Polarization Selectivity in Vibrational Electron-Energy-Loss Spectroscopy

Abstract

Orientation-dependent aloof-beam vibrational electron-energy-loss spectroscopy is carried out on uniaxial icosahedral B12P2 submicron crystals. We demonstrate that the high sensitivity of the signal to the crystal orientation allows for an unambiguous determination of the symmetry of normal-modes occurring at the Brillouin zone center of this anisotropic compound. The experimental results are assessed using first-principles quantum mechanical calculations (density functional theory) of the dielectric response of the specimen. The high spatial resolution inherent to this technique when implemented in the transmission electron microscope thus opens the door to nanoscale orientationdependent vibrational spectroscopy.

Protein secondary structure signatures from energy loss spectra recorded in the electron microscope

“…The reason is that the spectra we record are very sensitive to the direction of the scattering wave vector, which is equivalent to polarisation. This sensitivity has also been demonstrated for inorganic materials like B 12 P 2 24 . Furthermore, as originally demonstrated by Rothschild 25 for bacteriorhodopsin the ratio of amide II to amide I is sensitive to the orientation.…”

“…This sensitivity has also been demonstrated for inorganic mate-rials like B 12 P 2 . 24 Furthermore, as originally demonstrated by Rothschild 25 for bacteriorhodopsin the ratio of amide II to amide I is sensitive to the orientation. Our scattering wave vectors are in the plane of the specimen, whose normal is the beam direction.…”

Atomic-scale probing of heterointerface phonon bridges in nitride semiconductor

“…S4 . Considering scattering wave vectors are predominately in the plane of the specimen perpendicular to the electron beam ( 43 , 44 ), the phonon dispersions, the projected in-plane Brillouin zones, and in-plane components of the phonon density of states (PDOS) of Si and AlN calculated from the MD are displayed in Fig. 1 C .…”

Properties of Dipole-Mode Vibrational Energy Losses Recorded From a TEM Specimen

“…Dipole-active modes are excited by electromagnetic radiation, as well as fast electrons. The dielectric theory of energy loss, developed for valence-electron excitation and plasmon losses (Ritchie, 1957), can therefore be used (Lucas & Sunjic, 1971, 1972) to describe vibEELS features, making use of infrared-absorption data or dielectric functions calculated from first principles (Forbes & Allen, 2016; Radtke et al, 2019).…”