Coherent twin boundaries form periodic lamellar twinning in a wide variety of semiconductor nanow... more Coherent twin boundaries form periodic lamellar twinning in a wide variety of semiconductor nanowires, and are often viewed as near-perfect interfaces with reduced phonon and electron scattering behaviors. Such unique characteristics are of practical interest for high-performance thermoelectrics and optoelectronics; however, insufficient understanding of twin-size effects on thermal boundary resistance poses significant limitations for potential applications. Here, using atomistic simulations and ab-initio calculations, we report direct computational observations showing a crossover from diffuse interface scattering to superlattice-like behavior for thermal transport across nanoscale twin boundaries present in prototypical bulk and nanowire Si examples. Intrinsic interface scattering is identified for twin periods larger than or equal to 22.6 nm, but also vanishes below this size to be replaced by ultrahigh Kapitza thermal conductances. Detailed analysis of vibrational modes shows that modeling twin boundaries as atomically-thin 6H-Si layers, rather than phonon scattering interfaces, provides an accurate description of effective cross-plane and in-plane thermal conductivities in twinning superlattices, as a function of the twin period thickness.
Coherent twin boundaries, which form periodic lamellar twinning in a wide variety of semiconducto... more Coherent twin boundaries, which form periodic lamellar twinning in a wide variety of semiconductor nanowires, are often viewed as near-perfect interfaces with reduced phonon and electron scattering behaviors. Such unique characteristics are of practical interest for high-performance thermoelectrics and optoelectronics; however, insufficient evidence for the existence of coherent heat conduction in nanotwinned materials poses significant limitations for potential applications. Here, using atomistic simulations and ab-initio calculations, we report direct computational observations showing intrinsic nanotwin effects on thermal conductivity of twinning superlattices in prototypical bulk and nanowire Si examples. Incoherent phonon transport is identified for twin periods $\geq$ 15.1 nm and coherent transport for twin periods $\leq$ 3.8 nm. Remarkably, a regime of semi-coherent phonon transport is unveiled for twin periods spreading between these two limits, described by quasi-ballistic ...
A new phase transition at 258K is suggested by a weak anomaly of the dielectric constant without ... more A new phase transition at 258K is suggested by a weak anomaly of the dielectric constant without modification of the infrared spectra for ν > 10 cm-1. It should be a polar-polar phase transition like in the 285 K well-known transition.On the opposite, another phase transition is found from modification in the infrared spectrum between 4 and 80 K, without significant change of the static dielectric constant.
Coherent twin boundaries form periodic lamellar twinning in a wide variety of semiconductor nanow... more Coherent twin boundaries form periodic lamellar twinning in a wide variety of semiconductor nanowires, and are often viewed as near-perfect interfaces with reduced phonon and electron scattering behaviors. Such unique characteristics are of practical interest for high-performance thermoelectrics and optoelectronics; however, insufficient understanding of twin-size effects on thermal boundary resistance poses significant limitations for potential applications. Here, using atomistic simulations and ab-initio calculations, we report direct computational observations showing a crossover from diffuse interface scattering to superlattice-like behavior for thermal transport across nanoscale twin boundaries present in prototypical bulk and nanowire Si examples. Intrinsic interface scattering is identified for twin periods larger than or equal to 22.6 nm, but also vanishes below this size to be replaced by ultrahigh Kapitza thermal conductances. Detailed analysis of vibrational modes shows that modeling twin boundaries as atomically-thin 6H-Si layers, rather than phonon scattering interfaces, provides an accurate description of effective cross-plane and in-plane thermal conductivities in twinning superlattices, as a function of the twin period thickness.
Coherent twin boundaries, which form periodic lamellar twinning in a wide variety of semiconducto... more Coherent twin boundaries, which form periodic lamellar twinning in a wide variety of semiconductor nanowires, are often viewed as near-perfect interfaces with reduced phonon and electron scattering behaviors. Such unique characteristics are of practical interest for high-performance thermoelectrics and optoelectronics; however, insufficient evidence for the existence of coherent heat conduction in nanotwinned materials poses significant limitations for potential applications. Here, using atomistic simulations and ab-initio calculations, we report direct computational observations showing intrinsic nanotwin effects on thermal conductivity of twinning superlattices in prototypical bulk and nanowire Si examples. Incoherent phonon transport is identified for twin periods $\geq$ 15.1 nm and coherent transport for twin periods $\leq$ 3.8 nm. Remarkably, a regime of semi-coherent phonon transport is unveiled for twin periods spreading between these two limits, described by quasi-ballistic ...
A new phase transition at 258K is suggested by a weak anomaly of the dielectric constant without ... more A new phase transition at 258K is suggested by a weak anomaly of the dielectric constant without modification of the infrared spectra for ν > 10 cm-1. It should be a polar-polar phase transition like in the 285 K well-known transition.On the opposite, another phase transition is found from modification in the infrared spectrum between 4 and 80 K, without significant change of the static dielectric constant.
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