Suspended Single-walled Carbon Nanotubes Research Articles

13 nm Exciton Size in (6,5) Single-Wall Carbon Nanotubes.

Electron-hole correlation lengths, also termed exciton size, for (6,5) single-wall carbon nanotubes (SWNTs) are determined using femtosecond time-resolved pump-probe spectroscopy. The phase space filling model is used to obtain the sizes of the first subband exciton in samples of isolated and of bundled SWNTs. The experiments indicate that the exciton size of (13 ± 3) nm is a factor of 6 higher than previous experimental estimates and theoretical predictions for vacuum suspended SWNTs. This surprising result may be attributed at least in part to the effect of the dielectric environment on exciton sizes and supports recent theoretical findings predicting that screening in SWNTs may enhance rather than reduce electron-hole interactions for separations larger than the tube diameter. Thereby, the work also points to the unique nature of screening and electronic correlations in one-dimensional semiconductors.

Tight-binding normal mode analysis of suspended single-wall carbon nanotubes

We present a detailed normal mode analysis of suspended single-wall carbon nanotubes based on a non-orthogonal tight-binding formalism and a new methodology for classifying vibrational modes, using geometry-adapted merit functions. The fundamental modes are in good agreement with experiments and previous calculations. The analysis of the high-order vibrations evidences interesting non-classical features, while the sensitivity of the normal modes to the nanotube geometry provides new insights useful for practical realizations of mass resonators.

Dispersion and functionalization of single-walled carbon nanotubes (SWCNTS) for nanocomposite applications

We present an easy and reliable method of functionalizing and dispersing single-walled carbon nanotubes (SWCNTs) for nanocomposite production. This was achieved via a mixture of the concentrated acids HNO3 /H2 SO4 , followed by sonication in appropriate solvents (Ethanol, Acetone and/or Dimethylformamide). SWCNTs were functionalized to attach carboxylic moieties on the walls of the nanotubes, which aided in the production of SWCNTs suspensions in acetone, ethanol and dimethylformamide in which nanotubes remained dispersed for a period of two (2) weeks. Energy dispersion analysis (EDS), scanning electron microscopy (SEM) and Raman spectroscopy were used to characterize the functionalized SWCNTs.

Chemical Vapor Deposition Using Ethylene Gas toward Low Temperature Growth of Single-Walled Carbon Nanotubes

We demonstrate the growth of single-walled carbon nanotubes (SWNTs) using ethylene-based chemical vapor deposition (CVD) and ferritin-induced catalytic particles toward growth temperature reduction. We first optimized the gas composition of H₂ and C₂H₄ at 500 and 30 sccm, respectively. On a planar SiO₂ substrate, high density SWNTs were grown at a minimum temperature of 760℃. In the case of growth using nanoporous templates, many suspended SWNTs were also observed from the samples grown at 760℃; low values of I D /I G in the Raman spectra were also obtained. This means that the temperature of 760℃ is sufficient for SWNT growth in ethylene-based CVD and that ethylene is more effective that methane for low temperature growth. Our results provide a recipe for low temperature growth of SWNT; such growth is crucial for SWNT-based applications.

Three-dimensional dynamic behavior of suspended single wall carbon nanotubes

We investigate the nonlinear dynamics of high aspect ratio single wall carbon nanotubes (SWCNTs) both theoretically and experimentally. A nonlinear stretchable string model was used to describe the complicated dynamics of very slender SWCNTs with tension dominated stiffness and its transition from linear to nonlinear response. Finite difference spacial and time discretization were implemented and the resulting system of ordinary differential equations was solved numerically. A fabrication process developed to incorporate SWCNTs into patterned silicon structure was used to fabricate structures of taut, long SWCNTs suspended over trenches. Time depending electric fields were applied to the SWCNTs and their mechanical resonance responses were captured based on averaged electrical measurements (i.e., electrical resistance) of the oscillating SWCNTs. Measured resonance frequencies are reasonably consistent with those extracted from our model as resonance frequency of 24.3MHz was measured comparing to the calculated frequency of 20.4MHz. The transition from linear to nonlinear regime was demonstrated experimentally.

