We have measured heavy-ion-induced ($Z_P$=2,10,18,36,54; 15 keV/u≤$E_P$/$M_P$≤600 keV/u secondary-electron (SE) yields from sputter-cleaned entrance (${\gamma }_B$) and exit surfaces (${\gamma }_F$) of thin solid foils (C, Al, Ti, Ni, and Cu; d≊1000 Å) in ultrahigh vacuum (p${=10\mathrm{}}^{\mathrm{-}7}$ Pa). A pronounced increase of the forward to backward SE yield ratio R=${\gamma }_F$/${\gamma }_B$ with increasing $Z_P$ is observed. The SE yield to energy-loss ratio ${\Lambda }^{\mathrm{*}}$=γ/$S_e$ has been found to be smaller for heavy ions (HI) than for light ions (H and He); i.e., ${\Lambda }^{\mathrm{*}}$(HI)<${\Lambda }^{\mathrm{*}}$(He)<${\Lambda }^{\mathrm{*}}$(H). Also, at low projectile velocities ($v_P^2$<50 keV/u), the value of ${\Lambda }^{\mathrm{*}}$ increases with decreasing $v_P$. The velocity and projectile dependence of both R and ${\Lambda }^{\mathrm{*}}$ 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 $S_e^{\mathrm{*}}$ near the surfaces. The near-surface energy losses are reduced compared to tabulated bulk energy loss values $S_e$ both for forward and backward emission under the assumption of a proportionality between SE yields and dE/dx. The $Z_P$-dependent reduction factors, i.e., the ratios $S_e^{\mathrm{*}}$/$S_e$, as well as material parameters Λ=γ/$S_e^{\mathrm{*}}$, 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 ≤$E_P$/$M_P$≤16 MeV/u) and projectile nuclear charges $Z_P$ (1≤$Z_P$≤92) is found.

• Received 31 July 1989

DOI:https://doi.org/10.1103/PhysRevA.41.2521