Summary: Spontaneous Pattern Formation from Focused and Unfocused Ion Beam Irradiation
Alexandre Cuenat and Michael J. Aziz
Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138.
We study the formation and self-organization of "ripples" and "dots" spontaneously appearing
during uniform irradiation of Si, Ge, and GaSb with energetic ion beams. Features have been
produced both with sub-keV unfocused Ar+
ions and with a 30 keV Ga+
Focused Ion Beam. We
follow the evolution of features from small amplitude to "nanospikes" with increasing ion dose.
It appears that the edge of the sputtered region influences the patterns formed, an effect that may
make it possible to guide the self-organization by the imposition of lateral boundary conditions
on the sputter instability.
Self-organization of surface morphological features to produce structures of potential use in
nanotechnology is in its infancy. A few processes leading to self-organized patterns, particularly
in heteroepitaxial growth, have been identified and studied. However, control of the self-
organization process remains an issue. We have been investigating alternative processes leading
to self-organized surface structures - in particular, "sputter patterning" produced by unfocused
ion irradiation. Spontaneous rippling of surfaces by ion irradiation was first observed on glass