Building cavities in microspheres and nanospheres

This paper describes a simple method of sculpturing cavities in silica spheres by reactive ion etching using a polymer as the mask, and investigates the changing process in detail. The morphology of the cavity in the silica structure undergoes transformation in three steps: (1) increase of the diameters of the opening of the cavities; (2) increase of the depth of the cavities; and (3) change in geometry of the resulting structure. As a result, silica bowls or silica rings could be obtained by controlling the etching stage, and this approach can be extended to a wide range, from a micrometer to a nanometer, based on the silica spheres.