Browsing by Author "Kono, Junichiro"
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Item 2D Optoelectronics: Challenges and Opportunities(2015-12-17) Lei, Sidong; Ajayan, Pulickel M; Lou, Jun; Kono, JunichiroIndium Selenide (InSe) is one of atomically layered 2D materials attracting broad interests recently, because of its good optoelectronic properties. Based on the challenges of 2D optoelectronics, several topics will be covered in this defense, such as trap states and low absorption rate. InSe is selected as a platform to study these topics. The localized states and trap states in InSe system was characterized through low temperature photocurrent measurement to reveal the evolution of band structure and origin of the localized states in few layered InSe. It is found the surface electron orbitals contribute to the localized states. By modifying the surface electron via metallic ions, the Fermi level can be tuned significantly and the inertia surface of the pristine 2D surface can be sensitized for functionalization. Via this method, the InSe photodetector can be improved by organic photosensitive molecules. On the other hand, local gating can induce trap states in 2D materials, helping to improve the photoresponse, but slowing down the response speed. By utilizing this effect, 2D charge coupled device can be fabricated to serve as flexible image sensor which can help correct the optical aberration. The discussion is based on InSe, however, the principle is very universal that can be easily apply to other 2D system. The research can help to promote the research and device development in 2D optoelectronics.Item 3D microfabrication of single-wall carbon nanotube/polymer composites by two-photon polymerization lithography(Elsevier, 2013) Ushiba, Shota; Shoji, Satoru; Masui, Kyoko; Kuray, Preeya; Kono, Junichiro; Kawata, SatoshiWe present a method to develop single-wall carbon nanotube (SWCNT)/polymer composites into arbitrary three-dimensional micro/nano structures. Our approach, based on two-photon polymerization lithography, allows one to fabricate three-dimensional SWCNT/polymer composites with a minimum spatial resolution of a few hundreds nm. A near-infrared femtosecond pulsed laser beam was focused onto a SWCNT-dispersed photo resin, and the laser light solidified a nanometric volume of the resin. The focus spot was three-dimensionally scanned, resulting in the fabrication of arbitrary shapes of SWCNT/polymer composites. SWCNTs were uniformly distributed throughout the whole structures, even in a few hundreds nm thick nanowires. Furthermore, we also found an intriguing phenomenon that SWCNTs were self-aligned in polymer nanostructures, promising improvements in mechanical and electrical properties. Our method has great potential to open up a wide range of applications such as micro- and nanoelectromechanical systems, micro/nano actuators, sensors, and photonics devices based on CNTs.Item Asymmetric excitation profiles in the resonance Raman response of armchair carbon nanotubes(American Physical Society, 2015) Hároz, Erik H.; Duque, Juan G.; Barros, Eduardo B.; Telg, Hagen; Simpson, Jeffrey R.; Walker, Angela R. Hight; Khripin, Constantine Y.; Fagan, Jeffrey A.; Tu, Xiaomin; Zheng, Ming; Kono, Junichiro; Doorn, Stephen K.We performed tunable resonance Raman spectroscopy on samples highly enriched in the (5,5), (6,6), (7,7), and (8,8) armchair structures of metallic single-wall carbon nanotubes. We present Raman excitation profiles (REPs) for both the radial breathing mode and G-band phonons of these species. G-band excitation profiles are shown to resolve the expected incoming and outgoing resonances of the scattering process. Notably, the profiles are highly asymmetric, with the higher-energy outgoing resonance weaker than the incoming resonance. These results are comparable to the asymmetric excitation profiles observed previously in semiconducting nanotubes, introduce a different electronic type, and broaden the structural range over which the asymmetry is found to exist. Modeling of the behavior with a third-order quantum model that accounts for the k dependence in energies and matrix elements, without including excitonic effects, is found to be insufficient for reproducing the observed asymmetry. We introduce an alternative fifth-order model in which the REP asymmetry arises from quantum interference introduced by phonon-mediated state mixing between the EM11 and K-momentum excitons. Such state mixing effectively introduces a nuclear coordinate dependence in the transition dipole moment and thus may be viewed as a non-Condon effect from a molecular perspective. This result unifies a molecularlike picture of nanotube transitions (introduced by their excitonic nature) with a condensed matter approach for describing their behavior.Item Automated Enrichment of Single-Walled Carbon Nanotubes with Optical Studies of Enriched Samples(2013-05-13) Canning, Griffin; Weisman, R. Bruce; Hafner, Jason H.; Kono, JunichiroThe design and performance of an instrument is presented whose purpose is the