup moves axially like a rigid body and radially with a breathing motion. This quasi-1D oscillation occurs due to the unique structure of a CSCNF that resembles a 1D harmonic chain. Our investigations show that treating a CSCNF as a 1D chain with three-dimensional oscillations explains why this material has the highest ballistic phonon transport ever observed..
89. Koji Takahashi, Norsyazwan Hilmi, Yohei Ito, Tatsuya Ikuta, Xing Zhang, Measurement of the thermal conductivity of nanodeposited material, International Journal of Thermophysics, 10.1007/s10765-009-0666-3, 30, 6, 1864-1874, 2009.12, The small size of nanomaterials deposited by either focused ions or electron beams has prevented the determination of reliable thermal property data by existing methods. A new method is described that uses a suspended platinum hot film to measure the thermal conductivity of a nanoscale deposition. The cross section of the Pt film needs to be as small as 50 nm × 500 nm to have sufficient sensitivity to detect the effect of the beam-induced nanodeposition. A direct current heating method is used before and after the deposition, and the change in the average temperature increase of the Pt hot film gives the thermal conductivity of the additional deposited material. In order to estimate the error introduced by the one-dimensional analytical model employed, a two-dimensional numerical simulation was conducted. It confirmed the reliability of this method for situations where the deposit extends onto the terminals by (1 μm or more. Measurements of amorphous carbon (a-C) films fabricated by electron beam induced deposition (EBID) produced thermal conductivities of 0.61 W • m -1 • K -1 to 0.73 W • m -1 • K -1 at 100 K to 340 K, values in good agreement with those of a-C thin films reported in the past..
90. Koji Takahashi, Norsyazwan Hilmi, Yohei Ito, Tatsuya Ikuta and Xing Zhang, Measurement of the Thermal Conductivity of Nanodeposited Material, International Journal of Thermophysics, Vol. 30, Issue 6, Page 1864 - 1874, 2009.11.
91. Koji Takahashi, Yohei Ito, Tatsuya Ikuta, Xing Zhang, Motoo Fujii, Experimental and numerical studies on ballistic phonon transport of cup-stacked carbon nanofiber, Physica B: Condensed Matter, 10.1016/j.physb.2009.05.001, 404, 16, 2431-2434, 2009.08, A carbon nanofiber material, consisting of a stacked graphene cups, with the potential to conduct heat ballistically has been discovered and tested. Its unexpected high thermal conductivity can be understood by the similarity to a one-dimensional harmonic chain where no phonon is scattered even for an infinite length. A non-equilibrium molecular dynamics simulation for this fiber validated this hypothesis by revealing a uniform temperature distribution between hot and cold reservoirs..
92. Koji Takahashi, Yohei Ito, Tatsuya Ikuta, Xing Zhang, and Motoo Fujii, Experimental and numerical studies on ballistic phonon transport of cup-stacked carbon nanofiber, Physica B: Condensed Matter, Vol 404, pp. 2431 (2009), 2009.06.
93. Yohei Ito, Koji Takahashi, Motoo Fujii and Xing Zhang, Estimating Error in Measuring Thermal Conductivity Using a T-type Nanosensor, Heat Transfer - Asian Research, Vol. 38, No.5, pp. 297-312, 2009, 2009.05.
94. Yohei Ito, Koji Takahashi, Tatsuya Ikuta, and Xing Zhang, Effect of Underetching on Thermal Conductivity Measurement of Suspended Nanofilm, Jpn. J. Appl. Phys, Vol. 48, No. 5 (2009) Published May 20, 2009 (5 pages) 05EB01, 2009.05.
95. Naoki Yoshihara, Hiroki Ago, Kenta Imamoto, Masaharu Tsuji, Tatsuya Ikuta, Koji Takahashi, Horizontally aligned growth of single-walled carbon nanotubes on a surface-modified silicon wafer, Journal of Physical Chemistry C, 10.1021/jp810036t, 113, 19, 8030-8034, 2009.05, For the integration with modern Si-based electronics, it is important to organize single-walled carbon nanotubes (SWNTs) into a rational structure on a Si wafer with a SiO2 oxide layer. In this study, the aligned growth of SWNTs was achieved on the SiO2/Si substrate whose surface was pretreated with CF4 plasma. The plasma treatment gave the radially extended steps which guided the SWNT growth. Back-gate field effect transistors were demonstrated with the aligned SWNTs. Our work presents the possibility of assembling SWNTs on SiO2/Si substrate through the formation of artificial step structures, which is a great step toward fully functional SWNT-on-Si devices..