Printing Highly Controlled Suspended Carbon Nanotube Network on Micro-patterned Superhydrophobic Flexible Surface.

Suspended single-walled carbon nanotubes (SWCNTs) offer unique functionalities for electronic and electromechanical systems. Due to their outstanding flexible nature, suspended SWCNT architectures have great potential for integration into flexible electronic systems. However, current techniques for integrating SWCNT architectures with flexible substrates are largely absent, especially in a manner that is both scalable and well controlled. Here, we present a new nanostructured transfer paradigm to print scalable and well-defined suspended nano/microscale SWCNT networks on 3D patterned flexible substrates with micro- to nanoscale precision. The underlying printing/transfer mechanism, as well as the mechanical, electromechanical, and mechanical resonance properties of the suspended SWCNTs are characterized, including identifying metrics relevant for reliable and sensitive device structures. Our approach represents a fast, scalable and general method for building suspended nano/micro SWCNT architectures suitable for flexible sensing and actuation systems.

Dissolution of single-walled carbon nanotubes in alkanol-cholic acid mixtures

A procedure for dispersing the single-walled carbon nanotubes (SWCNTs) for preparing stable suspensions with high concentrations of individual nanotubes in various alcohols was described. The obtained suspensions were studied by Raman spectroscopy. The solubility of the single-walled carbon nanotubes in alcohols was found to depend on the concentration of cholic acid. The ethanol-surfactant mixture was shown to be the best solvent for all alkanol-cholic acid mixtures (0.018 mol/kg) under study used for preparing time-stable suspensions of single-walled carbon nanotubes. The dissolving ability of aliphatic alcohols was found to decrease in the series: ethanol-isopropanol-tert-butanol-butanol-propanol.

Optical visualization and polarized light absorption of the single-wall carbon nanotube to verify intrinsic thermal applications

The predicted extraordinary properties of carbon nanotubes (CNTs) from theoretical calculations have great potential for many applications. However, reliable experimental determination of intrinsic properties at the single-tube level is currently a matter of concern, and many challenges remain because of the unhandled and nanoscale size of individual nanotubes. Here, we demonstrated a prototype to detect the intrinsic thermal conductivity of the single-wall carbon nanotube (SWCNT) and verify the significant non-resonant optical absorption behavior on tiny nanotubes by integrating the nanotube and ice into a new core-shell design. In particular, a reversible optical visualization method based on the individual suspended ultra-long SWCNT was first developed by wrapping a nanotube with ice in the cryogenic air environment. The light-induced thermal effect on the hybrid core-shell structure was used to melt the ice shell, which subsequently acted as a temperature sensor to verify the intrinsic thermal conductivity of the core-like nanotube. More interestingly, we successfully determined for the first time the thermal response phenomenon of the tiny absorption cross section in SWCNT in the vertical-polarization configuration and the significant non-resonant absorption behavior in the parallel-polarization configuration. These investigations will provide a better understanding for the unique optical behaviors of CNT and enable the detection of intrinsic properties of various one-dimensional nanostructures such as nanotubes, nanowires, and nanoribbons. Growing ice on a carbon nanotube not only enables the nanotube to be optically imaged but also permits its thermal properties to be measured. Isolated single-walled carbon nanotubes with diameters of just a few nanometres are usually impossible to observe using an optical microscope. Now, Xiao Zhang and other scientists in China have discovered a non-destructive and reversible way to optically observe carbon nanotubes and measure their thermal properties. Their method involves growing a few-micrometre-thick layer of ice on a suspended nanotube by placing it in a cryogenic environment. The researchers then melted the ice by irradiating the ice-coated nanotube with a laser beam, while inferring the nanotube s temperature from a shift in its Raman signal. From this information, they could determine the intrinsic thermal conductivity and the light absorption behavior of the nanotube.

