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International audience; In this study, lead metasilicate glasses (PbSiO3) were densified at different maximum pressures in a diamond anvil cell (DAC) at room temperature. The densified glass samples were investigated ex-situ by Raman spectroscopy to probe their pressure-induced plastic deformation limit and permanent structural modifications on the Q(n) distribution. With a high Pb content, this glass exhibits a low elastic limit at similar to 4 GPa, which is linked to an initial compact structure. Spectral curve fitting of the high-frequency region of the Raman spectra, consisting of symmetric Si-O stretching modes, exhibit subtle Q(n) population modifications with maximum pressure. This reveals silica network depolymerization where the proportion of non-bridging oxygens (NBO) increases at the expense of bridging oxygens (BO). Possible densification mechanisms are discussed in contrast to those known in other silicate glasses.

Macroscopic Suprasil F300 type silica glasses densified under high pressure and high temperature were irradiated with 2.5 MeV electrons. This paper focuses on the point defects generation in those densified silica glasses. We demonstrated that the unattributed 540 nm emission band was clearly enhanced when the irradiated glasses exhibit a higher density either initially generated by high pressure cycle or by irradiation at high dose (> 3 GGy). The spectral shape of the emission band related to Non Bridging Oxygen Hole Center (NBOHC) is also modified with a broader FWHM due to an additional contribution near 610 nm indicating a larger distribution of NBOHC species in these densified glasses.

International audience; Depending on the composition of silicate glasses, their elastic moduli can increase or decrease as function of the temperature. Studying the Brillouin frequency shift of these glasses versus temperature allows the a-thermal composition corresponding to an intermediate glass to be determined. In an intermediate glass, the elastic moduli are independent of the temperature over a large temperature range. For sodium alumino-silicate glasses, the a-thermal composition is close to the albite glass (NaAlSi3O8). The structural origin of this property is studied by in situ high temperature Raman scattering. The structure of the intermediate albite glass and of silica are compared at different temperatures between room temperature and 600 °C. When the temperature increases, it is shown that the high frequency shift of the main band at 440 cm−1 in silica is a consequence of the cristobalite-like alpha-beta transformation of 6-membered rings. This effect is stronger in silica than bond elongation (anharmonic effects). As a consequence, the elastic moduli of silica increase as the temperature increases. In the albite glass, the substitution of 25% of Si4+ ions by Al3+ and Na+ ions decreases the proportion of SiO2 6-membered rings responsible for the silica anomaly. The effects of the silica anomaly balance the anharmonicity in albite glass and give rise to an intermediate a-thermal glass. Different networks, formers or modifiers, can be added to produce different a-thermal glasses with useful mechanical or chemical properties.

From initial calcium aluminosilicate glass, transparent glass-ceramics have been successfully synthesized under simultaneous high pressure and temperature (SHPT). Possible homogeneous volumetric crystallization of this glassy system, which was not achieved previously by means of conventional heat treatment, has been put in evidence with a SHPT procedure. Structural, mechanical, and optical properties of glass and glass-ceramic obtained were investigated. Raman spectroscopy and X-ray diffraction allowed to identify two main crystalline phases: merwinite [Ca3Mg(SiO4)2] and diopside [CaMgSi2O6]. A Raman scanning profile showed that the formation of merwinite is quite homogeneous over the bulk sample. However, the sample surface also contains significant diopside crystals. Instrumented Berkovich nanoindentation was applied to determine the effect of SHPT on hardness from glass to glass-ceramic. For Eu-doped samples, the broadband emission due to 4f65d1 → 4f7 transition of Eu2+ was studied in both host systems. Additionally, the 5D0 → 7FJ transition of Eu3+ was used as an environment probe in the pristine glass and the glass-ceramic.

In situ micro-Raman spectroscopy was used to investigate the structural evolution of OH(-)-free calcium aluminosilicate glasses, under high pressure and at room temperature. Evaluation was made of the role of the SiO2 concentration in percalcic join systems, for Al/(Al + Si) in the approximate range from 0.9 to 0.2. Under high pressure, the intensity of the main band related to the bending mode of bridging oxygen ([Formula: see text][T-O-T], where T = Si or Al) decreased gradually, suggesting that the bonds were severely altered or even destroyed. In Si-rich glasses, compression induced a transformation of Q (n) species to Q (n-1). In the case of Al-rich glass, the Al in the smallest Q (n) units evolved from tetrahedral to higher-coordinated Al (([5])Al and ([6])Al). Permanent structural changes were observed in samples recovered from the highest pressure of around 15 GPa and, particularly for Si-rich samples, the recovered structure showed an increase of three-membered rings in the Si/Al tetrahedral network.

