Measurement of the stopping force of 0.05 MeV/u–0.5 MeV/u C, Si and Co ions through molybdenum foils by time of flight spectrometry

The stopping force of energetic ions in matter is of importance in many aspects of materials research and development using ion beams. Common applications include ion implantation, ion beam modification of materials and ion beam analysis. In most instances stopping force data is obtained from semi-empirical and theoretical formulations. While the accuracy of these data sources is now generally acceptable for light ions (H, He), more work still needs to be done to improve their predictive accuracy for heavier ions (Z ≥ 6). In this work we describe a simple experimental procedure used to generate stopping force data of carbon (C), silicon (Si) and cobalt (Co) ions through molybdenum (96Mo) over a continuous range of energies between 0.05 MeV/u and 0.5 MeV/u. The measurement was carried out using a Time of Flight – Elastic Recoil Detection Analysis (ToF-ERDA) set up. A 40 MeV 197Au9+ beam was used to recoil C, Si and Co ions from thick carbon, silicon dioxide and cobalt targets, respectively, towards a Mo stopper foil. The energy loss of the incident recoils through the stopper foil was calculated from the measured ToF across a fixed path length, with and without the stopper foil, and the stopping force then determined as the ratio of the energy loss to the measured foil thickness. Results were compared to semi-empirical calculations using Ziegler's Stopping and Range of Ions in Matter (SRIM) code, Sigmund and Schinner's ab initio theory as implemented in their PASS code and ab initio calculations using Grande and Schiewietz’s Convolution approximation for swift Particles (CasP 6.0) code. Results show notable differences between the theoretical formulations themselves, which makes comparison with experiment an intractable task. That said though, CasP performs better than the other two codes at low energies for the three ions studied, more so for carbon. At higher energies, towards the Bragg peak, all three codes overestimate experiment, to varying degrees.