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Inverse photoemission spectroscopy

The technique of inverse photoemission spectroscopy (IPES) is the opposite of the much more common Photoelectron spectroscopy process.  It relies on incident low energy electrons interacting with a material's unoccupied orbitals in the conduction band. As these electrons make the direct transition to fill the unoccupied states, the photons that are emitted are measured.  These photons are detected as a function of the kinetic energy (KE) of the incident electron beam.

KEY POINTS

  • Reversed process
  • Electron hits the surface
  • 3-step process
    • coupling into unoccupied state (conduction)
    • decay through scattering
    • photon emission
  • Electron energies above the Fermi level are measured
  • Energy \(\hbar \omega = E_i - E_f\)
  • Energy difference can be calculated with outgoing and incoming energy
  • Detection of energies between the Fermi and vacuum level is possible.
  • Angle resolved inverse photoemission can be used to obtain surface states.