Properties Of Single-walled Carbon Nanotubes Research Articles

The Electrical Properties of Single-walled Carbon Nanotubes

Carbon nanotubes are expected to be a new type of semiconductor material to replace the traditional silicon-based semiconductor material. The high carrier mobility, ideal subthreshold characteristics and ballistic transport characteristics of carbon nanotubes can effectively solve the short channel effect, performance and power consumption limits of silicon-based semiconductor devices. These excellent properties are due to the structure of carbon nanotubes. This paper focuses on the relationship between the structure of carbon nanomaterials and their electrical properties, and the advantages and prospects of using carbon nanotubes as semiconductor materials are also described.

The low doses of SWCNTs affect the expression of proliferation and apoptosis related genes in normal human astrocytes

The unique properties of single-walled carbon nanotubes (SWCNTs) make them viable candidates for versatile implementation in the biomedical devices. They are able to cross the blood–brain barrier, enter cells and accumulate in cell nuclei. We studied the effect of these carbon nanoparticles on the expression of genes associated with endoplasmic reticulum stress and proliferation, cell viability and cancerogenesis as well as microRNAs in normal human astrocytes. We have shown that treatment of normal human astrocytes by small doses of SWCNTs (2 and 8 ng/ml of medium for 24 hrs) affect the expression of DNAJB9, IGFBP3, IGFBP6, CLU, ZNF395, KRT18, GJA1, HILPDA, and MEST mRNAs as well as several miRNAs, which have binding sites at 3′-UTR of these mRNAs. These changes in the expression profile of individual mRNAs introduced by SWCNTs are dissimilar in magnitude and direction and are the result of both transcriptional and posttranscriptional mechanisms of regulation. It is possible that these changes in gene expressions are mediated by the endoplasmic reticulum stress introduced by carbon nanotubes and reflect the disturbance of the genome stability. In conclusion, the low doses of SWCNTs disrupt the functional integrity of the genome and possibly exhibit a genotoxic effect.

Studies of electrical, thermal, and mechanical properties of single-walled carbon nanotube and polyaniline of nanoporous nanocomposites

Hydrogel of single-walled carbon nanotubes and polyaniline has been used for thermopower engineering applications due to desirable thermal, electrical, and mechanical properties as well as tunable degradability. In this article, we fabricated nanoporous composite scaffolds from hydrogel of single-walled carbon nanotubes and polyaniline polymer using a standard in situ polymerization process. Our solution-based fabrication method prevented single-walled carbon nanotube aggregation which resulted in enhancing thermal, electrical, and mechanical properties with keeping optimum flexibility in the porous composite scaffold. We compared the mechanical, electrical, and thermal properties of nanoporous composites with different single-walled carbon nanotube loadings. The porous composite scaffold with a 25 wt% showed higher electrical conductivity, ultimate tensile strength, and tensile modulus. Lastly, our solution fabrication method prevents aggregation single-walled carbon nanotube and could help to build the thermoelectrical materials for flexible electronic applications.

Optical Property Tuning of Single-Wall Carbon Nanotubes by Endohedral Encapsulation of a Wide Variety of Dielectric Molecules.

Specific and tunable modification to the optical properties of single-wall carbon nanotubes (SWCNTs) is demonstrated through direct encapsulation into the nanotube interior of guest molecules with widely varying static dielectric constants. Filled through simple ingestion of the guest molecule, each SWCNT population is demonstrated to display a robust modification to absorbance, fluorescence, and Raman spectra. Over 30 distinct compounds, covering static dielectric constants from 1.8 to 109, are inserted in large diameter SWCNTs (d = 1.104-1.524 nm) and more than 10 compounds in small diameter SWCNTs (d = 0.747-1.153 nm), demonstrating that the general effect of filler dielectric on the nanotube optical properties is a monotonic energy reduction (red-shifting) of the optical transitions with increased magnitude of the dielectric constant. Systematic fitting of the two-dimensional fluorescence-excitation and Raman spectra additionally enables determination of the critical filling diameter for each molecule and distinguishing of overall trends from specific guest-host interactions. Comparisons to predictions from existing theory are presented, and specific guest molecule/SWCNT chirality combinations that disobey the general trend and theory are identified. A general increase of the fluorescence intensity and line narrowing is observed for low dielectric constants, with long linear alkane filled SWCNTs exhibiting emission intensities approaching those of empty SWCNTs. These results demonstrate an exploitable modulation in the optical properties of SWCNTs and provide a foundation for examining higher-order effects, such as due to nonbulk-like molecule stacking, in host-guest interactions in well-controlled nanopore size materials.

