Ion transport across solid-state ion channels perturbed by directed strain.

We combine quantum-chemical calculations and molecular dynamics simulations to consider aqueous ion flow across non-axisymmetric nanopores in monolayer graphene and MoS2. When the pore-containing membrane is subject to uniaxial tensile strains applied in various directions, the corresponding permeability exhibits considerable directional dependence. This anisotropy is shown to arise from directed perturbations of the local electrostatics by the corresponding pore deformation, as enabled by the pore edge geometries and atomic compositions. By considering nanopores with ionic permeability that depends on the strain direction, we present model systems that may yield a detailed understanding of the structure-function relationship in solid-state and biological ion channels. Specifically, the observed anisotropic effects potentially enable the use of permeation measurements across strained membranes to obtain directional profiles of ion-pore energetics as contributed by groups of atoms or even individual atoms at the pore edge. The resulting insight may facilitate the development of subnanoscale pores with novel functionalities arising from locally asymmetric pore edge features.

Highly mechanosensitive ion channels from graphene-embedded crown ethers.

The ability to tune ionic permeation across nanoscale pores profoundly impacts diverse fields from nanofluidic computing to drug delivery. Here, we take advantage of complex formation between crown ethers and dissolved metal ions to demonstrate graphene-based ion channels highly sensitive to externally applied lattice strain. We perform extensive room-temperature molecular dynamics simulations of the effects of tensile lattice strain on ion permeation across graphene-embedded crown ether pores. Our findings suggest the first instance of solid-state ion channels with an exponential permeation sensitivity to strain, yielding an order of magnitude ion current increase for 2% of isotropic lattice strain. Significant permeation tuning is also shown to be achievable with anisotropic strains. Finally, we demonstrate strain-controllable ion sieving in salt mixtures. The observed high mechanosensitivity is shown to arise from strain-induced control over the competition between ion-crown and ion-solvent interactions, mediated by the atomic thinness of graphene.

[The application of forensic medical knowledge for the reconstruction of historical events].

The objective of the present study was to summarize the results of many year investigations on the application of forensic medical methods and experience for the reconstruction of historical events including identification of the ancient Russian saints' hallows and statesmen's remains, elucidation of the genuine causes of death of the members of the Russian Imperial House of Romanovs based on the recently discovered archival materials, restoration of the character of the injuries suffered by Aleksander II, M.I. Kutuzov, P. Demidov, G. Gapon., and G. Rasputin, the attribution A.S. Pushkin's memorial belongings based on the biological traces, and the like.

Manipulation of graphene's dynamic ripples by local harmonic out-of-plane excitation.

With use of carefully designed molecular dynamics simulations, we demonstrate tuning of dynamic ripples in free standing, thermally fluctuating graphene by applying a local out-of-plane sinusoidal excitation. The local dynamic morphology can be controlled via varying external modulation and the boundary conditions. We fully account for the discrete atomistic structure of graphene, as well as natural energy dissipation due in part to its remarkably high thermal conductivity. In addition to stable dynamic rippling patterns, we observed an unexpected flattening of graphene well below the thermal limit. Our results provide insight into the dynamic response of atomically thin layers to an external time-varying excitation in the presence of realistic thermal fluctuations and energy loss. This suggests intriguing possibilities for modulating the electrical and optical properties of atomically thin membranes via local dynamic morphology control.

Atomistic simulation of a graphene-nanoribbon-metal interconnect.

We report a molecular statics simulation of the physical processes responsible for binding and lattice distortions in a nanoscale electrical interconnect with realistic boundary conditions. The interconnect consists of a graphene ribbon interfaced with the (111) crystallographic surfaces (over 11,000 atoms overall) of two nickel electrodes. We quantify the graphene lattice distortions by mapping strains, as well as out-of-plane atomic displacements on a grid, throughout the simulated interconnect. The results suggest strongly localized graphene lattice distortions at the edges and strains that do not exceed 0.5% elsewhere. Such strains are not expected to affect the electrical properties of the graphene nanoribbon interconnect. A stand-alone graphene nanoribbon is simulated in order to identify the effect of electrodes partially supporting the graphene nanoribbon. Our results indicate that the electrodes reduce the in-plane strains induced by the nanoribbon edges, while causing rippling of the graphene lattice. The average graphene-nickel intersurface separation and the cohesive energy for the top-fcc configuration are calculated at ∼2.13 Å and 68.22 meV Å(-2). In order to describe the interatomic interactions in the simulation, we utilize a set of accurate atomistic potentials for graphene on a nickel surface. The approach is based on the modified embedded atom method (MEAM) for the C-C and Ni-Ni interactions, and a Morse-type potential, which takes the surface configuration into account, for the Ni-C interactions. Our focus is on the Ni-(111) crystallographic surface interfaced with graphene in top-fcc, top-hcp, and hcp-fcc initial configurations. The interactions were validated by calculating the equilibrium binding energy and intersurface distance. The resulting binding energies and equilibrium intersurface separations obtained are in very good agreement with previous experimental and ab initio data obtained by use of density functional theory (DFT).

Simulation of lattice strain due to a CNT-metal interface.

We report an atomistic molecular statics study of strains in single wall carbon nanotubes (SWCNTs) interfaced with a planar nickel surface. We calculate axial and radial strain distributions along the SWCNT axis. We demonstrate axial strains of up to 2% extending over a distance of ∼ 10 nm away from the interface along the CNT axis. In addition to the effect of strains on the thermal and mechanical properties of a CNT-metal contact, our results suggest a significant contribution to the contact electrical resistance via local strain-induced modification in the SWCNT electron energy band structure.