Eu 3+ -doped lutetium oxide (Eu:Lu 2 O 3 ) nanocrystalline films were grown on fused-silica substrates by pulsed laser deposition. Depending on deposition conditions (oxygen pressure, temperature and laser energy), the structure of the films changed from amorphous to crystalline and the cubic or monoclinic phases were obtained with varying preferential orientation and crystallite size. The monoclinic phase could be prepared for the first time at temperatures as low as 240 °C and in a narrow range of parameters. Although this phase has been previously reported for powder samples, it occurs only for high pressures and high temperatures preparation conditions. The refractive indices were measured by m-lines spectroscopy for both crystalline phases and their dispersion curve fitted by the Sellmeier expression. The specific Eu 3+ fluorescence properties of the different phases, monoclinic and cubic, were registered and show modifications due to the disorder induced by the nanometric size of the crystallites, emphasised in particular by quasi-selective excitation in the charge transfer band.

Light scattering in glasses is due to inhomogeneities described as density fluctuations and concentration fluctuations. Both fluctuations are characterized by fictive and chemical fictive temperatures, Tf and T f ′ respectively. A SiO2–Al2O3–P2O5 fiber amplifier glass doped with Er3+ is studied. From Raman scattering the fictive temperature of a fiber is determined to be 130 °C higher than in a preform. In situ small angle X-rays scattering (SAXS) measurements on a sample with an initial fictive temperature of 1100 °C show a structural relaxation below Tg and no evidence of evolution of concentration fluctuations up to 1400 °C. These measurements demonstrate that in a strong glass such as that considered in this work, Tf and T f ′ can be monitored separately allowing a high T f ′ favouring the dispersion of the doping ions and a low Tf decreasing the Rayleigh scattering and increasing the transmission of the signal.

Elastic (Rayleigh) and inelastic (Brillouin and Raman) scatterings are altogether measured in the same experimental conditions for germanium doped silica glass (5wt% GeO2). Taking into account that density and concentration fluctuations are frozen-in respectively at the fictive temperature Tf and at the chemical fictive temperature T f ′ , a quantitative comparison of the different scattering processes demonstrates that the concentration fluctuations are the main reasons for the increase of the scattering. However the depolarized Rayleigh scattering is much stronger than in pure silica and also contributes to the increase of the total scattering whereas the increase of the Raman cross section due to the GeO2 introduction is much smaller.

We studied the influence of germanium atom introduction into the silica network and the influence of heat treatements on the glass structure by doing Raman and infra-red spectra of vitreous germanium doped silica (5% wt GeO 2 , 95% wt SiO 2 ). Germanium incorporates into the network by substituting Si atoms and consequently, we observed band shifts and broadening of defect peaks D 1 and D 2 . The peak positions are directly correlated with the structural state characterized by the glass fictive temperature T F of the different samples.

Silicon dioxide and titanium dioxide films were deposited at low temperature by electron cyclotron resonance (ECR) plasma enhanced chemical vapor deposition (PECVD) using respectively O2 and tetraethoxysilane (TEOS) or titanium isopropoxide (TIPT) as precursors. To control the thickness and the refractive index during deposition, the plasma reactor was equipped with an in situ spectroscopic ellipsometer. Deposition kinetics and layer properties were investigated by spectroscopic ellipsometry, X-ray photoelectron spectroscopy (XPS) and chemical etch rate. A double film antireflection coating was fabricated and reflectance was measured using a UV-visible near-infrared spectrometer. Results reported demonstrate that deposition of SiO2 and TiO2 films at low temperature by PECVD is a promising method to produce antireflection coatings for solar cells.

The growth of anodic oxides of crystalline Si in an O2 plasma has been studied. The kinetics are found to follow those expected when neutral O atoms in the plasma capture an electron at the substrate surface and diffuse through the growing oxide under the influence of an applied positive electric field. The oxides have been characterized using infrared spectroscopy, glancing incidence x-ray reflectometry, and electric capacitance/voltage measurements. Shifts to lower wave numbers of the transverse and longitudinal optic infrared modes associated with the asymmetric stretch of the bridging O’s with respect to thermally grown oxide values are observed. We conclude that these shifts result from structural modifications induced by ultraviolet photons present in the O plasma. A simple model suggests that the plasma grown oxides have a density ∼3.8% larger than thermal SiO2 and an average Si–O–Si bridging bond angle ∼1.6° smaller. The plasma grown oxides are inhomogeneous in the volume, the bond angle shift increasing to ∼−2.3°, and the density decreasing to +2% with respect to thermal oxide near the Si substrate/SiO2 interface. X-ray reflectivity data, which are consistent with film inhomogeneity, enable us to determine the film thickness and surface (air/SiO2) roughness. The latter is always ⩽1 nm. Electrical measurements suggest that the oxides contain fixed oxide charges and interface states which can be reduced by low temperature annealing. The leakage currents remain high, however.

Polyamorphic transitions in silica are studied under pressure up to 26.2 GPa by Raman and Brillouin spectrocopies. The first reversible polyamorphic transition is characterized by an abrupt decrease of the Si–O–Si inter-tetrahedral angle θ at 2.5 GPa corresponding to the elastic anomaly of silica. This result is interpreted as a reversible transition between two Low Density Amorphous phases LDA β ↔ LDA α similar to the β–α transition of cristobalite crystal under pressure. The second polyamorphic transition is observed for silica glass samples compressed up at different maximum pressures P max between 12 GPa and 26.2 GPa and recovered at ambient pressure. It corresponds to an irreversible and progressive transformation from the LDA α phase to a High Density Amorphous (HDA) phase. This HDA phase is characterized by an increase of the statistic distribution of 4- and 3-membered rings of SiO 4 tetrahedra with a narrowing of inter-tetrahedral angle distribution. A vanishing of the elastic anomaly in the HDA phase is observed.

