Explain the principle and working of X-ray photoelectron spectroscope.

10.B] With neat diagram, explain the principle, construction and working of X-ray photoelectron spectroscope.

Answer:-

• Principle
  • Surface analysis by XPS involved irradiation of the sample by low-energy (and mono-energetic) X-rays and the subsequent analysis of the energy of emitted electrons. Typically used x-rays are K lines of Mg (1.2536 keV) and Al (1.4866 keV).
  • The penetration depth of these photons in solids is limited to a few microns. Thus, interactions take place between the incident photons are the surface atoms leading to the photoelectric emission of electrons.
  • The kinetic energy (K.E.) of the emitted electrons is expressed as KE=hv-B.E+Φ_s. Here ℎv is the energy of the photon, B.E. is the binding energy of the atomic orbital from the electron is realeased, Φ_s is the work-function of the spectrometer.

Construction and Working

1. A typical X-ray photoelectron spectrometer consists of an X-ray source, an electron energy analyser, and a photo-electron detector.
2. X-ray source emits monochromatized x-ray with a narrow line width of energy ℎv falls on the sample and photo electrons are emitted from the sample.
3. The ejected photo-electrons are transferred to an electron energy analyser( An electrostatic hemispherical
4. analyzer (HSA)) through the electron lens and separated according to their kinetic energy.
5. The separated electrons are subjected to channel electron multiplier which is connected to Microcomputer.
6. The transfer lens system retards the photo-electrons there by enhancing the energy resolution of the analyzer (≤ 0.1 eV).