Chemical kinetics of the Si(111) surface nitridation process at temperatures below the structural phase transition (7$\times$7)$\to$(1$\times$1)

A study of the influence of the conditions of silicon nitride crystalline phase formation on the process kinetics as a result of controlled nitridation of the reconstructed (7$\times$7) Si(111) surface at varying substrate temperatures in the range 700–800$^\circ$C has been carried out. From the analysis of the diffraction patterns obtained by the reflection high-energy electron diffraction technique, it is found that the formation kinetics of the two-dimensional (8$\times$8) crystalline phase in the temperature range of 700–800$^\circ$C differs from that of the high-temperature nitridation and exhibits normal activation-reaction behaviour, indicating the presence of an activation barrier. The activation barrier of 0.6 eV associated with the formation heat of a mobile silicon atom from the adatoms of the (7$\times$7) structure involved in the formation of the SiN (8$\times$8) crystalline phase on the ordered silicon (7$\times$7) superstructure has been determined and a kinetic scheme of the process has been proposed.