Anisotropic and temperature dependent mechanical properties of carbon honeycomb

Periodic surface structure of 4H-SiC by 46.9 nm laser

This paper presents an experimental study on the laser-induced atomic and close-to-atomic scale (ACS) structure of 4H-SiC using a capillary-discharged extreme ultraviolet (EUV) pulse of 46.9 nm wavelength. The modification mechanism at the ACS is investigated through molecular dynamics (MD) simulations. The irradiated surface is measured via scanning electron microscopy and atomic force microscopy. The possible changes in the crystalline structure are investigated using Raman spectroscopy and scanning transmission electron microscopy. The results show that the stripe-like structure is formed due to the uneven energy distribution of a beam. The laser-induced periodic surface structure at the ACS is first presented. The detected periodic surface structures with a peak-to-peak height of only 0.4 nm show periods of 190, 380, and 760 nm, which are approximately 4, 8, and 16 times the wavelength. In addition, no lattice damage is detected in the laser-affected zone. The study shows that the EUV pulse is a potential approach for the ACS manufacturing of semiconductors.

Effect of Na-ion intercalation on the thermal conductivity of carbon honeycomb nanostructure

This work studies the thermal conductivity of Na-ion intercalated carbon honeycomb (CHC) via the combination of first-principles calculation and molecular dynamics simulation. The effects of ion concentration, ion charge, temperature, and strain are explored. The simulation results show that the thermal conductivity of CHC presents a nonmonotonic dependence on the ion concentration. The enhanced phonon scattering and increased phonon group velocities of CHC induced by its interaction with the Na ions are responsible for the nonmonotonic dependence. Both the increases in the ion charge and temperature reduce the thermal conductivity. In contrast, a compressive strain of around -3% can increase the thermal conductivity by eliminating the phonon softening effect caused by the volume expansion of CHC during the ion intercalation. However, further increasing the strain negatively or positively from -3% leads to a decrease in the thermal conductivity. The simulation results presented in this work are beneficial in understanding the thermal properties of CHC when it is used as an electrode in ion batteries and supercapacitors.

Highly efficient desalination performance of carbon honeycomb based reverse osmosis membranes unveiled by molecular dynamics simulations

Seawater desalination is vital to our modern civilization. Here, we report that the carbon honeycomb (CHC) has an outstanding water permeability and salt rejection in the seawater desalination, as revealed by molecular dynamics simulations. More than 92% of ions are rejected by CHC at applied pressures ranging from 50 to 250 MPa. CHC has a perfect salt rejection at pressures below 150 Mpa. On increasing the applied pressure up to 150 MPa, the salt rejection reduces only to 92%. Pressure, temperature and temperature gradient are noted to play a significant role in modulating the water flux. The water flux increases with pressure and temperature. With the introduction of a temperature gradient of 3.5 K nm^-1, the seawater permeability increases by 33% as compared to room temperature. The water permeability of the CHC is greater than other carbon materials and osmosis membranes including graphene (8.7 times) and graphyne (2.1 times). It indicates the significant potential of the CHC for commercial application in water purification.

Enhancement of Diffusion Assisted Bonding of the Bimetal Composite of Austenitic/Ferric Steels via Intrinsic Interlayers

We investigate the effect of the intrinsic interlayers on the diffusion assisted bonding properties of the austenitic steel (stainless steel 316L) and ferric steels (Low-carbon steel Q345R) in a hot rolling process by molecular dynamics simulations and experiment. The introduction of an intrinsic interlayer (Cr or Ni) widens the diffusion region, leading to enhancement of bonding. The thickness of the diffusion region enlarges with an increase of temperature, with an enhancement factor of 195% and 108%, for Cr and Ni interlayer, respectively, at the temperature of 1800 K. Further diffusion analysis reveals the unsymmetrical diffusion near the interface. Our experimental investigation evidenced our computation discovery.

Simulated mechanical properties of finite-size graphene nanoribbons

There are many simulation studies of mechanical properties of graphene nanoribbons (GNR), but there is a lack of agreement regarding elastic and plastic behavior. In this paper we aim to analyze mechanical properties of finite-size GNR, including elastic modulus and fracture, as a function of ribbon size. We present classical molecular dynamics simulations for three different empirical potentials which are often used for graphene simulations: AIREBO, REBO-scr and REAXFF. Ribbons with and without H-passivation at the borders are considered, and the effects of strain rate and different boundaries are also explored. We focus on zig-zag GNR, but also include some armchair GNR examples. Results are strongly dependent on the empirical potential employed. Elastic modulus under uniaxial tension can depend on ribbon size, unlike predictions from continuum-scale models and from some atomistic simulations, and fracture strain and progress vary significantly amongst the simulated potentials. Because of that, we have also carried out quasi-static ab-initio simulations for a selected size, and find that the fracture process is not sudden, instead the wave function changes from Blöch states to a strong interaction between localized waves, which decreases continuously with distance. All potentials show good agreement with DFT in the linear elastic regime, but only the REBO-scr potential shows reasonable agreement with DFT both in the nonlinear elastic and fracture regimes. This would allow more reliable simulations of GNRs and GNR-based nanostructures, to help interpreting experimental results and for future technological applications.

Adsorption and Diffusion of Hydrogen in Carbon Honeycomb

Carbon honeycomb has a nanoporous structure with good mechanical properties including strength. Here we investigate the adsorption and diffusion of hydrogen in carbon honeycomb via grand canonical Monte Carlo simulations and molecular dynamics simulations including strength. Based on the adsorption simulations, molecular dynamics simulations are employed to study the effect of pressure and temperature for the adsorption and diffusion of hydrogen. To study the effect of pressure, we select the 0.1, 1, 5, 10, 15, and 20 bars. Meanwhile, we have studied the hydrogen storage capacities of the carbon honeycomb at 77 K, 153 K, 193 K, 253 K and 298 K. A high hydrogen adsorption of 4.36 wt.% is achieved at 77 K and 20 bars. The excellent mechanical properties of carbon honeycomb and its unique three-dimensional honeycomb microporous structure provide a strong guarantee for its application in practical engineering fields.

Effect of Angle, Temperature and Vacancy Defects on Mechanical Properties of PSI-Graphene

The PSI-graphene, a two-dimensional structure, was a novel carbon allotrope. In this paper, based on molecular dynamics simulation, the effects of stretching direction, temperature and vacancy defects on the mechanical properties of PSI-graphene were studied. We found that when PSI-graphene was stretched along 0° and 90° at 300 K, the ultimate strength reached a maximum of about 65 GPa. And when stretched along 54.2° and 155.2° at 300 K, the Young’s modulus had peaks, which were 1105 GPa and 2082 GPa, respectively. In addition, when the temperature was raised from 300 K to 900 K, the ultimate strength in all directions was reduced. The fracture morphology of PSI-graphene stretched at different angles was also shown in the text. In addition, the number of points removed from PSI-graphene sheet also seriously affected the tensile properties of the material. It was found that, compared with graphene, PSI-graphene didn’t have the negative Poisson’s ratio phenomenon when it was stretched along the direction of 0°, 11.2°, 24.8° and 34.7°. Our results provided a reference for studying the multi-angle stretching of other carbon structures at various temperatures.