extraction of samples highly enriched in one species of single-walled carbon nanotubes from density gradient ultracentrifugation. This instrument extracts high purity samples which are characterized by various optical studies. The samples are found to be enriched in just a few species of nanotubes, with the major limitation to enrichment being the separation, rather than extraction. The samples are then used in optical and microscopic studies which attempt to determine the first absorption coefficient (S1) of the (6,5) species of nanotube. Initial experiments give a value of 9.2 ± 2.6 cm2 C atom-1. Future work is proposed to improve upon the experiment in an attempt to reduce possible errorsItem Band structure dependent electronic localization in macroscopic films of single-chirality single-wall carbon nanotubes(Elsevier, 2021) Gao, Weilu; Adinehloo, Davoud; Li, Xinwei; Mojibpour, Ali; Yomogida, Yohei; Hirano, Atsushi; Tanaka, Takeshi; Kataura, Hiromichi; Zheng, Ming; Perebeinos, Vasili; Kono, JunichiroSignificant understanding has been achieved over the last few decades regarding chirality-dependent properties of single-wall carbon nanotubes (SWCNTs), primarily through single-tube studies. However, macroscopic manifestations of chirality dependence have been limited, especially in electronic transport, despite the fact that such distinct behaviors are needed for many applications of SWCNT-based devices. In addition, developing reliable transport theory is challenging since a description of localization phenomena in an assembly of nanoobjects requires precise knowledge of disorder on multiple spatial scales, particularly if the ensemble is heterogeneous. Here, we report an observation of pronounced chirality-dependent electronic localization in temperature and magnetic field dependent conductivity measurements on macroscopic films of single-chirality SWCNTs. The samples included large-gap semiconducting (6,5) and (10,3) films, narrow-gap semiconducting (7,4) and (8,5) films, and armchair metallic (6,6) films. Experimental data and theoretical calculations revealed Mott variable-range-hopping dominated transport in all samples, while localization lengths fall into three distinct categories depending on their band gaps. Armchair films have the largest localization length. Our detailed analyses on electronic transport properties of single-chirality SWCNT films provide significant new insight into electronic transport in ensembles of nanoobjects, offering foundations for designing and deploying macroscopic SWCNT solid-state devices.Item Broadband, Polarization-Sensitive Photodetector Based on Optically-Thick Films of Macroscopically Long, Dense, and Aligned Carbon Nanotubes(Nature Publishing Group, 2013) Nanot, Sebastien; Cummings, Aron W.; Pint, Cary L.; Ikeuchi, Akira; Akiho, Takafumi; Sueoka, Kazuhisa; Hauge, Robert H.; Leonard, François; Kono, JunichiroIncreasing performance demands on photodetectors and solar cells require the development of entirely new materials and technological approaches.Wereport on the fabrication and optoelectronic characterization of a photodetector based on optically-thick films of dense, aligned, and macroscopically long single-wall carbon nanotubes. The photodetector exhibits broadband response from the visible to the mid-infrared under global illumination, with a response time less than 32 ms. Scanning photocurrent microscopy indicates that the signal originates at the contact edges, with an amplitude and width that can be tailored by choosing different contact metals. A theoretical model demonstrates the photothermoelectric origin of the photoresponse due to gradients in the nanotube Seebeck coefficient near the contacts. The experimental and theoretical results open a new path for the realization of optoelectronic devices based on three-dimensionally organized nanotubes.Item Carbon nanotube fiber terahertz polarizer(AIP Publishing, 2016) Zubair, Ahmed; Tsentalovich, Dmitri E.; Young, Colin C.; Heimbeck, Martin S.; Everitt, Henry O.; Pasquali, Matteo; Kono, JunichiroConventional, commercially available terahertz (THz) polarizers are made of uniformly and precisely spaced metallic wires. They are fragile and expensive, with performance characteristics highly reliant on wire diameters and spacings. Here, we report a simple and highly error-tolerant method for fabricating a freestanding THz polarizer with nearly ideal performance, reliant on the intrinsically one-dimensional character of conduction electrons in well-aligned carbon nanotubes(CNTs). The polarizer was constructed on a mechanical frame over which we manually wound acid-doped CNT fibers with ultrahigh electrical conductivity. We demonstrated that the polarizer has an extinction ratio of ∼−30 dB with a low insertion loss (<0.5 dB) throughout a frequency range of 0.2–1.1 THz. In addition, we used a THzellipsometer to measure the Müller matrix of the CNT-fiber polarizer and found comparable attenuation to a commercial metallic wire-grid polarizer. Furthermore, based on the classical theory of light transmission