Surface islands nucleated by a beam of energetic self-ions

Many processes that control materials synthesis hinge on a nucleation event that initiates a first order phase transition. Symmetries that constrain nucleation of elementary nanostructures are therefore of general interest. Using low-energy electron microscopy, we observe the flux at which adatom and advacancy islands nucleate when clean Pt(111), in the temperature range 750- 1300 K, is bombarded by a beam of Pt- ions of various energies. The results reveal a previously unobserved symmetry between the chemical potentials μ* required to nucleate the two types of island. Linear response theory is employed to relate μ* to ion beam flux; the observations confirm that its use is valid above 1000 K. The observed magnitudes of μ* agree within a factor 3 with predictions made earlier by Pimpinelli and Villain. In addition, the observations show that adatoms and advacancies on Pt(111) form a strongly reacting assembly, with the life cycle of thermal point defects determined mainly by formation and annihilation as pairs, rather than by processes at fixed sinks such as surface step edges.