Thermally induced nonlinear vibration of single-walled carbon nanotubes

The thermally induced nonlinear vibration of single-walled carbon nanotubes (SWNTs) was investigated, focusing on the peak broadening and/or multiple peaks of the frequency spectra. From Poincar\'e maps of SWNT tip trajectories, we observed two distinguishable patterns of vibration: planar and nonplanar (whirling) motion which appeared repeatedly. The alternation of the pattern is sometimes accompanied by a change of rotational direction. Proposed approximate solutions of nonlinear beam equations can reproduce well the alternation of the patterns for both cantilevered and suspended SWNTs. By using this analytical approach, we have found that multiple peaks of experimentally observed frequency spectra are due to the repeated and sudden alternations of two modes, induced by nonlinear effects.

Effects of Various Carbon Nanotube Suspensions on A549, THP-1, and Peritoneal Macrophage Cells

The effects of iron content, fiber length, and stability of carbon nanotube (CNT) suspension on cells were examined. Five kinds of single-wall carbon nanotube (SWCNT) suspensions were prepared: with catalytic iron, without iron, long SWCNTs (stable), short SWCNTs (stable), and short SWCNT (unstable). These suspensions were applied to A549, THP-1, and mouse peritoneal macrophage cells. After a 24-h exposure, the mitochondrial activity, cell membrane damage, intracellular oxidative stress, and expression of cytokine genes were determined. Among these properties of SWCNTs, stability of CNT suspension had the most influence on the cells, whereas the effects of iron content and fiber length were small. The unstable SWCNT suspension caused a substantial increase in intracellular ROS levels. Additionally, the cellular effects of stable multi-wall carbon nanotubes (MWCNTs) were examined. The MWCNT suspension did not show any cellular effects. Overall, influences of CNT suspension on mitochondrial activity and cell membrane damage were small. These results suggest that the physical properties of CNT suspension are important factors for their cellular effects. Thus, CNT suspensions prepared with the same material but having different physical properties would differ in the cellular effects they exert, including cytotoxicity. Therefore, physical characterization of CNT suspensions is essential to the evaluation of CNT toxicity. In particular, stability of CNT suspension notably influenced the intracellular ROS level.

Single-Walled Carbon Nanotubes – Graphene Mixture as a Dye Monolayer for Dye-Sensitized Solar Cells

The suspension of single-walled carbon nanotubes (SWCNTs) was produced by acid functionalization process. After that, the reduced graphene oxide (r-GO) suspension was added into SWCNTs suspension in order to produce a solution of SWCNTs-Graphene mixture. The solution of SWCNTs-Graphene mixture was then deposited onto titanium dioxide (TiO2) layer as a dye monolayer in dye-sensitized solar cell (DSSC) device using drop – casting methods. Beforehand, the TiO2 layer was cured with two different temperatures which was 450°C and 550°C. The electrical properties of the device, including the response and efficiency, were studied and compared with different curing temperatures.

Molecularly imprinted polymer grown on multiwalled carbon nanotube surface for the sensitive electrochemical determination of amoxicillin

We described a novel electrochemical sensor for amoxicillin (AMOX), which was constructed by multiwalled carbon nanotubes@molecularly imprinted polymer (MWCNTs@MIP), single walled carbon nanotube (SWCNT) and dendritic Pt-Pd nanoparticle (NP). Firstly, ionic liquid (IL, i.e. 3-propyl-1-vinylimidazolium bromide) was grafted onto MWCNTs surface to form MWCNTs@IL by using an ionic exchange strategy. Then, the resulting MWCNTs@IL was used as monomer to synthesize MWCNTs@MIP. Meanwhile, dendritic Pt-Pd bimetallic NP was prepared by using hexadecylpyridinium chloride and hexamethylenetriamine as synergetic structure-directing agents, and then it was dispersed into SWCNT suspension. After that, the hybrid suspension was dropped on a glassy carbon electrode, followed by coating with MWCNTs@MIP. Under the optimal conditions, the obtained sensor presented linear response to AMOX in the ranges of 1.0×10−9∼1.0×10−6molL−1 and 1.0×10−6∼6.0×10−6, respectively, and its detection limit was 8.9×10−10molL−1. This sensor was used to detect AMOX in real samples with satisfactory results.

