Fig. 2: 4D-EELS measurement of phonon dispersion in an individual zigzag BNNT.
From: Four-dimensional vibrational spectroscopy for nanoscale mapping of phonon dispersion in BN nanotubes
a–c Schematic of the experimental geometry. Left panels illustrate the beam position (yellow arrows). Right panels show the diffraction plane. Blue and green rectangles illustrate the position of the slot aperture used in d–f (Supplementary Movie 1) and g–i (Supplementary Movie 2), respectively. The underlying black dot patterns are simulated electron diffraction patterns, in which the vertical direction is parallel to the tube axis. d–f Phonon dispersion line profiles along a radius of the BNNT, acquired with the slot aperture placed along the blue rectangle in a–c. d, f correspond to the tube center and the edge respectively, and e is acquired between them. Dashed circles and squares mark bright spots from Bragg diffraction and multiple scattering processes. g–i Same as d–f, except that the aperture is long the green rectangle in a–c. j–l Calculated EELS intensity (statistical factor corrected) for a bulk h-BN crystal along high-symmetry lines ΓKMKΓ (j), ΓMΓMΓ (k), and ΓAΓAΓ (l). Gray curves are calculated dispersion for bulk h-BN crystals.
