Properties Of Single-walled Carbon Nanotubes Research Articles

The Effects of Hydrogen Annealing on Carbon Nanotube Field-Effect Transistors.

We have systematically investigated the effects of hydrogen annealing on Ni- and Al-contacted carbon nanotube field-effect transistors (CNTFETs), whose work functions have not been affected by hydrogen annealing. Measured results show that the electronic properties of single-walled carbon nanotubes are modified by hydrogen adsorption. The Ni-contacted CNTFETs, which initially showed metallic behavior, changed their p-FET behavior with a high on-current over 10 µA after hydrogen annealing. The on-current of the as-made p-FETs is much improved after hydrogen annealing. The Al-contacted CNTFETs, which initially showed metallic behavior, showed unipolar p-FET behavior after hydrogen annealing. We analyzed the energy band diagrams of the CNTFETs to explain experimental results, finding that the electron affinity and the bandgap of single-walled carbon nanotubes changed after hydrogen annealing. These results are consistent with previously reported ab initio calculations.

On the role of surface oxygen during nascent single-walled carbon nanotube cap spreading and tube nucleation on iron catalysts

Single-walled carbon nanotubes (SWCNTs) are commonly grown in oxygen-rich environments. The precursor used as input for the SWCNT synthesis reaction typically provides oxygen atoms either as a pure gas or as an oxygen-containing compound. Similarly, metal oxide substrates are used to support the catalysts or as reactor wall materials and can transfer oxygen atoms while in contact with the catalytic particles. It has been proposed and experimentally observed that the interaction of the metal catalyst with specific promoters (e.g., oxygen, sulfur, hydrogen) triggers significant changes in the SWCNT properties during spreading, nucleation and growth. However, very few studies address the carbon-catalyst surface interactions in rich oxygen environments. Here we show that an increased surface oxygen concentration in the neighborhood of a spreading nascent carbon shell reduces the strength of interaction of the carbon shell with the iron catalyst's surface and increases the probability of carbon nucleation and SWCNT lift-off. The evolution of the carbon-surface interaction during the spreading and nucleation phases suggests that closed pentagons at the rim are preferentially formed in oxidized iron surfaces, and they exhibit the strongest and most stable interaction with the iron surface.

Band structure dependent electronic localization in macroscopic films of single-chirality single-wall carbon nanotubes

Significant 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.

Sensing Organophosphorus Compounds with SWCNT Films.

Promising electrical properties of single-walled carbon nanotubes (SWCNTs) open a spectrum of applications for this material. As the SWCNT electronic characteristics respond well to the presence of various analytes, this makes them highly sensitive sensors. In this contribution, selected organophosphorus compounds were detected by studying their impact on the electronic properties of the nanocarbon network. The goal was to untangle the n-doping mechanism behind the beneficial effect of organic phosphine derivatives on the electrical conductivity of SWCNT networks. The highest sensitivity was obtained in the case of the application of 1,6-Bis(diphenylphoshpino)hexane. Consequently, free-standing SWCNT films experienced a four-fold improvement to the electrical conductivity from 272 ± 21 to 1010 ± 44 S/cm and an order of magnitude increase in the power factor. This was ascribed to the beneficial action of electron-rich phenyl moieties linked with a long alkyl chain, making the dopant interact well with SWCNTs.

High‐Performance ITO‐Free Perovskite Solar Cells Enabled by Single‐Walled Carbon Nanotube Films

AbstractThe unprecedented advancement in power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) has rendered them a promising game‐changer in photovoltaics. However, unsatisfactory environmental stability and high manufacturing cost of window electrodes are bottlenecks impeding their commercialization. Here, a strategy is introduced to address these bottlenecks by replacing the costly indium tin oxide (ITO) window electrodes via a simple transfer technique with single‐walled carbon nanotubes (SWCNTs) films, which are made of earth‐abundant elements with superior chemical and environmental stability. The resultant devices exhibit PCEs of ≈19% on rigid substrates, which is the highest value reported to date for ITO‐free PSCs. The facile approach for SWCNTs also enables application in flexible PSCs (f‐PSCs), delivering a PCE of ≈18% with superior mechanical robustness over their ITO‐based counterparts due to the excellent mechanical properties of SWCNTs. The SWCNT‐based PSCs also deliver satisfactory performances on large‐area (1 cm2 active area in this work). Furthermore, these SWCNT‐based PSCs can retain over 80% of original PCEs after exposure to air over 700 h while ITO‐based devices only sustain ≈60% of initial PCEs. This work paves a promising way to accelerate the commercialization of ITO‐free PSCs with reduced material cost and prolonged lifetimes.

