STM 2D and 3D images of the same area on a Ge hut cluster facet: (a) 2D micrograph and (b) 3D topograph; h
Ge = 10Å, T
gr = 360°C, U
s = +2.1 V, I
t = 80 pA. The sides of the cluster base lie along the  direction; structural units revealed on the free surfaces of the (001) terraces and interpreted as PD are marked out.