Figure 3

SEM images of evolved nanostructures grown at 950°C. (a) Overall top view SEM image of the sample obtained with the concentration gradient of Si vapor source, where the gas flow direction is indicated by double arrows. (b) SEM image of a single post from the upper part indicated in (a). (c) SEM image of a single post from middle part indicated in (a). (d) SEM image of a single post from the bottom part indicated in (a).