Stability, rheology, and thermophysical properties of surfactant free aqueous single-walled carbon nanotubes and graphene nanoplatelets nanofluids: a comparative study

A comparative study, for the first time, was conducted on thermophysical and rheological properties of single-walled carbon nanotubes (SWCNT) and graphene nanoplatelets (GNP) nanofluids. Highly stable aqueous 0.5, 1.0, and 2.0 wt% SWCNT and GNP nanofluids were successfully prepared with no surfactant, through ultrasound technology. The preparation was explained in detail, adjusting pH to around 8 where nanofluids would be expected to be stable. The highest zeta potential of −60.5 mV was obtained for 2.0 wt% SWCNT nanofluids. Shear thinning was observed for all nanofluids at low shear rates. Unlike shear thickening of GNP, Newtonian behavior of SWCNT nanofluids was detected at high shear rate region. The effect of ultrasound technology was directly verified by scanning electron microscopy (SEM), resulting in GNP size reduction and separation of bundles for SWCNT. The results revealed that SWCNT nanofluids showed a remarkable zeta potential value for heat transfer systems compared to GNP nanofluids.

(Invited) Different Pathways of Fluorescent SWCNT Modifications with Aromatic Reactants

Modification of electronic and chemical properties of single-wall carbon nanotubes (SWCNTs) by covalent side-wall functionalization can produce a stable material with purposely-enhanced electronic and optical properties. In the report we describe a new type of reactions between simple aromatic compounds and SWCNTs, creating different fluorescent trapping states in SWCNTs. The photoreactions take place in aqueous suspensions of SWCNTs with small addition of soluble or even very-slightly soluble organic aromatic compounds excited by UV light. The reaction rates depend on the aromatic compound structure and proportional to its concentration, and in some cases, as with aniline or iodoaniline, new strong and well-resolved spectral sidebands appear within one minute. Total SWCNT photoluminescence intensity can increase, and the increase was in some cases by a factor of 5 as compare to original species. The shifted emission bands and the trapping nature of them, when the main part of the nanotube is performing as an absorbing antenna delivering excitation energy to the modified sites, may be interesting for a variety of optical and electronic applications.Most notably, in most cases of these photochemical reactions, the shifted emission spectra from modified SWCNTs become different, displaying never observed previously structure upon removal of molecular oxygen from the solution. For instance, treatment with normal dissolved oxygen gives a rise to a new emission band red-shifted for (6,5) SWCNTs by 160 meV from the pristine position, which is similar to many previously studied reactions starting with oxygen doping. Corresponding results will appear for other species as well. However, if the molecular oxygen is removed from the suspension by degassing or gas substitution, same UV treatments will lead to two different emission bands red-shifted by 140 and 270 meV, one less shifted and one more shifted, thus indicating different chemical products of the reactions. These new bands grow with different rate under UV illumination. Variance spectroscopy of such samples shows the presence of individual “multicolor” nanotubes with three distinct emission bands, one original/unmodified plus two shifted. The reaction demonstrates new possibilities for creation different trapping states on individual nanotubes, and opens new options for tuning electronic and optical properties of nanotubes for possible applications.

(Invited) In Vivo and Ex Vivo Biomarker Quantification Via Single-Walled Carbon Nanotube Near-Infrared Fluorescence

Optical nanosensors hold the promise of rapid, minimally-invasive longitudal monitoring of analytes within a patient or at the bedside. Such devices will allow for informed clinical intervention based on changes in disease state profiles. We are designing nanosensors based on the optical properties of single-walled carbon nanotubes (SWCNT) for use in both in vivo and ex vivo formats. SWCNT fluorescence is in the ‘tissue-transparent’ near-infrared spectrum, allowing for fluorescence measurements through biological tissue and fluids. Further, SWCNT fluorescence is photostable and responds rapidly, allowing for multiple measurements over time. We are engineering SWCNT-based sensors such that their fluorescence emission responds to multiple cancer biomarkers and inflammatory proteins. Various deployment formats include semipermeable implantable membranes, injectable hydrogel materials, and chip-based devices. Within each device, we are comparing sensor response with its physicochemical properties to optimize sensor functionality. Finally, we are deploying each sensor device in patient serum, other clinical tissues, and in live animal models of disease. For each, we are using custom-built near-infrared probe spectroscopy with rapid point-and-detect functionality. We expect these translational sensor devices to have potential as research tools or clinical diagnostics to detect disease at early stages, evaluate disease response to treatment, or monitor disease progression. These aims will allow physicians to make rapid, informed decisions on patient prognosis and treatment.

