text: The energy loss of a backscattered ion is dependent on two processes: the energy lost in scattering events with sample nuclei, and the energy lost to small-angle scattering from the sample electrons.  The first process is dependent on the scattering cross-section of the nucleus and thus on its mass and atomic number.  For a given measurement angle, nuclei of two different elements will therefore scatter incident ions to different degrees and with different energies, producing separate peaks on an N(E) plot of measurement count versus energy. These peaks are characteristic of the elements contained in the material, providing a means of analyzing the composition of a sample by matching scattered energies to known scattering cross-sections.  Relative concentrations can be determined by measuring the heights of the peaks.
  The second energy loss process, the stopping power of the sample electrons, does not result in large discrete losses such as those produced by nuclear collisions.  Instead it creates a gradual energy loss dependent on the electron density and the distance traversed in the sample.  This energy loss will lower the measured energy of ions which backscatter from nuclei inside the sample in a continuous manner dependent on the depth of the nuclei.  The result is that instead of the sharp backscattered peaks one would expect on an N(E) plot, with the width determined by energy and angular resolution, the peaks observed trail off gradually towards lower energy as the ions pass through the depth occupied by that element. Elements which only appear at some depth inside the sample will also have their peak positions shifted by some amount which represents the distance an ion had to traverse to reach those nuclei.
  In practice, then, a compositional depth profile can be determined from an RBS N(E) measurement.  The elements contained by a sample can be determined from the positions of peaks in the energy spectrum.  Depth can be determined from the width and shifted position of these peaks, and relative concentration from the peak heights.  This is especially useful for the analysis of a multilayer sample, for example, or for a sample with a composition which varies more continuously with depth.
  This kind of measurement can only be used to determine elemental composition; the chemical structure of the sample cannot be determined from the N(E) profile.  However, it is possible to learn something about this through RBS by examining the crystal structure.  This kind of spatial information can be investigated by taking advantage of blocking and channeling.