Carbon Nanotube Heterojunctions Research Articles

Nonlocal strain gradient-based nonlinear vibration analysis of nonlinear FG three-phase HJCNT/MWCNT/epoxy composite microbeam resonators using a modified micromechanical model

This paper aims to study nonlinear dynamic behavior of functionally graded (FG) three-phase composite microbeam resonators made of an epoxy matrix and two reinforcements namely multi-walled carbon nanotubes (MWCNTs) and hetero-junction carbon nanotubes (HJCNTs). The effective mechanical properties of the composite microbeam are obtained using the modified Halpin-Tsai micromechanical model. The microbeam surrounding medium is simulated using a two-parameter elastic foundation. The von-Karman’s geometric nonlinearity relations are incorporated and the equations of motion are derived based on the nonlocal strain gradient Euler–Bernoulli beam model. A new closed-form analytical solution is obtained using the homotopy perturbation method. The effects of vibration amplitude, nanofiber volume fraction, nanofiber distribution pattern, small-scale parameters and the foundation parameters on the nonlinear frequency and deflection of the FG three-phase composite microbeams are studied in detail. The findings of the paper are valuable for researchers in the field of microbeam resonators.

On the vibrational behavior of the conventional and hetero-junction carbon nanotubes

The shortcomings and insufficiency in the state-of-the-art investigations about the resonance in the hetero-junction carbon nanotubes with respect to the number of models and connection types highlight the necessity of a comprehensive study of the resonance frequency of these nanostructures for applications of these nanomaterials in nanodevices, such as nano-scale electromechanical systems (NEMS) and NEMS-based resonators. Hence in this study, 50 conventional and 73 hetero-junction middle-length (15 nm) carbon nanotubes, with armchair-armchair, zigzag-zigzag, armchair-zigzag, armchair-chiral, zigzag-chiral and chiral-chiral connections, were modeled. Then, the resonance in their structure was comprehensively studied using the finite element method to present a more reliable estimated range for the natural frequency (fundamental frequency) of hetero-junction carbon nanotubes. The analysis showed that the natural frequency of conventional carbon nanotubes lies in the range of 7.09 and 48.75 GHz. An inverse correlation between this quantity and the aspect ratios of the conventional carbon nanotubes was found, leading to proposing a mathematical relation for the prediction of such an inverse correlation. The natural frequency of hetero-junction carbon nanotubes oscillated between 4.04 and 60.20 GHz. The results revealed that the natural frequency of hetero-junction carbon nanotubes lies outside the frequency range of their constructive carbon nanotubes and majorly depends on the boundary conditions and the difference between the diameters of the connected tubes. Finally, it was observed that the existence of an armchair carbon nanotube in the structure of hetero-junction models improves their vibrational stabilities.

A broadband 3D microtubular photodetector based on a single wall carbon nanotube-graphene heterojunction.

In this paper, a three-dimensional (3D) photodetector based on a single wall carbon nanotube (SWCNT) and graphene heterojunction has been fabricated by a self-rolled-up process. In the designed structure, graphene acted as the conductive channel and SWCNTs absorbed the incident light ranging from the visible to near-infrared bands. Compared to planar (two-dimensional, 2D) devices, 3D microcavities provided a natural resonant cavity to enhance the optical field, which improved the photoresponsivity. This 3D heterojunction photodetector realized a broadband photodetection from 470 to 940 nm with an ultrahigh photoresponsivity of 4.9 × 104 A W-1 (@ 590 nm) and 1.9 × 104 A W-1 (@ 940 nm), a fast photoresponse speed of 1.6 ms, and an excellent sensitivity of 2.28 × 1011 Jones. Besides, the fabricated photodetector showed favorable mid-infrared detection with a photoresponsivity of 3.08 A W-1 at 10.6 μm. Moreover, the photodetector exhibited a promising room-temperature imaging capability. The 3D heterojunction photodetector would provide a feasible pathway to realize graphene-based photodetectors with high performance and could be extended to be integrated with other light absorptive materials.

