RBS

In RBS an energetic (1-3 MeV) beam of He ions is incident on the surface and the energy spectrum of the backscattered ions is recorded. The energy loss of the He ions is predominantly inelastic but there are occasional elastic collisions (~ one in 4000) resulting in a backscattering event. The energy of these backscattered particles (governed by the kinematic factor) provides information regarding the mass of the host atom from which the scattering event has occurred, which then provides a mass scale. At the same time the rate of energy loss of the ions, combined with knowledge of the stopping power cross sections of He in the matrix, provides a depth scale. One can then derive concentration vs. depth from the resulting spectra.

RBS is the only surface analysis technique, which does not rely upon use of standards for quantification. The sensitivity in RBS is a function ~ Z². and hence it is best suited for analysis of heavier elements or layers on lighter substrates.

The technique is suitable for depth profiling of thin film structures, and determination of stoichiometry in oxides and nitrides or silicides.

Other applications include determination of Ge fraction in SiGe, Al or In fraction in GaN and AlGAs bearing in mind that the RBS measurements make no assumptions regarding the degree of relaxation of such layers.

In channelling mode the beam is aligned in a low index crystallographic plane of the host material will allow quantitative measure of damage e.g. dislocations, stacking faults, interstitials and point defects. It can also be used for atom location in the lattice.

The main application areas are damage and damage recovery studies in solids.

NRA and ERD

For the measurement of light elements Nuclear Reaction Analysis (NRA) and Elastic Recoil Detection (ERD) are employed.
In NRA the yield of the nuclear fragments (a, g)  are measured. These nuclear fragments are a result of resonant reactions produced from the energetic He or H reactions with the host atoms.
The applications include accurate and absolute determination of N and O in thin oxynitrides.

ERD measures forward scattered elements not backscattered elements. Elements which are lighter than the projectile element are scattered forward, therefore H can be measured by appropriate positioning of a detector in relation to the sample.
The concentration of these elements can be quantitatively measured using the same principles as RBS.