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Two-dimensional SiC has been successfully prepared in an experiment (Phys. Rev. Lett2023,130, 076203), which provides new material candidates for power devices. In this work, molecular dynamics simulations are employed to investigate the tunable thermal transport properties of the SiC monolayer by grain boundaries (GBs). The thermal conductivity of SiC shows a pronounced dependence on the number and angle of the GBs interfaces. The inherent pentagon-heptagon structure at GBs induces atomic forces between atoms at the GBs, leading to a certain out-of-plane displacement of these atoms at the interface. Appropriate external strain can flatten the GB interface, thereby enhancing the thermal conductivity. However, further increasing the strain will decrease the thermal conductivity due to enhanced phonon anharmonicity. Moreover, the interface thermal conductance at the GBs also exhibits obvious dependence on the angle of GBs and temperature, which is explained by the atomic stress at the GBs interface. Furthermore, using phonon packet analysis, we found that the phonon interface scattering at GBs differs from that in the two-dimensional heterostructure. This finding reveals the intrinsic thermo-mechanical coupling mechanism governing thermal conduction in two-dimensional SiC, also suggesting its application in thermal management in the thermo-mechanical sensor. [ABSTRACT FROM AUTHOR]

Defect engineering has been considered as an effective way for controlling the heat transport properties of two-dimensional materials. In this work, the effects of point vacancies and grain boundaries on the mechanical and thermal performances of SiC and GeC monolayers are investigated systematically by molecular dynamics calculations. The failure strength in SiC and GeC is decreased by introducing vacancies at room temperature, and the stress–strain relationship can be tuned significantly by different kinds of vacancies. When the grain boundary of 21.78° is applied, the maximal fracture strengths can be as large as 27.56% for SiC and 23.56% for GeC. Also, the thermal properties of the two monolayers show a remarkable dependence on the vacancies and grain boundaries. The high vacancy density in SiC and GeC can induce disordered heat flow and the C/Ge point defect is crucial for thermal conductivity regulation for the Si/GeC monolayer. More importantly, the SiC and GeC monolayers with a grain boundary of 5.09° show excellent interfacial thermal conductance. Our findings are of great importance in understanding SiC and GeC monolayers and seeking their potential applications. [ABSTRACT FROM AUTHOR]

Very recently, two-dimensional MoSi2N4 has been synthetized (Y.-L. Hong, Z. Liu, L. Wang, T. Zhou, W. Ma, C. Xu, S. Feng, L. Chen, M.-L. Chen and D.-M. Sun, Chemical vapor deposition of layered two-dimensional MoSi2N4 materials, Science, 2020, 369, 670–674.). In this work, we systematically explore the mechanical, electronic, and catalytic properties of the MX2Y4 (M = Cr, Hf, Mo, Ti, W, Zr; X = Si, Ge; Y = N, P, As) monolayers by first-principles calculations. These observed monolayers exhibit an isotropic Young's moduli of 165–514 N m−1 and a Poisson's ratio of 0.26–0.33. The calculated band structures indicate that their bandgaps are in the range of 0.49–2.05 eV at the HSE06 level. In particular, a high electron mobility of about 1.04 × 104 cm2 V−1 s−1 is observed in TiSi2N4 monolayers, which shows potential for high-speed electronic devices. MX2Y4 monolayers also reveal decent performances in the hydrogen evolution reaction. More importantly, the Gibbs free energy change of the TiSi2N4 (ZrSi2N4) monolayer is as small as 0.078 eV (−0.035 eV), even being comparable with that of Pt (−0.09 eV). This investigation suggests that the MoSi2N4 family monolayers have potential advanced applications such as photocatalytic, electrocatalytic, and photovoltaic devices. [ABSTRACT FROM AUTHOR]

Coiled carbon nanotubes (CNTs) have attracted much attention thanks to their unique geometrical structure along with outstanding mechanical and thermal properties. However, the relationship between the geometrical parameters and mechanical and thermal properties of coiled CNTs remains largely unexplored. Herein, coiled CNTs are constructed with various geometries by phase‐field crystal (PFC) modeling and their mechanical and thermal properties are investigated by molecular dynamics (MD) simulations. It is found that the effect of geometrical parameters of coiled CNTs on the Young's modulus can be well captured by analytical formulas derived from the mechanical spring tube model. These extensive MD simulations show that the Young's modulus of coiled CNTs increases with an increase in coil pitch l and CNT radius r, but decreases with an increase in coil radius R. Furthermore, using the nonequilibrium MD (NEMD) method, it is found that the thermal conductivity of coiled CNTs decreases with an increase in coil radius R, but increases slightly with an increase of coil pitch l and CNT radius r. Valuable insights into the mechanical and thermal properties of coiled CNTs are provided and the findings here may serve as useful guidelines for the design of coiled CNTs for device applications. [ABSTRACT FROM AUTHOR]