Defect Mediated Desorption of the KBr(001) Surface Induced by Single Highly Charged Ion Impact

The individual impacts of slow ($300\mathrm{eV}/\mathrm{amu}$) highly charged Xe ions induce nanometer sized pitlike structures on the KBr (001) surface. The volume of these structures shows a strong dependence on the ions potential energy. Total potential sputter yields from atomically flat (001) terraces are determined by imaging single ion impact sites. The dependence of the sputter yield on the ions initial charge state combined with structure formation at low and high-fluence irradiations indicates that agglomeration of defects into complex centers plays a major role in the desorption process induced by the potential energy.

Figure 1

Contact mode AFM topographic images of a KBr(001) surface (a) unirradiated, and (b) irradiated with ${\mathrm{Xe}}^{34+}$ at a kinetic energy of $300\mathrm{eV}/\mathrm{amu}$ and a fluence of $7\times {10}^9{\mathrm{cm}}^{-2}$. Created nanopits are seen as dark spots in (b).

Figure 2

Pit volume (left axis) and corresponding total sputter yield (right axis) as a function of the potential energy of the ions. The corresponding charge states are given on the upper scale. The insets show topographic AFM images ($270\mathrm{nm}\times 270\mathrm{nm}$) for irradiation with the lowest and highest charge state, at fluences of $3.5\times {10}^{10}{\mathrm{cm}}^{-2}$ and $3\times {10}^9{\mathrm{cm}}^{-2}$, respectively.

Figure 3

Topographic contact AFM images (a),(b) and corresponding distributions of pit width (c), (d) and pit depth (e),(f) for: (a),(c),(e) pits created by collective effects during high-fluence irradiation with ${\mathrm{Xe}}^{3+}$, $\Phi =2\times {10}^{13}{\mathrm{cm}}^{-2}$, and (b),(d),(f) pits created by single and double impact of ${\mathrm{Xe}}^{25+}$, $\Phi =1\times {10}^{11}{\mathrm{cm}}^{-2}$. The fluence in (b),(d),(f) is 200 times smaller than in (a),(c),(e) but also 10 times higher than for the single impact irradiation like shown in Fig. 1. The dashed lines in (c),(f) show the corresponding size distribution from a low-fluence ($\Phi <1\times {10}^{10}{\mathrm{cm}}^{-2}$) irradiation.