Chirality luminescent properties of single-walled carbon nanotubes during redox reactions

The optical measurement of single-walled carbon nanotubes (SWNTs) is a useful approach for understanding chirality characteristics because the excitation and emission wavelengths that produce the maximum emission intensity are unique to the chirality of SWNTs. The emission properties of SWNT chirality are useful in various biological applications and are envisaged to be applicable in nanobiosensors. Therefore, it is necessary to detect even small environmental changes, such as redox reactions, and it is important to identify optimal chirality according to the applications. In this study, we focused on the presence of SWNTs with different chiralities within the same SWNT powder, and we investigated the correlation between the rate of change of the emission intensity due to redox reactions and SWNT chirality. We measured the redox change rate of chirality, which was difficult to detect because of the low emission intensity, by increasing the exposure time during photoluminescence (PL) measurement. 0.5 mg of SWNT powder and 1 mL of double-stranded DNA (dsDNA) stock solution were mixed and sonicated using a probe-type sonicator on ice. The supernatant of the prepared dsDNA-SWNT dispersion was stored after centrifugation. Hydrogen peroxide (H 2 O 2 ; final concentration: 0.03%) was added to this dispersion for oxidation, and then, a catechin aqueous solution (final concentration 1.5 μg/mL) was added to the solution to measure PL. The exposure time was 90 s to obtain sufficient emission intensity. The measurement results showed that the magnitude of the rate of change of the PL intensity due to redox reaction was different for each chirality. Focusing on the (8,6) and (9,4) chiralities, which showed a large rate of change, the PL intensity decreased by 57.4% and 54.6% from the initial state, respectively, when H 2 O 2 was added. Subsequently, these values increased by 1024% and 558% with the addition of a catechin aqueous solution, respectively. Furthermore, from the comparison of the PL detection results and optical response characteristics of each chirality, it was observed that the rate of change of the PL intensity of SWNTs during redox reactions using H 2 O 2 and catechin had the strongest correlation with the SWNT diameter. • The exposure time was increased to 90 s to facilitate comparison of PL intensities between chiralities. • The responsiveness of chirality with small emission intensity was detected, which was difficult to detect in previous studies. • The PL change rate during redox using H 2 O 2 and catechin showed the strongest correlation with the SWNTs diameter. • The larger the diameter of SWNTs, the higher will be the PL change rate during redox reactions.

Enhanced field emission properties of single-walled carbon nanotube from dip-coating catalyst

Here we use a simple method of dip-coating catalyst to prepare single walled carbon nanotube (SWCNT), and study its cathode field emission property. The field emission performances of SWCNT films are not significantly different when the hydrogen flow quantities are in the range of 10–50 sccm. SWCNT prepared by different catalyst are also used as cathode to test field emission performance. SWCNT fabricated by Mo and Co (SWCNT-MoCo) cathode has a better field emission property than SWCNT prepared by Mo, Co and Fe, with lower Eon and Eth (electric field at the emission current density of 10 μA/cm2 and 0.1 mA/cm2) of 1.95 V/μm and 2.47 V/μm, which is because that SWCNT-MoCo cathode has a higher density of field emitter, so that under the same electric field SWCNT-MoCo cathode has more tips and sites to emit electrons. This method is simple and easy to operate, and the purity of the cathode film is high, with few impurities, which can be further applied in the future.

Sp3-Functionalization of Single-Walled Carbon Nanotubes Creates Localized Spins.

