X-ray Photoelectron Spectroscopy (XPS)

X-ray photoelectron spectroscopy (XPS), also known as ESCA (electron spectroscopy for chemical analysis) is a surface analysis technique which provides both elemental and chemical state information virtually without restriction on the type of material which can be analysed. The sample is illuminated with x-rays - monochromatic or unfiltered Al Kα or Mg Kα - and photoelectrons are emitted from the surface. The kinetic energy of these emitted electrons is characteristic of the element from which the photoelectron originated. The position and intensity of the peaks in an energy spectrum provide the desired chemical state and quantitative information.

Ultraviolet Photoemission Spectroscopy (UPS)

Ultra violet photoemission spectroscopy (UPS) is analogous to XPS but the excitation source is a helium discharge source.  Depending on the operating conditions of the source the photon energy can be optimised for He I = 21.22eV or He II = 40.8eV which is significantly lower energy than Al or Mg Kα used in XPS.  This technique measures the valence electrons and can be used to determine the sample work function. 

Reflection electron energy loss spectroscopy (REELS)

Electron energy loss spectroscopy (EELS) involves the exposure of the sample to a focussed beam of monoenergetic electrons, typically < 3keV.  As these electrons interact with the material some of them will undergo inelastic scattering whereby they lose some kinetic energy. 

Ion Scattering Spectroscopy (ISS)

A beam of positive ions frequently derived from He or Ar is directed at the surface. Some of these ions are reflected with the loss of energy appropriate to the simple binary elastic collision of the ion beam with a particular surface atom.  An ISS spectrum is easily obtained by recording the number of scattered primary ions collected per second as a function of their energy from zero to the energy of the primary beam. The technique is uniquely sensitive to the outermost layer of the surface and is complementary to SIMS (secondary ion mass spectrometry).

Inverse photoemission spectroscopy (IPES)

As the name suggests, the technique of inverse photoemission spectroscopy (IPES) is the opposite of the much more common photoemission (XPS) process.  It relies on incident low energy electrons interating with a materials 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.  

Auger Electron Spectroscopy (AES)

Auger electron spectroscopy (AES) employs a beam of electrons as surface a probe. As a result of electronic rearrangements within the atoms, Auger electrons characteristic of each element present at the surface are emitted from the surface.   Since the probe electrons can be focused to diameters <0.5μm high spatial resolution analysis (scanning Auger microprobe, SAM) can be performed.  Rastering the focused electron beam synchronously with a video display, using scanning electron microscope (SEM) techniques, produces physical images and element distribution maps of the surface.