Tunable Spin Polarization of Zigzag–Zigzag Heterojunction Carbon Nanotubes

Adjusting the spin polarization of carbon nanotubes is critical for achieving functional applications of spintronic devices such as magnetic switches. Herein, heterojunction carbon nanotubes (HCNTs) are constructed by connecting two different zigzag edges to achieve this goal. First‐principles calculations indicate spin ferromagnetic (FM) or antiferromagnetic (AFM) coupling in the corresponding structure, which can be regulated by the number of carbon atoms at the zigzag edges of the HCNTs. Further calculations related to the charged HCNTs indicate that electronic ground states of the same structure can be transformed from spin AFM to spin FM coupling states. Thus, the behavior of spin polarization for zigzag–zigzag HCNTs can also be regulated by the charge. This finding opens up a new approach for spin adjustment, which can potentially contribute to the design of spintronic devices.

A nanopump using carbon nanotube hetero-junction driven by symmetric temperature gradients

In this work, we report a thermal pump using a carbon nanotube (CNT) hetero-junction, which is formed by connecting two CNTs of different diameters. Through molecular dynamics simulations, it is shown that water flows can be generated by symmetric temperature gradients. The flow velocity and flow rate reach 1.47 m/s and 47.2 μm3/min, respectively, under a symmetric temperature gradient of 7.5 K/nm. It is also demonstrated that the flow direction can be controlled by the direction of the temperature gradient. A theoretical model is developed on the basis of the excess enthalpy of water in the CNT hetero-junction to describe the flow. Furthermore, the effect of CNT chirality on the water flow is also studied. It is found that water transport in armchair CNT hetero-junctions is more favorable than that in zigzag CNT hetero-junctions. The numerical demonstrations in this work provide a new nanoscale design for generating fluid flows by symmetric temperature gradients, which can be used for chip-level cooling.

Energy storage performance of 2D MoS2 and carbon nanotube heterojunctions in symmetric and asymmetric configuration

Excellent cyclic stability and fast charge/discharge capacity demonstrated by supercapacitors foster research interest into new electrode materials with 100% cycle life and high specific capacitance. We report an improvement in the electrochemical performance of MoS2/multiwalled carbon nanotubes (MWCNT) nanohybrid and intensively explored its performance in symmetric and asymmetric supercapacitor (ASC) assembly. The symmetric assembly of MoS2/MWCNT exhibits capacitance of around 274.63 F g−1 at 2 A g−1 with higher specific energy/power outputs (20.70 Wh kg−1/1.49 kW kg−1) as compared to the supercapacitor based on pristine MoS2 (5.82 Wh kg−1/1.07 kW kg−1). On the other hand, a unique all-carbon-based ASC assembled with MoS2/MWCNT and VSe2/MWCNT composite with K2SO4 as electrolyte delivers the highest energy density of 32.18 Wh kg−1 at a power density of 1.121 kW kg−1 with exceptional cycling stability and excellent retention of about 98.43% even after 5000 cycles. These outstanding results demonstrate the excellent electrochemical properties of both symmetric and asymmetric systems with high energy density and performance, which further enable them to be a potential candidate for supercapacitor applications.

Mechanical Characterisation of Single-Walled Carbon Nanotube Heterojunctions: Numerical Simulation Study.

The elastic properties of single-walled carbon nanotube heterojunctions were investigated using conventional tensile, bending and torsion tests. A three-dimensional finite element model was built in order to describe the elastic behaviour of cone heterojunctions (armchair–armchair and zigzag–zigzag). This comprehensive systematic study, to evaluate the tensile, bending and torsional rigidities of heterojunctions, enabled the formulation analytical methods for easy assessment of the elastic properties of heterojunctions using a wide range of their geometrical parameters.

Inkjet‐Printed Ternary Inverter Circuits with Tunable Middle Logic Voltages

AbstractA multi‐valued logic (MVL) technology is considered to be a promising way to improve data processing capabilities with higher bit density. Unique negative transconductance characteristics in van der Waals (vdW) p‐n heterojunction‐based devices enabled recent demonstrations of MVL circuits. Herein, inkjet‐printed ternary inverters are presented for the first time by connecting anti‐ambipolar transistors, based on indium oxide/single‐walled carbon nanotube (SWCNT) heterojunctions, and SWCNT transistors. Inkjet printing allows systematic control of anti‐ambipolar transistor characteristics by forming vdW heterojunctions reliably. The anti‐ambipolar transistor characteristics are widely tuned by simply changing the number of SWCNT printing in heterojunction channels. Tunable middle logic voltages in ternary inverters are achieved by using the changes in anti‐ambipolar transistor characteristics. This work provides a guideline for tuning device characteristics of anti‐ambipolar transistors and ternary inverters.

