Surface nanopatterning by ion-beam sputtering (IBS) at low and intermediate energies is both a technical and a scientific challenge. When energetic ions impact with a target, a competition between both stabilizing and destabilizing physical mechanisms shapes the surface. Partly motivated by the experimental capability to produce ordered nanodots or control crater formation and growth, many theoretical approaches have appeared in the last few years to improve the early approach by Bradley and Harper. Thus, frequently they focus on how to incorporate new effects directly into an evolution equation for the surface. In contrast, the so-called "hydrodinamic" theory of erosion describes the dynamics at two different levels: that of mobile species diffusing over the very surface and the underlying topography. This approach allows to obtain a consistent effective equation for the surface, and has been proved successful in its comparison with experiments, motivating us to reformulate it from a more rigorous point of view. Specifically, in the spirit of Fluid Mechanics, we describe IBS from symmetries and conservation laws. Our approach takes into account relevant physical mechanisms that take place under the surface (beyond the description of collision cascades), such as e.g. the amorphization of the layers close to the surface, in order to formulate the appropriate constitutive laws and boundary conditions. We also show how previous theories can be understood within this general framework, that may suggest new and intriguing experiments.
2009 Materials Research Society Fall Meeting
Publication date: November 2009.
M. Castro, R. Cuerno, What's happening beneath the surface? A unified physical picture of ion beam erosion, 2009 Materials Research Society Fall Meeting. Boston, United States of America, 30 November - 04 December 2009