Dr. Erhard Rothe
Arrays of Nanobumps Created with Laser Light Applied to Micrometer-Sized Spheres
Research in association with: Ronald Baird and Reema Piparia

Department of Chemical Engineering and Materials Science

Laser-processing of material surfaces has been extensively investigated. The smallest size of the resulting features was, until recently, limited by diffraction to be about half that of the laser beam's wavelength. Others have circumvented that limit with the use of near-field microscopes in which light is directed into a fiber tip and the surfaces are located within the tip's "near-field" radiation. Some applications have been ablation, etching, nanolithography, and chemistry.

We use an alternative approach in which thousands of nanoscale features are simultaneously formed on a surface. The technique starts with a monolayer of transparent spheres, of about 1 micrometer diameter, that lie on a silicon surface. The monodisperse spheres self-assemble into hexagonal arrays starting from a colloidal suspension of spheres. When a laser shot strikes such an array, the light concentrates in a small region lying around the tangent points of each sphere and the surface, so that the surface lies in the "near field." The intensified light serves to structure the surface into hexagonal arrays of nanobumps that lie where the spheres were. Those nanobumps are typically 40nm high and 200nm wide.

Biosketch

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