Chemical functionalization-introduced sp3 quantum defects in single-walled carbon nanotubes (SWCNTs) have shown compelling optical properties for their potential applications in quantum information science and bioimaging. Here, we utilize temperature- and power-dependent electron spin resonance measurements to study the fundamental spin properties of SWCNTs functionalized with well-controlled densities of sp3 quantum defects. Signatures of isolated spins that are highly localized at the sp3 defect sites are observed, which we further confirm with density functional theory calculations. Applying temperature-dependent line width analysis and power-saturation measurements, we estimate the spin-lattice relaxation time T1 and spin dephasing time T2 to be around 9 μs and 40 ns, respectively. These findings of the localized spin states that are associated with the sp3 quantum defects not only deepen our understanding of the molecular structures of the quantum defects but could also have strong implications for their applications in quantum information science.

Electronic Raman Scattering in Suspended Semiconducting Carbon Nanotube.

The electronic Raman scattering (ERS) features of single-walled carbon nanotubes (SWNTs) can reveal a wealth of information about their electronic structures. Previously, the ERS processes have been exclusively reported in metallic SWNTs (M-SWNTs) and attributed to the inelastic scattering of photoexcited excitons by a continuum of low-energy electron-hole pairs near the Fermi level. Therefore, the ERS features have been thought to appear exclusively in M-SWNTs but not in semiconducting SWNTs (S-SWNTs), which are more desired in many application fields such as nanoelectronics and bioimaging. In this work, the experimental observation of the ERS features in suspended S-SWNTs is reported, the processes of which are accomplished via the available high-energy electron-hole pairs. The excitonic transition energies with an uncertainty in the order of ±1 meV can be directly obtained via the ERS spectra, compared to a typical uncertainty of ±10 meV in conventional electronic spectroscopies. The ERS features can facilitate further systematic studies on the properties of SWNT, both metallic and semiconducting, with defined chirality.

Bernoulli-Euler beam theory of single-walled carbon nanotubes based on nonlinear stress-strain relationship

Recent experiments and density functional tight-binding (DFTB) calculations indicated the nonlinear elastic properties of graphene. However, this nonlinear stress-strain relationship has not been applied to the carbon nanotubes (CNTs) that can be viewed as graphene sheets that have been rolled tubes. In this paper, using the nonlinear stress-strain relationship of graphene, a new Bernoulli-Euler beam model of single-walled carbon nanotubes (SWCNTs) is presented for the first time. The static bending and the first-order mode forced vibrations of SWCNTs are investigated according to the new model. The results indicate that the nonlinear stress-strain relationship has a significant influence on the mechanical properties of SWCNTs.

Optimization of Optoelectronic Properties of Patterned Single-Walled Carbon Nanotube Films.

We propose a novel strategy to enhance optoelectrical properties of single-walled carbon nanotube (SWCNT) films for transparent electrode applications by film patterning. First, we theoretically considered the effect of the conducting pattern geometry on the film quality factor and then experimentally examined the calculated structures. We extend these results to show that the best characteristics of patterned SWCNT films can be achieved using the combination of initial film properties: low transmittance and high conductivity. The proposed strategy allows the patterned layers of SWCNTs to outperform the widely used indium-tin-oxide electrodes on both flexible and rigid substrates.

(Invited) In Vivo Analyte Detection Via Single-Walled Carbon Nanotube Near-Infrared Fluorescence

