Single-dislocation phonons: atomic-scale measurement and their thermal properties

TL;DR

This study measures atomic-scale dislocation phonons at a Si/Ge interface using electron energy loss spectroscopy, revealing their effects on local thermal transport and potential for defect engineering in thermoelectrics.

Contribution

It introduces atomic-scale measurement of dislocation phonons and links their localized modes to thermal transport properties at interfaces.

Findings

Dislocation causes phonon redshift within 2-4 nm of the core.

Dislocation can either enhance or reduce local interfacial thermal conductance.

Localized phonon modes are correlated with microstructural features.

Abstract

Nanoscale defects such as dislocations, have a significant impact on the phonon thermal transport properties in non-metallic materials. To unravel these effects, understanding of defect phonon modes is essential. Herein, at the atomic scale, the localized phonons of individual dislocation at a Si/Ge interface are measured via monochromated electron energy loss spectroscopy in a scanning transmission electron microscope. These modes are then correlated with the local microstructure, further revealing the dislocation effects on the local thermal transport properties. The dislocation causes phonon redshift in several milli-electron-volts within about two to four nanometers of the core, where both of the strain field and Ge-segregation play roles. With the presence of dislocation, the local interfacial thermal conductance can be either enhanced or reduced, depending on the complex interaction and competition between lattice-disorder (dislocation) and element-disorder (heterointerface mixing and Ge-segregation) at the interface. These findings provide valuable insights to improve the thermal properties of thermoelectric generators and thermal management systems through proper defect engineering.