A study of damage induced in semiconductors and metals during microchanneling measurements

The combination of nuclear analysis techniques and the spatial resolution obtained by microbeams is of great interest in materials characterization. The nuclear microbeam of the laboratory LARN (Namur, Belgium) has been equipped with a goniometer, allowing the use of the microchanneling technique. When using the nuclear microprobe with MeV energy helium ions in RBS channeling analysis we can produce a significant number of defects: the small beam size obtained with the microbeam leads to an increase of several orders of magnitude in the ion dose (ions/surface unit) required for the analysis. In this paper investigations of the defect buildup (increasing rate of dechanneling) for semiconductors (GaSb, GaAs, Si) and metals (Fe, Al, W) as a function of the total incident fluence for a 2.0 MeV focused helium microbeam (about 100 μm in diameter) are discussed. We have observed that, when the microchanneling analysis technique is used, the beam-induced defects accumulate very rapidly on compound semiconductors, but less rapidly on monoatomic samples. We have determined the evolution of χMin values as a function of total helium beam fluences for several targets. These data can be used to estimate the highest ion dose (ions/surface unit) that is compatible with a low sample degradation during the collection of RBS spectra in channeling measurements. (orig.)