Transcript Auger electron spectroscopy

Introduction to Electron Energy Loss
Spectroscopy
Xiaozhe Zhang
10/31/2014
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 104 to 10-3 eV:
• Core level excitation: 100 ~ 104 eV (CLEELS)
• Plasmon and interband excitation: 1 ~ 100 eV (EELS)
• Phonon and adsorbate vibration excitation: 10-3 ~ 1 eV (HREELS)
Core Level Electron Energy Loss
Spectroscopy (CLEELS)
The energy of the inelastically
scattered electron is:
ES  EP  (EK   C )
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.
Electron Energy Loss Spectroscopy
• A plasmon is a collective oscillation of electron density in the bulk
and its energy is quantized:
P
 4  ne 2
 
 m




1/ 2
,
E  
• 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:
S 

P
2
Electron Energy Loss Spectroscopy
• EELS spectra are recorded either as N(E) or d2N(E)/dE2
EELS of Al, showing multiple losses
of bulk and surface plasmons
EELS of SiO2 layer on Si. Use of different
primary energies (penetration depth) allows
depth profiling
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.
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 surface
Thank you for your time!