Energy Loss Spectroscopy Xiaozhe Zhang 10312014 Electron Energy Loss Spectroscopy Inelastic scattering is a fundamental scattering process in which the kinetic energy of an incident particle is not conserved in contrast to elastic scattering ID: 217688
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Slide1
Introduction to Electron Energy Loss Spectroscopy
Xiaozhe
Zhang
10/31/2014Slide2
Electron Energy Loss Spectroscopy
Inelastic
scattering
is a fundamental scattering process in which the kinetic energy of an incident particle is not conserved (in contrast to elastic scattering).
Inelastic
scattering events might lead to well-defined energy losses, covering a wide energy range from 10
4
to 10
-3
eV:
Core
level excitation: 100
~
10
4
eV (CLEELS)
Plasmon
and
interband
excitation: 1
~
100 eV (EELS)
Phonon
and
adsorbate
vibration excitation: 10
-3
~
1 eV (HREELS)Slide3
Core Level Electron Energy Loss Spectroscopy (CLEELS)
The
energy of the
inelastically
scattered electron is:Slide4
Electron Energy Loss Spectroscopy
The loss peaks are typically
much smaller
than
Auger peaks
, therefore one measures the second derivative.
The loss energy defines the energy levels and CLEELS can be used for
elemental identification
.
As the fine structure of the spectra depends on the density of states (DOS) of the final (empty) states it can be used to identify the unoccupied DOS.Slide5
Electron Energy Loss Spectroscopy
A
plasmon
is a collective oscillation of electron density
in
the bulk and its energy is quantized:
n: number of valence electron per cubic meter, e: electron charge (1.6e-19), ε0:
permittivity of free space (8.8e-12), m: electron mass (9.1e-31)
In many cases there exists also a
surface plasmon
, localized
at the surface, its energy is
:Slide6
Electron Energy Loss Spectroscopy
EELS spectra are recorded either as
N(E) or d2
N(E)/
dE
2
EELS of Al, showing multiple losses
of bulk and surface
plasmons
EELS of SiO
2
layer on
Si. Use
of different primary energies (penetration depth) allows depth profilingSlide7
High-Resolution Electron Energy Loss Spectroscopy (HREELS)
High resolution electron energy loss spectroscopy (HREELS) is a tool used in
surface science
. The inelastic scattering of electrons from surfaces is utilized to study
electronic excitations or vibrational modes
of the surface or of
molecules adsorbed to a surface. Hence in contrast to other electron energy loss spectroscopies (EELS) HREELS deals with small energy losses in the range of 10
−3
eV to 1 eV. It plays an important role in the investigation of surface structure, catalysis, dispersion of surface phonons and the monitoring of epitaxial
growth.Slide8
High-Resolution Electron Energy Loss Spectroscopy
Most frequently HREELS is used to measure
adsorbate
vibrations. Identification of the
adsorbate
species
, the
adsorption site
and the
spatial orientation
of the
adsorbate
is possible.
In
HREELS not only the electron energy loss can be measured, often the angular distribution, of electrons of a certain energy loss, in reference to the specular direction gives interesting insight to the structures on the surfaceSlide9
Thank you for your time!