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We report the growth of nano-ripple on, initially, smooth Si surface due to chemically guided additional instability generation during 10 keV C+ bombardment at grazing (700) ion incidence. Also, the transformation of the ripple structure to triangular nano-pyramidal structure at higher ion fluence is investigated in details. It is shown that the chemical nature of the surface changes due to silicon carbide formation at the ion impact sites, and the surface becomes a mixture of Si and SiC. The differential sputtering of Si from pure Si and SiC, generates an additional instability which leads to trigger the ripple pattern on the surface. The variation of height amplitude, lateral correlation length and slope angles of the developed structures are investigated and explained in terms of existing continuum theory. At very high ion fluence the transformation of the structure into three dimensional triangle (octahedron) is revealed and the mechanism is explained in the light of variation of local ion impact angel and its consequent effects.

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