Wednesday, May 3, Lori Student Center, Room 228, 4:30pm

Ion-bombardment induced ripple formation on solid surfaces


Mark Bradley
Department of Physics
Colorado State University


When an amorphous solid is eroded by an off-normal incidence ion beam, a ripple topography often results. In this talk, I will discuss a theory explaining the origin of these waves. For incidence angles close to the normal, we find that the ripple wave vector is parallel to the surface component of the beam direction. The ripple orientation is rotated by 90 degrees when the beam is close to grazing incidence. These predictions of the linear theory, and the theoretical expression for the selected wavelength, are in good agreement with experiment. When the instability is fully developed, the waves can have a well-defined wavelength and localized defect structures, in some ways resembling the rolls seen in Rayleigh-Benard convection. Our most recent work is an attempt to understand this new type of pattern formation.
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Please direct any comments to
Gerhard Dangelmayr at gerhard@math.colostate.edu.