Absence of a Crystal Direction Regime in which Sputtering Corresponds to Amorphous Material

Erosion of material by energetic ions, i.e., sputtering, is widely used in industry and research. Using experiments and simulations that, independently of each other, obtain the sputter yield of thousands of individual grains, we demonstrate here that the sputter yield for heavy keV ions on metals changes as a continuous function of the crystal direction. Moreover, we show that polycrystalline metals with randomly oriented grains do not sputter with the same yield as the amorphous material. The key reason for this is attributed to linear collision sequences rather than channeling.

Figure 1

IPFs for 30 keV Ga bombardment of W: (a) BCA simulations of the projected range of Ga; (b) BCA simulations of the sputter yield; (c) MD simulations of the sputter yield; (d) experimental sputter yield from four individual measurements; (e) experimental data of (d) corrected by rotation matrix multiplication according to PCA; (f) secondary electron emission. The white areas in the triangles in (d)–(f) represent crystal orientations for which no grains exist in the measured area.

Figure 2

Number of crystal directions versus sputter yield (green, cyan, and blue lines) and projected range (red line), assuming an isotropic distribution of surface orientations. The average sputter yield of polycrystalline and amorphous W as obtained by the BCA simulations is indicated by the vertical dashed lines. The inset shows an example of a linear collision sequence, which exists only in crystalline targets, observed in the MD simulations.