Single Single-walled Carbon Nanotubes Research Articles

Enhancing the performance of thermal energy storage by adding nano-particles with paraffin phase change materials

Abstract Phase change materials (PCMs) are now being extensively used in thermal energy storage (TES) applications. Numerous researchers conducted experiments using various circumstances and materials to optimize storage performance. A study was conducted to compare the numerical research of the melting process of paraffin wax using a hybrid nano-integrated paraffin PCM with graphene oxide (GO) and single-walled carbon nanotubes (SWCNTs) in a TES unit. Hence, this research focuses on a sustainable TES system using hybrid nanomaterials (PCM + GO, PCM + SWCNTs, PCM + GO + SWCNT) with varying concentrations of nanoparticles. The objective is to improve the thermal characteristics of PCMs. The main aim of this study is to examine the numerical analysis of the system inside a TES that has a rectangular form. The numerical experiments were conducted using the finite-volume solver Ansys Fluent. The obtained findings show the thermophysical characteristics fluctuations with respect to the solid volume fractions, liquid fraction, temperature, and velocity inside the TES system. Implementing an effective heat transfer mechanism from the point of capture to storage and later consumption necessitates the employment of a heat transfer fluid. The inclusion of SWCNT particles at a concentration of just 10% has been seen to expedite the melting phenomenon. Furthermore, incorporating GO in conjunction with SWCNT alleviates this phenomenon, resulting in a melting behavior that resembles that of unadulterated paraffin. Additionally, the introduction of just 1% GO, combined with SWCNT, leads to a rapid alteration in surface heat transfer coefficient compared to the scenario with single SWCNT and paraffin. These insights hold practical relevance for the development of TES systems in various applications.

Evolution of catalyst design for controlled synthesis of chiral single-walled carbon nanotubes.

Single-walled carbon nanotubes (SWCNTs) possess superb properties originating from their unique chiral structures. However, accurately controlling the structure of SWCNTs remains challenging due to the structural similarities of their chiral structures, which hinders their widespread application in various fields, particularly in electronics. In recent years, much effort has been devoted to preparing single chiral SWCNTs by adopting three constructive strategies, including growth condition control for structurally unstable liquid catalysts, employing stable solid catalyst design, and pre-synthesis of carbon seeds with a well-defined shape. This review comprehensively discusses the state-of-the-art developments in these approaches as well as their advantages and disadvantages. Moreover, insights into the key challenges and future directions are provided for acquiring chirally pure SWCNTs.

(Invited) Stochasticity in the Number of Quantum Defects in Fluorescent Carbon Nanotubes

Single wall carbon nanotubes (SWCNTs) display chirality dependent near infrared (NIR) fluorescence. Their optoelectronic properties can be further tuned by incorporating quantum defects/organic color centers (OCC) via reactions with diazonium salts. The absolute number of defects per SWCNT determines the properties but is not exactly known. Measuring it is complicated because typical SWCNT samples contain multiple chiralities, that congest the spectra and prevents to distinguish defects from different chiralities. Aqueous two-phase extraction (APTE) is a powerful technique to isolate specific chiralities. Here, we show that quantum defects do not affect APTE, which indicates that the chemical potential is not substantially affected and pinpoints to low numbers of defects. The purity of (6,5)-SWCNTs allows us to image the NIR fluorescence contributions (E11 below 1050 nm, and E11 * above 1050 nm) on the single SWCNT level and defect incorporation itself on the single molecule level. Interestingly, one observes a stochastic distribution of the numbers of defects, which can be explained by a Poisson distribution. We find a mean number of defects of 0-3 per SWCNT. These results indicate the large variance between ensemble and single particle picture. In summary, we show that single quantum defects can be counted by NIR imaging and that stochasticity plays a crucial role for their optical properties.