Application of hetero junction CNTs as mass nanosensor using nonlocal strain gradient theory: An analytical solution

This paper aims to propose an analytical solution for dynamic analysis of the hetero junction carbon nanotubes (HJCNTs)-based mass nanosensors using a nonlocal strain gradient Timoshenko beam model. To have a more precise nanosensor, it is necessary to have deep information about the vibration characteristics of the nanostructure. So, two main goals are followed in this paper. At first, the vibration of HJCNTs with general (elastic) boundary conditions and without attached mass are studied using a proposed analytical solution. Afterward, the HJCNT is applied as a cantilever mass sensor for sensing light as well as heavy masses attached to its tip. For the large and heavy masses, the rotary inertia of the attached mass is also considered in the analysis. The governing differential equations are derived based on the Hamilton's principle and solved by an analytical method, which is based on the modified Fourier series. The weighted residual method is employed for obtaining the variationally consistent boundary conditions using the known equations of motion of the structure. The field quantities are obtained in the closed forms. The convergence and accuracy of the proposed solution are validated through some special cases available in the literature. The effects of small scale parameters and the elastic boundaries on the frequency and mode shapes of HJCNTs are studied. Moreover, the factors that affect the frequency shift of HJCNT-mass sensor are discussed. The obtained results introduce HJCNTs as new mass nanosensors that can operate more efficiently than uniform CNTs. This paper can be greatly useful in designing HJCNT-mass sensors and may serve as a benchmark for the future research in this field.

Graphene and Carbon Nanotube Heterojunction Transistors with Individual Gate Control.

Heterogeneously integrated nanomaterial devices show interesting characteristics for transistors and sensors due to their band diagram or steep material junctions. If these junctions and band alignments can be tuned by an electrical input bias, the device platform not only could be expanded but also could be used to explore fundamental characteristics. However, most reports on hetero-nanomaterial junctions use a global back-gate voltage, which makes it difficult to control band alignment at an interface. To explore device junctions, this study reports a laterally integrated heterojunction of graphene and a carbon nanotube (CNT) network film with individual gate electrodes to tune the band alignment corresponding to the Fermi level shift of graphene in contact with the semiconducting CNT network film. By developing the fabrication process, multiple gate structures are designed to apply a gate bias to CNTs and graphene separately. The threshold voltage shift of the CNT transistor depends on the gate voltage of graphene. Based on the thermionic emission theory, the barrier height between graphene and CNTs for both the conduction and valence band sides varies from 70 to 85 meV, with a linear change as a function of the applied gate voltage to graphene. Although the current Fermi level shift is small, this device platform may realize the exploration of fundamental properties and device concepts.

Lateral vibrations of embedded hetero-junction carbon nanotubes based on the nonlocal strain gradient theory: Analytical and differential quadrature element (DQE) methods

In the current paper, lateral vibrations of embedded hetero-junction carbon nanotubes (HJCNTs) are investigated. HJCNT and its surrounding medium are idealized as two different connected nonlocal strain gradient Rayleigh beams and a two-parameter (Pasternak) elastic foundation, respectively. The governing differential equation is derived based on the Hamilton's principle, and the classical and higher order boundary conditions are obtained using the weighted residual approach. The sixth-order differential equation is then solved analytically and numerically. The differential quadrature element method based on the Hermit interpolation functions is employed and developed to the stepped nanobeams to establish the reliability of the analytical method. The effects of the nonlocal parameter, the strain gradient parameter, the type of boundary conditions, the type of adopted higher order boundary conditions and the elastic foundation parameters on the frequency and mode shapes are studied and discussed in details. This paper provides an appropriate source not only for the vibrational study of HJCNTs, but also for comparing the vibration results of embedded uniform or stepped nanobeams obtained based on different theories that consider the size-dependent effects.