(Invited) Variance Spectroscopy: A New Bridge Between Ensemble and Single-Particle Studies

We have developed a new experimental technique that probes variations in the spectra from small regions of heterogeneous bulk samples resulting from statistical variations in composition. The method is demonstrated with suspensions of single-walled carbon nanotubes (SWCNTs) containing mixtures of distinct structural species. Using dilute SWCNT samples, focused excitation beams, multichannel detection, and quick data collection, we capture several thousand emission spectra sampling different spatial regions of the sample. The data are analyzed to find both the mean emission intensity and the variance of emission intensity as a function of wavelength. Those spectra are then combined to extract information that is not available from conventional experiments, including the abundances of different (n,m) species and their relative emission efficiencies. The variance data are further analyzed for correlations between intensity fluctuations at different wavelengths. This gives novel two-dimensional maps that reveal the spectra of homogeneous sub-populations within the heterogeneously broadened bulk spectra. The off-diagonal features in these maps show spatially correlated concentration variations for nanotubes of different types, which expose the earliest stages of SWCNT aggregation. Variance spectroscopy should prove a powerful new experimental tool that can extract sub-ensemble level detail from measurements on bulk nanoparticle samples.

(Invited) Post-Growth Manipulation of Horizontally Aligned Single-Walled Carbon Nanotubes

Horizontally aligned single-walled carbon nanotubes (SWNTs) are promising for electronic applications such as field-effect transistors (FETs). In addition to the density-controlled CVD growth [1,2] and chirality characterization of aligned SWNTs on quartz substrates, we will discuss two manipulation techniques of SWNT arrays. First is the full-length removal of metallic SWNTs by using organic film-assisted electrical breakdown, which gives semiconducting SWNT arrays suitable for scalable device fabrication [3]. We applied the electrical breakdown technique to SWNT array covered with organic films such as poly(methyl methacrylate) (PMMA) and realized that metallic nanotubes continues to burn as fuses for fireworks. This method yielded not only a high on/off ratio (~10,000) and fine spatial resolution (~55 nm) in the same way as in-air breakdown, but also long removal length (>10 µm) which is unattainable by conventional breakdown. Thermal calculations revealed that burned edges of a SWNT keep high temperature with oxidation heat generation of surrounding organic materials even after Joule heat stops. The second manipulation technique is the bundling of selected parts of SWNT arrays. Horizontally aligned SWNTs were peeled off from original substrates by using polymer films with lithographically-defined resist structures. Then, the resist was dissolved to give partially suspended SWNTs over trenched polymer films, and neighboring suspended SWNTs formed bundles by capillary process. Finally the structures were placed on target substrates to give partially bundled SWNTs. This technique would be available for controlling percolative transport of SWNT networks. Reference: [1] S. Chiashi, H. Okabe, T. Inoue, J. Shiomi, T. Sato, S. Kono, M. Terasawa, S. Maruyama, J. Phys. Chem. C, 116 (2012) 6805. [2] T. Inoue, D. Hasegawa, S. Badar, S. Aikawa, S. Chiashi, S. Maruyama, J. Phys. Chem. C, 117 (2013) 11804. [3] K. Otsuka, T. Inoue, S. Chiashi and S. Maruyama, Nanoscale, 6 (2014) 8831.

Gold deposition effects on photoluminescence and Raman scattering spectra of suspended single-walled carbon nanotubes

Gold (Au) deposition effects on suspended single-walled carbon nanotubes (SWCNTs) were investigated by photoluminescence (PL) and Raman scattering spectroscopies. Deposited Au atoms formed particles on the SWCNT surface. The PL intensity decreased with increasing Au coverage, while the enhancement of the G-band in Raman scattering spectra was observed owing to the surface-enhancement Raman scattering (SERS) effect. The changes in the optical transition energy obtained from the PL spectra and Raman shift of the G-band revealed that tensile strain, which reached 5 × 10−3, occurred along the tube axis and was proportional to the Au coverage. The Au coverage dependence of the uniaxial strain can be understood in terms of the difference in the thermal expansion between SWCNT and Au.

