Pristine Single-walled Carbon Nanotubes Research Articles

(Invited) Carbon Nanotubes for Plant Genetic Engineering

Plants will benefit from genetic engineering to feed our growing global population in the midst of climate change, to provide our most clinically-relevant drugs, and for our environmental remediation efforts. New generation genome engineering technologies, such as CRISPR/Cas, hold the potential to alter plant genes in a precise and targeted manner. The first step of any plant genetic engineering application is to deliver important biomolecular cargoes into the desired subcellular locations of plant cells. However, the limitations of traditional plant gene delivery methods, i.e. Agrobacterium and gene gun, prevent plant genetic engineering from reaching its full potential.Given the lack of efficient biomolecule delivery vehicles to plants and potential impact of plant biotechnology on food security and sustainability, we developed nanoparticle-based platforms to efficiently deliver small interfering RNA1,2 and plasmid DNA3,4 cargoes into plant cells in a species-independent manner, which eliminates the use of gene gun and addresses the main delivery bottlenecks of plant genetic engineering. We show that pristine single walled carbon nanotubes (SWCNTs) can adsorb small interfering RNA molecules through pi-pi stacking for plant delivery, whereas a covalently modified and positively charged SWCNT platform is more efficient for large double-stranded DNA delivery to mature plant leaf cells.This talk will first briefly summarize the development, characterization and biological verification of each nanoparticle platform for plant delivery applications. Next, I will present our recent results of CRISPR/Cas gene editing in plant leaves using the SWCNT DNA delivery platform5. The talk will be concluded by discussing the several assays performed to demonstrate the effect of nanoparticles on plant health, including an RNA-sequencing analysis of nanoparticle-treated plant leaves6. We believe the SWCNT delivery technologies that are discussed in this talk will have an immense impact on food security and sustainability by enabling the generation of improved plants that can rapidly reach the market in a cost-effective manner. Demirer G.S.*, Zhang H.* et al., DNA Nanostructures Coordinate Gene Silencing in Mature Plants. PNAS (2019). Demirer G.S. et al., Carbon Nanocarriers Deliver siRNA to Intact Plant Cells for Efficient Gene Knockdown. Science Advances (2020). Demirer G.S. et al., High Aspect Ratio Nanomaterials Enable Delivery of Functional Genetic Material Without Transgenic DNA Integration in Mature Plants. Nature Nanotechnology (2019). Demirer G.S. et al., Carbon nanotube–mediated DNA delivery without transgene integration in intact plants. Nature Protocols (2019). Demirer G.S. et al., Nanotechnology to advance CRISPR–Cas genetic engineering of plants. Nature Nanotechnology (2021).González-Grandío E., Demirer, G.S. et al. Carbon nanotube biocompatibility in plants is determined by their surface chemistry. bioRxiv (2021).

Quantum Defects for Sensing and Mechanistic Studies

Single wall carbon nanotubes (SWCNT) fluoresce in the near infrared (NIR) and have been assembled with biopolymers such as DNA to form highly sensitive molecular sensors. They change their fluorescence when they interact with analytes. Despite the progress in engineering of these sensors the underlying mechanisms are still not understood. Here, we identify processes and rate constants that explain the photophysical signal transduction by exploiting sp3 quantum defects in the sp2 carbon lattice of SWCNTs. As a model system we use ssDNA coated (6,5)-SWCNTs, which increase their NIR emission (E11, 990 nm) up to + 250 % in response to the important neurotransmitter dopamine. In contrast, SWCNTs coated with DNA but with a low number of NO2-Aryl sp3 quantum defects decrease both their E11 (-35%) and defect related E11* emission (- 50%) at 1130 nm. Consequently, the interaction with the analyte does not change the radiative exciton decay pathway alone. Furthermore, the fluorescence response of pristine SWCNTs increases with SWCNT length, suggesting that exciton diffusion is affected. The quantum yield of pristine (6,5)-SWCNTs increases in response to the analyte from 0.6 % to 1.3 % and points to a change in non-radiative rate constants. These experimental results are explained by a Monte Carlo simulation of exciton diffusion, which supports a change of two non-radiative decay pathways together with an increase of exciton diffusion (3 rate constant model). In summary, we demonstrate how perturbation of a system with quantum defects reveals the photophysical mechanism and provides opportunities for novel sensing concepts.