Laser Fluence Dependent Modulation of Single Walled Carbon Nanotube Photoluminescence

Single-walled carbon nanotubes (SWCNT) have a unique, non-photobleaching, bandgap photoluminescence (PL) that has been of interest for sensor development. Take advantage of these properties, colloidal dispersions of single SWCNTs in aqueous solvents are often formed by creating a surface corona phase (CP) using amphiphilic materials. As SWCNT PL emission following photoexcitation can be significantly dependent on its local environment, the CP can be used to tune its photophysical properties, often as a design parameter for sensor development. Recent sensor experiments have shown that reporting and controlling laser excitation can be a method to significantly reduce measurement variability. In this work, we study this phenomenon of excitation fluence (EF) (mW/area) dependent PL modulation for aqueous dispersed SWCNTs. By using a continuously stirred chamber excited at a single location, the stirring rate can be a means of controlling SWCNT excitation exposure. SWCNT wrapped in both DNA and SDS SWCNT CPs showed a decreased quantum yield of nearly 40% with increasing EF while those with sodium cholate and phospholipid-PEG CPs remain invariant. Through spectroscopy and heat transfer modeling, we determined that the observed effect is unlikely to have a significant direct local solution heating contribution from SWNCT photoabsorption. Finally, we used previously studied SWCNT sensor constructs, for ascorbic acid and dopamine, to show how EF can affect calibration and eventual sensor applications. This work highlights the importance of measuring, testing, reporting and controlling for EF while developing SWCNT based photophysical sensors. This newly characterized property can also serve as a unique parameter to tune optical responsivity.

Towards Single-Molecule Analyte Sensing with Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWCNTs) have been at the forefront of research for well over a decade due to their unique optical properties. Specifically, the inherent and photostable fluorescence of SWCNTs has been used to create sensitive near-infrared (NIR) sensors for a variety of target analytes, such as dopamine and cholesterol. However, most of the SWCNT sensors are employed in the solution-phase, severely limiting the efficacy due to ensemble measurements which can significantly confound any optical readout. One potential solution involves imaging individual SWCNTs deposited on a surface, unfortunately it is well known that SWCNT florescence is adversely affected by the inherently rough surfaces that are conventionally used for their observation, which emphasizes the need for a novel platform. We therefore devised a spin-coated hydrogel platform that contained SWCNTs in a single focal plane and enabled fluorescent imaging without significantly perturbing their optical properties when compared to the solution-phase. As SWCNT fluorescent microcopy is limited by diffraction, several strategies were employed to improve the sensitivity of analyte detection. When single SWCNTs longer than the diffraction limit were examined, spectral heterogeneity was observed along the length of each SWCNT, suggesting an application in single-molecule analyte detection. A common surfactant sodium deoxycholate (SDC) was investigated as an analyte as it exchanges with DNA oligonucleotides on the surface of DNA-SWCNTs, by which the kinetic response can be used to estimate DNA binding strength. We employed DNA-SWCNTs in the hydrogel platform and observed the kinetic response of individual SWCNTs in response to the addition of SDC. Importantly, the diffusion was intentionally slowed by modifying the top hydrogel layer to examine the kinetic response on a longer time scale, in contrast to the nearly instantaneous response in solution. We observed a decoupling of the spectral properties of each SWCNT, where the fluorescence intensity responded later than the emission wavelength. We then utilized a 1-dimensional diffusion model to estimate the local concentration of each SWCNT. We hypothesize that differences in the SDC functionalization morphology on SWCNTs have a significant impact on this observed effect.

Stochastic Formation of Quantum Defects in Carbon Nanotubes.

Small perturbations in the structure of materials significantly affect their properties. One example is single wall carbon nanotubes (SWCNTs), which exhibit chirality-dependent near-infrared (NIR) fluorescence. They can be modified with quantum defects through the reaction with diazonium salts, and the number or distribution of these defects determines their photophysics. However, the presence of multiple chiralities in typical SWCNT samples complicates the identification of defect-related emission features. Here, we show that quantum defects do not affect aqueous two-phase extraction (ATPE) of different SWCNT chiralities into different phases, which suggests low numbers of defects. For bulk samples, the bandgap emission (E11) of monochiral (6,5)-SWCNTs decreases, and the defect-related emission feature (E11*) increases with diazonium salt concentration and represents a proxy for the defect number. The high purity of monochiral samples from ATPE allows us to image NIR fluorescence contributions (E11 = 986 nm and E11* = 1140 nm) on the single SWCNT level. Interestingly, we observe a stochastic (Poisson) distribution of quantum defects. SWCNTs have most likely one to three defects (for low to high (bulk) quantum defect densities). Additionally, we verify this number by following single reaction events that appear as discrete steps in the temporal fluorescence traces. We thereby count single reactions via NIR imaging and demonstrate that stochasticity plays a crucial role in the optical properties of SWCNTs. These results show that there can be a large discrepancy between ensemble and single particle experiments/properties of nanomaterials.