96. Hiroki Ago, Naoki Ishigami, Tetsushi Nishi, Ken Ichi Ikeda, Masaharu Tsuji, Tatsuya Ikuta, Koji Takahashi, Unidirectional growth of single-walled carbon nanotubes, Journal of the American Chemical Society, 10.1021/ja8080549, 130, 51, 17264-17265, 2008.12, Unidirectional growth of single-walled carbon nanotubes (SWNTs) was achieved using the patterned Co-Mo salt catalyst on the r-plane sapphire substrate. This is in marked contrast with the SWNTs grown on an a-plane sapphire and ST-cut quartz, on which the SWNTs grew bidirectionally. This new growth mode is not dependent on the gas flow and attributed to the asymmetric surface atomic arrangement of the sapphire surface..
97. Xing ZHANG, Koji TAKAHASHI, Motoo FUJII, Charge and Heat transport in Polysrystalline Metallic Nanostructures, Chinese Physics Letters, Vol. 25, Number 9, pp.3360-3363, 2008, 2008.09.
98. Deposition Rate and Position Shifting of Paraffin-Based EBID.
99. Koji Takahashi, Yohei Ito, Tatsuya Ikuta, Takashi Nishiyama, Motoo Fujii, Xing Zhang and Andrzej Huczko, , Thermal conductivity of SiC nanowire formed by combustion synthesis, High Temperatures-High Pressures, Vol. 37, Number 2, pp.119-125, 2008, 2008.04.
100. Measuring Thermal Conductivity of Nano Deposition Usinh Pt Hot Film.
101. Estimating Error of Measuring Thermal Conductivity Using T-Type Nano Sensor.
102. X. Zhang , H. Q. Xie, M. Fujii, H. Ago, K. Takahashi, T. Ikuta, H. Abe and T. Shimizu, Thermal and Electrical Properties of a Suspended Nanoscale Thin Film , INTERNATIONAL JOURNAL OF THERMOPHYSICS, Vol. 28 (1): 33-43 FEB 2007 , 2007.02.
103. Influence of Grain Boundary Scattering on the Electrical and Tthermal Conductivities of Polycrystalline Gold Nanofilms.
104. X. Zhang, H. Xie, M. Fujii, K. Tajahashi, T. Ikuta, H. Ago, H. Abe, T. Shimizu, Experimental study on thermal characteristics of suspended platinum nanofilm sensors, Int. J. Heat and Mass Transfer, Vol. 49 pp.3879-3883, 2006.08.
105. Q. G. Zhang, X. Zhang, B. Y. Cao, M. Fujii, K. Tajahashi, T. Ikuta, Influence of grain boundary scattering on the electrical properties of platinum nanofilms, Applied Physics Letters, Vol. 89, 114102, 3p, 2006.01.
106. M. Fujii, X. Zhang, H. Xie, H. Ago, K. Takahashi, T. Ikuta, H. Abe and T. Shimizu, Measuring the Thermal Conductivity of a Single Carbon Nanotube, Physical review Letters, 10.1103/PhysRevLett.95.065502, 95, 6, Vol.95, 065502 4p, 2005.08.
107. X. Zhang, H. Xie, M. Fujii, H. Ago, K. Takahashi, T. Ikuta, H. Abe and T. Shimizu, Thermal and electrical conductivity of a suspended platinum nanofilm, Applied Physics Letters, 10.1063/1.1921350, 86, 17, Vol.86, 171912 3p, 2005.01.
108. MEMS Technology and Space Propulsion.
109. Microfluidics of liquid propellant microthruster for pico-satellites
Yasuhiko Osaki, Koji Takahashi
IEEJ Transactions on Sensors and Micromachines, Vol.123, No.10, pp.436-441, 2003.
110. Ryoji DOIHARA and Koji TAKAHASHI , Numerical Calculation of Laser-Induced Bubble near a Solid Boundary until the Second Collapse , JSME Int. Journal, Ser. B, Vol.44, No.2, pp.238-246, May, 2001 , 2001.05.
111. Chou, F. C., J. R. Lukes, X. G. Liang, K. Takahashi, and C. L. Tien, Molecular Dynamics in Microscale Thermophysical Engineering, Annual Review of Heat Transfer, Vol. 10, pp.141-176, 1999 , 1999.08.
112. K. Takahashi, J. G. Weng, and C. L. Tien, Marangoni Effect in Microbubble Systems, Microscale Thermophysical Engineering, 3, 3, 169-182, Vol.3, No.3, pp.169-182, 1999 , 1999.08.