## 3 Results and Discussion
### Structural Properties
#### 3.1.3 Fourier Transform Infrared Spectroscopy  
Figure 5 shows the typical FTIR spectra before and after annealing of a pure SOG film (a), embedded films (b), and coated films (c) containing red light-emitting Si-NCs. The same behavior was observed in coated and embedded films with blue light-emitting Si-NCs. The typical IR (infrared) vibration modes from silicon oxide films [31; 32] at 1078 cm\({}^{-1}\) ( Si-O-Si stretching), 800 cm\({}^{-1}\) (O-Si-O bending), and 457 cm\({}^{-1}\) (Si-O-Si rocking) can be observed in all of the cases. All the absorption spectra show a peak at 1400 cm\({}^{-1}\) due to the Si-CH\({}_{2}\) stretching bonds, as well as some other peaks related to vibration modes associated with hydrogen bonds at 935 cm\({}^{-1}\) (Si-OH stretching) and >3200 (H\({}_{2}\)O) cm\({}^{-1}\). The latter decreases in intensity or disappears after the thermal annealing [31; 32]. It is noticeable that both before and after annealing, the IR spectra of the pure SOG film are similar to the IR spectra obtained from the coated and embedded films with Si-NCs (Figure 5b,c). Figure 6 shows the IR peak related to the Si-O-Si asymmetric stretching mode deconvoluted in their longitudinal (LO) and transversal (TO) modes of the different samples, in order to qualitatively assess the structural changes produced by the thermal annealing [7; 33; 34; 35]. Figure 4: Grazing incidence XRD (X-ray diffraction) (0.5\({}^{\circ}\)) patterns from coated (**a**) and embedded films; (**b**) with **red** and **blue** light-emitting Si-NCs, before and after annealing at 1100 \({}^{\circ}\)C for 3 h in N\({}_{2}\) atmosphere. In all of the spectra in Figure 6, it is possible to see the stretching peak (at \(\sim\)1078 cm\({}^{-1}\)) and the asymmetric stretching peak (from 1100 cm\({}^{-1}\) to 1200 cm\({}^{-1}\)). Notice that these spectra show a shift to lower or higher wavenumbers depending on its structure or composition after annealing. The stretching infrared (IR) peak observed in coated samples with red and blue Si-NCs shifts towards a lower wavenumber after thermal annealing, as observed in Figure 6a,b, respectively. However, this IR band shifts towards the opposite direction for the embedded red and blue Si-NCs films, as observed in Figure 6c,d, respectively. A deconvolution of the IR stretching peak (symmetric and asymmetric) in the LO and TO modes shows a change in the full width at a half maximum (FWHM) associated with the formation of amorphous phases of SiO\({}_{2}\) (peak at \(\sim\)1025 cm\({}^{-1}\)) in the Si-NCs/SOG interface after thermal annealing. This is an indication of a possible combination of non-stoichiometric and stoichiometric SiO\({}_{2}\)[7; 36]. The Si-NCs could react with the oxygen atoms of the SOG due to the silicon atoms presenting a higher probability of having oxygen neighboring atoms, forming Si=O related bonds [14]. This is confirmed by the shift of about 16.4 cm\({}^{-1}\) and 13.7 cm\({}^{-1}\) to lower wavenumbers of the stretching Si-O-Si peak for each coated film, as observed in Figure 6a,b. In addition, the observed broadening of the IR stretching peak could be related to a strain between the Si-NCs and the SiO\({}_{2}\)-based SOG film, producing the formation of a high defect density after the thermal annealing in N\({}_{2}\) atmosphere [37]. On the other hand, the shift of the IR stretching peak found in the embedded Si-NCs towards higher wavenumbers after thermal annealing could be related to the formation of a stoichiometric and dense film (shifts of 15.9 cm\({}^{-1}\) and 16.2 cm\({}^{-1}\) for red and blue embedded Si-NCs film, respectively). Therefore, a structural rearrangement occurs in these films due to the thermal annealing, improving the stoichiometry because of the phase separation between the Si and SiO\({}_{2}\)[38; 34].