(Invited) One-Dimensional Features of Electron Transport in Single-Walled Carbon Nanotube Thin Films

Single-walled carbon nanotubes (SWCNTs) are excellent conductors with high flexibility, high thermal conductivity, and high transparency. Flexible and transparent SWCNT thin films and SWCNT yarns with high mechanical strength have been produced, and in particular, the improvement of electrical conduction characteristics of these SWCNT aggregates has been studied intensively. The electrical conductivity of SWCNT aggregates have improved year by year, but it is worse than those of a single SWCNT, so far. SWCNT aggregates contain complex structures such as SWCNTs with different chirality structures, many junctions, and bundle structures, which could be the cause of deterioration of transport characteristics, however, it has not been clarified.In this study, we focused on low-density SWCNT thin films and investigated their electron transport characteristics. The low-density SWCNT thin film has a simple network structure since the network consists of the bundles of a small number of long SWCNTs. Here, the magnetic field dependence, temperature dependence, and gate voltage dependence of the electrical conductivity were measured and analyzed.The SWCNT thin films were synthesized by a floating catalyst CVD method, and they were transparent (90%T), and electrically conductive [1]. The thin film consisted of a network structure of bundles, which consisted of about 10 SWCNTs. The films were mixtures with metallic and semiconducting SWCNTs. The electrical resistivity of the SWCNT thin film was measured by the four-point probes method, and the gate voltage (Vg) was applied using an ionic liquid. The direction of the magnetic field was perpendicular to the thin film surface. The areal density of SWCNT length was estimated from the light absorption cross-section of the SWCNT thin films, and then the electrical resistivity was calculated from the actual volume of SWCNTs excluding the void space.SWCNTs generally show p-type characteristics in the atmosphere in the back-gate configuration due to the dope effects of oxygen and/or water molecules. However, the Vg dependence of the electrical resistivity of the thin film showed a bipolar behavior under the ionic liquid gate. The change ratio of the resistivity in the Vg range (-3 to +3 V) was more than 10, which suggested that not only did the non-conductive semiconducting SWCNT become conductive, but the number of percolation paths increased accordingly. Raman scattering spectroscopy also exhibited that semi-conducting SWCNTs were heavily doped by the ionic liquid gating. The electrical resistivity decreased down to approximately 20 μΩcm at room temperature with Vg=-3 V. The temperature dependence in the temperature range (30-110 K) with Vg=-3 V was explained by the variable range hopping (VRH) model with the dimensionality of one, although the SWCNT thin films are two-dimensional structures. Hall resistivity of the thin film slightly changed at different Vg, however, it was almost negligible. It is probably because most of the SWCNT thin films were linear bundle parts, and the bundle diameter was a few nm, which is much smaller than the cyclotron radius [2]. Additionally, the thermoelectric measurement was performed. The Vg dependence of thermoelectrical conductivity showed one-dimensional characteristics [3]. These measurements showed one-dimensional features of electron transport properties of SWCNT thin films. A single SWCNT can be regarded as a one-dimensional system, but in general, one-dimensional features do not appear in the electron transport of SWCNTs in the form of thin films or yarns. In this study, probably because the thin film has a very low density (light transmittance 90% T) and forms a network consisting of a thin bundle structure, the one-dimensional features clearly appeared. The one-dimensionality is one of the origins of the excellent properties of SWCNTs and it is could be a useful index for improving electrical conductivity.AcknowledgmentsI would like to thank H. Date (Univ. of Tokyo) for the experiments and measurements, Prof. T. Fujii (Univ. of Tokyo) for the measurements, and Prof. E. I. Kauppinen for the sample supply.[1] A.G. Nasibulin, et al., ACS Nano, 5 (2011) 3214.[2] M. L. Roukes, et al., Phys. Rev. Lett., 59 (1987) 3011.[3] Y. Ichinose, et al., Phys. Rev. Mater., 5 (2021) 025404.

Single-Walled Carbon Nanotubes Inhibit TRPC4-Mediated Muscarinic Cation Current in Mouse Ileal Myocytes.

