Single-Dislocation Phonons: Atomic-Scale Measurement and Their Thermal Properties

Nanoscale defects such as dislocations have a significant impact on the phonon thermal transport properties in non-metallic materials. To unravel these effects, an understanding of defect phonon modes is essential. Herein, at the atomic scale, the localized phonons of individual dislocations 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 a phonon redshift of several milli-electron-volts within about two to four nanometers of the core, where both 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.