(Invited) Empirical Modeling of Broadband Complex Optical Spectra of Single-Chirality-Enriched Carbon Nanotube Films for Optical Design

Exceptional optical properties of single-walled carbon nanotubes (SWCNTs) potentially provide various promising applications including photonic and thermo-optic [1] devices. However, systematic knowledge on the broadband optical spectra of macroscopic films composed of single-chirality-enriched SWCNTs [2] has still been limited. We will report an empirical model of the broadband complex optical spectra of single-chirality-enriched SWCNTs films, as can be readily used by engineers for optical design. [1] T. Nishihara, A. Takakura, Y. Miyauchi, and K. Itami, Nat. Commun. 9, 3144 (2018). [2] Y. Yomogida, T. Tanaka, M. Zhang, M. Yudasaka, X. Wei, and H. Kataura, Nat. Commun. 7, 12056 (2016).

Surface Coating- and Light-Controlled Oxygen Doping of Carbon Nanotubes

Tuning the optical properties of single-wall carbon nanotubes (SWCNTs) via oxygen doping has been a simple and effective approach to create fluorescent quantum emitters. We performed oxygen doping of SWCNTs in water utilizing chirality-pure (6,5) enantiomers with different surface coatings of DNA and surfactants by ultraviolet (UV) light irradiation. We found the reaction to be primarily dependent on the wavelength of UV light and the specific coating material on the nanotube surface. Particularly, DNA coatings react more readily with the reactive oxygen species that is photochemically produced under short-wavelength UV light than SWCNTs, preventing oxygen doping of nanotubes from occurring. The surface coverage of SWCNTs created by coating materials plays a weaker role in controlling the reaction efficiency of oxygen doping. This is demonstrated clearly by the lack of oxygen doping for two (6,5) enantiomers wrapped by DNA with drastically different surface coverages. These findings reveal important mechanisms of oxygen doping of SWCNTs, providing methods of controlling optical properties of nanotubes for developing unique applications.

Enhancing thermoelectric properties of single-walled carbon nanotubes using halide compounds at room temperature and above

Carbon nanotubes (CNTs) are materials with exceptional electrical, thermal, mechanical, and optical properties. Ever since it was demonstrated that they also possess interesting thermoelectric properties, they have been considered a promising solution for thermal energy harvesting. In this study, we present a simple method to enhance their performance. For this purpose, thin films obtained from high-quality single-walled CNTs (SWCNTs) were doped with a spectrum of inorganic and organic halide compounds. We studied how incorporating various halide species affects the electrical conductivity, the Seebeck coefficient, and the Power Factor. Since thermoelectric devices operate under non-ambient conditions, we also evaluated these materials' performance at elevated temperatures. Our research shows that appropriate dopant selection can result in almost fivefold improvement to the Power Factor compared to the pristine material. We also demonstrate that the chemical potential of the starting CNT network determines its properties, which is important for deciphering the true impact of chemical and physical functionalization of such ensembles.

Beam Theory of Thermal-Electro-Mechanical Coupling for Single-Wall Carbon Nanotubes.

The potential application field of single-walled carbon nanotubes (SWCNTs) is immense, due to their remarkable mechanical and electrical properties. However, their mechanical properties under combined physical fields have not attracted researchers’ attention. For the first time, the present paper proposes beam theory to model SWCNTs’ mechanical properties under combined temperature and electrostatic fields. Unlike the classical Bernoulli–Euler beam model, this new model has independent extensional stiffness and bending stiffness. Static bending, buckling, and nonlinear vibrations are investigated through the classical beam model and the new model. The results show that the classical beam model significantly underestimates the influence of temperature and electrostatic fields on the mechanical properties of SWCNTs because the model overestimates the bending stiffness. The results also suggest that it may be necessary to re-examine the accuracy of the classical beam model of SWCNTs.

In data science we trust: Machine learning for stable halide perovskites

The exploration of the compositional space of halide perovskites is prohibitively costly using traditional experimental research strategies. Sun and colleagues demonstrated a physics-informed, machine-learning-guided, experimental approach that overturns this limitation enabling a rapid and efficient maximization of stability in mixed-cation perovskites.

