A Study of Electromechanical Properties and Applications of Carbon Nanotubes (original) (raw)
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Nanomechanics of single and multiwalled carbon nanotubes
Physical Review B, 2004
Buckling behavior of single-walled and multiwalled carbon nanotubes is studied under axial compression in this work. Brenner's ''second generation'' empirical potential is used to describe the many-body short-range interatomic interactions for single-walled carbon nanotubes, while the Lennard Jones model for the van der Waals potential is added for multiwalled carbon nanotubes. Single-, two-, three-, and four-walled nanotubes are considered in the simulations in order to examine the effects of the number of layers on the structural properties of the multiwalled nanotubes. Results indicate that there exists an optimum diameter for singlewalled nanotubes at which the buckling load reaches its maximum value. The buckling load increases rapidly with the increase of the diameter up to the optimum diameter. A further increment beyond this diameter results in a slow decline in buckling load until a steady value is reached. The effects of layers on the buckling load of multiwalled nanotubes are also examined.
Carbon nanotube mats (buckypapers) were prepared from three commercial grades of single-walled carbon nanotubes (SWCNTs) and by two processing variants (i.e. filtration of centrifuged and uncentrifuged dispersions). Material properties such as Young's modulus, tensile strength, electrical conductivity, electrical capacitance, specific surface area and morphology were investigated and put in relation to the in-plane actuation performance in an aqueous electrolyte (1 M NaCl). A dynamic mechanical analyzer was adapted for actuation strain measurements on the samples under various tensile prestress levels. High SWCNT purity and dispersibility were found to be crucial for preparing dense and strong cohesive mats with good actuation performance. (D. Suppiger). C A R B O N 4 6 ( 2 0 0 8 ) 1 0 8 5 -1 0 9 0 a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c a r b o n
Nano electro mechanical systems with single walled carbon nanotubes as functional elements
4th IFAC Symposium on Mechatronic Systems (2006), 2006
Sensors are key components in mechatronic systems. Further system miniaturization will demand for continuous down-scaling of sensor functions in such systems most likely towards nano scale. Then new sensor device concepts will emerge to maintain performance, e.g. sensitivity, or to utilize unique functional properties of nano scale structures. This paper presents concepts to create nano electro mechanical sensors based on carbon nanotubes (CNTs). Suspended single walled CNT based cantilever and bridge structures and a membrane based CNT pressure sensor are introduced and discussed. Measurements on the pressure sensor prove metallic single walled CNTs as exceptional piezoresistive electro mechanical transducers with gauge factors above 200.
Piezoelectric Response of Multi-Walled Carbon Nanotubes
Materials, 2018
Recent studies in nanopiezotronics have indicated that strained graphene may exhibit abnormal flexoelectric and piezoelectric properties. Similar assumptions have been made with regard to the properties of carbon nanotubes (CNTs), however, this has not so far been confirmed. This paper presents the results of our experimental studies confirming the occurrence of a surface piezoelectric effect in multi-walled CNTs under a non-uniform strain. Using atomic force microscopy, we demonstrated the piezoelectric response of multi-walled CNTs under compression and bending. The current generated by deforming an individual CNT was shown to be −24 nA. The value of the surface potential at the top of the bundle of strained CNTs varied from 268 mV to −110 mV, depending on strain type and magnitude. We showed that the maximum values of the current and the surface potential can be achieved when longitudinal strain predominates in a CNT. However, increasing the bending strain of CNTs does not lead to a significant increase in current and surface potential, due to the mutual compensation of piezoelectric charges concentrated on the CNT side walls. The results of the study offer a number of opportunities and challenges for further fundamental research on the piezoelectric properties of carbon nanotubes as well as for the development of advanced CNT-based nanopiezotronic devices.
A variety of outstanding experimental results on the elucidation of the elastic properties of carbon nanotubes are fast appearing. These are based mainly on the techniques of high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM) to determine the Young's moduli of single-wall nanotube bundles and multi-walled nanotubes, prepared by a number of methods. These results are confirming the theoretical predictions that carbon nanotubes have high strength plus extraordinary flexibility and resilience. As well as summarising the most notable achievements of theory and experiment in the last few years, this paper explains the properties of nanotubes in the wider context of materials science and highlights the contribution of our research group in this rapidly expanding field. A deeper understanding of the relationship between the structural order of the nanotubes and their mechanical properties will be necessary for the development of carbon-nanotube-based composites. Our research to date illustrates a qualitative relationship between the Young's modulus of a nanotube and the amount of disorder in the atomic structure of the walls. Other exciting results indicate that composites will benefit from the exceptional mechanical properties of carbon nanotubes, but that the major outstanding problem of load transfer efficiency must be overcome before suitable engineering materials can be produced. 62.20.x; 62.20.Dc; 61.48.+c; 61.16.Ch; 61.16.By Rolling up a graphene sheet on a nanometre scale [1] has dramatic consequences on the electrical properties . The small diameter of a carbon nanotube (CNT) also has an important effect on the mechanical properties, compared with traditional micron-size graphitic fibres . Perhaps the most striking effect is the opportunity to associate high flexibility and high strength with high stiffness, a property that is absent in graphite fibres. These properties of CNTs open the way for a new generation of high performance composites. Theoretical studies on the mechanical properties of CNTs * Corresponding author
Analysis of Carbon Nanotubes on the Mechanical Properties at Atomic Scale
This paper aims at developing a mathematic model to characterize the mechanical properties of single-walled carbon nanotubes (SWCNTs). The carbon-carbon (C−C) bonds between two adjacent atoms are modeled as Euler beams. According to the relationship of Tersoff-Brenner force theory and potential energy acting on C−C bonds, material constants of beam element are determined at the atomic scale. Based on the elastic deformation energy and mechanical equilibrium of a unit in graphite sheet, simply form ED equations of calculating Young's modulus of armchair and zigzag graphite sheets are derived. Following with the geometrical relationship of SWCNTs in cylindrical coordinates and the structure mechanics approach, Young's modulus and Poisson's ratio of armchair and zigzag SWCNTs are also investigated. The results show that the approach to research mechanical properties of SWCNTs is a concise and valid method. We consider that it will be useful technique to progress on this type of investigation.
