Electron Backscatter Diffraction (EBSD)
Platinum thin film. The smallest grains in this map are less than 20 nm wide.
It should be noted while grains as small as 8 nm have been imaged, these grains are at the tail end of a distribution with an average grain size of approximately 50 nm.
M. M. Nowell (1998). "Texture and Grain Boundary Structure Dependence of Hillock Formation in Thin Metal Films." Materials Research Society Symposium Proceedings 516: 115-120.