Single-walled carbon nanotubes (SWCNTs) are characterized by a combination of rather unique physical and chemical properties, which makes them interesting biocompatible nanostructured materials for various applications, including in the biomedical field. SWCNTs are not inert carriers of drug molecules, as they may interact with various biological macromolecules, including ion channels. To investigate the mechanisms of the inhibitory effects of SWCNTs on the muscarinic receptor cation current (mICAT), induced by intracellular GTPγs (200 μM), in isolated mouse ileal myocytes, we have used the patch-clamp method in the whole-cell configuration. Here, we use molecular docking/molecular dynamics simulations and direct patch-clamp recordings of whole-cell currents to show that SWCNTs, purified and functionalized by carboxylation in water suspension containing single SWCNTs with a diameter of 0.5–1.5 nm, can inhibit mICAT, which is mainly carried by TRPC4 cation channels in ileal smooth muscle cells, and is the main regulator of cholinergic excitation–contraction coupling in the small intestinal tract. This inhibition was voltage-independent and associated with a shortening of the mean open time of the channel. These results suggest that SWCNTs cause a direct blockage of the TRPC4 channel and may represent a novel class of TRPC4 modulators.

A Spin-Coated Hydrogel Platform Enables Accurate Investigation of Immobilized Individual Single-Walled Carbon Nanotubes.

Single-walled carbon nanotubes (SWCNTs) have been used in a variety of sensing and imaging applications over the past few years due to their unique optical properties. In the solution phase, SWCNTs are employed as near-infrared (NIR) fluorescence-based sensors of target analytes via modulations in emission intensity and/or wavelength. In an effort to lower the limit of detection, research has been conducted into isolating SWCNTs adhered to surfaces for potential single molecule analyte detection. However, it is known that SWCNT fluorescence is adversely affected by the inherently rough surfaces that are conventionally used for their observation (e.g., glass coverslip), potentially interfering with fluorescence-based analyte detection. Here, using a spin-coating method with thin films of alginate and SWCNTs, we demonstrate that a novel hydrogel platform can be created to investigate immobilized individual SWCNTs without significantly perturbing their optical properties as compared to solution-phase values. In contrast to the glass coverslip, which red-shifted DNA-functionalized (6,5)-SWCNTs by an average of 3.4 nm, the hydrogel platform reported emission wavelengths that statistically matched the solution-phase values. Additionally, the heterogeneity in the wavelength measurements, as determined from the width of created histograms, was reduced nearly by a factor of 3 for the SWCNTs in the hydrogel platform when compared to glass coverslips. Using long SWCNTs, i.e., those with an average length above the diffraction limit of our microscope, we show that a glass coverslip can induce optical heterogeneity along the length of a single SWCNT regardless of its surface functionalization. This is again significantly mitigated when examining the long SWCNTs in the hydrogel platform. Finally, we show that upon the addition of a model analyte (calcium chloride), the optical response can be spatially resolved along the length of a single SWCNT, enabling localized analyte detection on the surface of a single nanoscale sensor.

Individual SWCNT Transistor with Photosensitive Planar Junction Induced by Two‐Photon Oxidation

AbstractThe fabrication of planar junctions in carbon nanomaterials is a promising way to increase the optical sensitivity of optoelectronic nanometer‐scale devices in photonic connections, sensors, and photovoltaics. Utilizing a unique lithography approach based on direct femtosecond laser processing, a fast and easy technique for modification of single‐walled carbon nanotube (SWCNT) optoelectronic properties through localized two‐photon oxidation is developed. It results in a novel approach of quasimetallic to semiconducting nanotube conversion so that metal/semiconductor planar junction is formed via local laser patterning. The fabricated planar junction in the field‐effect transistors based on individual SWCNT drastically increases the photoresponse of such devices. The broadband photoresponsivity of the two‐photon oxidized structures reaches the value of 2 × 107 A W−1 per single SWCNT at 1 V bias voltage. The SWCNT‐based transistors with induced metal/semiconductor planar junction can be applied to detect extremely small light intensities with high spatial resolution in photovoltaics, integrated circuits, and telecommunication applications.

Charge and Thermoelectric Transport in Polymer-Sorted Semiconducting Single-Walled Carbon Nanotube Networks.

