Twins and their boundaries during homoepitaxy on Ir(111)

The growth and annealing behavior of strongly twinned homoepitaxial films on Ir(111) have been investigated by scanning tunneling microscopy, low-energy electron diffraction, and surface x-ray diffraction. In situ surface x-ray diffraction during and after film growth turned out to be an efficient tool for the determination of twin fractions in multilayer films and to unravel the nature of lateral twin crystallite boundaries. The annealing of the twin structures is shown to take place in a two-step process; first, the length of the lateral twin crystallite boundaries is reduced, without affecting the amount of twinned material, and then, at much higher temperatures, the twins themselves anneal. Within moderately annealed films lateral twin crystallite boundaries are visible at the film surface as fractional steps from which strain fields extend. The nature of these boundaries is discussed.