An abrupt switch between the two photoluminescence bands within alkylated silicon nanocrystals

Photoluminescence (PL) spectra from a series of alkylated silicon nanocrystals (SiNCs) derived from porous silicon wafers formed through etching at different current densities have been investigated. SiNCs from wafers etched at high current density (382 mA cm(-2)) emit orange at 609 nm while smaller SiNCs formed from wafers etched at current density of 13 mA cm(-2) emit blue (395 nm), yet counter to current understanding of quantum confinement and its role within bandgap engineering, luminescence from SiNCs from wafers etched at intermediate current densities show no transition between the two bands, rather an abrupt switch between them is observed. SEM images show that as the silicon surface undergoes electrochemical etching under high current density many of the smaller nanostructures are destroyed leaving only the larger, more resilient nanostructures available to undergo hydrosilation. X-ray photoelectron spectroscopy measurements identify that both 'blue' and 'orange' SiNCs comprise a large degree of Si-C and Si-O thus the nature of the orange emission is likely related to defect states in silica or suboxide formed near the Si/SiO2 interface which populate the bandgap and modify the emission character. This is the first paper in the literature to unveil the relationship between etching current density and PL emission bands of alkylated SiNCs.