Understanding the charge transport mechanisms in chirality-selected single-walled carbon nanotube (SWCNT) networks and the influence of network parameters is essential for further advances of their optoelectronic and thermoelectric applications. Here, we report on charge density and temperature-dependent field-effect mobility and on-chip field-effect-modulated Seebeck coefficient measurements of polymer-sorted monochiral small-diameter (6,5) (0.76 nm) and mixed large-diameter SWCNT (1.17-1.55 nm) networks (plasma torch nanotubes, RN) with different network densities and length distributions. All untreated networks display balanced ambipolar transport and electron-hole symmetric Seebeck coefficients. We show that charge and thermoelectric transport in SWCNT networks can be modeled by the Boltzmann transport formalism, incorporating transport in heterogeneous media and fluctuation-induced tunneling. Considering the diameter-dependent one-dimensional density of states (DoS) of the SWCNTs composing the network, we can simulate the charge density and temperature-dependent Seebeck coefficients. Our simulations suggest that scattering in these networks cannot be described as simple one-dimensional acoustic and optical phonon scattering as for single SWCNTs. Instead the relaxation time is inversely proportional to energy (τ ∝ (E - EC)s, s = -1, EC being the energy of the first van Hove singularity), presumably pointing toward the more two-dimensional character of scattering events and the necessity to include scattering at the SWCNT junctions. Finally, our observation of higher power factors in trap-free, 1,2,4,5-tetrakis(tetramethylguanidino)benzene-treated (6,5) networks than in the RN networks emphasizes the importance of chirality selection to tune the width of the DoS. To benefit from both higher intrinsic mobilities and a large thermally accessible DoS, we propose trap-free, narrow DoS distribution, large-diameter SWCNT networks for both electronic and thermoelectric applications.

Strongly localized states in a single carbon nanotube with polymer molecules

A single-walled carbon nanotube (SWCNT) with conjugated polymer molecules is analyzed via optical spectroscopy. The presence of strongly localized excitonic states in the SWCNT is confirmed using time-integrated photoluminescence (PL). The PL spectrum exhibits extremely narrow width (~0.8 meV) which is attributed to the strong confinement of the states by polymer molecules. In addition, I observed that the excited states are gradually filled as a function of the excitation power, which supports the localized excitonic behavior. Only the ground excitonic state is observed at low excitation powers, but three additional PL peaks appear as the excitation power is increased. Especially, the power-dependent PL spectrum shows a blueshift and increased width, which can be elucidated in terms of quantum confined stark effect and the screening of induced electric fields. Overall, I demonstrate that the presence of polymer molecules induces several localized states in a single SWCNT.

Click Chemistry on Defects to Create Multifunctional Fluorescent Carbon Nanotubes

Single-walled carbon nanotubes (SWCNT) are versatile materials for imaging and sensing in the near infrared (nIR) range. Non-covalent adsorption with (bio)polymers such as DNA is a powerful approach to functionalize SWCNTs. This approach lead to a broad range of biosensors. However, covalent approaches would be beneficial for many applications because of higher stability and photophysical signal transduction. One route to covalent functionalization is reactions with diazonium salts that create covalent defects and a red-shifted peak in the nIR fluorescence spectrum attributed to a formerly dark exciton.Here, we used novel synthesized diazonium salts to create defects that can be easily further functionalized with click chemistry reactions (Thiol-en and azid-alkine). The modified SWCNTs were additionally non-covalently wrapped in biopolymers for solubilization and characterized via nIR spectroscopy and atomic force microscopy (AFM). Using this approach we covalently conjugated diverse molecules including small aliphatic molecules, peptides, DNA and nanobodies to the SWCNT backbone. Successful functionalization was verified by conjugation of organic visible fluorophores and single SWCNT colocalization. Additionally, these multifunctional SWCNTs were used as building block for biosensors that detect disease markers.In summary, we present a general approach to conjugate a broad range of molecules to SWCNTs using defect chemistry and demonstrate applications in biosensing.

Charge Modulation Spectroscopy of Pristine and sp3-Functionalized Single-Walled Carbon Nanotube Networks

