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:

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:

Electron Energy Loss Spectroscopy EELS spectra are recorded either as N(E) or d2N(E)/dE2 EELS of SiO2 layer on Si. Use of different primary energies (penetration depth) allows depth profiling EELS of Al, showing multiple losses of bulk and surface plasmons

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

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