Abstract
The temporal evolution of a periodic ripple pattern on a silicon surface undergoing erosion by argon ion bombardment has been studied for two angles of ion incidence of 60° and 70° using ex situ atomic force microscopy (AFM) in ambient condition. The roughness amplitude grows exponentially with sputtering time for both the angle of ion incidence followed by a slow growth process that saturates eventually with almost constant amplitude. Within the exponential growth regime of amplitude, however, ripple wavelength remains constant initially and increases subsequently as a power law fashion , where for a 60° angle of ion incidence followed by a saturation. Wavelength coarsening was also observed for 70° but ordering in the periodic ripple pattern is destroyed quickly for 70° as compared to 60°. The ripple orientation, average ripple wavelength at the initial stage of ripple evolution, and the exponential growth of ripple amplitude can be described by a linear continuum model. While the wavelength coarsening could possibly be explained in the light of recent hydrodynamic model based continuum theory, the subsequent saturation of wavelength and amplitude was attributed to the effect of geometrical shadowing. This is an experimental result that probably gives a hint about the upper limit of the energy of ion beam rippling for applying the recently developed type of nonlinear continuum model.
- Received 1 March 2007
DOI:https://doi.org/10.1103/PhysRevB.76.075323
©2007 American Physical Society