When an electric field is placed across a thin polymer film on a conducting surface--such as gold, aluminum or in this case, silicon, small waves on the surface of the film are amplified and grow into columns. Here, in this optical micrograph, the formation of the columns was captured when the columns began to merge together. This occurs since the system is trying to reduce the amount of surface. If you look carefully at the image, there is a characteristic periodicity in the features that have formed, which tells you about the properties of the polymer. The different areas in the film result from slight changes in the film thickness across the film. Each of the features in this image is about the size of a human hair.
Image credit: ©VISUAL, Materials Research Science and Engineering Center, University of Massachusetts, Amherst