Xiao-Wen Lei

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 Youngs modulus of armchair and zigzag graphite sheets are derived. Following with the geometrical relationship of SWCNTs in cylindrical coordinates and the structure mechanics approach, Youngs modulus and Poissons 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.

An atomic-resolution nanomechanical mass sensor based on circular monolayer graphene sheet: Theoretical analysis of vibrational properties

Graphene sheet (GS) is a two-dimensional material with extremely favorable mass sensor properties. In this work, the potential of a nanoscale mass sensor based on individual single layer GS is examined. An atomic-resolution nanomechanical mass sensor is modeled by a fixed supported circular monolayer GS with attached nanoparticles, based on a continuum elastic model and Rayleighs energy method. We analyze the vibrational properties of the GS used as a mass sensor in detail, and the relationship between the attached mass and the vibrational frequency (frequency shift) of the GS is simulated and discussed using the two models. The sensitivity of vibrational frequency (frequency shift) to both aspect ratio and vibration mode is demonstrated, and comparison of the two models proves their accuracy and that of the simulation of the monolayer GS mass sensor.

Equivalent Young's modulus and thickness of graphene sheets for the continuum mechanical models

The Youngs modulus and the thickness of graphene sheets (GSs) are the two major material constants when continuum mechanical models are used to analyze the mechanical behaviors of GSs. It should be pointed out that the equivalent Youngs modulus and the thickness of GSs should correspond to both stretching and bending loading conditions. In this Letter, the same as “Yakobson paradox,” we predicted the equivalent Youngs modulus and the thickness of GSs using an analytical method linked with an atomic interaction based continuum model and a continuum elastic model. Based on the proposed method, by unifying the Youngs modulus of GSs in the cases of both stretching and bending, and by determining the matching thickness in the same time, the equivalent Youngs modulus and the thickness of GSs utilized in continuum mechanical models are calculated and proposed to be 2.81 TPa and 1.27 A, respectively.

Wave propagation in embedded double-layer graphene nanoribbons as electromechanical oscillators

Graphene nanoribbons (GNRs) are potential nanomaterial electromechanical oscillators because of their outstanding mechanical and electronic properties. Double-layer GNRs (DLGNRs), which are two-layer finite-wide counterparts of crystalline graphene sheets coupled to each other via van der Waals interaction forces, present two kinds of vibrational modes in flexural wave propagation. These two modes are defined as the in-phase mode and anti-phase mode. In this study, based on the nonlocal Timoshenko beam theory and Winkler spring model, the wave propagation characteristics of DLGNRs embedded in an elastic matrix are investigated by dividing the vibrational mode into the in-phase mode and anti-phase mode. This will provide more accurate guidance for the application of DLGNRs. When the nonlocal effects and elastic matrix are considered, three critical frequencies are found. These are defined as the cutoff, escape, and low-cutoff frequencies. Moreover, the results show that the wave propagation characteristics...

Buckling Instability of Carbon Nanotube Atomic Force Microscope Probe Clamped in an Elastic Medium

Carbon nanotubes (CNTs) can be used as atomic force microscope (AFM) probes due to their robust mechanical properties, high aspect ratio and small diameter. In this study, a model of CNTs clamped in an elastic medium is proposed as CNT AFM probes. The buckling instability of the CNT probe clamped in elastic medium is analyzed based on the nonlocal Euler―Bernoulli beam model and the Whitney―Riley model. The clamped length of CNTs, and the stiffness of elastic medium affect largely on the stability of CNT AFM probe, especially at high buckling mode. The result shows that the buckling stability of the CNT AFM probe can be largely enhanced by increasing the stiffness of elastic medium. Moreover, the nonlocal effects of buckling instability are investigated and found to be lager for high buckling mode. The theoretical investigation on the buckling stability would give a useful reference for designing CNT as AFM probes.

Radial breathing mode of carbon nanotubes subjected to axial pressure

In this paper, a theoretical analysis of the radial breathing mode (RBM) of carbon nanotubes (CNTs) subjected to axial pressure is presented based on an elastic continuum model. Single-walled carbon nanotubes (SWCNTs) are described as an individual elastic shell and double-walled carbon nanotubes (DWCNTs) are considered to be two shells coupled through the van der Waals force. The effects of axial pressure, wave numbers and nanotube diameter on the RBM frequency are investigated in detail. The validity of these theoretical results is confirmed through the comparison of the experiment, calculation and simulation. Our results show that the RBM frequency is linearly dependent on the axial pressure and is affected by the wave numbers. We concluded that RBM frequency can be used to characterize the axial pressure acting on both ends of a CNT.