through an array of metallic wires, we demonstrated the most striking difference between the CNT-fiber and metallic wire-grid polarizers: the latter fails to work in the zero-spacing limit, where it acts as a simple mirror, while the former continues to work as an excellent polarizer even in that limit due to the one-dimensional conductivity of individual CNTs.Item Carbon nanotube woven textile photodetector(American Physical Society, 2018) Zubair, Ahmed; Wang, Xuan; Mirri, Francesca; Tsentalovich, Dmitri E.; Fujimura, Naoki; Suzuki, Daichi; Soundarapandian, Karuppasamy P.; Kawano, Yukio; Pasquali, Matteo; Kono, JunichiroThe increasing interest in mobile and wearable technology demands the enhancement of functionality of clothing through incorporation of sophisticated architectures of multifunctional materials. Flexible electronic and photonic devices based on organic materials have made impressive progress over the past decade, but higher performance, simpler fabrication, and most importantly, compatibility with woven technology are desired. Here we report on the development of a weaved, substrateless, and polarization-sensitive photodetector based on doping-engineered fibers of highly aligned carbon nanotubes. This room-temperature-operating, self-powered detector responds to radiation in an ultrabroad spectral range, from the ultraviolet to the terahertz, through the photothermoelectric effect, with a low noise-equivalent power (a few nW/Hz1/2) throughout the range and with a ZT-factor value that is twice as large as that of previously reported carbon nanotube-based photothermoelectric photodetectors. Particularly, we fabricated a ∼1-m-long device consisting of tens of p+−p− junctions and weaved it into a shirt. This device demonstrated a collective photoresponse of the series-connected junctions under global illumination. The performance of the device did not show any sign of deterioration through 200 bending tests with a bending radius smaller than 100 μm as well as standard washing and ironing cycles. This unconventional photodetector will find applications in wearable technology that require detection of electromagnetic radiation.Item Characterizations of two-photon absorption process induced by defects in aluminum nitride using Z-scan method(IOP Publishing, 2024) Zhou, Jingan; Li, Tao; Zhao, Xuan; Zhang, Xiang; Doumani, Jacques; Xu, Mingfei; He, Ziyi; Luo, Shisong; Mei, Zhaobo; Chang, Cheng; Robinson, Jacob T.; Ajayan, Pulickel M.; Kono, Junichiro; Zhao, Yuji; Smalley-Curl InstituteIn this work, we reported two-photon absorption (TPA) measurements for aluminum vacancies in Aluminum nitride single crystals. We measured the linear transmission and identified the defect levels. Using the Z-scan method, we measured the TPA coefficients of the transitions between defect levels from 380 nm to 735 nm. The transition occurs between the aluminum vacancies defect levels. Furthermore, the power dependence shows good linear fitting, confirming the TPA mechanism. These results will be helpful for the design and fabrication of ultra-low loss waveguides and integrated photonics in the ultraviolet spectral range.Item Charged iodide in chains behind the highly efficient iodine doping in carbon nanotubes(American Physical Society, 2017) Zubair, Ahmed; Tristant, Damien; Nie, Chunyang; Tsentalovich, Dmitri E.; Headrick, Robert J.; Pasquali, Matteo; Kono, Junichiro; Meunier, Vincent; Flahaut, Emmanuel; Monthioux, Marc; Gerber, Iann C.; Puech, PascalThe origin of highly efficient iodine doping of carbon nanotubes is not well understood. Relying on first-principles calculations, we found that iodine molecules (I2) in contact with a carbon nanotube interact to form monoiodide or/and polyiodide from two and three I2 as a result of removing electrons from the carbon nanotube (p-type doping). Charge per iodine atom for monoiodide ion or iodine atom at end of iodine chain is significantly higher than that for I2. This atomic analysis extends previous studies showing that polyiodide ions are the dominant dopants. Moreover, we observed isolated I atoms in atomically resolved transmission electron microscopy, which proves the production of monoiodide. Finally, using Raman spectroscopy, we quantitatively determined the doping level and estimated the number of conducting channels in high electrical conductivity fibers composed of iodine-doped double-wall carbon nanotubes.Item Coherent Light-Matter Coupling and Nonequilibrium Carrier Dynamics in Single-Chirality Carbon Nanotubes(2018-03-02) Cong, Kankan; Kono, JunichiroSingle-wall carbon nanotubes (SWCNTs) are unique one-dimensional (1D) condensed matter systems in which strongly enhanced Coulomb interactions are combined with unusual band structure. There are metallic and semiconducting SWCNTs, in both of which electron-electron interactions have significant impact on their electronic and optical properties. In this dissertation work, we used ultrafast optical pump-probe spectroscopy to investigate nonequilibrium dynamics of photogenerated electron-hole pairs, or excitons, in a