Engineering nanostructured superlattices provides an effective solution toward the realization of high-performance thermoelectric device and thermal management materials,where the anisotropic thermal conductivity is c...Engineering nanostructured superlattices provides an effective solution toward the realization of high-performance thermoelectric device and thermal management materials,where the anisotropic thermal conductivity is critical for designing orientation-dependent thermal devices.Herein,the lattice thermal conductivity anisotropy of Al/Ag superlattices as one typical example of superlattice materials is investigated utilizing non-equilibrium molecular dynamics simulations.The cross-plane and in-plane lattice thermal conductivities of one-dimensional superlattices are in the ranges of 0.5–3.2 W/(m·K)and 1.8–5.1 W/(m·K)at different period lengths,respectively,both of which are smaller than those of bulk materials.More specifically,the cross-plane lattice thermal conductivity of superlattices increases with the period length,while the in-plane phonon thermal conductivity first increases and then trends to convergence,resulting in the non-monotonic thermal anisotropy value.To further reveal the microscopic phonon transport mechanism,the interfacial phonon thermal resistance,density of states and spectral phonon transmission coefficient including anharmonic phonon properties under different period lengths are calculated.Our results can be helpful for understanding phonon transport in low-dimensional materials and provide guidance for optimizing the thermal conductivity anisotropy of superlattice materials in the application ranging from thermoelectric devices to thermal management in micro/nano systems.展开更多
Energy dissipation has always been an attention-getting issue in modern electronics and the emerging low-symmetry two-dimensional(2D)materials are considered to have broad prospects in solving the energy dissipation p...Energy dissipation has always been an attention-getting issue in modern electronics and the emerging low-symmetry two-dimensional(2D)materials are considered to have broad prospects in solving the energy dissipation problem.Herein the thermal transport of a typical 2D ternary chalcogenide Ta_(2)NiS_(5) is investigated.For the first time we have observed strongly anisotropic in-plane thermal conductivity towards armchair and zigzag axes of suspended few-layer Ta_(2)NiS_(5) flakes through Raman thermometry.For 7-nm-thick Ta_(2)NiS_(5) flakes,theκz i g z a g is 4.76 W·m^(−1)·K^(−1) andκa r m c h a i r is 7.79 W·m^(−1)·K^(−1),with a large anisotropic ratio(κa r m c h a i r/κz i g z a g)of 1.64 mainly ascribed to different phonon mean-free-paths along armchair and zigzag axes.Moreover,the thickness dependence of thermal anisotropy is also discussed.As the flake thickness increases,theκa r m c h a i r/κz i g z a g reduces sharply from 1.64 to 1.07.This could be attributed to the diversity in phonon boundary scattering,which decreases faster in zigzag direction than in armchair direction.Such anisotropic property enables heat flow manipulation in Ta_(2)NiS_(5) based devices to improve thermal management and device performance.Our work helps reveal the anisotropy physics of ternary transition metal chalcogenides,along with significant guidance to develop energy-efficient next generation nanodevices.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52176078,52006130,and 51827807)China Postdoctoral Science Foundation(Nos.2020M670321 and 2021T140359)。
文摘Engineering nanostructured superlattices provides an effective solution toward the realization of high-performance thermoelectric device and thermal management materials,where the anisotropic thermal conductivity is critical for designing orientation-dependent thermal devices.Herein,the lattice thermal conductivity anisotropy of Al/Ag superlattices as one typical example of superlattice materials is investigated utilizing non-equilibrium molecular dynamics simulations.The cross-plane and in-plane lattice thermal conductivities of one-dimensional superlattices are in the ranges of 0.5–3.2 W/(m·K)and 1.8–5.1 W/(m·K)at different period lengths,respectively,both of which are smaller than those of bulk materials.More specifically,the cross-plane lattice thermal conductivity of superlattices increases with the period length,while the in-plane phonon thermal conductivity first increases and then trends to convergence,resulting in the non-monotonic thermal anisotropy value.To further reveal the microscopic phonon transport mechanism,the interfacial phonon thermal resistance,density of states and spectral phonon transmission coefficient including anharmonic phonon properties under different period lengths are calculated.Our results can be helpful for understanding phonon transport in low-dimensional materials and provide guidance for optimizing the thermal conductivity anisotropy of superlattice materials in the application ranging from thermoelectric devices to thermal management in micro/nano systems.
基金supported by the National Natural Science Foundation of China(NSFC,Nos.11874423 and 11404399)the National Defense Science and Technology Innovation Zone,and the Scientific Researches Foundation of National University of Defense Technology(Nos.ZK20-16 and ZZKY-YX-08-06).
文摘Energy dissipation has always been an attention-getting issue in modern electronics and the emerging low-symmetry two-dimensional(2D)materials are considered to have broad prospects in solving the energy dissipation problem.Herein the thermal transport of a typical 2D ternary chalcogenide Ta_(2)NiS_(5) is investigated.For the first time we have observed strongly anisotropic in-plane thermal conductivity towards armchair and zigzag axes of suspended few-layer Ta_(2)NiS_(5) flakes through Raman thermometry.For 7-nm-thick Ta_(2)NiS_(5) flakes,theκz i g z a g is 4.76 W·m^(−1)·K^(−1) andκa r m c h a i r is 7.79 W·m^(−1)·K^(−1),with a large anisotropic ratio(κa r m c h a i r/κz i g z a g)of 1.64 mainly ascribed to different phonon mean-free-paths along armchair and zigzag axes.Moreover,the thickness dependence of thermal anisotropy is also discussed.As the flake thickness increases,theκa r m c h a i r/κz i g z a g reduces sharply from 1.64 to 1.07.This could be attributed to the diversity in phonon boundary scattering,which decreases faster in zigzag direction than in armchair direction.Such anisotropic property enables heat flow manipulation in Ta_(2)NiS_(5) based devices to improve thermal management and device performance.Our work helps reveal the anisotropy physics of ternary transition metal chalcogenides,along with significant guidance to develop energy-efficient next generation nanodevices.
