the experiments performed by Compsoto, et al., ERDA spectrum was obtained for a thin film of polystyrene (PS) on a deuterated polystyrene (dPS) matrix after annealing for 240 seconds at 171 °C. This spectrum is shown in figure 16 on the left. It must be noted that the plot above is simply the normalized yield at each channel number from a thin dPS layer (about 200 Angstroms) on top of a thick PS. Normalized yield is usually the number of atoms detected. Channeling, however occurs when a beam of ions is carefully aligned with a major symmetry direction of a single crystal, such as a crystal axis or a plane. In this condition, most of the beam is steered through the channels formed by the string of atoms. Channeled particles cannot get close enough to the atomic nuclei to undergo scattering. Several mathematical operations were then performed, electronically, to obtain a concentration versus depth-profile as shown below in figure 17. Please refer to the source for detailed explanation of the mathematical equations. In addition to all these applications, ERDA is one of the methods to follow elemental transport mechanism. More importantly, hydrogen transport near interfaces induced by corrosion and wear can be probed using ERDA. ERDA can also be used to perform composition diagnosis in various media. Characterizing how polymer molecules behave at free polymer surfaces at interfaces between incompatible polymers and at interfaces with inorganic solid substances is crucial to our fundamental understanding and for improving the performance of polymers in high-tech applications. For example, the adhesion of two polymers strongly depends on the interactions occurring at the interface, between polymer segments. LI-ERDA is one of the most attractive methods for investigating these aspects of polymer science quantitatively. A typical LI- ERDA spectrum obtained using this technique to study elemental concentration and depth profile of polymers is shown in the figure 18 below. It is ERDA spectra of a thin (20 nm) dPS tracer film on a thick (500 nm) PS matrix. Hydrogen and deuterium profiles can be measured using various polymer blends by using this technique. Green and Russel have studied the segregation of deuterated polystyrene/polymethamethacrylate copolymer at the interface of polystyrene, and polymethylmethacrylate homopolymer at the interface of polystyrene and polymethylmetacrylate homopolymer using ERDA with 2.8 MeV 4He+ ions. They also studied the interface properties of copolymers/Al or Si structures. Figure 19 shows the results obtained which