Formation of a graphene-like SiN layer on the surface Si(111)

The kinetics of the formation and thermal decomposition of a two-dimensional SiN-(8 $\times$ 8) nitride layer on a Si(111) surface is studied. The SiN-(8 $\times$ 8) structure is a metastable intermediate phase formed during the nitridation of silicon before the formation of a stable amorphous Si$_3$N$_4$ phase. Studying the SiN-(8 $\times$ 8) structure by scanning tunneling microscopy shows its complex structure: it consists of an adsorption (8/3 $\times$ 8/3) phase, with the lateral period 10.2 $\mathring{\mathrm{A}}$, and a honeycomb structure with a $\sim$6 $\mathring{\mathrm{A}}$ side of a hexagon that is turned 30$^{\circ}$ with respect the adsorption phase. The band gap of the SiN-(8 $\times$ 8) phase is measured and found to be $\sim$2.8 eV, which is smaller compared to the band gap of the $\beta$-Si$_3$N$_4$ crystal phase 5.3 eV. The interplanar spacings in the (AlN$_3$)/(SiN)$_2$ structure on the Si(111) surface are measured. The spacings are 3.3 and 2.86 $\mathring{\mathrm{A}}$ in SiN and AlN, respectively. Such interplanar spacings are indicative of weak van der Waals interaction between the layers. A model of the SiN-(8 $\times$ 8) structure as a flat graphene-like layer is suggested. The model is consistent with the diffraction and microscopy data.