In this study, we have investigated temporal evolution of silicon surface topography under 500-eV argon ion bombardment for two angles of incidence, namely 70° and 72.5°. For both angles, parallel-mode ripples are observed at low fluences (up to 2 × 1017 ions cm-2) which undergo a transition to faceted structures at a higher fluence of 5 × 1017 ions cm-2. Facet coarsening takes place at further higher fluences. This transition from ripples to faceted structures is attributed to the shadowing effect due to a height difference between peaks and valleys of the ripples. The observed facet coarsening is attributed to a mechanism based on reflection of primary ions from the facets. In addition, the role of sputtering is investigated (for both the angles) by computing the fractional change in sputtering yield and the evolution of surface roughness.PACS81.05.Cy, 81.16.Rf, 61.80.Jh, 87.64.Dz

In this paper evolution of silicon surface topography, under low energy ion bombardment, is investigated at higher oblique incident angles in the range of 63⁰-83⁰. Si(100) substrates were exposed to 500 eV argon ions. Different surface morphology evolves with increasing angle of incidence. Parallel-mode ripples are observed up to 67⁰ which undergo a transition to perpendicular-mode ripples at 80⁰. However, this transition is not a sharp one but undergoes a series of unusual pattern formation at intermediate angles. Complete smoothening of silicon surface is observed at incident angles beyond 80⁰. The observed patterns are attributed to surface confined viscous flow and sputter erosion under ion bombardment.

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Self-organized pattern evolution on SiO surface under low energy Ar-ion irradiation has been investigated extensively at varied ion energies, angles of ion incidence, and ion flux. Our investigations reveal an instability on SiO surface in an angular window of 40° ̶ 70° and for a comprehensive range of Ar-ion energies (200-1000 eV). Different topographical features, viz. ripples, mounds, and elongated nanostructures evolve on the surface, depending upon the angle of incidence and ion fluence. The results are compiled in the form of a parametric phase diagram (ion energy versus angle of incidence) which summarizes the pattern formation on SiO surface. To understand the evolution of observed patterns, we have carried out theoretical estimation, taking into account the synergetic roles of ion induced curvature-dependent sputter erosion and prompt atomic redistribution. It is shown that irradiation-induced mass redistribution of target atoms plays a crucial role in determining the critical angle of ion incidence for pattern formation on SiO under the present experimental conditions, whereas the contribution of curvature-dependent sputtering needs to be considered to understand the existence of the angular window of pattern formation. In addition, ion-beam shadowing by surface features are shown to play a dominant role in the formation of mounds and elongated structures at higher ion fluences.