Impact Features Induced By Single Fast Ions Of Different Charge-State On Muscovite Mica

The influence of the charge state q on surface modifications induced by the impact of individual fast, heavy ions on muscovite mica was investigated. Beams of 593 MeV197 Auq+ with well-defined initial charge states over a relatively broad range of values (30 to 51) and at different irradiation geometries were used. At normal incidence, the impact features are rounded protrusions (hillocks) with greater than or similar to 20 nm in diameter. At grazing angles, besides the hillocks, craters and elongated tails (up to 350 nm-long) extending along the direction of ion penetration are produced. It is shown that the impact features at normal incidence depend strongly on the initial charge state of the projectiles. This dependence is very weak at grazing angles as the ion reaches the equilibrium charge state closer to the surface. At normal ion incidence, the hillock volume scales with q(3.3 +/- 0.6). This dependence stems largely from the increase in the hillock height, as a weak dependence of the diameter was observed.