ERDA, the idea is to place an ion beam source at a grazing angle to the sample. In this set up, the angle is calculated as to allow the incident ions to scatter off of the sample so that there is no contact made with the detector. The physical basis that has given the method its name stems from the elastic scattering of incident ions on a sample surface and detecting the recoiling sample atoms while the incident ions backscatter at such an angle, that they do not reach the detector; this is typically in reflection geometry, illustrated in figure shown: Another method for preventing incident ions from making contact with the detector is to use an absorber foil. During analysis of the elastically recoiled particles, an absorber foil with selected specific thickness can be used to "stop" the heavy recoil and beam ions from reaching the detector; reducing the background noise. Incorporating an absorber into the experimental set up can be the most difficult to achieve. The stopping of the beam using either direct or scattered methods can only be accomplished without also stopping the light impurity atoms, if it is heavier (beam ions) than the impurity atoms being analyzed. There are advantages when using absorber films: 1) The large beam Z1 gives rise to a large Rutherford cross section and because of the kinematics of heavy-on-light collisions that cross section is nearly independent of the target, if M1>> M2 and M ~2Z; this helps in reducing the background. 2) The higher stopping power provides a good depth resolution of ~300 Angstroms, limited in fact by straggling in the absorber. The major criterion for absorber foils used in ERDA is whether a recoiling impurity atom can be transmitted through the absorber, preferably a commercially available metal foil, while stopping heavy particles. Since the lighter atoms leave the absorber with smaller energies, the kinematic calculations do not provide much help. Favorable results have been obtained by using heavier ion beams of approximately 1 MeV/ nucleon. The best overall candidate is the 35Cl ion beam; although, 79Br would give better sensitivity by one order of magnitude compared to the 35Cl ion beam. The mass resolution, of the detector at θ= 0°, of thin samples is ΔM/Δx ~ 0.3 amu/1000 Angstroms of the profile width. With thick samples, the mass resolution is feasible at θ≤30°. In thicker samples there is some degradation