ABSOLUTE CALIBRATION OF THE O-16 (ALPHA,ALPHA) O-16 ELASTIC-SCATTERING RESONANCE AT 7.30-7.65 MEV AND APPLICATIONS TO OXYGEN DEPTH PROFILING

The differential cross-section of the O-16(alpha, alpha)O-16 elastic scattering resonance at 7.30-7.65 MeV has been calibrated with an overall accuracy of 4% at 170-degrees scattering angle (laboratory frame of reference) using anodized Ta2O5 films of pre-calibrated thickness as standards. This extremely strong (about 170 times the Rutherford cross-section) and broad (about 300 keV wide) resonance varies slowly with energy in the range 7.34-7.64 MeV, has a maximum value of 837 mb/sr at 7.61 MeV, and falls off abruptly above 7.64 MeV and below 7.34 MeV. The angular dependence of the resonance was measured in the range 140-172-degrees at incident energy 7.62 MeV and was found to increase monotonically toward 180-degrees. This strong resonance allowed us to measure the oxygen content in the very heavy element target ThO2 pellets and in oxidized InP substrates with detection sensitivity in the atomic monolayer range. The large width of this resonance allowed oxygen depth profiling to several microns with depth resolution a few tens of nm. Measurements combined with RUMP computer simulations using TRIM stopping cross-sections and our measured values of the elastic resonance scattering cross-section have been used to depth profile SiO2 surface and buried layers in SIMOX structures.