Electronic Stopping of Slow Protons in Oxides: Scaling Properties

Electronic stopping of slow protons in ZnO, VO2 (metal and semiconductor phases), HfO2, and Ta2O5 was investigated experimentally. As a comparison of the resulting stopping cross sections (SCS) to data for Al2O3 and SiO2 reveals, electronic stopping of slow protons does not correlate with electronic properties of the specific material such as band gap energies. Instead, the oxygen 2p states are decisive, as corroborated by density functional theory calculations of the electronic densities of states. Hence, at low ion velocities the SCS of an oxide primarily scales with its oxygen density.
Financial support of this work by the FWF (FWF-Project No. P22587-N20 and FWF-Project No. P25704-N20) is gratefully acknowledged. M. A. and J. I. J. acknowledge financial support by the Gobierno Vasco-UPV/EHU Project No. IT756-13, and the Spanish Ministerio de Economía y Competitividad (Grants No. FIS2013-48286-C02-02-P and FIS2016-76471-P). Fabrication and characterization of VO2 films at Vanderbilt University (CMG and RFH) was supported by a grant from the National Science Foundation (DMR-1207507). A research infrastructure fellowship of the Swedish Foundation for Strategic Research (SSF) under Contract No. RIF14-0053 supporting accelerator operation is acknowledged.