Abstract
We have measured heavy-ion-induced (=2,10,18,36,54; 15 keV/u≤/≤600 keV/u secondary-electron (SE) yields from sputter-cleaned entrance () and exit surfaces () of thin solid foils (C, Al, Ti, Ni, and Cu; d≊1000 Å) in ultrahigh vacuum (p Pa). A pronounced increase of the forward to backward SE yield ratio R=/ with increasing is observed. The SE yield to energy-loss ratio =γ/ has been found to be smaller for heavy ions (HI) than for light ions (H and He); i.e., (HI)<(He)<(H). Also, at low projectile velocities (<50 keV/u), the value of increases with decreasing . The velocity and projectile dependence of both R and can be described within simple extensions of Schou’s SE emission transport theory and a semiempirical Sternglass-type model introduced by Koschar and co-workers as caused by nonequilibrium projectile energy losses near the surfaces. The near-surface energy losses are reduced compared to tabulated bulk energy loss values both for forward and backward emission under the assumption of a proportionality between SE yields and dE/dx. The -dependent reduction factors, i.e., the ratios /, as well as material parameters Λ=γ/, are deduced from the SE yield measurements. Nevertheless, a rough overall proportionality γ∼dE/dx over four decades of both forward and backward secondary-electron yields γ and electronic energy losses dE/dx in a wide range of projectile velocities (15 keV/u ≤/≤16 MeV/u) and projectile nuclear charges (1≤≤92) is found.
- Received 31 July 1989
DOI:https://doi.org/10.1103/PhysRevA.41.2521
©1990 American Physical Society