The controlled decoration of single-walled carbon nanotubes (SWCNTs) with luminescent sp3 defects has emerged as a powerful approach to enhance their usually low photoluminescence (PL) quantum yields and achieve tuneable emission across the near-infrared even for polymer-wrapped nanotubes [ACS Nano 2019, 13, 9259]. However, their application in optoelectronic devices requires a detailed understanding of the impact of sp3 functionalization on their electrical performance. While isolated sp3 defects on single SWCNTs increase the resistance by a few kΩ, the effect of functionalization on charge transport in networks of semiconducting SWCNTs remains unexplored. Charge modulation spectroscopy is ideally suited to probe the mobile charge carriers in SWCNT networks and has previously corroborated the notion that charge accumulation and transport in mixed SWCNT networks is highly chirality- and gate voltage-dependent. Here, we use charge-modulated PL (CMPL) spectroscopy to study the current pathways in field-effect transistors based on networks of pristine and functionalized (6,5) SWCNTs. We find that the defects are very efficiently sampled by mobile carriers and consequently, sp3-functionalized SWCNTs actively participate in the charge transport in these networks. In combination with voltage-dependent PL and electroluminescence measurements, our CMPL method provides fundamental insights into the interaction of charge carriers with sp3 defects in SWCNT thin film devices.Fig. 1: Schematic of the charge modulation PL spectroscopy setup (left) and CMPL spectra of pristine and functionalized (6,5) SWCNT network field-effect transistors (right). Figure 1

Investigation of the Dissociation Mechanism of Single-Walled Carbon Nanotube on Mature Amyloid-β Fibrils at Single Nanotube Level.

Amyloid fibrils originating from the fibrillogenesis of misfolded amyloid proteins are associated with the pathogenesis of many neurodegenerative diseases, such as Alzheimer's, Parkinson's, and Huntington's diseases. Carbon nanotubes have been extensively applied in our life and industry due to their unique chemical and physical properties. Nonetheless, the details between carbon nanotubes and mature amyloid fibrils remain elusive. In this study, we explored the interplay between single-walled carbon nanotubes (SWCNTs) and preformed amyloid-β (Aβ) fibrils by atomic force microscopy at the single SWCNT level, together with ThT fluorescence, cellular viability assays, infrared spectroscopy, and molecular dynamics (MD) simulations. The results demonstrated that SWCNTs could partially destroy the preformed Aβ fibrils and form the Aβ-surrounded-SWCNTs conjugates, as well as reduce the β-sheet structures. Peak force quantitative nanomechanical measurements revealed that the conjugates have lower Young's modulus than fibrils. Furthermore, our MD simulation demonstrated that the dissociation ability was dependent on the binding sites of Aβ fibrils. Overall, this study provides an insight into the dissociation mechanism between SWCNT and Aβ fibrils, which could be beneficial for the study of bionanomaterials and the development of other potential drug candidates for amyloidosis.

Improved Electrophoretic Deposition of Vertical Single Wall Carbon Nanotubes with Nanoscopic Electrostatic Lenses.

Under certain conditions, electrophoretic deposition (EPD) of single-wall carbon nanotubes (SWCNTs) onto metal at the base of nanoscale insulating windows can result in a single SWCNT per window, bonded at one end to the metal. During EPD charge, buildup on the insulator creates electrostatic lenses at the windows that control the trajectory of the SWCNTs. The aim is to develop a reproducible process for deposition of individual vertically oriented SWCNTs into each window to enable novel devices. The length of the SWCNTs is shown to be the most critical parameter in achieving results that could be used for devices. In particular, single nanotube deposition in windows by EPD was achieved with SWCNTs with lengths on the order of the window depth. By performing current vs voltage (IV) measurements against a platinum wire in a phosphate buffer and by modeling the data, the presence of the nanotube can be detected, the contact interface can be studied, and the nanotube’s viability for device applications can be determined. These results provide a basis for process integration of vertical SWCNTs using EPD.

Ag-doping behavior on (8, 0) single-walled carbon nanotube with single C-vacancy or pyridine-like N3 defect: a DFT study

Single C-vacancy and pyridine-like N3 defect are usually formed on the single-walled carbon nanotube (SWCNT) and they have unique properties for potential applications. In this paper, we use density functional theory to investigate the discrepancies of such two structures from the geometric and electronic aspects. Our results indicate that the existed single vacancy in the SWCNT can lead to somewhat electron localization because of the lone pair electrons; while the N3 embedded SWCNT ( N3-SWCNT) has stronger chemical reactivity and electron localization than the single vacancy SWCNT (SV-SWCNT) due to the great charge transfer between N3 group and C atom on the tube sidewall. Through the investigation of Ag-doping on the above two nano-structures, we found that the single Ag atom is much more stably adsorbed on the N3- SWCNT sidewall compared with SV-SWCNT, forming higher binding energy and higher electron transfer. Our calculation would shed light on the physicochemical property of SWCNT-based material and thus extend their potential applications in many fields.

