HIGH-RESOLUTION MEDIUM-ENERGY BACKSCATTERING SPECTROMETRY

We describe a new form of backscattering spectrometry using medium-energy ions and time-of-flight detection that is particularly useful in characterizing surfaces and thin films. The technique uses incident ions with energies from a few tens of keV up to about 500 keV. It combines the advantages of conventional Rutherford backscattering, including insensitivity to the scattered ion's charge, with increased surface sensitivity, increased depth resolution and reduced target damage. Several ions have been used successfully for analyses, with He+ and Li+ at 270 keV and C2+ at 500 keV being particularly useful because of the range of cross sections and the resolution for depth profiling that they offer. Measurements of heavy constituents on low-mass substrates have been demonstrated at the 2 x 10(12)/cm2 level and depth resolutions of less than 4 nm are routinely achievable. In this article we review the current status of the technique with particular emphasis on its use in applications which are complementary to conventional MeV Rutherford backscattering.