(Digital Presentation) Excitonic Photoluminescence Properties of Locally Functionalized Single-Walled Carbon Nanotubes Using Molecular Modifiers

Excitons in single-walled carbon nanotubes (SWCNTs) show unique properties due to strong quantum confinement and weak dielectric screening effects which give rise to high binding energies based on strong Coulombic interactions. By this feature, stable and mobile excitons are generated in SWCNTs and its radiative recombination produces photoluminescence (PL) in the near infrared (NIR) region. Recently, local chemical functionalization of SWCNTs has attracted great attention because of enhancement of their NIR PL properties.[1-5] This functionalization dopes local defects such as sp3 carbon to the semiconducting sp2 carbon networks of SWCNTs based on the covalent bond formation between the tube walls and modifier molecules. As a result, emissive doped sites that have narrower band gaps and exciton trapping features are created in the locally functionalized SWCNTs (lf-SWCNTs). For lf-SWCNTs, E 11* PL newly appears with red-shifted wavelengths and increased PL quantum yields compared with original E 11 PL of pristine SWCNTs. Currently, chemical functionalization methods and E 11* PL wavelength modulation techniques are being developed for further functionalization of lf-SWCNTs. [1-5] In this presentation, E 11* PL properties of lf-SWCNTs synthesized using newly designed chemical modifiers are discussed. For example, an azide compound is found to produce the emissive doped sites in lf-SWCNTs via a [2+1] cycloaddition reaction. The E 11* PL peak was observed at 1118 nm and N1s peak in X-ray photoelectron spectroscopy was detected around 400 eV regions based on the chemical bond formation. Moreover, solvatochromic PL energy shifts of the E 11* PL showed a different trend from those observed for typical lf-SWCNTs synthesized using diazonium chemistry. This result indicates that the chemical structures of the doped sites could be a key factor to modulate excitonic properties of localized excitons in lf-SWCNTs. Therefore, the molecular chemistry approach would provide unique exciton engineering tools for lf-SWCNTs and develop advanced excitonic NIR materials applicable to quantum cryptography technologies and high-performance bio/medical imaging and sensing.[1] T. Shiraki, Chem. Lett., 50, 397 (2021); [2] T. Shiraki et al., Acc. Chem. Res., 53, 1846 (2020); [3] S. Tretiak et al., Acc. Chem. Res., 53, 1791 (2020); [4] Y. Wang et al., Nat. Rev. Chem., 3, 375 (2019); [5] J. Zaumseil, Adv. Optical Mater. 2101576 (2021).

(Invited, Digital Presentation) Ortho-Substituent Structure Design in Aryldiazonium Salts for Defect Photoluminescence Modulation of Locally Functionalized Single-Walled Carbon Nanotubes

Photoluminescence (PL) of single-walled carbon nanotubes (SWCNTs) appears in the near infrared (NIR) region, which is applicable to advanced optical applications such as bioimaging and telecommunication devices. Local chemical functionalization of SWCNTs has been gathering great attention because of the enhancement of their NIR PL properties. Therein, defects such as sp3 carbon are locally doped to the crystalline sp2 carbon network of the tube walls by the chemical functionalization process.[1-4] As a result, the locally functionalized SWCNTs (lf-SWCNTs) emit new PL with red-shifted wavelengths and increased quantum yields from the doped sites (E 11* PL) compared to original E 11 PL of pristine SWCNTs. It is due to the doping effects to change electronic structures for narrower bandgap formation, by which mobile excitons in the tubes are trapped at the doped sites to be localized states for efficient PL conversion.The chemical functionalization approach allows us to use various chemical reactants for the doped site formation in lf-SWCNTs. The molecular effects including structural differences and molecular binding functions have resulted in versatile NIR PL wavelength modulation of lf-SWCNTs.[1-4] We have reported that E 11* PL generation phenomena were significantly varied depending on isomeric structures of substituted aryldiazonium salts (AD) used for lf-SWCNT synthesis.[5] Especially, ortho-substituted ADs (oADs) produced two PL around 1100 and 1250 nm-regions, respectively for the resulting lf-SWCNTs with (6,5) chirality. Here, we apply various substituent design for oADs and examine the substituent structure effects in terms of modulation of the PL emission properties of lf-SWCNTs. For example, oAD having a phenyl substituent resulted in enhancement of the ~1250 nm PL contribution. Other substituent effects are observed depending on substituent structures of oADs, from which interactions between the substituents and the tubes are considered to induce the observed PL spectral changes. The result indicates that local chemical functionalization using oAD has a high potential to largely modulate NIR PL wavelengths of lf-SWCNTs beyond 1000 nm regions.[1] T. Shiraki et al. Acc. Chem. Res., 53, 1846 (2020). [2] S. Tretiak et al., Acc. Chem. Res., 53, 1791(2020) [3] Y. Wang et al. Nat. Rev. Chem., 3, 375 (2019). [4] T. Shiraki, Chem. Lett., 50, 397 (2021). [5] T. Shiraki et al. Chem. Commun., 53, 12544 (2017).

