Reactive crystal growth in two dimensions: Silicon nitride on Si(111)

The nitridation of the Si(111) surface by reaction with ${\mathrm{NH}}_3$ was studied by low-energy electron microscopy (LEEM), low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). Reaction layers with periodicities of (8×8), (8/3× 8) / 3 ), (3/4× 3) / 4 ), and (3 √3 /4×3 √3 /4) were observed depending on the temperature of nitridation and duration of electron-beam exposure. The nucleation and growth of the nitride layer on well-oriented and miscut Si(111) surfaces were observed by STM and followed in real time by video LEEM. The (8×8) nitride islands nucleate and grow in the same manner as the (7×7) domains, with the apex of the triangle pointing in the [1¯ 1¯2] direction away from the step into the upper terrace. On the miscut surface, (8×8) nitride growth proceeds with widening of the terraces and step bunching. The (3/4× 3) / 4 ) multiplet structure, on the other hand, nucleates randomly on comtaminated sites on the surface, or evolves directly from the (8×8) structure.