graphene

We demonstrated outstanding compressibility of holey graphene nanosheets, which is impossible for pristine graphene. Holey graphene powder can be easily compressed into dense and strong monoliths with different shapes at room temperature without using any solvents or binders. 

ACS Nano, Article ASAP, http://pubs.acs.org/doi/abs/10.1021/acsnano.7b00227

When a solid object is stretched, in general, it shrinks transversely. However, the abnormal ones are auxetic, which exhibit lateral expansion, or negative Poisson ratio. While graphene is a paradigm 2D material, surprisingly, graphene converts from normal to auxetic at certain strains. Here, we show via molecular dynamics simulations that the normal-auxeticity mechanical phase transition only occurs in uniaxial tension along the armchair direction or the nearest neighbor direction. Such a characteristic persists at temperatures up to 2400 K.

Given a distribution of defects on a structured surface, such as those represented by 2-dimensional crystalline materials, liquid crystalline surfaces, and thin sandwiched shells, what is the resulting stress field and the deformed shape? Motivated by this concern, we first classify, and quantify, the translational, rotational, and metrical defects allowable over a broad class of structured surfaces. With an appropriate notion of strain, the defect densities are then shown to appear as sources of strain incompatibility.

http://dx.doi.org/10.1016/j.carbon.2016.09.043 This study considers two novel ideas to further explore and enhance the graphene membrane for desalination. Firstly, while earlier molecular dynamics (MD) simulations studies have used frozen membranes, free-standing membrane is considered here. Since 2D membranes are usually embedded on porous support in the experimental reverse osmosis (RO) process, the free-standing membrane can more accurately model the behavior expected during operation.

In the attached paper, we have shown that concomitant bending and stretching, whatever their value, concur to make bending stiffness decrease; moreover, concomitant bending and stretching make the stretching stiffness (or the Young modulus) increase until the applied forces reach a threshold value, then they make it decrease. Said differently, graphene is softer to bend when stretched and bent and harder to stretch when bent and moderately stretched.

In the attached paper, recently appeared on Computer Physics Communications, we have proposed an analytical benchmark and a simple consistent Mathematica program for graphene and carbon nanotubes, that may serve to test any molecular dynamics code implemented with REBO potentials. By exploiting the benchmark, we checked results produced by LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) when adopting the second generation Brenner potential, we made evident that this code in its current implementation produces results which are offset from those of the benchmark by a significant amount, and provided evidence of the reason.

Abstract

B. C. McGuigan, P. Pochet, and H. T. Johnson, Critical thickness for interface misfit dislocation formation in two-dimensional materials, Phys. Rev. B 93, 214103, 2016.

URL: http://link.aps.org/doi/10.1103/PhysRevB.93.214103

Two-Dimensional (2D) materials have been widely studied since the discovery of graphene in 2004.  Many of the initial works on the various 2D materials (graphene, MoS2 and other transition metal dichalcogenides, black phosphorus, and others like the monochalcogenides) by mechanicians focused on issues like ideal strength, and appropriate methods to calculate the bending modulus.  Some of these, and other issues, were reviewed by Sulin Zhang in a J-Club from March 2015 (http://imechanica

http://dx.doi.org/10.1142/S1758825116500216 Molecular dynamics (MD) simulations are performed to investigate the adsorption mechanics and conformational dynamics of single and multiple bovine serum albumin (BSA) peptide segments on single-layer graphene through analysis of parameters such as the root-mean-square displacements, number of hydrogen bonds, helical content, inter- action energies, and motions of mass center of the peptides.

The Poisson's ratio characterizes the resultant strain in the lateral direction for a material under longitudinal deformation.  Though negative Poisson's ratios (NPR) are theoretically possible within continuum elasticity, they are most frequently observed in engineered materials and structures, as they are not intrinsic to many materials.  In this work, we report NPR in single-layer graphene ribbons, which results from the compressive edge stress induced warping of the edges.

In the attached paper we have shown that graphene and carbon nanotubes are in a self-stress state in their natural equilibrium state, that is, the state prior to the application of external loads. We have identified different sources of self-stresses and accurately evaluated them; we have shown that they are by no means negligible with respect to load-related nanostresses.

Shuze Zhu, Joseph A. Stroscio, Teng Li, Phys. Rev. Lett. 115, 245501 (2015)

Electrons dance in pulled graphene

http://pubs.acs.org/doi/abs/10.1021/acsami.5b05615 Studies reveal that biomolecules can form intriguing molecular structures with fascinating functionalities upon interaction with graphene. Then, interesting questions arise. How does silk fibroin interact with graphene? Does such interaction lead to an enhancement in its mechanical properties?

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R. Rahman and J.T. Foster

Recent experiments reveal that a scanning tunneling microscopy (STM) probe tip can generate a highly localized strain field in a graphene drumhead, which in turn leads to pseudomagnetic fields in the graphene that can spatially confine graphene charge carriers in a way similar to a lithographically defined quantum dot (QD). While these experimental findings are intriguing, their further implementation in nanoelectronic devices hinges upon the knowledge of key underpinning parameters, which still remain elusive.

APPLIED PHYSICS LETTERS 104, 173103 (2014) DOI

I would like to share with you our recent paper published in the Journal of Applied Mechanics: J. Appl. Mech. 81(8), 081010 (Jun 02, 2014)

Abstract