High resolution electron energy loss spectroscopy

The high-resolution electron energy loss spectroscopy, and high-resolution electron energy loss spectroscopy (English High-Resolution Electron Energy Loss Spectroscopy, HREELS ) is an analytical method of surface physics. The measurement method is based on the uneleastischen scattering of electrons on a surface to characterize electronic excitations or vibrational modes of the surface or of adsorbates (eg atoms or molecules ) on this. In contrast to other electron energy loss spectroscopies (EELS ) small energy losses in the range of 1 meV are analyzed to 1 eV, which corresponds to the energy of light in the infrared range. The resulting spectra are similar to those in other spectroscopies of the same energy range as the infrared or Raman spectroscopy.

Operation

In the electron energy loss spectroscopy, an electron beam energy to a defined sample surface, usually a solid, fired (primary electron beams). These electrons interact with the sample and experience, depending on their primary energy characteristic energy losses due to inelastic scattering from the surface. The scattered electrons are then analyzed for energy. The intensity of each energy losses is recorded by the analyzer, and from this created a spectrum ( see chart). In order to meet the requirements of a high energy resolution is a special construction is needed. The most common case is a construction which. Harald Ibach et al has been developed. This consists of a double monochromator and an analyzer. Since magnetic fields are difficult to shield and residual magnetic fields, particularly in the scattering chamber of the spectrometer, the energy resolution will greatly reduce used in all parts of the energy-dispersive spectrometer only static methods. The monochromator and analyzer here are similar to those of a hemispherical analyzer. However, since much higher electron currents must be reached only 127 ° designs are used, rather than the 180 ° design of hemispherical analyzers. After the electrons have passed through the analyzer they are detected using a channeltron.

In high-resolution electron energy loss spectroscopy, the energy of the primary electrons is usually less than 10 eV. In addition, a special high-resolution spectrometer is used to detect even very small differences in the spectrum of the secondary electron beam.

Application

HREELS (for example, in the analysis of thin films ), and surface reactions (such as catalytic reactions ) are used inter alia in the study of surfaces. Furthermore, let the bonding of adsorbates ( atoms and molecules ) enlighten on solid surfaces.