Si rings, Si clusters, and Si nanocrystals—different states of ultrathin $SiOx$ layers

Amorphous $SiO/SiO2$ superlattices were prepared by reactive evaporation of SiO powder in an oxygen atmosphere. Infrared absorption and photoluminescence spectra were measured as a function of annealing temperature. Three photoluminescence emission bands were observed. A band centered at 560 nm is present in as-prepared samples and vanishes for annealing above $700 °C.$ The second band around 760 nm to 890 nm is detected for annealing temperatures above $500 °C.$ A strong red luminescence is observed for annealing temperatures above $900 °C.$ The origin of the different photoluminescence bands and different states of the phase separation of ultrathin $SiOx$ layers is discussed.