Role of Convergence and Collection Angles in the Excitation of Long-and Short-Wavelength Phonons with Vibrational Electron Energy-Loss Spectroscopy

Kartik Venkatraman, Peter A. Crozier

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

Current generation electron monochromators employed as attachments to scanning transmission electron microscopes (STEM) offer the ability to obtain vibrational information from materials using electron energy-loss spectroscopy (EELS). We show here that in crystals, long-and short-wavelength phonon modes can be probed simultaneously with on-axis vibrational STEM EELS. The long-wavelength phonons are probed via dipole scattering, while the short-wavelength modes are probed via impact scattering of the incident electrons. The localized character of the short-wavelength modes is demonstrated by scanning the electron beam across the edge of a hexagonal boron nitride nanoparticle. It is found that employing convergence angles that encompass multiple Brillouin zone boundaries enhances the short-wavelength phonon contribution to the vibrational energy-loss spectrum much more than that achieved by employing collection angles that encompass multiple Brillouin zone boundaries. Probing short-wavelength phonons at high spatial resolution with on-axis vibrational STEM EELS will help develop a fundamental connection between vibrational excitations and bonding arrangements at atomic-scale heterogeneities in materials.

Original languageEnglish (US)
Pages (from-to)1069-1077
Number of pages9
JournalMicroscopy and Microanalysis
Volume27
Issue number5
DOIs
StatePublished - Oct 1 2021

Keywords

  • Brillouin zone boundary
  • impact
  • localized
  • phonon
  • short wavelength
  • vibrational EELS

ASJC Scopus subject areas

  • Instrumentation

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