  This work unravels the atomic details of the interaction of solute atoms with
nanoscale crystalline defects. The complexity of this phenomenon is elucidated
through detailed atom probe tomographic investigations on epitaxially-strained,
compositionally metastable, semiconductor alloys. Subtle variations are
uncovered in the concentration and distribution of solute atoms surrounding
dislocations, and their dynamic evolution is highlighted. The results
demonstrate that crystal defects, such as dislocations, are instrumental in
initiating the process of phase separation in strained metastable layers.
Matrix regions, close to the dislocations, show clear signs of compositional
degradation only after a relatively short time from disrupting the local
equilibrium. The solute concentration as well as the density of non-random
atomic clusters increases while approaching a dislocation from the surrounding
matrix region. In parallel, far from a dislocation the lattice remains intact
preserving the metastable structure and composition uniformity. At advanced
stages of phase separation, the matrix outside the dislocation reaches the
equilibrium concentration, while dislocations act as vehicles of
mass-transport, providing fast diffusive channels for solute atoms to reach the
surface. Besides, the number of atomic clusters almost doubles and the number
of atoms per cluster increases steadily, moving along a dislocation towards the
surface. In addition to understanding the atomic features involved in the phase
separation of strained metastable alloys, the work also illustrates the
thermodynamic and kinetic behavior of solute atoms in the vicinity of a
nanoscale defect and describe quantitatively the key processes, thus providing
the empirical input to improve the atomic models and simulations.
