Temperature dependence of phonon-defect interactions: phonon scattering vs. phonon trapping

Abstract

The interactions between thermal phonons and defects are conventionally described as scattering processes, an idea proposed almost a century ago. In this contribution, ab-initio molecular-dynamics simulations provide atomic-level insight into the nature of these interactions. The defect is the Si|X interface in a nanowire containing a δ-layer (X is C or Ge). The phonon-defect interactions are temperature dependent and involve the trapping of phonons for meaningful lengths of time in defect-related, localized, vibrational modes. No phonon scattering occurs and the momentum of the phonons released by the defect is unrelated to the momentum of the phonons that generated the excitation. The results are extended to the interactions involving only bulk phonons and to phonon-defect interactions at high temperatures. These do resemble scattering since phonon trapping occurs for a length of time short enough for the momentum of the incoming phonon to be conserved.

Manipulation of Stacking Order in Td-WTe2 by Ultrafast Optical Excitation

“…Shear displacements are known to be strongly damped by defects and boundaries. 35 The intensity evolution of the 130 spot from such defective samples is shown in Figure 4 . Two sample thicknesses are included, 0.06 IMFP (∼6 nm) and 0.21 IMFP (∼20 nm).…”

“…TEM observations show that nonuniform samples that host defects often do not exhibit a strong shear phonon response in the temporal traces (TEM image in Supporting Information Figure S5). Shear displacements are known to be strongly damped by defects and boundaries . The intensity evolution of the 130 spot from such defective samples is shown in Figure .…”

Theoretical investigation of lattice thermal conductivity and electrophononic effects in SrTiO3

“…The thermal conductivity of a material must be high to keep a low thermal budget in a nanoscale device [3], for instance, while it should be as low as possible when it comes to the engineering of an efficient thermoelectric [4,5]. The thermal conductivity can be tuned to some extent by nanostructuring, adding defects [6,7], or designing periodic superstructures [8,9], but it would be desirable to be able to dynamically modify it. Besides an increased flexibility in materials design, this would also open the way to heat-based signal processing and computing [10].…”

Significantly High Thermal Rectification in an Asymmetric Polymer Molecule Driven by Diffusive versus Ballistic Transport

“…Despite lack of good methods to directly identify locons within tapered bottlebrush polymers, we previously demonstrated that even BB-2 has significantly more locons than PNb (backbone) in frequency ranges of 50−90 THz due to the existence of side chains, as shown in participation ratio plots of Figure 3d in ref 40. Locons do not significantly contribute to thermal conductivity, 52 could trap energy, 53 and become the bottleneck for heat conduction. Localization asymmetry can thus contribute to the spatial dependence of thermal conductivity.…”