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Why Every XPS Spectra has a Background
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Why Every XPS Spectra has a Background

Understanding Background in XPS Spectrum

Conceptual Overview of XPS Spectrum

  • The presence of a background in every X-ray Photoelectron Spectroscopy (XPS) spectrum is crucial for understanding the data, particularly noted in tungsten spectra.
  • The Y-axis represents the number of electrons counted per second, indicating that the background intensity correlates with electron detection by the XPS detector.

Electron Behavior and Energy Loss

  • The surface can be divided into three regions:
  • A region less than 10 nm where electrons undergo elastic collisions, retaining their energy.
  • A thicker micro-scale region where electrons lose all their energy due to multiple inelastic collisions.
  • In the middle region (just below 10 nm), electrons experience some energy loss but still reach the XPS detector with reduced kinetic energy.

Background Contribution and Energy Conservation

  • The background arises from lower-energy electrons emitted from specific regions, leading to higher binding energies observed in the spectrum.
  • According to conservation of energy principles, photon energy equals binding energy plus kinetic energy; thus, if binding energy increases, kinetic energy decreases correspondingly.

Implications on Electron Energy Levels

  • For example, if photon energy is set at 100 eV and binding energy is at 80 eV, then only 20 eV remains as kinetic energy. This indicates that photoelectrons may have lost significant amounts of their initial energies through elastic collisions.
Playlists: XPS - X-rays Photoelectron Spectroscopy
Video description

In X-rays photoelectrons spectroscopy (XPS), some photoelectrons produce the photoelectrons peaks, which originated from a very thin region ~ 10 nm. These electrons encounter no inelastic scattering and therefore loss no Kinetic Energy (KE) and they contains the MOST important information about the sample. Other type of electrons are generated at a very thick region where these electrons encounter multiple inelastic scattering and eventually lost its total KE. These electrons can not reached the XPS counter. The electrons which make the background of the XPS spectra comes from between these two regions i.e., the ~ 10 nm thin region and very deep thick region. These electrons encounter FEW inelastic collision and lost some of their KE. However, these electrons reach to the XPS detector with less KE and form the background of the XPS spectra. Cheers!