Rutherford Backscattering Spectrometry (RBS) is an element specific probe used to characterize thin films. The facility where our work is done is located at SUNY@Albany in the ion accelerator laboratory (click for a picture of the beamline). The theory behind RBS is that charged ions are incident upon a sample at energies on the order of MeV's. These ions penetrate the sample to varying depths depending on the type of beam, the type of sample, and the beam energy. A measurable amount of ions are then backscattered by atoms throughout the sample. Using a detector to collect the backscattered ions and their spectrum of energies, this information can provide a depth profile of each element in the sample. The schematic (above) shows the basic experimental setup. The incoming ion beam is passed through a series of microslits which reduce the beam spot size to several microns. This microbeam allows for local probing of non-uniform samples (such as integrated circuits).
The graph (below) shows a simulation of the RBS data for a 1.0 MeV Ne+ ion beam probing a 8500 Angstrom Al-0.5%Cu film. The right edge of the spectrum is due to copper lying at the surface and the width can be interpreted to give a depth profile of the copper concentration.