Phonon Transport within Periodic Porous Structures — From Classical Phonon Size Effects to Wave Effects

Abstract

ΩSolid angle SubscriptsGPnC SiNW Graphene phononic crystal Silicon nanowire NCJ_MC Nano-cross-junction system with its thermal conductivity calculated by the Monte Carlo method NCJ_AGFMC Nano-cross-junction system with its thermal conductivity calculated by the AGFMC method AbstractTailoring thermal properties with nanostructured materials can be of vital importance for many applications. Generally classical phonon size effects are employed to reduce the thermal conductivity, where strong phonon scattering by nanostructured interfaces or boundaries can dramatically supress the heat conduction. When these boundaries or interfaces are arranged in a

Two-step modification of phonon mean free paths for thermal conductivity predictions of thin-film-based nanostructures

“…In this work, a simple but accurate analytical model is developed, which extends our previous work on nanoporous films 14,20 to dry-etched nanowires and general thin-film-based nanoporous structures. The model predictions agree well with frequency-dependent phonon Monte Carlo (MC) simulations that incorporate the specularity of individual surfaces and the exact three-dimensional structures.…”

Nanostructured and Heterostructured 2D Materials for Thermoelectrics

“…With tunable phonon transport and electron band structures, these 2D porous structures are named as antidot lattices, nanomeshes, or phononic structures. [16], [151] Several 2D porous structures have been theoretically investigated for thermal, electronic, and thermoelectric properties, including the most studied graphene antidot lattices (GAL), [151 porous silicene, [162] and 2D MoS2 and phosphorene antidot lattices. [163[164] On the one hand, phonon transport in these porous structures can be significantly suppressed by boundary scattering and localization of phonons around the pores, as well as wave-like phonon interference in periodic structures.…”

“…[163[164] On the one hand, phonon transport in these porous structures can be significantly suppressed by boundary scattering and localization of phonons around the pores, as well as wave-like phonon interference in periodic structures. [16], [155], [156] On the other hand, the electronic band structure can be tailored in well-designed porous structures so that the Seebeck coefficient can be enhanced while the electrical conductivity can remain high. [157 [164] Up to now, several theoretical studies have demonstrated enhanced ZT values in 2D porous structures, as listed in Table 2.…”

“…As nanoconstrictions, this neck width is actually the minimum feature size within the nanoporous pattern and can yield the lower bound of the actual thermal and electrical conductivities. [16] In contrast with patterns with periodic nanopores, an accurate characteristic length determined by the geometry is available for 2D structures with aligned nanoslots. [168], [169] This introduces unique opportunities in the design and optimization of such nanoconstriction structures for thermoelectric applications.…”

“…In later studies, suppressed phonon transport is often found as another important benefit for nanostructured materials with strong boundary or interface phonon scattering. [15], [16] For charge carriers with usually shorter mean free paths (MFPs) than those for phonons, they are less scattered so that bulk-like electrical properties can be preserved. In general, S, σ, and k can be hopefully decoupled and independently manipulated by careful structure design.…”