High-resolution elastic recoil detection utilizing Bayesian probability theory

Abstract

Elastic recoil detection (ERD) analysis is improved in view of depth resolution and the reliability of the measured spectra. Good statistics at even low ion fluences is obtained utilizing a large solid angle of 5 msr at the Munich Q3D magnetic spectrograph and using a 40 MeV 197Au beam. In this way the elemental depth profiles are not essentially altered during analysis even if distributions with area densities below 1×10 14 atoms/cm 2 are measured. As the energy spread due to the angular acceptance is fully eliminated by ion-optical and numerical corrections, an accurate and reliable apparatus function is derived. It allows to deconvolute the measured spectra using the adaptive kernel method, a maximum entropy concept in the framework of Bayesian probability theory. In addition, the uncertainty of the reconstructed spectra is quantified. The concepts are demonstrated at 13C depth profiles measured at ultra-thin films of tetrahedral amorphous carbon (ta-C). Depth scales of those profiles are given with an accuracy of 1.4×10 15 atoms/cm 2.