ON THE BUCKLING AND VIBRATIONAL RESPONSE OF CARBON NANOTUBES WITH SPIRAL DEFORMATION

Perfect and spiral models of carbon nanotubes (CNTs) have been simulated based on the finite element method and their vibrational and buckling behavior has been investigated. In order to evaluate their natural frequency and critical buckling load, computational tests have been conducted. It has been concluded that the existence of any geometrical modification in the configuration of perfect CNTs results in a remarkable reduction in the natural frequency and critical buckling load of CNTs. It has been also revealed that the analytical solutions are in good agreement with the finite element simulation results in the cases of perfect and spiral CNTs

On the eigenmodes and eigenfrequencies of low-dimensional degenerated carbon structures: obtaining natural frequencies of ideal and structurally defected systems

We concentrated on evaluating the vibrational response of ideal and defected degenerated carbon nanostructures under the influence of different boundary conditions. In addition, an attempt has been made to investigate the relative deviation of the natural frequency of imperfect systems and to study the effect of defected regions on vibrational stability of the particles. It has been found that a single and pinhole vacancy defect have the least and the most impact on the natural frequency of nanostructures. Furthermore, the effect of CNT diameter on natural frequencies of low-dimensional systems has also been investigated in this research

Advances in mechanical analysis of structurally and atomically modified carbon nanotubes and degenerated nanostructures: a review

In the past few years, numerous research activities concerning the mechanical behavior of defected and imperfect carbon nanotubes have been conducted. It is reported that the superlative mechanical properties of these nano-structures, i.e. high stiffness, high strength and vibrational response, would be affected by existing or introducing defects and impurities in the structure of the nanotubes. Such defects may results from manufacturing routes or introduced on purpose to tailor certain physical properties. This review attempts to categorize and highlight the advanced breakthroughs and recent studies employed to investigate the mechanical properties, e.g. stiffness, buckling behavior and vibrational response of structural and atomically modified carbon nanotubes. The presented studies cover the mechanical behavior of nanotubes, both theoretically and experimentally which allowed a realistic prediction of the mechanical behavior of defected tubes in a closer form to those found in reality. It was concluded that any type of imperfection, either atomic or structural modification, influences the mechanical behavior of nanotubes and reduces the stiffness and structural stability, as well as vibrational response of these nano-structures. The present review includes: (i) a brief introduction to atomic and structural modification of nanotubes; (ii) a review of mechanical analysis of atomically and structurally modified models in two separate sections; and (iii) a detailed conclusion on the discussed studies and present the potential progress

On the influence of atomic moifications on the structural stability of carbon nanotube hybrids: numerical investigation

Connected carbon nanotubes (CNTs) with parallel longitudinal axes and with bending angles were simulated by a commercial finite element package and their buckling behavior was investigated by performing several computational examinations. In addition, the effect of defects on the structural stability of these heterojunctions was analyzed. For this purpose, two different nanotube hybrids (straight and kink heterojunction) were constructed in their perfect forms. In the second phase, three most likely atomic defects, i.e., impurities (doping with Si atoms), vacant sites (carbon vacancy) and introduced perturbations of the ideal geometry in different amounts to the perfect models, were simulated. To conclude our study, the buckling behavior of imperfect heterojunctions was numerically evaluated and compared with the behavior of the perfect ones. It was concluded that the existence of any type of defects in the configuration of nanotube hybrids leads to a lower critical load and as a result, lower buckling properties. This study provides a better insight into the prediction of straight and kink heterojunction CNTs behavior

Effect of Structural Phases on Mechanical Properties of Molybdenum Disulfide

Molybdenum disulfide (MoS2) is a promising layer-structured material for use in many applications due to its tunable structural and electronic properties in terms of its structural phases. Its performance including efficiency and durability is often dependent on its mechanical properties. To understand the effects of the structural phase on its mechanical properties, a comparative study on the mechanical properties of bulk 2H, 3R, 1T, and 1T′ MoS2 was conducted using the first-principles density functional theory. Since considerable applications of MoS2 are developed through strain engineering, the impact of the external pressure on its mechanical properties was also considered. Our results suggest a strong relationship between the mechanical properties of MoS2 and the structural symmetry of its crystal. Accordingly, the impacts of the external pressure on the mechanical properties of MoS2 also greatly vary with respect to the structural phases. Among all of the considered phases, the 2H and 3R MoS2 have a larger bulk modulus, Young's modulus, shear modulus, and microhardness due to their higher stability. Conversely, 1T and 1T′ MoS2 are less strong. As such, 1T and 1T′ MoS2 can be a better candidate for strain engineering.</p

Halogenation effect on physicochemical properties of Ti3C2 MXenes

Halogenated MXenes have been experimentally demonstrated to be promising two-dimensional materials for a wide range of applicability. However, their physicochemical properties are largely unknown at the atomic level. In this study, we applied density functional theory (DFT) to theoretically investigate the halogenation effects on the structural, electronic, and mechanical characteristics of Ti _3 C _2 , which is the most studied MXene material. Three atomic configurations with different adsorption sites for four kinds of halogen terminals (fluorine, chlorine, bromine, and iodine) were considered. Our DFT results reveal that the adsorption site of terminals has a considerable impact on the properties of MXene. This can be ascribed to the different coordination environments of the surface Ti atoms, which change d-orbital splitting configurations of surface Ti atoms and the stabilities of systems. According to the density of states, crystal orbital Hamilton population, and charge analyses, all the considered halogenated MXenes are metallic. The electronic and mechanical properties of the halogenated MXenes are strongly dependent on the electronegativity of the halogen terminal group. The Ti–F bond has more ionic characteristics, which causes Ti _3 C _2 F _2 mechanically behave in a more ductile manner. Our DFT results, therefore, suggest that the physicochemical properties of MXenes can be tuned for practical applications by selecting specific halogen terminal groups

Ruthenium single-atom modulated Ti3C2Tx MXene for efficient alkaline electrocatalytic hydrogen production

Single-atoms (SAs) supported on various substrates have emerged as a new form of electrocatalysts for hydrogen evolution reaction (HER). The exfoliated MXenes possess rich defects/vacancies and surface oxygen groups, can be favorably utilized to anchor SAs. Here, we take advantage of the exfoliated Ti3C2Tx to anchor Ru-SAs on Ti3C2Tx through a wet-chemistry impregnation process. The obtained RuSA@Ti3C2Tx possesses excellent HER activity, especially under high current densities. Remarkably, RuSA@Ti3C2Tx can readily attain high current densities of 1 and 1.5 A cm−2 at low over potentials of 425.7 and 464.6 mV, respectively, demonstrating its potential for practical applications. The A1g vibration frequency shift of the Raman spectrum is innovatively used to probe the surface -OH coverage on Ti3C2Tx, providing critical information for mechanistic studies. The experimental and theoretical studies reveal that the superior HER electrocatalytic activity of RuSA@Ti3C2Tx results from the Ru-SAs enhanced H2O adsorption and dissociation, and promoted H2 formation.</p