Multiple Scattering Causes the Low Energy–Low Angle Constant Wavelength Topographical Instability of Argon Ion Bombarded Silicon surfaces

We show that holes and perpendicular mode ripples that are generated at low argon ion beam energies and incidence angles on room temperature silicon targets (C. S. Madi et al, Phys. Rev. Lett. 101, 246102 (2008) and C. S. Madi et al, J. Phys. Condens. Matter 21, 224010 (2009)) are caused by multiple scattering events from the impingement of the primary ion beam on adjacent silicon shields. We show that in a geometry that minimizes these multiple scattering events, only ultra-smooth stable silicon surfaces are for incidence angles < 50° from normal. We present a revised topographical phase diagram of 250-1000 eV Ar + ion bombarded silicon surfaces in the linear regime of surface dynamics in the absence of secondary scattering effects. It is characterized only by a diverging wavelength phase transition from parallel mode ripples to a flat stable surface as the incidence angle falls below about 50° from normal incidence, and a crossover to perpendicular mode ripples as the incidence angle crosses above about 80°.