On the right, you see a picture of a surface which is starting
along a bad path. Light colors represent atoms in high layers
(isolated atoms and clumps we call islands), and dark colors
represent atoms in lower layers (vacancies and pits). Most of
the surface is pretty flat, but there is a big dark-grey pit!
This pit represents a region of the surface which has lagged
behind by a whole monolayer: pits like these will eventually
lead the surface to become rough. Experimentalists have various
ways to test whether their surfaces are growing layer by layer
(flat), or 3D (rough). One way is by using STM to directly image
the layers; another way is to scatter something off the surface
and look for oscillations in the ``Anti-phase intensity''. If a
layer completes and forms a perfectly flat surface, you get
anti-phase intensity of one; if the surface is rough (or flat
but half-covered with a new layer), the antiphase intensity goes
to zero. The dashed line in the picture on the left shows the
anti-phase intensity fo