sample in which a particular species, or chirality, of semiconducting SWCNTs was enriched. Specifically, we studied both an aqueous suspension and an aligned film of (6,5) SWCNTs. Depending on the pump photon energy, intensity, and polarization, different physical processes ensue after ultrafast pumping, including coherent light-matter interactions and incoherent relaxation of carriers/excitons. For example, under below-gap pumping, a transient blueshift of the exciton peak occurred, only during the pump pulse duration, a hallmark of the optical Stark effect. Under resonant pumping, transient splitting of the exciton peak was observed within the pulse duration, which is a manifestation of the Rabi doublet due to coherent light-matter interaction in the strong coupling regime. The Rabi doublet was observed only under resonant or near-resonant pumping conditions. In the case of a macroscopically aligned (6,5) SWCNT film sample, an anisotropic Rabi doublet of the exciton peak was observed under resonant pumping. In the case of above-gap excitation, incoherent relaxation processes dominated the dynamics of excitons. Analysis of these ultrafast, nonequilibrium, and strongly driven phenomena provided considerable new insight into the states and dynamics of electrons in the presence of extreme quantum confinement and strong many-body interactions.Item Colors of Single-Wall Carbon Nanotubes(Wiley, 2021) Wei, Nan; Tian, Ying; Liao, Yongping; Komatsu, Natsumi; Gao, Weilu; Lyuleeva‐Husemann, Alina; Zhang, Qiang; Hussain, Aqeel; Ding, Er-Xiong; Yao, Fengrui; Halme, Janne; Liu, Kaihui; Kono, Junichiro; Jiang, Hua; Kauppinen, Esko I.Although single-wall carbon nanotubes (SWCNTs) exhibit various colors in suspension, directly synthesized SWCNT films usually appear black. Recently, a unique one-step method for directly fabricating green and brown films has been developed. Such remarkable progress, however, has brought up several new questions. The coloration mechanism, potentially achievable colors, and color controllability of SWCNTs are unknown. Here, a quantitative model is reported that can predict the specific colors of SWCNT films and unambiguously identify the coloration mechanism. Using this model, colors of 466 different SWCNT species are calculated, which reveals a broad spectrum of potentially achievable colors of SWCNTs. The calculated colors are in excellent agreement with existing experimental data. Furthermore, the theory predicts the existence of many brilliantly colored SWCNT films, which are experimentally expected. This study shows that SWCNTs as a form of pure carbon, can display a full spectrum of vivid colors, which is expected to complement the general understanding of carbon materials.Item Complexed Multifunctional Metallic and Chalcogenide Nanostructures as Theranostic Agents(2013-12-03) Young, Joseph; Drezek, Rebekah A.; Hicks, Illya V.; Kono, JunichiroNanostructures have attracted substantial attention due to their distinctive properties and various applications. Nanostructures consisting of multiple morphologies and/or materials have recently become the focus of intense study with particular attention being paid to their optical and magnetic properties and the enhanced role of the interface between materials. Of particular interest are metallic-based plasmonic nanostructures, structures that support surface plasmon resonances that are sensitive to the environment, and ferrimagnetic-based nanostructures, structures that exhibit strong magnetic properties when exposed to an external field. These nanostructures provide theranostic potential in the context of cancer photothermal therapies, diagnostics and imaging. Additionally, chalcogenide based nanostructure complexes are particularly interesting. Metallic chalcogenides offer the ability to combine different types of linear and nonlinear optical properties, enable design of nanostructure complexes with surface plasmon resonance effects in new wavelength ranges, and act as photo-emitting agents for novel theranostic applications. In this thesis an in depth analysis of plasmonic, magnetic and photo-emitting nanostructures as theranostic agents is presented. We have created several multifunctional nanostructures and the factors contributing to the functional properties of these nanostructures are explored systematically through experimentation, theory, and simulations. Both in vivo and in vitro testing demonstrates the applicability of these nanostructures as theranostic agents.Item Computational Study of Electronic and Transport Properties of Novel Boron and Carbon Nano-Structures(2013-07-24) Sadrzadeh, Arta; Yakobson, Boris I.; Ajayan, Pulickel M.; Kono, JunichiroIn the first part of this dissertation, we study mainly novel boron structures and their electronic and mechanical properties, using ab initio calculations. The electronic structure and construction of the boron buckyball B80, and boron nanotubes as the α-sheet wrapped around a cylinder are studied. The α-sheet is considered so far to be the most stable structure energetically out