Doubly Differential Electron Yields from Thin Copper Foils Induced by Fast Ion Impact

The double-differential yields of electrons ejected from thin metal foils can provide detailed information on the transport properties of secondary electrons produced within condensed phase material by fast charged particles. Models of charged-particle track structure in condensed phase material depend on theoretical elastic and inelastic scattering cross sections based on material parameters. Because of the uncertainties in theoretical methods used to describe low-energy electron scattering in condensed matter and the infeasibility of direct measurements of cross sections in the condensed phase, electron transport models are tested by comparison of calculated and measured spectra of electrons that have undergone transport through the bulk and exited through the surface. Since energy and angular resolved electron yields provide the most stringent tests of theory, and electron scattering cross sections are most uncertain for low energies, we have applied time-of-flight methods to focus on the low-energy electrons emitted from thin (1 mum) copper foils produced by the transmission of 2- and 6-MeV protons and 1-MeV/u fluorine ions. Electron emission spectra for electron energies from 1 eV to several keV and emission angles from 15 to 155 degrees are presented. Although residual electric and magnetic fields are observed to affect spectra for electron energies less than about one electron volt, the data provide detailed information on low-energy electron transport in a region where elastic and inelastic electron scattering cross sections are most uncertain.