Buckling Analysis of Hetero-Junction Carbon Nanotubes

Abstract The buckling analysis of carbon nanotubes without and with hetero-junctions is described in this paper. The buckling behaviour was investigated by the finite element method and the carbon nanotubes were modelled as space frame structures. The results showed that the critical buckling force depends on the dimensions of carbon nanotubes. The critical buckling forces of hetero-junction carbon nanotubes are in range between critical buckling forces of carbon nanotubes of both used diameters with the same chiralities without hetero-junction.

Effect of metal oxide charge transfer layers on the photovoltaic performance of carbon nanotube heterojunction solar cells

Despite the prominence of silicon solar cells, various alternative solar cell technologies have attracted the attention of researchers. Several attempts have been made to bring down the cost and complexities involved in the fabrication of solar cells. In this work, solar cells with TiO2 as absorber layer and Multi-Walled Carbon Nanotubes (MWCNT) as active charge generation layer have been fabricated by spin coating nano pastes of TiO2 and MWCNT over transparent conducting substrates. An efficiency of 0.40% was observed for TiO2-MWCNT solar cells, which was further enhanced to 1.03% and 1.27% by insertion of Co3O4 and Cu2O layers respectively, in between the MWCNT and the carbon electrode. This significant increase in efficiency is attributed to the effective hole extraction by the metal oxide layers, which resolves the work function mismatch between the MWCNT and carbon electrode. These demonstrations reveal the advantages of using metal oxide interfacial layers for effective hole extraction in carbon nanotube based solar cells.

Free vibration analysis of dissimilar connected CNTs with atomic imperfections and different locations of connecting region

In this paper, the vibrational characteristics of hetero-junction carbon nanotubes (HJCNTs) are investigated using the well-known molecular mechanics approach. The paper contains two main novel parts. In the first part, the influence of connecting region location on the first five natural frequencies of perfect HJCNTs is investigated. In the second part, the effects of some common defects on fundamental frequencies are studied. The study is performed for different boundary conditions and different structures of HJCNTs. The results show that the frequencies and mode shapes are effectively influenced by changing the location of connecting region. Interestingly, it is found that the frequencies of HJCNTs can be even higher than those of their constituent CNTs for a specific location of connecting region. In the second part, it is shown that the fundamental frequency of HJCNTs decreases with introducing the defects. Furthermore, the frequency shift of defective structures with lower aspect ratios is more affected by the level of imperfections. Finally, the obtained numerical results are adopted to develop a predictive equation for calculating the fundamental frequency shift of defective straight HJCNTs based on the kind and level of defect, aspect ratio as well as the type of boundary conditions.

Self-Assembled Heterojunction Carbon Nanotubes Synergizing with Photoimmobilized IGF-1 Inhibit Cellular Senescence.

Synthesis of artificial and functional structures for bone tissue engineering has been well recognized but the associated cell senescence issue remains much less concerned so far. In this work, surface-modified polycaprolactone-polylactic acid scaffolds using self-assembled heterojunction carbon nanotubes (sh-CNTs) combined with insulin-like growth factor-1 are synthesized and a series of structural and biological characterizations are carried out, with particular attention to cell senescence mechanism. It is revealed that the modified scaffolds can up-regulate the expressions of alkaline phosphates and bone morphogenetic proteins while down-regulate the expressions of senescence-related proteins in mesenchymal stem cells, demonstrating the highly preferred anti-senescence functionality of the sh-CNTs modified scaffolds in bone tissue engineering. Furthermore, it is also found that with sh-CNTs, scaffolds can accelerate bone healing with extremely low toxicity in vivo.

On the buckling behavior of perfect and atomically defective hetero-junction carbon nanotubes

ABSTRACTBent and straight hetero-junction carbon nanotubes and their constructive homogeneous tubes were modeled based on the finite element method in their perfect and atomically defective forms with silicon impurities and carbon vacancies, and their buckling behavior was investigated. The results showed that the buckling strength of hetero-junction carbon nanotubes, which depends on the size of their kink and their constructive tubes' diameters, lies in the range of their constructive tubes' buckling strength. Armchair-armchair and zigzag-zigzag models also demonstrated higher buckling strength than the other hetero-junction models. Finally, the atomic defects were seen to considerably decrease the buckling strength of these nanomaterials.

