AG MASS-TRANSPORT ON SI(111) IN THE 350-450-DEGREES-C TEMPERATURE-RANGE

Ag mass transport on Si(111) has been studied by means of SEM and Auger analysis with spatial resolution, under ultra-high vacuum conditions. The spreading of Ag deposits is investigated in the 350-450-degrees-C temperature range where no desorption occurs. In order to avoid electromigration, the samples are heated by means of a halogen lamp. After the initial islands formation (Stranski-Krastanov growth mode) Ag begins to spread out of the initial deposit zone. The main features deduced from the concentration profiles analysis are: (i) for temperatures higher than approximately 400-degrees-C, the profiles show a rather constant concentration ending in a very sharp front side which may be attributed to an unrolling carpet mechanism; (ii) for temperatures lower than approximately 400-degrees-C, the corresponding profiles show two gradient zones; (iii) for both cases, a t3/4 kinetics law is found: it suggests that Ag/Si mass transport could be controlled by surface self diffusion of Ag atoms on the Ag 3D islands with an activation energy of approximately 2.4 eV/atom.