A continuum-discrete multiscale coupling method for pristine and defected single-walled carbon nanotubes

A continuum-discrete multiscale coupling (CDMC) method is developed for predicting the large deformation and buckling behaviors of pristine and defected single-walled carbon nanotubes (SWCNTs). With the use of the moving least squares (MLS) approximation as the linkage for the deformations of the discrete atomic structure and the corresponding continuum model, the delicate microstructures of pristine or defected SWCNTs which possess abnormal properties can be involved accurately in the mechanic model built by this CDMC method. Based on the proposed CDMC method, a variationally consistent meshless computational scheme is developed. As the degree of freedom of SWCNTs can be chosen freely in the context of CDMC method, the numerical computational efficiency is higher than that of the fully atomistic simulations. Various numerical tests are carried out for simulating the nonlinear large and buckling deformations of SWCNTs. The results compared with those of the fully atomistic simulations show that CDMC method is accurate and efficient for predicting the nonlinear mechanical properties of pristine and defective SWCNTs and has great potential for dealing with large scale boundary problems.

Differentiation of Bone Mesenchymal Stem Cells Into Vascular Endothelial Cell-Like Cells Using Functionalized Single-Walled Carbon Nanotubes.

Carbon nanotubes (CNTs) are a promising bioactive scaffold for bone regeneration because of their superior mechanical and biological properties. Vascularization is crucial in bone tissue engineering, and insufficient vascularization is a long-standing problem in tissue-engineered scaffolds. However, the effect of CNTs on vascularization is still minimal. In the current study, pristine single-walled carbon nanotubes (SWNTs) were purified to prepare different ratios of SWNTs/EDC composites, and their surface morphology and physicochemical properties of SWNTs/EDC were studied. Furthermore, the effect of SWNTs/EDC on vascularization was investigated by inducing the differentiation of bone mesenchymal stem cells (BMSCs) into vascular endothelial cell-like cells (VEC-like cells). Results showed that SWNTs/EDC composite was successfully prepared, and EDC was embedded in the SWNTs matrix and uniformly distributed throughout the composites. The AFM, FTIR spectra, and Raman results confirmed the formation of SWNTs/EDC composites. Besides, the surface topography of the SWNTs/EDC composites presents a rough surface, which may positively affect cell function. In vitro cell culture revealed that SWNTs and SWNTs/EDC composites exhibited excellent biocompatibility and bioactivity. The SWNTs/EDC composite at mass/volume ratios 1:10 had the best enhancement of proliferation and differentiation of BMSCs. Moreover, after culture with SWNTs/EDC composite, approximately 78.3% ± 4.2% of cultured cells are double-positive for FITC-UEA-1 and DiI-Ac-LDL double staining. Additionally, the RNA expression of representative endothelial cell markers VEGF, VEGF-R2, CD31, and vWF in the SWNTs/EDC composite group was significantly higher than those in the control and SWNTs group. With the limitation of our study, the results suggested that SWNTs/EDC composite can promote BMSCs differentiation into VEC-like cells and positively affect angiogenesis and bone regeneration.

