The study and analysis of surfaces involves both physical and chemical analysis techniques.

Several modern methods probe the topmost 1–10 nm of surfaces exposed to vacuum.  These include X-ray photoelectron spectroscopy, Auger electron spectroscopy, low-energy electron diffraction, energy loss spectroscopy, thermal desorption spectroscopy, ion scattering spectroscopy, secondary ion mass spectrometry, dual polarisation interferometry, and other surface analysis methods.  Many of these techniques require vacuum as they rely on the detection of electrons or ions emitted from the surface under study.

Moreover, ultra high vacuum is required (10⁻⁹ mbar or better), as it is necessary to reduce surface contamination by residual gases in the system, e.g. at 10⁻⁶ mbar it only takes 1 second to cover a surface with a contaminant, so much lower pressures are needed for measurements.

Auger Electron Spectroscopy (AES)

When an atom is probed by an external mechanism, such as a photon or a beam of electrons, a core state electron can be removed leaving behind a hole.   As this is an unstable state, the core hole can be filled by an outer shell electron, whereby the electron moving to the lower energy level loses an amount of energy equal to the difference in orbital energies.   Since orbital energies are unique to an atom of a specific element, analysis of the ejected electrons can yield information about the chemical composition of a surface.

Electron Sources

Electron sources are used in vacuum applications to stimulate desorption from surfaces or to 'flood' the surface with electrons to prevent charge build up in ion beam processes such as XPS or SIMS.   They can often be focussed to a small spot size and with the ability to raster the surface of interest.

Ion Sources

Ion guns (sources) are used in many areas of surface physics, and vacuum physics including secondary ion mass spectrometry and ion injection for MBE.  They are available with energies ranging from a few eV to 10's of keV and with beam spot sizes from a few 10's of µm to 10's of mm.

LEED / RHEED

Low Energy Electron Diffraction (LEED) is a state of the art technique for characterizing the surface structure of crystalline solids.   If a crystal is cut along a certain plane, then the atoms near the surface may well be disturbed from their equilibrium positions in the bulk.  This leads to changes in the relative positions of the surface and near surface atoms (surface reconstruction).   Such changes can be explored with LEED.

Reflection High-Energy Electron Diffraction (RHEED) is a versatile analytical tool for characterizing thin films during growth by molecular beam epitaxy, since it is very sensitive to surface structure and morphology.   RHEED is particularly suited to this application as it does not block the direction vertical to the surface of the crystal which is observed, and is particularly sensitive to surface roughness, down to monolayer sensitivity.

Rutherford Back Scattering (RBS)

Rutherford backscattering spectrometry (RBS) is an analytical technique used in materials science.   Sometimes referred to as high-energy ion scattering (HEIS) spectrometry, RBS is used to determine the structure and composition of materials by measuring the backscattering of a beam of high energy ions impinging on a sample.

Secondary ion mass spectrometry (SIMS) is a technique used in materials science and surface science to analyse the composition of solid surfaces and thin films by sputtering the surface of the specimen with a focused primary ion beam and collecting and analysing ejected secondary ions.   These secondary ions are measured with a mass spectrometer to determine the elemental, isotopic, or molecular composition of the surface.  SIMS is the most sensitive surface analysis technique, being able to detect elements present in the parts per billion range.

XPS / ESCA

X-ray photoelectron spectroscopy (XPS or ESCA) is a quantitative spectroscopic technique that measures the elemental composition, empirical formula, chemical state and electronic state of the elements that exist within a material.   XPS spectra are obtained by irradiating a material with a beam of X-rays while simultaneously measuring the kinetic energy and number of electrons that escape from the top 1 to 10 nm of the material being analysed.   XPS requires ultra-high vacuum (UHV) conditions.