The preparation of submicrometer-sized rings by embedding and selective etching of spherical silica particles

Silica particles were embedded in a polymer layer on a water surface in such a way that they protruded out of the top and the bottom surfaces, Etching of this layer with hydrofluoric acid vapors gradually removed the particles to yield membranes with pores that continuously widen until the particles are completely removed. Removing the polymer at intermediate stages of etching revealed that the particles are first converted into rings and sickles before they are finally completely destroyed.