of the two dimensional boron assemblies. We will argue however that there are other sheets close in energy, using cluster expansion method. The boron buckyball is shown to have different possible isomers. Characterization of these isomers according to their geometry and electronic structure is studied in detail. Since the B80 structure is made of interwoven double-ring clusters, we also investigate double-rings with various diameters. We investigate the properties of nanotubes obtained from α-sheet. Computations confirm their high stability and identify mechanical stiffness parameters. Careful relaxation reveals the curvature-induced buckling of certain atoms off the original plane. This distortion opens up the gap in narrow tubes, rendering them semi-conducting. Wider tubes with the diameter d 1.7 nm retain original metallic character of the α-sheet. We conclude this part by investigation into hydrogen storage capacity of boron-rich compounds, namely the metallacarboranes. In the second part of dissertation, we switch our focus to electronic and transport properties of carbon nano-structures. We study the application of carbon nanotubes as electro-chemical gas sensors. The effect of physisorption of NO2 gas molecules on electron transport properties of semi-conducting carbon nanotubes is studied using ab initio calculations and Green’s function formalism. It is shown that upon exposure of nanotube to different concentrations of gas, the common feature is the shift in conductance towards lower energies. This suggests that physisorption of NO2 will result in a decrease (increase) in conductance of p-type (n-type) nanotubes with Fermi energies close to the edge of valence and conduction band. Finally we study the effect of torsion on electronic properties of carbon nano-ribbons, using helical symmetry of the structures.Item Computer simulations on mechanical and electrical properties of nanoscale materials(2013-12-06) Hua, Ming; Yakobson, Boris I.; Lou, Jun; Kono, JunichiroNanoscale materials have highly regular atomistic structures with very few defects due to their small sizes. The small size and near-perfect structure give such materials unique properties compared with materials at a larger scale. This work investigates the structures and properties of several nanoscale materials using various computer simulation methods. The great strength of carbon nanotubes comes from the strong covalent bonding between carbon atoms, and has been of great interest in research, however both the theoretical and experimental results obtained are in a wide range. In this work, different atomic mechanisms about the nucleation of structural failure are proposed and analyzed, revealing the competition of two routes of forming defects--brittle bond breaking and plastic yield. The relevance of these two routes are shown to be dependent on nanotube symmetry, test time, and temperature. The nanotube strength is decided by the dominant route chosen under these parameters. Helical symmetry exists in many nanoscale structures, but it's far less utilized in computer simulations compared with translational and rotational symmetry. In this work a model for helical symmetry in tight-binding computational method is developed, then the implemented code are used to calculate the structure of thin silicon nanowires, as well as the properties of twisted armchair graphene nanoribbons, such as their deformation energy, band gap, and electrical conductance. Inspired by carbon nanotube, this work also investigates very thin silicon nanotubes. They are shown to have stable structures when filled with various metal atoms along the axis. They can also go through significant structural changes from one stable atomistic configuration to another. Such thin metal-endohedral silicon nanotubes can then combine to form thicker silicide wires that are morphologically identical to experimental disilicide wires synthesized from epitaxial growth.Item Continuous transition between weak and ultrastrong coupling through exceptional points in carbon nanotube microcavity exciton–polaritons(Springer Nature, 2018) Gao, Weilu; Li, Xinwei; Bamba, Motoaki; Kono, JunichiroNon-perturbative coupling of photons and excitons produces hybrid particles, exciton–polaritons, which have exhibited a variety of many-body phenomena in various microcavity systems. However, the vacuum Rabi splitting (VRS), which defines the strength of photon–exciton coupling, is usually a single constant for a given system. Here, we have developed a unique architecture in which excitons in an aligned single-chirality carbon nanotube film interact with cavity photons in polarization-dependent manners. The system reveals ultrastrong coupling (VRS up to 329 meV or a coupling-strength-to-transition-energy ratio of 13.3%) for polarization parallel to the nanotube axis, whereas VRS is absent for perpendicular polarization. Between these two extremes, VRS is continuously tunable through polarization rotation with exceptional points separating crossing and anticrossing. The points between exceptional