Films minces à base de Si nanostructuré pour des cellules ...

multilayered conguration. Therefore, the (SRSO+SRSN) pattern thickness of the
multilayer was calculated and found to be 8.8 nm.
This value is close to the expected pattern thickness of 8.5 nm (3.5 nm + 5 nm)
indicating that, the pattern thickness can be estimated from XRR technique to a
high degree of accuracy. Hence most of the MLs in this thesis were investigated by
XRR.
4.5.3 Fourier transform infrared spectroscopy
The FTIR spectrum of the as-grown ML recorded in Brewster incidence is showed
in gure 4.19a. It can be clearly seen that the spectrum is composed of multiple
peaks which overlap with each other due to the contribution of Si-O and Si-N bonds
from SRSO and SRSN sublayers respectively.
tel-00916300, version 1 - 10 Dec 2013
(a) Brewster incidence.
(b) Normal incidence.
Figure 4.19: FTIR spectra (thick line) of as grown 100(3.5/5) ML. The spectra is decomposed
into six gaussians and four gaussians in the Brewtser incidence and normal incidence
spectra respectively.
The spectrum is tted with six peaks, corresponding to the asymmetric stretching
modes of SRSO and SRSN sublayers. The peaks centered around 1175 cm −1 , 1059
cm −1 , 802 cm −1 and 758 cm −1 can be attributed to the LO 3 , TO 3 , LO 2 and TO 2
peaks of Si-O bonds respectively while those at 954 cm −1 and 866 cm −1 can be
ascribed to the LO & TO peaks of Si-N. All the peaks except TO Si−N mode are
shifted towards lower wavenumbers as compared to the (LO and TO) Si−N modes
observed in monolayers (ref. FTIR in Sec. 4.2.2). There may be three possible
reasons that induce this shift in the TO Si−N mode towards higher wavenumbers in
MLs:
1. Dierence in bonding angles in monolayer and ML congurations.
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