CNT biodevices for early liver cancer diagnosis based on biomarkers detection- a promising platform

Regarding the serious threat of liver cancer owing to the concealment and hard detection of liver tumors at an early stage, primary diagnosis becomes quite crucial to guarantee human health. So, in this work platinum-decorated single-walled carbon nanotubes (SWCNTs) were proposed as superior nanodevice for the detection of 1-Octen-3-ol (octenol), decane, and hexanal as liver cancer biomarkers in the exhaled breath of the patients. Herein, density functional theory (DFT) calculations have been utilized to scrutinize the structural and electronic properties of pristine and Pt-decorated SWCNTs. Obtained results showed that the gas molecules were weakly physisorbed on the pristine SWCNT with negligible charge transfer and large interaction distances. Contrariwise, after the decoration of the SWCNT with Pt metal atom, significant charges are transferred, and energy adsorption increased. The results disclosed that the energy adsorption has been enhanced, for example, energy adsorption increased two times for decane and hexanal molecules (−1.06, and −1.07 eV) upon adsorption on Pt-decorated SWCNT. Moreover, substantial charges with amount of 0.238, 0.245, and 0.223 e were transferred from octenol, decane, and hexanal to the surface, respectively. So, investigations revealed that these compounds are strongly chemisorbed on Pt-SWCNT with small interaction distances and along with the short recovery time of 1.7, 83.4, and 123 s at room temperature toward octenol, decane, and hexanal, respectively which make it a compelling nanodevice. Considering the findings, Pt-SWCNT is an excellent substrate for the sense of liver cancer biomarkers with desired recovery time and the results demonstrate its feasibility for potential application in the near future in the field of liver cancer diagnosis.

Enhancement of thermoelectric property of carbon nanotubes by p-type doping with judicious molecular design of spiro-bifluorene derivatives

Although thermoelectric composites of carbon nanotubes (CNTs) with organic polymers or small organic molecules have witnessed explosive achievements, judicious molecular design still remains a great challenge. Here, p-type doping using spiro-bifluorene derivatives is proposed to significantly improve single-walled CNT (SWCNT) thermoelectric performance. The composite shows an increase of ∼108% in room-temperature power factor relative to the pristine SWCNT (112.6 ± 4.3 μW m-1 K-2), with the maximum of 239.2 ± 4.2 μW m-1 K-2. The corresponding mechanism of effective p-type doping and strong interfacial interaction are elucidated by calculated energy levels, SWCNT surface coating and photophysical spectroscopic measurements. Finally, the thermoelectric device connected in series display an open-circuit voltage and an output power of 9.77 mV and 57.3 nW, respectively at a temperature gradient of 30 K. The results will benefit the exploitation of novel CNT-based TE composites and their applications.

Dry-transferred single-walled carbon nanotube thin films for flexible and transparent heaters

Single-walled carbon nanotubes (SWCNTs) are considered to be ideal candidates for flexible and transparent heaters (THs). However, the conventional wet-fabrication of SWCNT thin films makes the performance of SWCNT THs fail to meet the expectation. Herein, we synthesized high-quality SWCNT thin films by floating catalyst chemical vapor deposition (FCCVD), allowing the dry and direct process of transferring films on polyethylene terephthalate (PET) as THs. A pristine SWCNT TH with a transmittance of 73.5% displayed a reasonable heating performance, reaching the saturated temperatures of ∼53 and 85 °C at the driven voltages of 7 V and 12 V, respectively. Nevertheless, after doping the identical SWCNT film by AuCl3, it rises to ∼70 and 139 °C at 7 V and 12 V, respectively. We held the point that the improved heating performance was mainly attributed to the reduced sheet resistance and film densification by AuCl3 doping. We also found our SWCNT TH showed excellent thermal stability and mechanical flexibility. Due to the continuous synthesis and facile transfer of FCCVD, our SWCNT THs demonstrate potential applications in modern technologies, such as smart windows and defoggers.

