Transport of electrons induced by highly charged Ni (74 MeV/u) and Cu (9.6 MeV/u) ions in carbon: A study of target-thickness-dependent electron yields.

Abstract

We investigated the transport of heavy-ion-induced electrons in solids by both experiment and numerical simulation. We measured electron yields from the beam entrance and exit surfaces of thin carbon foils (d\ensuremath{\approxeq}3 \ensuremath{\mu}g/${\mathrm{cm}}^{2}$--50 mg/${\mathrm{cm}}^{2}$) bombarded with swift, highly charged ${\mathrm{Cu}}^{\mathit{q}+}$ (q=25--28 and ${\mathit{E}}_{\mathit{P}}$=9.6 MeV/u) and ${\mathrm{Ni}}^{\mathit{q}+}$ (q=26, 28 and ${\mathit{E}}_{\mathit{P}}$=74 MeV/u) ions. We obtained the transport lengths of high-energy (E\ensuremath{\gtrsim}100 eV) electrons and diffusion lengths of slow electrons (E\ensuremath{\lesssim}100 eV) and deduced a mean energy of the ejected electrons (\ensuremath{\approxeq}1 keV at 10 MeV/u and \ensuremath{\approxeq}8 keV at 74 MeV/u). The high-energy electrons represent a fraction of 15--20 % of the total electron yields at 9.6 MeV/u, but up to 35% at 74 MeV/u. We show that backscattering of fast, forward-emitted electrons towards the beam entrance surface cannot be neglected in fast-ion-induced electron emission. The experimental results are used as a benchmark for the improvement of our numerical simulation of the primary stage of the ion-matter interaction. \textcopyright{} 1996 The American Physical Society.