Implantable optical nanosensors hold the promise of rapid, minimally-invasive longitudal monitoring of analytes in a patient or animal. Such devices will allow for informed clinical intervention based on changes in drug, biomarker, or disease state profiles. We developed implantable nanosensors based on the optical properties of single-walled carbon nanotubes (SWCNT). SWCNT fluorescence is in the ‘tissue-transparent’ near-infrared spectrum, allowing for fluorescence measurements after implantation inside an animal. Further, SWCNT fluorescence is photostable, allowing for multiple measurements over time. We engineered separate SWCNT-based sensors such that their fluorescence emission responded to various analytes, including small molecule drugs as well as protein and nucleic acid biomarkers. Each sensor device was immobilized into a semi-permeable biocompatible membrane, allowing analyte penetration but retaining SWCNT inside. We implanted each sensor device into live mice, either in the peritoneal cavity or subcutaneously, and performed whole-mouse near-infrared fluorescence imaging to ensure the stability of the membrane and sensor brightness. We used a sensor implant specific for the chemotherapeutic doxorubicin to drug monitor transport within the animal. We used sensor implants specific for the ovarian cancer protein biomarker HE4 or for individual microRNA sequences to measure exogenous or cancer-generated quantities of each biomarker in mice. We expect these implantable sensors to have potential as research tools or clinical diagnostics to monitor pharmacokinetics or locally measure disease biomarkers in real-time.

A Multimodal Electronic Nose Based on High-Density Flexible Sensor Array of Carbon Nanotubes and Photoactive Macromolecules Hybrid Nanostructures

We report a multimodal electronic nose system based on photoactive carbonaceous hybrid nanomaterials for the detection and quantification of gaseous odors. The e-nose system comprises a high-density flexible sensor array, colorimetric and electrical measurement electronics, data acquisition software, and data analysis algorithms. The e-nose system combines the unique advantages of electrical, chemical, and physical properties of single-walled carbon nanotubes (SWNTs) with optical and chemical properties of various classes of organic macrocyclic compounds, such as pyrenes, porphyrins, and phthalocyanines, for multimodal gas sensing. Photoactive macromolecules such as metalloporphyrins and metallophthalocyanines have been previously developed into colorimetric sensors to various gas analytes. Their intrinsically low electrical conductivity prevents direct application of porphyrins and phthalocyanines in chemiresistive sensors. However, when used as a secondary sensing material via functionalization onto SWNTs, which intrinsically lacks chemical selectivity, these macromolecules confer their chemical selectivity and optical properties to the intrinsically semiconducting SWNT channel. This hybrid nanostructure allows both chemiresistive sensing and colorimetric sensing modalities. Another beneficial property of this hybrid nanostructure is the optoelectronic tunability of the nanomaterial to allow for direct modulation of chemical and electrical behaviors leading to tunable gas sensing capability.Using the high-density array containing 118 individually addressable sensors, over 60 different secondary sensing materials (functionalized onto SWNTs) were investigated, which include chemical derivatives of pyrenes, porphyrins, and phthalocyanines, which have a large variety of side-groups, and metal centers. Additionally, by integrating a large variety of secondary sensing materials into each sensing element of the 118-sensor array, we take advantage of the different chemical and electrical characteristics of each macromolecules which allow for different affinities to specific VOC species to enhance overall selectivity of the e-nose system. The functionality of the multimodal e-nose system was demonstrated to distinguish and quantify various volatile organic compounds (VOCs).

Mapping Single Walled Carbon Nanotubes in Photosynthetic Algae by Single-Cell Confocal Raman Microscopy.

Carbon nanotubes (CNTs) are among the most exploited carbon allotropes in the emerging technologies of molecular sensing and bioengineering. However, the advancement of algal nanobiotechnology and nanobionics is hindered by the lack of methods for the straightforward visualization of the CNTs inside the cell. Herein, we present a handy and label-free experimental strategy based on visible Raman microscopy to assess the internalization of single-walled carbon nanotubes (SWCNTs) using the model photosynthetic alga Chlamydomonas reinhardtii as a recipient. The relationship between the properties of SWCNTs and their biological behavior was demonstrated, along with the occurrence of excitation energy transfer from the excited chlorophyll molecules to the SWCNTs. The non-radiative deactivation of the chlorophyll excitation promoted by the SWCNTs enables the recording of Raman signals originating from cellular compounds located near the nanotubes, such as carotenoids, polyphosphates, and starch. Furthermore, the outcome of this study unveils the possibility to exploit SWCNTs as spectroscopic probes in photosynthetic and non-photosynthetic systems where the fluorescence background hinders the acquisition of Raman scattering signals.