(Invited) Thermoelectric properties of Fermi-level tuned and Aligned Single Wall Carbon Nanotubes

Single wall carbon nanotubes (SWCNTs) are one-dimensional materials with sharp van Hove singularities. Preparation of SWCNTs with a selected electronic structure, fabrication of their aligned thin films[1] and tuning their Fermi level allow us to reveal unique phenomena, which cannot be observed or correctly understood in conventional SWCNT random network thin films. For example, we observed anomalously large optical absorption for perpendicular polarization to the tube axis in highly doped aligned SWCNTs, which is related to intersubband transition plasmon phenomena in SWCNTs.[2] Here in this talk, we would like to discuss the thermoelectric phenomena in fermi level tuned and aligned SWCNTs. In our society, a large amount of heat at relatively low temperature, which is emitted from factories, houses, human bodies, and so on, is left unused. Development of high-performance flexible thermoelectric devices is crucial to efficiently convert such unused waste heat into electric power. Understanding of relationships between electrical conductivity, Seebeck coefficient, and thermal conductivity in thin films of flexible materials and tuning of these parameters is crucial to improve the performance. Since the seminal study by Hicks and Dresselhaus,[3] the thermoelectric properties of low dimensional materials have been intensively studied, but it still has been of great importance to experimentally clarify how the one dimensional electronic structures can influence and enhance its thermoelectric properties, although there are several important theoretical predictions for enhancement of thermoelectric properties in one-dimensional electronic systems.[3,4] SWCNTs are a model of one-dimensional flexible materials, and will play important roles for realization of high-performance flexible thermoelectric devices. Previously, we revealed how the location of Fermi-level influences the thermoelectric properties of semiconducting SWCNTs with diameter of 1.4 nm using electrolyte gating approaches.[5] However, in the previous study, the purity of chirality was not enough to clarify the intrinsic characteristics of semiconducting SWCNTs. In this talk, we will discuss the relationships between electronic structures, Fermi-level and thermoelectric properties using single chirality SWCNTs. In addition, we will discuss how the thermoelectric properties and conductivities exhibit isotropic or an-isotropic properties in aligned SWCNT thin films.[6] Acknowledgment: K.Y. acknowledges support by JST CREST through Grant Number JPMJCR17I5, Japan

Post-breakdown field emission behavior of a planar-structured single SWNT bundle in air

In this paper, we report the field emission (FE) behavior in air of a single-walled carbon nanotube (SWCNT) bundle after breakdown. Our samples have the planar structure on the SiO2/Si substrate of one breaking-tip of a single SWCNT bundle horizontally pointing to the sidewall of an electrode with a nano-sized gap, which were prepared using microfabrication techniques, AC dielectrophoresis (DEP) and current-induced breakdown in sequence. The current–voltage relationship was monitored under 0–100 V scanning DC voltage. The results show that the planar-structured SWCNT bundle in air presents a significantly different FE performance from the conventional vertical structured carbon nanotube (CNTs) FE devices in vacuum. Similarly, the former FE current also exhibits several interval phenomena instead of monotonically exponentially rising (Di Bartolomeo et al 2007 Carbon 45 2957–71), while the structural damage of CNT tips result from oxidation instead of defects largening as for the latter. This research is conducive to further knowledge of possible electrical behavior after CNT breakdown for the failure effect during the fabrication and operation of CNT-based electronic/sensing devices and systems.

(Invited) Fabrication of Copper/Carbon Nanotube Composite Films Using Plating Techniques

