Silicon oxycarbide glasses have been synthesized by inert atmosphere pyrolysis at 1000°C of gel precursors obtained by cohydrolysis of triethoxysilane, HSi(OEt),, and methyldiethoxysilane, HMeSi(OEt), . The oxycarbide structures have been carefully characterized by means of different techniques such as 29Si magic angle spinning nuclear magnetic resonance (MAS-NMR) and Raman spectroscopies, X-ray diffraction (XRD), and chemical analysis. Experimental results clearly indicate that, depending on the composition of the starting gels, the resulting oxycarbide glass either is formed by a pure oxycarbide phase or contains an extra carbon or silicon phase. By increasing the temperature up to 1500"C, the oxycarbide glasses display compositional and weight stability; however, the amorphous network undergoes structural rearrangements that lead to the precipitation of nano-sized p-Sic crystallites into amorphous silica. Crystallization of metallic silicon is also clearly observed at 1500°C for the samples in which the presence of Si-Si bonds was postulated at 1000°C.

The effect of nitrogen addition on the structural and electronic properties of hydrogenated amorphous carbon ͑a-C:H͒ films has been characterized in terms of its composition, sp 3 bonding fraction, infrared and Raman spectra, optical band gap, conductivity, and paramagnetic defect. The variation of conductivity with nitrogen content suggests that N acts as a weak donor, with the conductivity first decreasing and then increasing as the Fermi level moves up in the band gap. Compensated behavior is found at about 7 at. % N, for the deposition conditions used here, where a number of properties show extreme behavior. The paramagnetic defect density and the Urbach tailwidth are each found to decrease with increasing N content. It is unusual to find alloy additions decreasing disorder in this manner.

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An integrated experimental approach, based on inelastic light-scattering techniques, has been here employed for a multilength scale characterization of networking properties of cyclodextrin nanosponges, a new class of cross-linked polymeric materials built up from natural oligosaccharides cyclodextrins. By using Raman and Brillouin scattering experiments, we performed a detailed inspection of the vibrational dynamics of these polymers over a wide frequency window ranging from gigahertz to terahertz, with the aim of providing physical descriptors correlated to the cross-linking degree and elastic properties of the material. The results seem to suggest that the stiffness of cross-linked polymers can be successfully tuned by acting on the type and the relative amount of the cross-linker during the synthesis of a polymer matrix, predicting and controlling their swelling and entrapment properties. The proposed experimental approach is a useful tool for investigating the structural and physicochemical properties of polymeric network systems.

SiOC and SiBOC polymer-derived glasses show a complex nanostructure in which nanocrystalline β-SiC and sp 2 C coexists with nanoclusters of amorphous SiO 2 or SiO 2 -B 2 O 3 and with mixed silicon oxycarbide and boron oxycarbide units. The characterization of the nanostructure is performed with a multiple technique approach on SiOC and SiBOC glasses before and after HF etching. The acid attack dissolves the silica-based nanoclusters and allows indirect information on their size and amount to be obtained. By increasing the pyrolysis temperature from 1200 up to 1500 °C the oxide clusters grow in size and amount in both SiOC and SiBOC glasses. Compared to the B-free SiOC glass, SiBOC is more easily etched and develops higher porosity and larger pore size. Boron has also an important effect on the ordering of the sp 2 C phase: it leads to thicker sp 2 C nanocrystals. This effect is remarkable because it starts at low temperature (1500 °C) compared to the usual temperature, 1800 °C, reported in the literature for different forms of nanocrystalline carbon. Raman analysis of SiBOC glasses pyrolyzed at 1500 °C clearly shows the presence of the D′ band at 1617 cm -1 . From this experimental result it is postulated that B enters into the graphene layers forming BC 3 units. Finally, the shift toward lower wavenumbers of the Raman spectra recorded on SiOC and SiBOC glasses after etching seems to reveal a high compressive stress acting along the basal sp 2 C planes of the graphite nanocrystals.