Introduction to Electron Energy Loss Spectroscopy

Xiaozhe Zhang10/31/2014

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:

)( CKPS EEE

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:

• 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:

E

m

neP ,

42/12

2P

S

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!