Activation of catalyst particles for single-walled carbon nanotube synthesis

In this work, we evaluate the effect of ferrocene delivery in the reactor on the growth of single-walled carbon nanotubes (SWCNTs) in an aerosol CVD utilizing carbon monoxide as a feedstock. For this purpose, we assess the reactor output parameters varying a gas flow rate through a ferrocene vapor injector in the hot zone with other conditions (temperature, total flow rate, and reactant concentration) being fixed. Our experimental results reveal the adjustment of the ferrocene injection strategy (injector flow rate) to cause a 9-fold improvement in the synthesis yield while preserving the SWCNT properties. We show the catalyst injection optimization to enhance catalyst activation degree as a result of a streamline catalyst delivery, preventing particle over-growth; the experimental data are supported by the computational fluid dynamics. We believe our work to highlight the importance of appropriate aerosol CVD reactor engineering and to facilitate the optimization of reactor productivity, which is one of the fundamental milestones towards SWCNT-based technology.

Sorting of single-wall carbon nanotubes by aqueous two-phase systems

<p indent=0mm>All intrinsic properties of single-wall carbon nanotubes (SWCNTs) are directly determined by their chirality. Commercially available SWCNTs powder samples are usually mixtures of various chiralities. High-performance carbon nanotube devices, sensing, imaging and other applications require the use of SWCNTs with consistent properties, which imposes requirements on the structural sorting of SWCNTs. As an emerging technology for sorting SWCNTs, the aqueous two-phase (ATP) extraction method exhibits stable and reliable sorting results. It is simple, efficient, and easy to scale up and does not require complicated equipment. This review focused on the aqueous two-phase sorting of surfactant-SWCNTs and DNA-SWCNTs. By explaining the effects of dispersant, salt, pH and other sorting conditions on sorting result, the sorting mechanism of aqueous two-phase extraction of SWCNTs are explained. In the end, the characteristics of the aqueous two-phase extraction of DNA-SWCNTs and surfactant-SWCNTs are compared, followed by the discussion of its possible research directions in the future.

Effect of Electrochemical Oxidation on Physicochemical Properties of Fe‐Containing Single‐Walled Carbon Nanotubes

AbstractMetal catalysts are necessary for fabricating carbon nanotubes, but are often considered impurities in the end products, and arduous steps are used to remove catalyst residues from the nanotube structure. However, as metals can be electrocatalytic, instead of removing them we can utilize their role in detection of analgesics. Herein, we study the physicochemical properties of Fe‐containing single‐walled carbon nanotubes (SWCNTs), and the effect of simple oxidative pretreatment on them. We show that a gentle anodic pretreatment i) increased the amount of oxidized Fe nanoparticles, most likely exhibiting phases Fe3O4 and Fe2O3 and ii) effectively removed disordered carbonaceous material from SWCNT bundles surfaces. Pretreatment had only a marginal effect on sensitivity towards analgesics. However, interestingly, selectivity of Fe‐SWCNTs towards paracetamol and morphine could be modified with pretreatment. Through this kind of in‐depth investigation, we can, to a certain extent, correlate various material properties of SWCNTs with the observed electrochemical performance. This approach allows us to evaluate what factors in SWCNTs truly affect the electrochemical detection of biomolecules.

Comparative study of the electron–electron interactions on optoelectronic properties of carbon nanotube within orthogonal and nonorthogonal tight-binding model

We investigate the electron–electron (e–e) interactions effect on the optoelectronic properties of single-walled carbon nanotubes (SWCNTs). We study theoretically the effect of e–e interactions on the optoelectronic properties of zigzag carbon nanotubes and obtain some useful expressions for the band structure and optical absorption of nanotubes for the first nearest-neighbor (1NN) and second nearest-neighbor (2NN) approximation in tight-binding (TB) model. Our computational approach is based on combination of the orthogonal (o-TB) and nonorthogonal (n-TB) tight-binding method with Hubbard model for zigzag SWCNTs. In nonorthogonal tight-binding model we consider the effect of orbital overlap on optoelectronic properties of nanotubes. We also obtain the optical absorption spectrum of zigzag SWCNTs under e–e interactions effect with considering orthogonal and nonorthogonal tight-binding method for 1NN and 2NN approximation. We investigate optical absorption for the incident light polarized parallel to the tube axis and obtain all allowed optical transitions. Our results show some variations in the band structure and optical absorption spectrum of nanotubes under e–e interactions effect when we use orthogonal tight-binding model compare with nonorthogonal tight-binding model.

