Heavy ion backscattering analysis with a time-of-flight detector

Abstract

We describe a time-of-flight spectrometer for heavy ion RBS. Start and stop signals for the flight time measurement are obtained by detecting the secondary electrons emitted from two thin foils traversed by the ions. MicroChannel plates are used to provide very fast timing signals. The achieved energy resolution of the system is 30 keV (FWHM) at 2 MeV and 75 keV at 10 MeV for 35Cl, which permits a depth resolution of approximately 100 Å for indium profiles in GaAs (normal beam incidence). For 16O the energy resolution is 45 keV at 6 MeV and 110 keV at 12 MeV. We present RBS spectra of thin-layer multielement targets. As possible applications we show indium profiles in In x Ga 1− x As heterostructures, As and Ga profiles in a thin layer GaAs sample and a measurement of the silver isotopic ratio in a sputtering experiment.