s- and p-Polarized Infrared Specular Reflectance of Vitreous Silica at Oblique Incidences: Detection of LO Modes

Abstract

Infrared (IR) specular reflectance spectra of a semi-infinite sample of vitreous silica (v-SiO2) were obtained with the use of both s- and p-polarized light and oblique incidence angles. The optical constants of the material and hence its longitudinal optic/transverse optic (LO-TO) functions were determined through the Kramers–Krönig analysis (KKA) of its s-polarized 20° off-normal reflectance spectrum. p-Polarized spectra had their reflection maxima blue-shifting as the incidence angle increased, while they remained unchanged for the s-polarized spectra. Since an LO mode generally lies at wavenumbers higher than its respective TO mode, such a blue shift may be due to the detection of the LO mode in addition to the TO mode as incidence angle increased. The only exception to this observation was the high-frequency shoulder, which underwent a sharp intensification as the incidence increased. The present work shows that it is indeed brought about by the weakly IR active asymmetrical mode (AS2) but only because it takes place immediately after the intense AS1 mode, which causes the refraction index spectrum to have a broad dip below unity. Such a dip is proven to be responsible for the sharp increase in the high-frequency shoulder of the reflectance spectra.

Compositional and structural changes at the anodic surface of thermally poled soda-lime float glass

“…The peak positions remain nearly the same with the angle of incidence, but an increase in the relative intensity of the shoulder at about 1200 cm −1 was observed, which is generally noticed for other silicate glasses and for vitreous silica. [12][13][14] For the pristine and cathodic surfaces this shoulder becomes a more defined band only when the incident angle is higher than 60°. The bands at 1070 cm −1 are narrower at the anodic surface.…”

“…This band is attributed to the bending vibration of the Si-O-Si bonds with the oxygen oscillating along the axis bisecting the angle of this bond. 13,18 According to Galeener et al 19 the frequency of this vibrational mode is given by With the shift of this band to 816 cm −1 , due to poling, the angle should have decreased to ϳ128°, according to Eq. ͑3͒.…”

Physical properties of silicate glasses doped with SnO2

“…8. The band attribution of silicate glasses have been exhaustively presented in the literature, always with respect to that of vitreous silica [9,10]. The most pronounced change is observed for the band at 970 cm À1 which intensity reduces slightly with increasing SnO 2 content.…”

Structural difference between near interface oxides grown on Si and C faces of 4H-SiC characterized by infrared spectroscopy

“…We attributed these peaks to the TO and LO modes of the asymmetric stretching vibration of Si-O-Si bond absorption, respectively. 7,16 Actually the intensities of these absorption peaks were dependent on the film thickness. As shown in Fig.…”