We demonstrate experimentally all-optical switching on a silicon chip at telecom wavelengths. The switching device comprises a compact ring resonator formed by horizontal silicon slot waveguides filled with highly nonlinear silicon nanocrystals in silica. When pumping at power levels about 100 mW using 10 ps pulses, more than 50% modulation depth is observed at the switch output. The switch performs about 1 order of magnitude faster than previous approaches on silicon and is fully fabricated using complementary metal oxide semiconductor technologies.

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

Precipitation and crystallization of Si nanocrystals have been monitored by means of Raman spectroscopy. SiOx films with different compositions have been deposited by low-pressure chemical-vapor deposition technique onto silica substrates and treated to temperatures exceeding 800 °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 °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 at. %. For small Si nanocrystals a strong hydrostatic stress has been observed, induced by a very abrupt transition with the surrounding SiO2. 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 Al 1−x In x 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 Ϸ6 eV and differences with earlier reports are discussed. Very large Stokes' shifts of 0.4-0.8 eV are observed in the composition range 0.13Ͻ x Ͻ 0.24, increasing approximately linearly with InN fraction despite the change of sign of the piezoelectric field.

Ge 1−x Sn x nanorods (NRs) with a nominal Sn content of 28% have been prepared by a modified microwavebased approach at very low temperature (140 °C) with Sn as growth promoter. The observation of a Sn-enriched region at the nucleation site of NRs and the presence of the low temperature -Sn phase even at elevated temperatures support a template-supported formation mechanism. The behaviour of two distinct Ge 1−x Sn x compositions with high Sn content of 17% and 28% upon thermal treatment has been studied and reveal segregation events occurring at elevated temperatures, but also demonstrate the temperature window of thermal stability. In situ transmission electron microscopy investigations revealed a diffusion of metallic Sn clusters through the Ge 1−x Sn x NRs associated with temperatures where the material composition changes drastically. These results are important for the explanation of distinct composition changes in Ge 1−x Sn x and the observation of solid diffusion combined with dissolution and redeposition of Ge 1−y Sn y (x>y) exhibiting a reduced Sn content. Absence of metallic Sn results in increased temperature stability by ~70 °C for Ge 0.72 Sn 28 NRs and ~60 °C for Ge 0.83 Sn 17 nanowires (NWs). In addition, a composition-dependent direct bandgap of the Ge 1−x Sn x NRs and NWs with different composition is illustrated using Tauc plots. ASSOCIATED CONTENT Supporting Information. Additional SEM, TEM, EDX and XRD data are provided. Moreover, a video for the phase separation in the TEM is supplied. This material is available free of charge via the Internet at http://pubs.acs.org.

We present Raman-scattering measurements on InxGa1−xN over the entire composition range of the alloy. The frequencies of the A1(LO) and E2 modes are reported and show a good agreement with the one-mode behavior dispersion predicted by the modified random-element isodisplacement model. The A1(LO) mode displays a high intensity relative to the E2 mode due to resonant enhancement. For above band-gap excitation, the A1(LO) 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 SiO x films deposited by plasma-enhanced chemical-vapor deposition have been studied for different Si excesses up to 24 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 eV in the nanosecond regime and at 1.50 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 ϳ −10 −8 cm 2 / W͒ and nonlinear absorption coefficient ͑␤ ϳ 10 −6 cm/ W͒. Under femtosecond excitation conditions, a smaller nonlinear refractive index is found ͑n 2 ϳ 10 −12 cm 2 / W͒, 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.

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