A Monochromatic Atom-wide Electron Probe for Nanoscale Materials Excitations
Maureen Joel Lagos
Department of Materials Science and Engineering
Canadian Centre for Electron Microscopy
McMaster University, Ontario, Canada
Wednesday, October 2, 2019
C2-361 (Reading Room)
Atomic-wide electron beams can be produced routinely in aberration-corrected scanning transmission electron microscopes. Over the last few years, a new technology of monochromators was developed to deliver electron probes with remarkable sub-10 meV energy resolution. This combination of spatial resolution with energy resolution is permitting the study of elementary excitations (phonons, infrared plasmons, etc.) in nanoscale structures and the study of the local response of atom-scale features (defects, interfaces, etc) in nanomaterials.
In this talk I will present three studies of spatially-resolved phonon spectroscopy in nanostructures using a ~ 1.5 Å probe and 7 meV energy resolution. i) Phonon Mapping: We detected and mapped bulk and surface phonon modes in a single nanocube. A large variety of surface phonon polariton modes can be excited and their behaviour is size dependent. We also detected bulk optical (~ 80 - 90 meV) and acoustic (~ 30 - 50 meV) modes, containing lattice contributions spanning the whole Brilloiun zone, and located mainly within the inner regions of the nanocube. ii) Phonon-Plasmon Coupling: We study the phonon-plasmon coupling between an aluminum antenna attached to silica rod. The coupling is driven by the interaction between the dipolar mode of the antenna and the surface phonon polaritons of the silica. Nanoscale Temperature Measurement: iii) We measured the “local” temperature of single objects by comparing the energy loss and energy gain scattering intensities. We verified that the inelastic electron scattering by phonons obeys the Principle of Detailed Balance. Temperature measurements with sub-nanometer spatial resolution could be achieved using highly-localized phonon signal.
Our results provide progress in understanding electron inelastic scattering from lattice vibrations in nanosized volumes of matter, and promise a bright future for wide exploration of highly-localized vibrational excitations in nanostructures with complex atom-size features and evaluation of phononic response of new emergent materials.
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