Formation of silicon nanocrystals under friction

It is found using triboluminescence (TL) that nanocrystals of silicon (ncSi) with linear dimensions of about 4 nm are formed from a single crystal of silicon (Si) under friction. The time dependence of the intensity of TL signals is investigated. It consists of many superimposed signals. An analysis of their dynamics shows that nanocrystals are located on the microcrack faces formed during fracture. At the same time, a powder flies out of the friction region. Using the photoluminescence (PL) and Raman spectroscopy methods, the size of silicon nanocrystals in the powder was determined. It is about 2.2 nm. Probably, microcracks grow further in the time interval between friction and recording the Raman and PL spectra (several hours), which leads to an approximately twofold decrease in the size of nanocrystals.