A time-of-flight technique has been used to measure the remnant charge of laser-produced pulses of multicharged ${\mathrm{C}}^{\mathit{k}+}$ (k=1–4), ${\mathrm{Al}}^{\mathit{m}+}$ (m=3–6), and ${\mathrm{Pb}}^{\mathit{n}+}$ (n=2–6) ions incident on a clean amorphous Au surface under UHV conditions. Remnant charge states were investigated for 15°, 30°, and 45° scattering angles for C and Al ions and 15° only for Pb. For all angles considered, C and Pb were found to be completely neutralized after scattering from the Au surface. The remnant singly charged state of Al, however, was detected in all instances in addition to neutral Al atoms with charge fractions being ∼60%. Detailed charge fractions were determined for incident ${\mathrm{Al}}^{\mathit{z}+}$ (z=3–5) with energies ≊400 eV/z. The scattering angle was fixed at 15° while the incoming angle was varied from 3° to 12°. The results obtained could be fitted with the expected form of a decaying exponential. The charge fractions showed a dependence on the outgoing path while being independent of the incoming path. Although the characteristic velocity for a particular incident ${\mathrm{Al}}^{\mathit{z}+}$ charge state (hence constant energy determined by an electrostatic analyzer) was found to be constant, the inclusive case for all three aluminum incident charge states required an energy-dependent characteristic velocity in order to obtain a reasonable fit for the remnant charge fraction as a function of a decaying exponential. The results are interpreted to be indicative of the importance of the ground-state energy level of the projectile as compared to the Fermi level of the metal and how it evolves close to the metal surface as well as the importance of the distance of closest approach of the projectile to the metal first atomic layer.

• Received 9 December 1991

DOI:https://doi.org/10.1103/PhysRevB.45.12019