Rutherford Backscattering Spectrometry
Rutherford Backscattering spectrometry (RBS) is most commonly used non-destructive nuclear analytical methods. RBS is widely used for study of thin layers and for study of multilayer systems with thickness from nm to µm. RBS is very suitable for elemental depth analysis. From such measurement it is possible to determine, with some limitations, both the atomic mass and concentration of elemental target constituents as a function of depth below the surface.
Measurement with this method may be performed on amorphous as well as crystalline materials. It involves measurement of the numbers and energy distribution of energetic ions (usually MeV light ions such He+) backscattered from atoms within the near-surface region of solid targets. Ions for RBS are usually light ions (H+, He+) with energy units MeV.
Energy of backscattered ions, which we detect, is connected with energy loss in scattering on the elements nucleus and with the energy loss of ions between passing through the sample. The RBS detection limit is between 1011 – 1015 at.cm-2. RBS depth resolution is an average of 5 nm.
Features of RBS:
high sensitivity for heavy elements on a light substrates
good detection sensitivity for light elements in a heavy matrix only in special cases
good depth resolution (average 5 nm)
Parameters of RBS:
ions: H+, He+
energy of ions: order of MeV
detection limit: up to 1mg/g
depth range: about micrometer
Theory of RBS
Sample is irradiated with light ions (usually 2-3 MeV (H+or He+)) and the elastically backscattered projectiles at large angles are detected. The mass of the target atoms could be identified from the energy of the backscattered projectile. The backscattered particles are detected by the semiconductor detectors Si(Au), the accessible depth 2-10 mm. The heavy element detection limit in the light matrix is up to 1mg/g. The lower mass causes higher transferred energy. The mass resolution is given by detector energy resolution, the energy and projectile mass. The ussage of heavier ions enables us to reach the mass resolution DM<2.