Carbon nanotubes (CNTs) [1,2] have excellent thermal conductivity [3], extremely high current-carrying capacity (ampacity), i.e., stable electrical resistance in the presence of high currents [4], and superior mechanical properties [5,6]. Metal/CNT composites are therefore expected to be potential functional materials, and there have been many investigations concerning the fabrication of metal/CNT composites [7,8]. Composite plating is one promising process for the fabrication of metal/CNT composite films, and its application to such has been investigated [9]. In particular, Cu/CNT composite films are expected to be used for electronics applications. CNTs are generally categorized into single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs). CNTs have anisotropic electrical and thermal conductivity, i.e., they have higher electrical and thermal conductivity in the axis direction than in the direction perpendicular to the axis direction. In this study, Cu/MWCNT and Cu/SWCNT composite films were fabricated using composite plating techniques, including electroplating and electroless plating. The dispersibility of CNTs in the plating baths is extremely important for composite plating with CNTs that are hydrophobic. Polyacrylic acid (mean molecular weight 5000) is an effective dispersant for MWCNTs in an acidic copper sulfuric bath [10], and Cu/MWCNT composite films with a homogeneous MWCNT distribution have been formed by electroplating using such a Cu/MWCNT composite bath [11,12]. Metal/MWCNT composite films, including the Cu/MWCNT composite film, intrinsically have a tendency toward a bumpy surface morphology due to the (anisotropic) electrical conductivity of MWCNTs [13]. However, a relatively flat surface morphology could be obtained using appropriate current densities (cathode overpotentials) [14] or surfactants [15]. In addition, reverse current electrodeposition could be used to increase the MWCNT content in Cu/MWCNT composite films [16]. Cu/MWCNT composite films have also been obtained by electroless plating using an alkaline bath. Ethylenediaminetetraacetic acid (EDTA), glyoxylic acid and sodium dodecyl sulfate (SDS) + hydroxypropyl cellulose (HPC) were used as a complexing agent, a reducing agent and surfactants for MWCNTs, respectively [17]. The Cu/MWCNT composite films were also successfully fabricated on an acrylonitrile butadiene styrene resin substrate [18]. SWCNTs have the smallest diameter among CNTs and have a tendency to form a characteristic aggregate known as a bundle. This bundle cannot be disintegrated to a primary particle, i.e., single SWCNTs, with the addition of dispersants alone. The use of both a powerful mechanical disintegration method and a dispersant is effective for the disintegration of SWCNT bundles. The selection of dispersants for SWCNTs is also important. In this study, trimethyl stearyl ammonium chloride (TMSAC), which is a cationic surfactant, was selected to prepare a Cu/SWCNT composite electroplating bath [19]. Cu/SWCNT composite films with relatively homogeneous SWCNT distribution were formed by electroplating. Cu/SWCNT composite films with homogeneously dispersed SWCNTs were also fabricated by electroless plating using a bath containing EDTA, glyoxylic acid, SDS+HPC (Fig. 1) [20]. References A. Oberlin, M. Endo and T. Koyama, J. Cryst. Growth, 32, 335 (1976).S. Iijima, Nature, 354, 56 (1991).S. Berber, Y.K. Kwon and D. Tomanek, Phys. Rev. B, 84, 4613 (2000).Z. Yao, C.L. Kane and C. Dekker, Phys. Rev. Lett., 84, 2941 (2000).M.F. Yu, O. Lourie, M.J. Dyer, K. Moloni, T.F. Kelly and R.S. Ruoff, Science, 287, 637 (2000).J.P. Lu, Phys. Rev. Lett., 79, 1297 (1997).S. Cho, K. Kikuchi, T. Miyazaki, K. Takagi, A. Kawasaki and T. Tsukada, Scr. Mater., 63, 375 (2010).A.K. Shukla, N. Nayan, S.V.S.N. Murty and S.C. Sharma, Mater. Sci. Eng. A, 560, 365 (2013).X.H. Chen, J.C. Peng, X.Q. Li, E.M. Deng, J.X. Wang and W.Z. Li, J. Mater. Sci. Lett., 20, 2057 (2001).S. Arai and M. Endo, Electrochem. Commun., 5, 797 (2003).S. Arai and M. Endo, Electrochem. Solid-State Lett., 7(3), C25 (2004).S. Arai and M. Endo, Electrochem. Commun., 7, 19 (2005).S. Arai, M. Endo and N. Kaneko, Carbon, 42, 641 (2004).S. Arai, T. Saito and M. Endo, J. Electrochem. Soc., 157(3), D147 (2010).S. Arai, T. Saito and M. Endo, J. Electrochem. Soc., 157(3), D127 (2010).S. Arai, Y. Suwa and M. Endo, J. Electrochem. Soc., 158(2), D49 (2011).S. Arai and T. Kanazawa, ECS J. Solid State Sci. Technol., 3, P201 (2014).S. Arai and T. Kanazawa, J. Electrochem. Soc., 162 (1), D68 (2015).T. Ogasawara, M. Shimizu and S. Arai, Proc. ADMETA Plus 2017, pp. 54-55 (2017).S. Arai, T. Osaki, M. Hirota and M. Uejima, Mater. Today Commun., 7, 101 (2016). Figure 1