Reactive oxygen species generation and dispersant-dependent electron transfer through single-walled carbon nanotubes in water

Although induction of oxidative stress is widely accepted as one of the major cytotoxic effects of carbon nanotubes (CNTs), there is no solid understanding of how biological redox reactions are affected and how reactive oxygen species (ROS) are generated by CNTs, especially when they are coated with various dispersing agents. In this study, we investigated electron transfer from biological reducing agents through nonfunctionalized single-walled carbon nanotubes (SWCNTs) to molecular oxygen, generating ROS in the process. Electron transfer rates in the colloidal SWCNT suspensions depended on the dispersant used to stabilize them, with six dispersants examined. Oxidation of both nicotinamide adenine dinucleotide (NADH) and dithiothreitol was catalyzed by SWCNTs coated with either cetyltrimethylammonium bromide (CTAB) or Suwannee River natural organic matter (SRNOM). SWCNTs coated with other types of surfactants showed only slight effect. In the presence of NADH or dithiothreitol, generation of ROS also was dispersant-dependent, with CTAB- and SRNOM-coated SWCNTs generating significant amounts of superoxide anion and hydrogen peroxide. In systems containing xanthine and xanthine oxidase, accumulated charge on the SWCNTs appeared to be transferred to superoxide anion, resulting in indirect disproportionation of superoxide anion, forming more hydrogen peroxide.

Modification of polymethylmethacrylate by means of diffusion introduction of single-walled carbon nanotubes in supercritical carbon dioxide

Amorphous polymethylmethacrylate has been modified by means of impregnation suspension of single-walled carbon nanotubes in alcoholic solution in supercritical carbon dioxide. Properties of the so formed composite have been studied. Thermal stability of the polymer has increased after the modification.

Reactions on single-walled nanotubes: 1. Radiation-stimulated reactions in aqueous suspensions of single-walled carbon nanotubes in surfactant solutions

Chical reactions initiated by 60Co γ-radiation in the suspensions of single-wall carbon nanotubes (SWCNTs) in the aqueous solutions of a surfactant, cetyltrimethylammonium bromide (CTAB), have been studied. In a pure aqueous solution of CTAB, the radiolysis of water leads to the appearance of OH radicals, which induce the oxidation of CTAB molecules. In the suspensions, CTAB molecules are concentrated on SWCNTs and oriented in one direction and the OH radicals induce the crosslinking of surfactant molecules. A moss-like coating is formed on the nanotubes, and the suspension is converted into jelly. The coating does not have covalent bonds with the nanotube walls. The formation of the polymer is due to the packing of molecules around the nanotube, rather than their chemical properties.

Dispersion and Individualization of SWNT in Surfactant-Free Suspensions and Composites of Hydrosoluble Polymers

We propose a simple and original way to prepare surfactant-free SWNT/hydrosoluble polymer composites with high concentrations of individual SWNT. We first disperse single-walled carbon nanotubes (SWNT) in aqueous suspensions using bile salts (BS), and we mix them with a solution of hydrosoluble polymer, poly(vinylpyrrolidone) (PVP) or poly(vinyl alcohol) (PVA). We measure the yield using visible–NIR absorption spectroscopy, and we probe both the chemical environment of the nanotubes and the effectiveness of individualization from coupled Raman/photoluminescence studies. We evidence a direct exchange of BS molecules and PVA chains at the surface of SWNT. By contrast, no direct exchange is observed with PVP. On the other hand, we show that a simple dialysis process leads to the preparation of aqueous suspensions of SWNT covered by PVP or PVA with high yields and an effective individualization of the nanotubes.

Carbon Nanotubes as a Nonlinear Buckled Beam for Nanoelectromechanical Systems

In this paper, we examine the nonlinear nanoelectromechanical effect on a doubly clamped suspended single-walled carbon nanotube which could be used for pressure sensor. Coulomb-blockade effects will be explored and investigated. We adopt the full expression of curvature term in the elastic energy and use a modified Euler’s method to determine the nanotube’s maximum displacement in all bending regimes. We find that while the approximate solution given by Sapmaz et al. [1] underestimates the maximum displacement of the buckled nanotube in the weak bending regime, the approximate solution fails to obtain the correct maximum displacement as given by our numerical solution. Accordingly, the effect of curvature must be properly addressed for this nanoelectromechanical system to be used as an accurate sensor.