  Ga-rich GaAs (001) surfaces are successfully observed during high-temperature
annealing by scanning tunneling microscopy (STM). With a substrate temperature
of 550 C, reflection high-energy diffraction patterns and reflectance
anisotropy spectra confirm a (4x2) Ga-stabilized surface. STM images clearly
show alteration of the surface reconstructions while scanning. It is postulated
that detaching and attaching of Ga adatoms may be the cause of these surface
dynamics. For these conditions it is determined that zeta(4x4), zeta2(4x4) and
zeta(4x6) reconstructions co-exist on the surface. The zeta2(4x4)
reconstruction contains a Ga tetramer cluster and in more Ga-rich conditions,
the zeta2(4x6) surface has a Ga octamer cluster.

Atomic and Molecular Clusters;Chemical Physics