HIGH-RESOLUTION DEPTH PROFILING IN NEAR-SURFACE REGIONS OF SOLIDS BY NARROW NUCLEAR-REACTION RESONANCES BELOW 0.5-MEV WITH LOW-ENERGY SPREAD PROTON-BEAMS

The application of proton-induced narrow resonances in nuclear reactions as probes for depth profiling near-surface regions of solids has been investigated at projectile energies below 400 keV. The measurements were performed at the Universitat Munster 400 kV accelerator, which provided intense proton beams with an energy spread of about 15 eV. The energy stability of the accelerator was better than +/-3 eV. Narrow resonances in the reactions O-18(p,gamma)F-19, O-18(p,alpha)N-15, Na-23(p,gamma)Mg-24, and Si-29(p,gamma)P-30 were studied. For resonances with an intrinsic width in the electronvolt range, the thermal Doppler broadening dominates the effective energy resolution. With such narrow resonances as probes, contaminants on the surface with a thickness as small as some atomic layers have a significant influence on the shape of the yield curve and for optimal results uhv conditions are required. The method is illustrated with depth profiling experiments of O-18 and Na-23 with potential near-surface depth resolutions of some tens of Angstroms.