[2] Once the two atoms meet they may bond to form a particle with a higher mass and a lower random walk velocity.
"[3] Subsequent atoms deposited on the substrate eventually meet and bond with the island, further increasing its size and stability.
Eventually the island can grow to fill the entire substrate with a single large grain.
[4] As these atoms meet, they will bond to their local neighbors before having the chance to migrate to a distant island.
In this way a large number of separate islands are formed and can grow independently.