Atomic resolution mapping of localized phonon modes at grain boundaries

Abstract

Phonon scattering at grain boundaries (GBs) is significant in controlling nanoscale device thermal conductivity. However, GBs could also act as waveguides for selected modes. To measure localized GB phonon modes, meV energy resolution is needed with sub-nm spatial resolution. Using monochromated electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) we have mapped the 60 meV optic mode across GBs in silicon at atomic resolution and compared it to calculated phonon densities of states (DOS). The intensity is strongly reduced at GBs characterised by the presence of five- and seven-fold rings where bond angles differ from the bulk. The excellent agreement between theory and experiment strongly supports the existence of localized phonon modes and thus of GBs acting as waveguides.

Merged article (8 pages, 3 figures, 1 table) and Supplementary Information (8 pages, 8 figures)

References in corpus (2)

• Non-classical mechanical states guided in a phononic waveguide
• Localized Phonon Densities of States at Grain Boundaries in Silicon

Cited by in corpus (5)

• Real-Space Visualization of Frequency-Dependent Anisotropy of Atomic Vibrations
• Perspective on Atomic-Resolution Vibrational Electron Energy-Loss Spectroscopy
• Electron Ptychography Reveals Correlated Lattice Vibrations at Atomic Resolution
• Single-dislocation phonons: atomic-scale measurement and their thermal properties
• Extended defects as a source of phonon confinement in polycrystalline Si and Ge films