A strategy is presented to optimize out-of-autoclave processing of quasi-isotropic carbon fiber-reinforced\ud laminates. Square panels of 4.6 mm nominal thickness with very low porosity ð6 0:2%Þ were manufactured\ud by compression molding at low pressure (0.2 MPa) by careful design of the temperature cycle to\ud maximize the processing window. The mechanisms of void migration during processing were ascertained\ud by means of X-ray microtomography and the effect of ply clustering on porosity and on void shape was\ud explained. Finally, the effect of porosity and ply clustering on the compressive strength before and after\ud impact was studied

We present Raman-scattering measurements on ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ over the entire composition range of the alloy. The frequencies of the $A_1\left(\mathrm{LO}\right)$ and $E_2$ modes are reported and show a good agreement with the one-mode behavior dispersion predicted by the modified random-element isodisplacement model. The $A_1\left(\mathrm{LO}\right)$ mode displays a high intensity relative to the $E_2$ mode due to resonant enhancement. For above band-gap excitation, the $A_1\left(\mathrm{LO}\right)$ peak displays frequency shifts as a function of the excitation energy due to selective excitation of regions with different In contents, and strong multiphonon scattering up to 3LO is observed in outgoing resonance conditions.

Linear and nonlinear optical properties of silicon suboxide $\mathrm{Si}{\mathrm{O}}_x$ films deposited by plasma-enhanced chemical-vapor deposition have been studied for different Si excesses up to $24\mathrm{at.}\%$ . The layers have been fully characterized with respect to their atomic composition and the structure of the Si precipitates. Linear refractive index and extinction coefficient have been determined in the whole visible range, enabling to estimate the optical bandgap as a function of the Si nanocrystal size. Nonlinear optical properties have been evaluated by the $z$ -scan technique for two different excitations: at $0.80\mathrm{eV}$ in the nanosecond regime and at $1.50\mathrm{eV}$ in the femtosecond regime. Under nanosecond excitation conditions, the nonlinear process is ruled by thermal effects, showing large values of both nonlinear refractive index $(n_2\sim -{10}^{-8}{\mathrm{cm}}^2∕\mathrm{W})$ and nonlinear absorption coefficient $(\beta \sim {10}^{-6}\mathrm{cm}∕\mathrm{W})$ . Under femtosecond excitation conditions, a smaller nonlinear refractive index is found $(n_2\sim {10}^{-12}{\mathrm{cm}}^2∕\mathrm{W})$ , typical of nonlinearities arising from electronic response. The contribution per nanocrystal to the electronic third-order nonlinear susceptibility increases as the size of the Si nanoparticles is reduced, due to the appearance of electronic transitions between discrete levels induced by quantum confinement.

Precipitation and crystallization of Si nanocrystals have been monitored by means of Raman spectroscopy. ${\text{SiO}}_x$ films with different compositions have been deposited by low-pressure chemical-vapor deposition technique onto silica substrates and treated to temperatures exceeding $800°\text{C}$ . The evolution of the Raman signal with the thermal budget reveals that the silicon transition from amorphous to crystalline state shifts to higher temperatures as the Si content in the layers is lowered. A rather complete crystallization of the nanoparticles is achieved after annealing at $1250°\text{C}$ for a Si excess lower than 20%, while for higher excesses the crystalline fraction reaches only 40%, suggesting the formation of a crystalline core surrounded by an amorphous shell. The Raman spectra have been analyzed by a phonon confinement model that takes into account stress effects. An increasing nanocrystal size, from 2.5 to 3.4 nm, has been estimated when the Si excess varies from 16 to $29\text{at}\text{.}\%$ . For small Si nanocrystals a strong hydrostatic stress has been observed, induced by a very abrupt transition with the surrounding ${\text{SiO}}_2$ . Its magnitude correlates with the increase in thermal budget required for the crystallization of the amorphous clusters. This study underlines the fundamental role of hydrostatic stress in retarding the crystallization of Si nanoclusters.

Optical energy gaps are measured for high-quality ${\mathrm{Al}}_{1-x}{\mathrm{In}}_x\mathrm{N}$ -on-GaN epilayers with a range of compositions around the lattice match point using photoluminescence and photoluminescence excitation spectroscopy. These data are combined with structural data to determine the compositional dependence of emission and absorption energies. The trend indicates a very large bowing parameter of $\approx 6\mathrm{eV}$ and differences with earlier reports are discussed. Very large Stokes’ shifts of $0.4–0.8\mathrm{eV}$ are observed in the composition range $0.13<x<0.24$ , increasing approximately linearly with InN fraction despite the change of sign of the piezoelectric field.