THIN-LAYER ANALYSIS WITH HEAVY-ION RBS

Rutherford backscattering with heavy ions offers some specific advantages for the analysis of surfaces and very thin films. Due to the larger dependence of the kinematical factor on the target mass the mass resolution is increased. In addition, the high energy loss of the heavy ions allows for very good depth resolution at the sample surface. In this work we present the results obtained with C-13, O-16, Si-28, and Cl-35 beams of energies between 10 and 25 MeV. Even for the heaviest target elements (200 amu) a mass resolution of better than 1% (FWHM) can be obtained by choosing the optimum projectile mass and energy. A depth resolution of approximately 1 mug/cm2 (i.e. a few nm) is reached at the sample surface. For the detection of the backscattered ions a time-of-flight spectrometer has been used in order to obtain a sufficiently high energy resolution for the heavy projectiles. The details of this apparatus and experimental results of the analysis of a variety of thin layer systems are presented.