Space-confined synthesis of SWNT bundles wrapped by MoS2 crystalline layers as flexible sensors and detectors

Single-walled carbon nanotubes (SWNTs) are ideal template for constructing one-dimensional (1D) heterojunctions with intriguing optical and electrical properties, yet it remains challenging to wrap foreign materials around SWNTs due to their very small diameter and large curvature. Here, we present a space-confined method to synthesize SWNT bundles wrapped by MoS2 crystalline layers (SWNT@MoS2) film by embedding a pristine SWNT film within a porous multi-walled nanotube sponge, which acts as a liquid precursor container for hydrothermal reaction. We find that crystalline MoS2 sheets could be formed around the outer surface of SWNT bundles uniformly and continuously, with tailored number of multi-layers (3–17 layers), for bundle sizes ranging from several to hundreds of nanometers. The resulting SWNT@MoS2 network shows much enhanced light response and gas sensitivity, presenting promising applications as flexible photo-detectors and toxic gas sensors. Our scalable synthesis method and SWNT-based coaxial-cables will be useful in future developing innovated 1D van der Waals heterojunctions and flexible nanoelectronic systems.

Study of electronic and mechanical properties of single walled Carbon nanotube (SWCNT) via substitutional Boron doping in zigzag and armchair pattern

Herein, we have studied the electronic and mechanical properties of Boron (B) doped (6,1) SWCNT in zigzag and armchair pattern by using Density Functional Theory (DFT) and ab−initio Molecular Dynamics (MD) simulations. A systematic periodic B-doping on (6,1) SWCNT was performed along with two different patterns: armchair(along the tube axis) and zigzag (along the tube curvature). The DFT calculations showed the dependence of the electronic properties of the SWCNT on the doping pattern as well as odd and even number of doping concentration. We also found the significant variation in mechanical response of the SWCNT tube on the dopant concentrations and doping patterns. Doping with one B atom enhanced the failure stress value by 70% but the Young’s modulus value reduced by 4.57% as compared with the pristine (6,1) SWCNT.

Highly efficient doping of carbon nanotube films with chloroauric acid by dip-coating

Single-walled carbon nanotube (SWCNT) based transparent and conductive films (TCFs) are one of the most prospective materials for novel flexible and stretchable electronic devices. Development of reproducible and scalable doping procedure is the key step towards the widespread implementation of SWCNT TCFs. Here, we thoroughly investigate a dip-coating technique for SWCNT doping as a promising approach for the practical manufacturing of SWCNT films with high performance. We examine the effect of dip-coating parameters on optical and electrical properties of the films using HAuCl4 solution in isopropyl alcohol (IPA) and in situ investigate doping effects. This method appeared to easily fine-tune the optoelectronic parameters of SWCNT films and achieve a record sheet resistance value of 36 Ohm/sq. at the 90% transmittance in the middle of visible spectral range by increasing a work function value from 4.8 (for pristine SWCNTs) to 6.0 eV. The proposed approach allows efficient, uniform, and reproducible fabrication of highly conductive and transparent SWCNT films and opens an avenue for precise tailoring of SWCNT Fermi level for optoelectronic devices.

Highly Efficient Response of Ammonia Gas Sensor Based on Surfactant‐Free Sorted‐Semiconducting Single‐Walled Carbon Nanotubes at Room Temperature

A comparative analysis of sorted semiconducting (sc‐) single‐walled carbon nanotubes (SWCNTs) films, metallic (m‐) SWCNTs films, pristine SWCNTs films, and graphene‐based simple two‐terminal sensors for the applications of ammonia gas sensing is presented. The comparison of the sensing response of different devices by separately measuring the SWCNTs film resistance and the contact resistance between SWCNTs and the electrodes reveals that the performance mainly relies on the modification of tube conductivity under exposure to gas. Moreover, the measurements show that the highest sensitivity of the devices is achieved by use of sc‐SWCNTs as the conducting channels. Sensor coated with surfactant‐free sc‐SWCNTs shows a sensitivity of 0.78% ppm at 5–100 ppm ammonia (NH3) concentrations that happened to be ≈28, ≈22, and ≈173 times more sensitive than pristine‐SWCNTs, m‐SWCNTs, and graphene‐based sensors, respectively, at 50 ppm and ≈4.5 times the previously reported sc‐SWCNTs‐based sensor at 5 ppm. Notably, all the experiments values are achieved at room temperature without any extra heating treatment for the recovery process. These results show that surfactant‐free sc‐SWCNTs provide a promising way of creating sensors with improved selectivity and sensitivity, which predicts the auspicious prospects in the development of future applications.