points form equienergy arcs onto which the upper and lower polaritons coalesce. The demonstrated on-demand ultrastrong coupling provides ways to explore topological properties of polaritons and quantum technology applications.Item Creating a near-perfect circularly polarized terahertz beam through the nonreciprocity of a magnetoplasma(Optica Publishing Group, 2023) Ju, Xuewei; Hu, Zhiqiang; Zhu, Guofeng; Huang, Feng; Chen, Yanqing; Guo, Cuixia; Belyanin, Alexey; Kono, Junichiro; Wang, XiangfengCompared to other parts of the electromagnetic spectrum, the terahertz frequency range lacks efficient polarization manipulation techniques, which is impeding the proliferation of terahertz technology. In this work, we demonstrate a tunable and broadband linear-to-circular polarization converter based on an InSb plate containing a free-carrier magnetoplasma. In a wide spectral region (∼ 0.45 THz), the magnetoplasma selectively absorbs one circularly polarized mode due to electron cyclotron resonance and also reflects it at the edges of the absorption band. Both effects are nonreciprocal and contribute to form a near-zero transmission band with a high isolation of –36 dB, resulting in the output of a near-perfect circularly polarized terahertz wave for an incident linearly polarized beam. The near-zero transmission band is tunable with magnetic field to cover a wide frequency range from 0.3 to 4.8 THz.Item Creation and Optical Characterization of Functional Defects in Two-Dimensional Materials(2018-11-28) Kerwin, James Thomas; Kono, JunichiroThe optical properties of two-dimensional materials change with the introduction of defects into the lattice. In this work, we characterize some of the optical properties of a binary alloy, MoxW1-xS2, and hexagonal boron nitride (h-BN) as they change in the presence of defects. Under laser illumination and optical heating, we find that damage to the binary alloy leads to brightening in the photoluminescence intensity, and with increased exposure, oxidation of the material. It is also possible to induce sub-bandgap emission in h-BN when the lattice is damaged. Using electron beam lithography techniques, we are able to controllably induce defects into the material and, consequently, create sub-bandgap fluorescent emitters that follow the lithographically patterned array. Under the right conditions, some of these emitters show single-photon emission, which is observable at room temperature. These properties can be used advantageously to create areas of bright emission in optoelectronic devices.Item Cross-Polarized Excitons and Plasmons Aligned Carbon Nanotubes(2018-07-17) Katsutani, Fumiya; Kono, JunichiroSingle-wall carbon nanotubes (SWCNTs) exhibit strong absorption resonances for parallel -polarized light, arising from one-dimensional excitons with enormous binding energies, promising for a variety of applications in optoelectronics. However, how SWCNTs respond to light polarized perpendicular to the nanotube axis has not been explored experimentally due to the unavailability of suitable samples. In this study, we have observed new types of excitonic and plasmonic resonances for perpendicular-polarized light in aligned SWCNT films. Specifically, first, we observed an interband absorption resonance for perpendicular polarization through so-called cross-polarized excitons in a single-chirality aligned SWCNT film. This direct observation by absorption spectroscopy allowed us to determine the oscillator strength quantitatively. Second, we observed intersubband plasmons for perpendicular polarization when and only when gated and aligned SWCNT films. This observation allowed us to provide insight into the collective dynamic response of interacting electrons in one dimension.Item Destabilization of Surfactant-Dispersed Carbon Nanotubes by Anions(Springer, 2017) Hirano, Atsushi; Gao, Weilu; He, Xiaowei; Kono, JunichiroThe colloidal stability of surfactant-dispersed single-wall carbon nanotubes (SWCNTs) is determined by microscopic physicochemical processes, such as association, partitioning, and adsorption propensities. These processes can be controlled by the addition of solutes. While the effects of cations on the colloidal stability of SWCNTs are relatively well understood, little is known about the effects of anions. In this study, we examined the effects of anions on the stability of SWCNTs dispersed by sodium dodecyl sulfate (SDS) using sodium salts, such as NaCl and NaSCN. We observed that the intensity of the radial breathing mode Raman peaks rapidly decreased as the salts were added, even at concentrations less than 25 mM, indicating the association of SWCNTs. The effect was stronger with NaSCN than NaCl. We propose that the association of SWCNTs was caused by thermodynamic destabilization of SDS assemblies on SWCNT surfaces by these salts, which was confirmed through SWCNT separation experiments using aqueous two-phase extraction and gel chromatography. These results demonstrate that neutral salts can be used to control the colloidal stability of surfactant-dispersed SWCNTs.