Chapter 16
VLEED Capability and Sensitivity
Abstract VLEED offers such a unique tool that collects information of bond geometry, valence density-of states (DOS), and SPB outside the second atomic layer
with high sensitivity and reliability. Based on the principle of Fourier transformation, VLEED calculation derives consistent information obtained with electron
spectroscopy, crystallography, and morphology on an atomic scale.
Highlights
• The ReV(z) diffracts elastically the electron beam and determines its phase shift.
• The ImV(z, E) diffracts inelastically the electron beam and determines is amplitude
loss.
• Covering the valence band energy, VLEED beam is subject to energy loss by
absorption.
• VLEED signal is only sensitive to relaxation of the outermost two atomic layers.
16.1 Uniqueness of Solution
Independent treatment of the geometric and the SPB parameters in simulation of
VLEED spectrum could lead to solution uncertainty [1], because the diffraction intensity depends on the arrangement of scattering centers with different cross-sections
and the interference of the diffracted beams by the SPB. The geometrical arrangement
determines the phase change of diffracted beams. The cross section of diffraction
varies with the effective charges of the scattering centers. The interference determines
the amplitude of the diffracted waves. Therefore, reaction with charge transportation
and polarization modifies the atomic positions and the SPB. Proper combination
of the geometry, SPB and the parametrization wise ensures the solution certainty
in decoding the VLEED spectrum to represent the true situation happened during
reaction.
© The Editor(s) (if applicable) and The Author(s), under exclusive license
to Springer Nature Singapore Pte Ltd. 2020
C. Q. Sun, Electron and Phonon Spectrometrics,
https://doi.org/10.1007/978-981-15-3176-7_16
315
VLEED Capability and Sensitivity
Abstract VLEED offers such a unique tool that collects information of bond geometry, valence density-of states (DOS), and SPB outside the second atomic layer
with high sensitivity and reliability. Based on the principle of Fourier transformation, VLEED calculation derives consistent information obtained with electron
spectroscopy, crystallography, and morphology on an atomic scale.
Highlights
• The ReV(z) diffracts elastically the electron beam and determines its phase shift.
• The ImV(z, E) diffracts inelastically the electron beam and determines is amplitude
loss.
• Covering the valence band energy, VLEED beam is subject to energy loss by
absorption.
• VLEED signal is only sensitive to relaxation of the outermost two atomic layers.
16.1 Uniqueness of Solution
Independent treatment of the geometric and the SPB parameters in simulation of
VLEED spectrum could lead to solution uncertainty [1], because the diffraction intensity depends on the arrangement of scattering centers with different cross-sections
and the interference of the diffracted beams by the SPB. The geometrical arrangement
determines the phase change of diffracted beams. The cross section of diffraction
varies with the effective charges of the scattering centers. The interference determines
the amplitude of the diffracted waves. Therefore, reaction with charge transportation
and polarization modifies the atomic positions and the SPB. Proper combination
of the geometry, SPB and the parametrization wise ensures the solution certainty
in decoding the VLEED spectrum to represent the true situation happened during
reaction.
© The Editor(s) (if applicable) and The Author(s), under exclusive license
to Springer Nature Singapore Pte Ltd. 2020
C. Q. Sun, Electron and Phonon Spectrometrics,
https://doi.org/10.1007/978-981-15-3176-7_16
315