CO2 electroreduction to high value-added chemicals is a prospective approach to realize the utilization of CO2 resources and mitigate the greenhouse effect. Ethylene (C2H4), as an important chemical materials, is...

With excellent physical and chemical properties, 2D TMDC materials have been widely used in engineering applications, but they inevitably suffer from the dual effects of strain and device size, thermal transport inside the materials need to be further discussed.

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Exploring the possibility of nanostructures to modulate thermal conductivity (TC) contributes to promote a deeper comprehension of phonon diffusion and transport processes with the design of thermally insulated devices with high ZT values, and the GaAs nanowires (NWs) widely used in optoelectronic and microelectronic devices exhibit nondiffusive phonon thermal transport phenomena attributed to size effects, while ignoring the wave effects of phonons. Here, we simulate the TC of pillar-based GaAs NWs using Non-Equilibrium Molecular Dynamics and Monte Carlo simulations. The spatial distribution of density of states, temperature and heat flow distribution clouds, phonon participation rate, dispersion curves and phonon transmittance of atoms were calculated to investigate the phonon thermal transport processes in pillar-based NWs. The calculation results show that the pillar-based surface reduce the TC by 16%, the TC of pristine NW increases with axial and equivalent diameter, and the TC of pillar-based NW increases nonlinearly with axial length and increases with radial length. The phonon-surface scattering intensity is enhanced by the perturbation introduced by the pillared surface with a substantial decrease in phonon transmission capacity and a break in long-wavelength phonon transport even annihilated, which leads to surface phonon localization. Nanopillars not only enhance the phonon-surface scattering intensity at low frequencies, but also reconfigure the dispersion curve to reduce the group velocity. A series of flat resonance phonon modes are generated throughout the whole spectrum due to the hybridization between the local resonance phonon modes of the nanopillar and the phonon modes of the substrate NWs, resulting in the phonon modes shifting to lower frequencies.The pillar-based surface induced surface phonon localization and local resonance phenomenon contributes to the modulation of phonon thermal transport in GaAs-based field-effect transistors.

Herein, several molecular systems are simulated by molecular dynamics to study the decomposition process and fluctuation−dissipation characteristics of spherical methane hydrates under different conditions. The spherical radius and the movement of the hydrate−liquid water interface during decomposition are measured. Different fitted formulas of the variation of methane numbers are obtained from the decomposition of spherical and bulk methane hydrates. Fluctuation−dissipation characteristics for spherical methane hydrates with different radii are analyzed, which show that increasing the scale of hydrates can increase the relaxation time and slow down the fluctuation process. The variations of the hydrogen bond and hydrogen-bond lifetime are calculated. For hydrate phase water, the peak of the hydrogenbond lifetime lies between 8 and 10 ps. After complete decomposition, the hydrogen-bond lifetime mainly distributes in 0 and 2 ps and the peak disappears. The effects of temperature, cage occupancy, liquid phase environment, and spherical hydrate scale are explored. The decomposition activation energy for the spherical hydrate with a radius of 20 Å is calculated to be 52.23 kJ/mol. It can speed up the decomposition rate as well as the diffusion of methane and water molecules with a lower cage occupancy. For the effect of the liquid phase environment, it is found that the number of liquid water rarely affects the decomposition. However, when the Na + and Cl − concentrations change from 0 to 10%, the decomposition time reduces from ∼511 to ∼369 ps, which indicates that there is an obviously positive impact on decomposition.