“Nucleation” cracks on the surface of a silicon crystal

The (100) surface of a silicon crystal after cutting a blank with a diamond disk and subsequent polishing is studied by white light interference profilometry and photoluminescence spectroscopy (PL). It is found that it is covered with “grooves”. Their length is 10–40 $\mu$m, and the depth is quantized and has four predominant values – 1, 2.6, 3.6, and 4.5 nm. Four bands at 1.63, 1.62, 1.68, and 2.25 eV are observed in the PL spectra of the surface which appear due to confinement, i.e., an increase in the band gap and violation of the law of conservation of momentum in nanocrystals. The sizes of the nanocrystals of 2, 2.3, 3, and 4 nm are determined by the energy of the maxima of these bands. Fractoluminescence (FL) signals containing four maxima each are observed when cutting silicon or hitting it with a striker. The signals are formed when dislocations break through the barriers that appear at the places of intersection of the slip planes and formation of “nucleation” cracks. The sizes of the cracks are determined to be 1.9, 3, 3.2, and 6 nm by the rate of the growth in the intensity of the maxima. The coincidence of the values of the depths of the grooves, sizes of the crystals, and “nucleation” cracks makes it possible to draw a conclusion that the grooves are “nucleation” cracks.