Single walled carbon nanotubes in high concentrations is cytotoxic to the human neuronal cell LN18

Single walled carbon nanotubes have been used in biological applications for targeted drug delivery, and as scaffolds for regeneration and diagnosis of diseases due to their excellent properties. However, their extensive application in biology is stifled by toxicity issues. The present study focuses on the effect of pristine single walled carbon nanotubes (P-SWCNT) and carboxylic functionalized single walled carbon nanotubes (C-SWCNT) on the human neuronal cell line LN18 at concentrations of 5, 10, 20, 40 µgmL−1 and time durations of 0–48 h. Cytotoxicity was evaluated by measuring the viability using Trypan Blue, MTT, and Live Dead Cell Assays, and oxidative stress was evaluated by the ROS and Lipid Peroxidation Assays. The IC70 values as measured by the cell viability assay at 12 h were found to be 20 and 10 µgmL−1 for P-SWCNT and C-SWCNT respectively. A significant amount of ROS was produced with P-SWCNT and C-SWCNT at 40 µgmL−1 and 6 h incubation onwards. At 24 and 48 h, a threefold increase in MDA concentration was observed at 40 µgmL−1 of P-SWCNT and C-SWCNT and was measured to be 0.814 ± 0.0042 nM. Analysis of the cellular outcomes revealed that the toxicity of P-SWCNT and C-SWCNT was dose-time dependent with higher toxicity observed for the latter as compared to the former. Hence, it can be concluded that P-SWCNT and C-SWCNT are toxic to LN18 cells at higher concentrations.

Probing iron adsorption on the internal and external wall of pristine and N-doped carbon nanotube

Herein, density functional theory (DFT) calculations were used to compare the interaction pattern of iron atoms on the internal and external wall of pristine and nitrogen-doped (6, 6) single walled carbon nanotubes. Among the four investigated cases, the interaction strength of Fe in ascending order follows 3Fe@CNT, 4Fe@N-CNT, 5Fe/CNT and 4Fe/N-CNT, where “/” and “@” indicate adsorption on the external and internal wall of CNT, respectively. The enhancement of N-doped surface can be ascribed to the activated carbon atoms neighbouring the dopant. The distortion analysis shows that both 3Fe@CNT and 4Fe@N-CNT adsorption system cause less structural distortion on the internal surface of the nanotube, while 4Fe/N-CNT system presents the largest distortion. Density of state analysis predicts that the metal atom inside and outside demonstrates distinct electronic properties and the internal metal particle shows a more dispersed bonding pattern with the carbon surface due to the concave nature of internal surface. The calculated dispersion energy for different adsorption systems provides more evidence for the delocalised interaction pattern, and 4Fe@N-CNT exhibits the largest dispersion interaction.

First-principles study on structural, electronic, and magnetic properties of 3d transition metal-substituted chiral (6, 3) carbon nanotube

The effect of doping the chiral (6, 3) single-wall carbon nanotube (SWCNT) with 3d-transition metals (TM) was examined by using the M06–2X Minnesota functional level. Physical, chemical, and electrical properties of the TM-doped SWCNT were investigated through calculating the parameters such as the dipole magnetic moments, Mulliken charges, the atomic dipole moment corrected Hirshfeld, the density of states, and formation energy. Results showed that bond lengths and angles of the pristine SWCNT decrease by doping it with the 3d-TM atoms from left to right in a row periodic table and the formation process of TM-doped SWCNT is endothermic. The values of natural bond orbital indicate that the charge transfer between carbon atoms and the Sc, Cu, Zn dopants on the CNT are more than the other 3d-TM dopants. The electron localization function results reveal the decrease in the type of covalence bond of C–Fe, C–Cu, and C–Zn compared with the other dopants. We find that doping the pure CNT with Sc, V, Co, Mn, Cu atoms can donate the magnetic properties to the pristine SWCNT.

