rutherford backscattering spectroscopy abbr., RBS (rus. спектроскопия резерфордовского обратного рассеяния otherwise спектроскопия рассеяния быстрых ионов abbr., РОР) — a type of ion scattering spectroscopy based on analysis of energy spectra of He+ ions or protons with energies of 1-3 MeV scattered in the direction opposite relative to the sample.

Description

Rutherford backscattering spectroscopy, as well as ion scattering spectroscopy, makes it possible to acquire information about the chemical composition and crystallinity of samples as a function of the distance from the sample's surface (depth) and about the surface structure of a single-crystal sample. The main feature of this method is the use of high-energy ions which penetrate deep inside a solid body and are scattered back from deep-lying atoms. The energy lost by an ion in this process is the sum of two contributions. First, it is the continuous loss of energy when the ion moves back and forth within the solid body's volume (the so-called stopping loss). The rate of energy loss for stopping (stopping power, for most materials is well known which facilitates switching from the scale of energy to the scale of depths. Second, it is a single-time loss of energy in scattering whose magnitude is determined by the mass of the scattering atom. As an example, the diagram on the Figure shows the formation of the spectrum of a sample which is a thin film on a substrate. A film of thickness d manifests itself in the spectrum as a plateau of width ΔE. The right edge of the plateau corresponds to ions elastically scattered from the surface; the left edge – to ions scattered from the film atoms on the film-substrate interface. Scattering from the substrate atoms at the interface corresponds to the right edge of the substrate signal.

To study the structure of monocrystal samples with Rutherford backscattering spectroscopy, the channeling effect is used. The essence of this effect is that when the ion beam is oriented along the main monocrystal symmetry directions the ions that have escaped direct collision with the surface atoms can penetrate deeply into the crystal to a depth of up to hundreds of nanometres moving through the channels formed by rows of atoms. By comparing the spectra generated when the ion beam is orientated along the channeling directions and along directions different from them, information on the crystalline perfection of the sample can be obtained. Analysing the values of the so-called surface peak, which is a consequence of direct collision of ions with surface atoms, information about surface structure can be obtained such as the presence of reconstructions, relaxations and adsorbates.

Illustrations

Schematic diagram of spectrum of ions with mass 
Schematic diagram of spectrum of ions with mass m1 and initial energy E0, scattered from a specimen that is made up of a substrate consisting of atoms with mass m2 and a film from atoms with mass m3 having thickness d. For simplicity purposes, both the film and the substrate are considered amorphous, which allows avoiding structural effects [2].

Authors

  • Zotov Andrey V.
  • Saranin Alexander A.

Sources

  1. Oura K. et al. Surface Science: An Introduction // Springer, 2010 - 452 pp.
  2. Feldman L. C., Mayer J.W., Picraux S. T. Materials analysis by ion channeling: Submicron crystallography. — N.Y.: Acad. press, 1982. — 300 p.

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