Sahu et al. Nanoscale Research Letters 2011, 6:178 http://www.nanoscalereslett.com/content/6/1/178 Page 4 of 10 Figure 2 Cross-sectional EFTEM image of the sample S4 containing 33 at.% of Si excess after annealing at 1100°C for 30 min in N2 ambient. stoichiometric phase present in the as-deposited SRN films toward a biphasic Si/Si3N4 mixture cannot be ruled out. The phase separation process has been reported for silicon-rich SiOx films, which also indicates a shift of Si-O band toward higher wave numbers [24,25]. As discussed earlier, a phase separation occurs when SRSN samples are annealed at high temperature (≥ 950°C), resulting in the formation of Si-nps embedded in a nearly stoichiometric silicon nitride matrix [26]. Photoluminescence Figure 4a shows the PL spectra of the as-deposited sam- ples. All the samples exhibit broad and strong visible PL at room temperature. The mechanism for strong lumi- nescence from SiNx materials is commonly suggested from the combination of Si/SiNx interface luminescence, gap state luminescence/band-tail luminescence, and luminescence from Si nanodots/clusters. In this investi- gation, efforts have been made to minimize Si/SiNx interface luminescence with the introduction of high- quality thermal SiO2 before SiNx deposition, which gives rise to enhanced interface quality with minimal interfa- cial defect states. Details regarding interface traps will be discussed in the C-V analysis part. As evident from Figure 4a,b, with increase in nitrogen content in the SRSN films, the PL peak shifts to higher energies together with an increase in the relative intensity and width. This behavior is commonly attributed to a model based on quantum confinement effect (QCE) [27-29]. From the QCE model point of view, PL blue shift is caused by the reduction in Si-np size, and the increase in emission efficiency can be correlated with the onset