A New Composite Material on the Base of Carbon Nanotubes and Boron Clusters B12 as the Base for High-Performance Supercapacitor Electrodes

We explore the quantum capacitance, stability, and electronic properties of single-walled carbon nanotubes decorated with B12 icosahedral boron clusters by first-principle calculation methods implemented in the SIESTA code. After the optimization of the built supercells, the B12 clusters formed bonds with the walls of the carbon nanotubes and demonstrated metallic properties in all cases. The network of carbon nanotubes with its large area and branched surface is able to increase the capacity of the electric double-layer capacity, but the low quantum capacity of each nanotube in this network limits its application in supercapacitors. We found that the addition of boron clusters to both the outer and inner walls increased the quantum capacitance of carbon nanotubes. The calculation of the transmission function near the Fermi energy showed an increase in the conductivity of supercells. It was also found that an increase in the concentration of boron clusters in the structure led to a decrease in the heat of formation that positively affects the stability of supercells. The calculation of the specific charge density showed that with an increase in the boron concentration, the considered material demonstrated the properties of an asymmetric electrode.

Thermal properties of single-walled carbon nanotube forests with various volume fractions

Needs of a material for thermal management in reduced-sized electronic devices drive single-walled carbon nanotubes (SWCNTs) to be one of the most promising candidates due to their excellent thermal properties. Many numerical and experimental studies have reported on understanding thermal properties of the SWCNT for thermal device applications. In the present study, thermal diffusivity and conductivity of SWCNT forests in the axial direction with various volume fractions of SWCNTs were measured by laser flash analysis technique and the same properties of an individual SWCNT were derived. The volume fraction was controlled up to 25 vol% by biaxial mechanical densification which maintains SWCNT alignment. While the thermal diffusivity of SWCNT forests was almost constant, it increased when the volume fraction was higher than 17 vol%, suggesting that some SWCNTs, which did not serve as a thermal path in the case of lower volume fraction, were connected with the other SWCNTs. Through the increase of inferred thermal conductivity equivalent to an individual SWCNT after 17 vol%, we also realized that the enhancement of volume fraction of SWCNT forest diminished thermal boundary resistance in good agreement with the tendency inferred from the reported numerical data.

First Principles Study on Electronic and Optical Properties of Single Walled Carbon Nanotube for Photonics Application

Recent research works on single-walled carbon nanotube (SWCNT) based material has witnessed a great technological importance in photonic applications due to their unique optical characteristics. Present work aims to employ theoretical first principles study to explore the electronic and optical properties of SWCNT in the form of armchair nanotube. The theoretical simulation is done by using density functional theory (DFT) as implemented in the CASTEP computer code. Similar to almost gapless nature of graphene, formation of Fermi level of a relaxed SWCNT structure is found to be at a value approaching zero. The calculated electronic band structure shows a direct band gap of 0.259 eV with Dirac cone form between conduction and valence band. The optical spectrum shows a variation of real and imaginary of dielectric function with inter-band transition taking place along with frequency of the incident light. The absorption spectrum exhibits a significant degree of anisotropic characteristic with almost transparent nature ranging from near infrared to ultraviolet energy range. These optical spectra show excellent nonlinear optical features which remark the suitability in optoelectronic applications.

Compound influence of topological defects and heteroatomic inclusions on the mechanical properties of SWCNTs

The utility of carbon nanotubes as the reinforcement agents in polymer and metal matrix composites has opened up a new avenue in the development of novel composite materials with exceptional strength and stiffness to weight ratios. Such exploitation of superior mechanical properties of carbon nanotubes depends on their inherent irregularities and structural integration. The nanotubular structures of carbon are prone to topological defects and heteroatom dopants due to the inevitable complexities in nano-synthesis. The objective of this article is to quantify the compound influence of such inherent structural irregularities (such as single vacancy defects and nanopores) and foreign atom inclusions (such as nitrogen and boron atoms) on the mechanical characteristics (like constitutive relation, fracture strength, failure strain and Young’s moduli) of single-walled carbon nanotubes (SWCNT) under various multi-physical influences (such as temperature, strain rate, diameter and chirality) based on molecular dynamics (MD) simulations. The current investigation also includes a detailed analysis on the variation in mechanical characteristics of CNTs under different spatial distributions of defects and doping.

Detonation performance of nitroaromatic decorated carbon nanotubes

In this study, density functional theory (DFT) was employed to predict thermochemical and energetic properties for single-walled carbon nanotubes (SWCNTs) decorated with one and more nitroaromatic substituents. Heat of sublimation and crystal density of these molecules were estimated on the basis of molecular surface properties calculated by electrostatic potential (ESP) analysis. Heats of formation in gas and solid phases were calculated using isodesmic approach. These data were used to measure velocity, pressure, and heat of detonation based on valid theoretical equations. Results show that crystal density of these molecules is close to TNT and their heat of formation is much larger. The calculated velocity and pressure of detonation for these molecules are approximately 4–6 km/s and 20–123 kbar, respectively; which are in the range of high explosives. However, their performance is lower than TNT. The detonation performance of these molecules increases as the number of nitroaromatic substituents increases.

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.