Lattice thermal conductivity of β12 and χ3 borophene

Borophene allotropes have many unique physical properties due to their polymorphism and similarity between boron and carbon.In this work,based on the density functional theory and phonon Boltzmann transport equation,we investigate the lattice thermal conductivityκof bothβ12 andχ3 borophene.Interestingly,these two allotropes with similar lattice structures have completely different thermal transport properties.β12 borophene has almost isotropicκaround 90 W/(m·K)at 300 K,whileκofχ3 borophene is much larger and highly anisotropic.The room temperatureκofχ3 borophene along the armchair direction is 512 W/(m·K),which is comparable to that of hexagonal boron nitride but much higher than most of the two-dimensional materials.The physical mechanisms responsible for such distinct thermal transport behavior are discussed based on the spectral phonon analysis.More interestingly,we uncover a unique one-dimensional transport feature of transverse acoustic phonon inχ3 borophene along the armchair direction,which results in a boost of phonon relaxation time and thus leads to the significant anisotropy and ultrahigh thermal conductivity inχ3 borophene.Our study suggests thatχ3 borophene may have promising application in heat dissipation,and also provides novel insights for enhancing the thermal transport in two-dimensional systems.

A thermal conductivity switch via the reversible 2H–1T′phase transition in monolayer MoTe_(2)

The two-dimensional(2D)material-based thermal switch is attracting attention due to its novel applications,such as energy conversion and thermal management,in nanoscale devices.In this paper,we observed that the reversible 2H–1T′phase transition in MoTe_(2)is associated with about a fourfold/tenfold change in thermal conductivity along the X/Y direction by using first-principles calculations.This phenomenon can be profoundly understood by comparing the Mo–Te bonding strength between the two phases.The 2H-MoTe_(2)has one stronger bonding type,while 1T′-MoTe_(2)has three weaker types of bonds,suggesting bonding inhomogeneity in 1T′-MoTe_(2).Meanwhile,the bonding inhomogeneity can induce more scattering of vibration modes.The weaker bonding indicates a softer structure,resulting in lower phonon group velocity,a shorter phonon relaxation lifetime and larger Gr¨uneisen constants.The impact caused by the 2H to 1T′phase transition in MoTe_(2)hinders the propagation of phonons,thereby reducing thermal conductivity.Our study describes the possibility for the provision of the MoTe_(2)-based controllable and reversible thermal switch device.

A phononic rectifier based on carbon schwarzite host–guest system

Thermal rectification is a promising way to manipulate the heat flow,in which thermal phonons are spectrally and collectively controlled.As phononic devices are mostly relying on monochromatic phonons,in this work we propose a phononic rectifier based on the carbon schwarzite host–guest system.By using molecular dynamic simulations,we demonstrate that the phononic rectification only happens at a specific frequency of the hybridized mode for the host–guest system,due to its strong confinement effect.Moreover,a significant rectification efficiency,~134%,is observed,which is larger than most of the previously observed efficiencies.The study of length and temperature effects on the phononic rectification shows that the monochromaticity and frequency of the rectified thermal phonons depend on the intrinsic anharmonicity of the host–guest system and that the on-center rattling configuration with weak anharmonicity is preferable.Our study provides a new perspective on the rectification of thermal phonons,which would be important for controlling monochromatic thermal phonons in phononic devices.

Performance of a bi-layer solar steam generation system working at a high-temperature of top surface

Many efforts have been focused on enhancing the vapor generation in bi-layer solar steam generation systems for obtaining as much pure water as possible.However,the methods to enhance the vapor temperature is seldom studied although the high-temperature vapor has a wide use in medical sterilization and electricity generation.In this work,to probe the high-temperature vapor system,an improved macroscopic heat and mass transfer model was proposed.Then,using the finite element method to solve the model,the influences of some main factors on the evaporation efficiency and vapor temperature were discussed,including effects of the vapor transport conditions and the heat dissipation conditions.The results show that the high-temperature vapor could not be obtained by enhancing the heat-insulating property of the bi-layer systems but by applying the optimal porosity and proper absorbers.This paper is expected to provide some information for designing a bi-layered system to produce high-temperature vapor.