Nalini et al. Nanoscale Research Letters 2011, 6:156 http://www.nanoscalereslett.com/content/6/1/156 long time of 1 h and at higher temperature. Accounting for the interference effect, we can infer that SRSO/SiNx exhibits higher PL intensity than SRSO/SiO2. Thus, it can be seen that a replacement of the SiO2 sublayer by the SiNx sublayer and alternating it with the SRSO sub- layer not only favors luminescence but paves way to achieve a control over the thermal budget. Discussion The PL spectra of the SRSO/SiNx subjected to two dif- ferent annealing treatments show that the quenching of the PL signal after an RTA can be attributed to the non-radiative defects either at the interface of Si-nc and the SiO2 matrix or within the SiO2 matrix itself which traps the photon arising from the recombination of the exciton within the Si-nc. On the contrary, it can be seen that the SiNx sublayer favors luminescence even if this later could be attributed to the defects in the matrix. Noticing the shift in emission peak from 1.9 to 1.6 eV in the case of SiNx/SiO2 and SRSO/SiNx, respectively, it can be said that the sandwiching of SRSO between SiNx instead of SiO2 sublayers not only favors luminescence but also exhibits luminescence in a region attributed to the emission from Si-nc. This implies that though at this temperature SiNx shows a defect-related PL, when alternated with SRSO, the emission from Si-nc becomes dominant. On the other hand, the quenching of PL in classically annealed SRSO/SiNx is quite surprising as several authors have noticed an increase of the PL signal either from SRSO or SiNx after such annealing. It also should be noted that the ‘SRSO sublayer’ fabricated under the same conditions and alternated with SiO2 sublayer has a high emission. Hence one can conclude that the pre- sence of the SiNx sublayer quenches the PL. This can be attributed either to the coalescence of Si clusters at such an annealing treatment thereby overcoming the quan- tum confinement regime or to the non-radiative defects at the interface between SRSO and SiNx or in SiNx. The increase of the PL emission when increasing the number of layer could be the result of H diffusion during the deposition process which favors the recovering of the defects and the Si nanoparticles formation. Such a hypothesis is supported by the presence of N-H bonds revealed by FTIR experiments in the non-annealed mul- tilayers and that can be attributed to the Si-nc formation [17]. Another explanation could be the increase of strain with the number of layer that favors the Si-np formation resulting in an increase of the Si-np density and hence in the PL emission. However, the comparison in the inset of Figure 3 of the two types of multilayers demon- strates the advantage to replace the SiO2 sublayer by the SiNx. HRTEM experiments are in progress to under- stand the optical behavior of these multilayers. Page 4 of 5 Conclusion The multilayers were fabricated using the sputtering technique and the FTIR spectrum revealed its character- istic peaks. Although SiO2 is the most sought host matrix, we evidenced the interest of replacing it with the SiNx matrix. A higher intensity of PL emission was obtained for RTA when SiNx matrix was used whereas from the SiO2 matrix there was no considerable inten- sity at such an annealing treatment. We have achieved comparable intensity of emission within one minute of annealing and at a lesser temperature, in comparison to the classical annealing treatment that is done for longer time and slightly higher temperature. We also observe an increase in the PL emission with increase in the number of periods. High-resolution electron microscopy experiments are in progress to understand the effect of the annealing process on the achieved optical properties. This set of above-mentioned results paves the way for the fabrication of novel structures for solar cell device applications similar to the one recently reported by Di et al. [20]. Abbreviations PL: photoluminescence; RTA: rapid thermal annealing; Si-nc: Si-nanoclusters; SRSO: silicon-rich silicon oxide. Acknowledgements This study is supported by the DGA (Defense Procurement Agency) through the research program no. 2008.34.0031. Authors’ contributions RPN fabricated the multilayers under investigation and carried out the characterization studies.CD and JC made significant contribution to the optical properties and interference effect. FG conceived of the study and participated in the coordination and writing of the manuscript. All authors read and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Received: 24 September 2010 Accepted: 18 February 2011 Published: 18 February 2011 References 1. 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