microripple

Microripple refers to a regularly spaced pattern of ridges and troughs that forms on solid surfaces at micrometre or nanometre scales when the surface is subjected to certain processing conditions. These patterns resemble small-scale dunes or ripples and are typically characterized by a well-defined wavelength and amplitude that depend on the material and the process.

Formation mechanisms: The most studied route is ion-beam sputtering and oblique-angle deposition, where an instability caused by curvature-dependent erosion and surface diffusion yields oriented ripple structures. The ripple orientation is controlled by the incidence angle and can be parallel or perpendicular to the beam. The wavelength and amplitude depend on ion energy, flux, substrate temperature, diffusion rates, and crystallography. Similar microripples can also arise during chemical etching, thermal evaporation, or mechanical texturing, where surface mobility drives pattern formation.

Observation and scale: Microripples are detected with atomic force microscopy, scanning electron microscopy, or transmission electron microscopy. Wavelengths typically range from a few nanometres to sub-micrometre scales, though larger patterns can occur under certain conditions. The patterns may coarsen or rotate with time or under changing processing parameters, and may reach steady-state in some systems.

Applications and relevance: Controlled microripple formation provides a route to nanoscale templates for plasmonics, photonics, and surface engineering, including changes to wettability, friction, and optical reflectivity. They are also studied as a model system for pattern formation and surface dynamics.