Terahertz-infrared spectroscopy of wafer-scale films of single-walled carbon nanotubes treated by plasma

We investigated terahertz-infrared electrodynamic properties of wafer-scale films composed of plasma-treated single-walled carbon nanotubes (SWCNTs) and films comprising SWCNTs grown with different lengths. The spectra of complex conductance of the films were measured at frequencies 5–20 000 cm−1 and in the temperature interval 5–300 K. Terahertz spectral response of films of pristine SWCNTs is well described with the Drude conductivity model and a plasmon resonance located at ≈100 cm−1. Stepwise treatment of the films with oxygen plasma led to a gradual suppression of the Drude spectral weight from the low-frequency side. For films with the nanotubes shorter than 1 μm, i.e., close to electrons mean free path and localization length, scattering of charge carriers at the nanotubes edges is shown to additionally contribute to the carriers scattering rate and to the damping of plasmon resonance. The temperature coefficient of ac resistance (ac TCR) in both kinds of films is found to strongly increase in amplitude during cooling and frequency decrease. The values of ac TCR increase in films with longer time of plasma treatment and nanotubes with shorter length but reach saturation in films with exposure time longer than ≈100 s or composed from SWCNTs shorter than 1 μm.

N-doped direction-dependent electronic and mechanical properties of single-walled carbon nanotube (SWCNT) from a first-principles density functional theory (DFT) and MD-simulation

In this paper, the electronic and mechanical properties of Nitrogen (N) doped (6,1) single walled carbon nanotube (SWCNT) is analysed based on the first principles density functional theory (DFT) and Molecular dynamic (MD) calculation. A systematic N-doping on SWCNT was performed along zigzag (zz) and armchair (ac) direction, where the armchair doping is parallel to tube axis while zigzag is along the cross-section perpendicular to tube axis. The zz and ac doping resulted in variations in the electronic properties of the even and odd number of N-dopant atoms. To evaluate the mechanical properties, ab − initio MD-simulations was carried out. We found a dependence of the tensile response of the tube on the dopant concentration and doping pattern. Single N-doped system show enhanced tensile stress by 55% as compared to the pristine SWCNT with marginal changes in the young's modulus for all N-doped systems.

Identification of vacancy defects in carbon nanotubes using vibration analysis and machine learning

Point vacancies are the most common defects in a carbon nanotube (CNT) lattice. However, there is no standard technique to identify these defects. Moreover, the effect of such vacancies on the vibrational properties of CNTs is unknown. Therefore, this paper presents the first-ever technique for identification of vacancy defects in single-walled carbon nanotubes (SWCNT) using their vibrational analyses and machine learning. 240 SWCNT samples were modelled using molecular-structural-mechanics-approach and their modes obtained using finite element analyses. Then, an analytical expression for fundamental vibration frequency of a vacancy defective SWCNT was derived using log-linear multiple regression. This frequency is found to decrease with: (i) increase in the magnitude of point vacancies; (ii) decrease in diameter; and (iii) increase in length. A polynomial support vector machine (SVM) was developed that successfully classifies pristine and vacancy defective SWCNT samples at test accuracy greater than 90%. The proposed technique for identification of point vacancies combines the developed SVM classification with inverse estimation using the derived expression. This technique will be useful for the most crucial characterization of SWCNTs, i.e., characterizing pristine and vacancy defective samples. The derived expression will be useful in predicting vibration response of vacancy defective SWCNTs, and deciding their applications.

High performance of p-type and n-type thermoelectric materials based on liquid crystal mixture and single-walled carbon nanotube composites

Organic small molecule (OSM)/single-walled carbon nanotube (SWCNT) composites are promising thermoelectric (TE) materials, however the low Seebeck coefficient (S) limits their application. Here, a eutectic nematic mixture E7 was chosen to improve the S and power factor (PF) of SWCNTs by energy filtering process. As a result, the introduction of E7 can significantly decrease the carrier concentration of the composite with the mobility greatly enhanced, leading to an improved S (2.23 times of that of pristine SWCNTs). At the mass ratio of 1:0.25, the p-type SWCNT/E7 composites displayed a maximum PF of 428.59 ± 58.15 μW m−1 K−2, which was one of the highest values among OSM-based TE composites reported so far. In addition, after doped with triethylamine, SWCNT/E7 can convert from p-type to n-type. This study demonstrated that SWCNT/E7 composites showed great promise in TE materials and opened up a new avenue for the development of TE materials.