Analysis for thermal properties and some influence parameters on carbon nanotubes by an energy method

A modified energy method is developed to investigate the elastic properties of single-walled carbon nanotubes. The energy of a system is expressed by the force field functions of the molecular mechanics. Under the assumption of a small deformation and the principle of minimum potential energy, the system function is established. In addition to consider the change of bond stretch and bond angle, the inversion energy is also proposed in this study. Based on the established model, the closed-form expressions of temperature-dependent Young's modulus, Poisson's ratio and strain energy of armchair and zigzag carbon nanotubes are obtained. The results show that the effect of tube diameter and inversion energy on the elastic constants of carbon nanotubes (CNTs) is significant when the tube diameter is small. Under different thermal expansion coefficients, the Young's modulus of carbon nanotubes varies nonlinearly with the temperature, whereas the Poisson's ratio is insensitive to the temperature. It is also found that the temperature has a greater effect on the tensile deformation of zigzag CNTs, which provides a more accurate theoretical foundation for the tensile fracture of CNTs in a thermal environment.

Enhanced Thermoelectric Properties of Bilayer-Like Structural Graphene Quantum Dots/Single-Walled Carbon Nanotubes Hybrids.

In order to improve the thermoelectric properties of single-walled carbon nanotubes (SWCNTs), bilayer-like structures of graphene quantum dots (GQDs) and SWCNTs films (b-GQDs/SWCNTs) were prepared by directly coating GQDs on the surface of SWCNTs films. Compared to pristine SWCNT films (p-SWCNTs), the electrical conductivity of b-GQDs/SWCNTs increased while their Seebeck coefficient decreased. The special interface structure of GQDs and SWCNTs can not only improve carrier transport to increase electrical conductivity but also scatter phonons to reduce thermal conductivity. A maximum power factor (PF) of 51.2 μW·m-1·K-2 is obtained at 298 K for the b-GQDs/SWCNTs (2:100), which is higher than the PF of 40.9 μW·m-1·K-2 by p-SWCNTs. Incorporation of GQDs shows an obvious improvement in power factor and a significant reduction in the thermal conductivity for SWCNTs, and thus, preparation of b-GQDs/SWCNTs provides a new strategy to enhance the thermoelectric properties of SWCNTs-based materials.

Dispersion of Single-Walled Carbon Nanotubes in Biocompatible Environments

The unique physical and chemical properties of carbon nanotubes (CNTs), including SWCNTs (single-walled carbon nanotubes), allow their applications in many fields, including biomedicine. The optical properties of SWCNTs are attractive for application in the field of nanobiotechnology compared to MWCNTs (multi-walled carbon nanotubes). An important objective of SWCNT application for biomedical purposes is obtaining homogenous dispersions characterized by bioavailability and biocompatibility. The possibility of obtaining homogenous dispersions of different types of SWCNTs in biocompatible media for further use in different biomedical experiments and applications has been investigated. The sizes of SWCNT agglomerates in prepared dispersions were measured by the method of dynamic light scattering; bioavailability was studied by dark field microscopy in BEAS-2B bronchial epithelium cells. The dispersions were analyzed for the presence of bacterial contamination. Biocompatible and bioavailable dispersions have been obtained on the basis of cell culture media and 1% bovine serum albumin, which can be used in experiments on assessing the safety of SWCNTs at biological objects but have a number of limitations in the field of biomedicine. Dispergents based on lung surfactant components, which could be used in biomedical applications (DPPC and Survanta®), did not show efficency.