RBS
IBA Techniques

Rutherford backscattering spectrometry (RBS) is a powerful analytical technique used in materials science for the determination of the composition (and structure when combined with ion channeling). It is based on the measure of a backscattered beam of high energy ions impinging on a sample. At CMAM, the RBS capabilities are available in several experimental systems, comprising the Standard, the Internal µ-beam, and the External µ-beam lines.

RBS is one of the best-established IBA techniques in thin film characterization, in which a high energy (1-10 MeV) beam (helium or hydrogen) is directed at a sample. The ions that are elastically scattered by nuclei in the sample are detected: the higher the mass of an atom that is hit by a ion beam, the higher the energy of the ion will be after backscattering. This results in mass discrimination and, by counting the scattered ions as a function of energy, the number of atoms of each element present can be determined.

Apart from mass information, the main skill of RBS is the depth resolution (in the nm scale). During the flight path through the sample, the ions lose energy, and this energy loss per unit distance is known for every material, allowing the conversion of the RBS spectrum into a depth profile. For example, an ion scattered at a certain depth will lose more energy (on the way in and out of the target) than an ion scattered by the same atom but at the sample surface.

RBS colleted spectra

(a) RBS collected spectrum at the 3.035 MeV oxygen resonance for the oxidized sample at 700 ºC in O2+Ar enviroment. (b) Corresponding depth profile



Applications:

RBS:

  • - Composition of films, multilayers and bulk material
  • - Implantation profiles including dose calibration
  • - Surface and bulk contamination
  • - Interface mixing and reaction
  • - Diffusion profiles

RBS-Channeling:

  • - Epitaxial growth
  • - Implantation damage
  • - Polishing damage
  • - Lattice location of dopants and contaminants in single crystals

Values at CMAM:

  • - H or He beam between 1-10 MeV
  • - Fast measurement (10-20 min)
  • - Good control of the sample position (precise goniometer)
  • - 12 keV resolution with Si planar detectors