Eu3+-doped yttrium oxide (Eu:Y2O3) films were grown on fused-silica substrates by laser ablation. Depending on oxygen pressure, substrate temperature and laser energy density, the crystalline structure of the films, determined by X-ray diffraction and Raman spectroscopy, changes from monoclinic to cubic. The crystalline structure of the films is confirmed by Eu3+ fluorescence spectra and refractive indices, measured by m-line spectroscopy. The cubic crystalline films show low-loss waveguiding properties.

Vitreous GeO2 has been compressed at high temperature to investigate the effect of thermal activation on the structural reorganization during compression. The measurements were performed in-situ using micro Raman spectroscopy under pressure up to 6 GPa and temperature up to 400 °C. The evolution of the Raman shift of the main band (400–500 cm−1) with temperature during compression evidences a pressure window around 3 GPa within which temperature has a remarkable influence on the structure, in particular, the intermediate range order. We find that this change is well correlated with previous ex-situ density measurements from high pressure-high temperature densifications. Moreover, coordination changes from tetrahedrally (GeO4) to octahedrally (GeO6) coordinated GeO2 are accelerated with the heating during the compression.

The spectral line shapes and the absorption frequencies of the oxygen related infrared active vibrational modes in amorphous SiO2 are studied both experimentally and by simulation. Experimental data were obtained on oxides grown thermally in the temperature range from 800 to 1050 °C and on oxides deposited at 300 °C by plasma enhanced chemical deposition. The transverse optic (TO) mode centered around 1090 cm−1 is found to have a line shape and peak frequency which varies significantly with film thickness while the longitudinal optic (LO) mode at 1256 cm−1 is invariant. Data on both modes and on refractive index is used to demonstrate consistently that the 800 °C grown oxide is 1.6%–2.0% denser than that grown at 1050 °C. For thin oxides (

The kinetics of the oxidation of Si in a microwave excited O2 plasma have been studied at temperatures in the range of 260–390 °C. The substrate was positively biased and the total electron and O− ion current maintained constant by application of an electric field ∼5 MV cm−1 across the growing oxide. This field was established for thicknesses ≥10 nm. Total current densities were 2–6 mA cm−2 while the O− current was estimated to be 0.02–0.04 mA cm−2. Oxide growth kinetics are discussed in terms of a recent physical model. Chemical etch rates and refractive indices were measured and although similar to those of thermal oxide, infrared absorption spectra suggest that the internal network structure is not the same.

The longitudinal optic vibrational mode associated with the asymmetric stretch of the bridging oxygen atom has been studied in amorphous SiO2 grown by plasma assisted oxidation of Si. In films ≤70 nm thick the mode is observed displaced by −6 cm−1 with respect to the bulk value (1256 cm−1). Deconvolution of the spectra combined with chemical etchback of the films shows that they are inhomogeneous, the peak shift increasing to −12 cm−1 near the Si/SiO2 interface in films thicker than ∼20 nm.

Silicon dioxide films have been deposited using a SiH4+O2 microwave plasma excited by distributed electron cyclotron resonance. The ratio of flow rates of the reactive gas was O2/SiH4∼7. The substrate was not heated intentionally (T

Micro-Raman spectra are performed at different radial positions in order to determine the fictive temperature distribution in pure silica optical fibers. As-received and annealed optical fibers are compared and Raman results reveal a large decrease in the fictive temperature after annealing. The fictive temperature gradient between the core and the edge of the optical fiber can be eliminated after annealing and the spectroscopic decoupling between stress and the fictive temperature variation is discussed. The micro-Raman is a good probe in determining the spatial distribution of the fictive temperature in the micrometer length scale.

In situ micro-Raman spectroscopy was performed on lanthanum borogermanate (LBG) glasses, compressed in a diamond anvil cell at ambient temperature. Up to 5.6 GPa the structural changes are reversible, whereas experiments performed at 10 GPa and higher are characterized by hysteresis loops. A noticeable change of evolution of the main Raman band at 800 cm(-1) has been evidenced around 8 GPa. Indeed, at such a pressure, this Raman band is shifted in the opposite direction while the pressure is still increasing. This change of slopes may be the sign of a pressure-induced coordination number change. Upon decompression the Raman shift of this band follows a different path from the one during compression. When the sample is returned to ambient pressure, it shows a shifted and lightly modified Raman spectrum, suggesting that a new amorphous phase for LBG glass is reached under high pressure and still exists at atmospheric pressure. However, a comparison with LaBGeO(5) crystals with the same composition shows that this material has a full elastic behaviour in the same pressure range.