Using home-built experimental setups, electrical properties and electromechanical characterization of two systems based on multiwalled carbon nanotubes (MWNTs) were investigated at room temperature. The first system is formed by carbon nanotubes (CNTs) either isolated or in small groups on a gold substrate, while the second one concerns a macroscale three-dimensional entanglement of CNTs in powder form. The local electrical resistance on systems of the first type was measured using an atomic force microscopy with a conductive tip and showed a narrow distribution of resistance values as well for isolated CNTs as for small groups of them. However, in this latter case the average resistance value has been found to be one order of magnitude higher than that of individual CNTs, which was attributed to the contact resistance between CNTs. This parameter was then studied from a statistical viewpoint through electromechanical tests performed at a macroscopic scale. They consisted in applying an external compression to CNTs powder samples and measuring the evolution of the electrical resistance across the pressed material. These tests demonstrated an outstanding decrease of the electrical resistance resulting from the increasing number of random connections between CNTs under compression, and the experimental curves were fitted with an analytical model. Furthermore, it was deduced from this model that the elementary contact resistance between CNTs decreases under compression. The stability of this electrical contact was verified over several durations and under different constant applied loads.
Energetics, structure, mechanical and vibrational properties of single-walled carbon nanotubes
Nanotechnology, 1998
In this paper, we present extensive molecular mechanics and molecular dynamics studies on the energy, structure, mechanical and vibrational properties of single-wall carbon nanotubes. In our study we employed an accurate interaction potential derived from quantum mechanics. We explored the stability domains of circular and collapsed cross section structures of armchair (n, n), zigzag (n, 0), and chiral (2n, n) isolated single-walled carbon nanotubes (SWNTs) up to a circular cross section radius of 170Å. We have found three different stability regions based on circular cross section radius. Below 10Å radius only the circular cross section tubules are stable. Between 10 and 30Å both circular and collapsed forms are possible, however, the circular cross section SWNTs are energetically favorable. Beyond 30Å (crossover radius) the collapsed form becomes favorable for all three types of SWNTs. We report the behavior of the SWNTs with radii close to the crossover radius ((45, 45), (80, 0), (70, 35)) under uniaxial compressive and tensile loads. Using classical thin-plane approximation and variation of strain energy as a function of curvature, we calculated the bending modulus of the SWNTs. The calculated bending moduli are κ (n,n) = 963.44 GPa, κ (n,0) = 911.64 GPa, and κ (2n,n) = 935.48 GPa. We also calculated the interlayer spacing between the opposite sides of the tubes and found d (n,n) = 3.38Å, d (2n,n) = 3.39Å, and d (n,0) = 3.41Å. Using an enthalpy optimization method, we have determined the crystal structure and Young's modulus of (10,10) armchair, (17, 0) zigzag and (12, 6) chiral forms (which have similar diameter as (10,10)). They all pack in a triangular pattern in two dimensions. Calculated lattice parameters are a (10,10) = 16.78Å, a (17,0) = 16.52Å and a (12,6) = 16.52Å. Using the second derivatives of potential we calculated Young's modulus along the tube axis and found Y (10,10) = 640.30 GPa, Y (17,0) = 648.43 GPa, and Y (12, = 673.94 GPa. Using the optimized structures of (10, 10), (12, 6) and (17, 0), we determined the vibrational modes and frequencies.
THE ROLE OF POTENTIAL FUNCTIONS IN THE MECHANICAL BEHAVIOR OF THE SINGLE WALL CARBON NANOTUBES
Carbon nanotubes have been identi¯ed as the promising agents in reinforcing composite materials to achieve desired mechanical properties. In this study, three di®erent types of single wall carbon nanotubes (SWCNTs) are subjected to molecular dynamics simulation to investigate their mechanical properties taking di®erent interatomic potential functions. With unmodi¯ed Brenner's 2nd generation potential, a brittle fracture for all the SWCNTs is observed. But in tight-binding approach, the chiral and armchair SWCNTs exhibit somewhat extended plastic °ow region before failure. With unmodi¯ed Brenner's potential, high tensile strength and ductility are observed for the armchair and chiral tubes. Y value of these two tubes is less than 1 TPa but more than 1 TPa for a zigzag tube. Much decrease of tensile strength and strain are noticed when we apply smoothing of the Brenner's potential at cut-o® region. Failure stresses are dropped to much lower values for the three tubes. Ductility of the armchair and chiral tubes are also a®ected considerably by the choice of potential. Applying smoothing in the cut-o® region to conserve the energy, the results show better agreement with the experimental ¯ndings.