The effects of connecting region length on the natural frequencies of straight and non-straight hetero-junction carbon nanotubes

In the present study, the vibrational properties of straight and non-straight hetero-junction carbon nanotubes (HJCNTs) are investigated. The molecular mechanics technique in combination with the finite element method is applied to obtain the first four natural frequencies as well as the corresponding mode shapes. The effects of connecting region length on the frequencies of straight and non-straight structures with clamp-clamp and clamp-free boundary conditions (BCs) are discussed in details. The results show that for the clamp-free BCs, the first and second frequencies increase with increasing the connecting length whereas the third and fourth ones decrease. Also, for the clamp-clamp BCs, increasing the connecting length leads to decrement in the first two frequencies while the changes of the second two frequencies depend on the total length of the structure. Moreover, for the clamp-clamp BCs, the mode shapes are affected by the total length of the structures. Finally, to avoid resonance and its damage in dynamic applications, for some modes of excitation appropriate structures are proposed.

Tuning the driving force for exciton dissociation in single-walled carbon nanotube heterojunctions.

Understanding the kinetics and energetics of interfacial electron transfer in molecular systems is crucial for the development of a broad array of technologies, including photovoltaics, solar fuel systems and energy storage. The Marcus formulation for electron transfer relates the thermodynamic driving force and reorganization energy for charge transfer between a given donor/acceptor pair to the kinetics and yield of electron transfer. Here we investigated the influence of the thermodynamic driving force for photoinduced electron transfer (PET) between single-walled carbon nanotubes (SWCNTs) and fullerene derivatives by employing time-resolved microwave conductivity as a sensitive probe of interfacial exciton dissociation. For the first time, we observed the Marcus inverted region (in which driving force exceeds reorganization energy) and quantified the reorganization energy for PET for a model SWCNT/acceptor system. The small reorganization energies (about 130 meV, most of which probably arises from the fullerene acceptors) are beneficial in minimizing energy loss in photoconversion schemes.

Numerical Simulation of the Mechanical Behaviour of Single-Walled Carbon Nanotube Heterojunctions

The study of the mechanical behaviour of single-walled carbon nanotube heterojunctions has been carried out, implementing nanoscale continuum approach. A three-dimensional finite element model is used in order to evaluate the elastic behaviour of cone heterojunctions. It is shown that the bending rigidity of heterojunctions is sensitive to bending conditions. The torsional rigidity does not depend on torsion conditions. Both rigidities of the heterojunction are compared with those of the thinner and thicker constituent nanotubes.

Numerical investigation on the influence of atomic defects on the tensile and torsional behavior of hetero-junction carbon nanotubes

The finite element method was employed for the numerical simulation of hetero-junction carbon nanotubes with all possible connection types and their corresponding fundamental homogeneous tubes. Then, atomically defective hetero-junction carbon nanotubes were modeled by introducing silicon impurities and vacant sites into their structures. Finally, the elastic and shear moduli of all the models were evaluated under tensile and torsional loads, based on the assumption of linear-elastic deformation of these nanomaterials. The results showed that armchair and zigzag carbon nanotubes have the highest Young's and shear moduli respectively, among homogeneous carbon nanotubes. The mechanical tests on the hetero-junction carbon nanotubes revealed that these nanotube types have lower moduli when compared to their fundamental tubes. It was clearly observed that armchair–armchair and zigzag–zigzag hetero-junction carbon nanotubes have the highest Young's modulus among the hetero-junction carbon nanotubes while the shear modulus peaks were seen in zigzag-zigzag models. On the other hand, the lowest values for the Young's and shear moduli of hetero-junction carbon nanotubes were obtained for the models with armchair-zigzag kinks. It was also discovered that the atomic defects in the structure of hetero-junction carbon nanotubes lead to a decrease in their Young's and shear moduli which seems to follow a linear trend and could be expressed by a mathematical relation in terms of the amount of the atomic defect in their structures which could be used for the prediction of the tensile and torsional strength of the atomically defective hetero-junction carbon nanotubes for their proper selection and applications in nanoindustry.