Comparison of top-view FESEM images of the three samples: (a) S3, (b) S2, (c) S1. (d) High-resolution FESEM image of sample S1. The positions (red circles) indicate that sub-10-nm gaps have been formed between the neighboring particles on this film.
Zhu et al. Nanoscale Research Letters 2012 7:613 doi:10.1186/1556-276X-7-613