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The studies were conducted to assess the structural evolution and nucleation of Si-nanocrystal in silicon-rich silicon oxide films produced by PECVD (plasma enhanced chemical vapor deposition), as a function of the annealing temperature. The findings reveal the active role played by the hydrogen and nitrogen atoms in the formation of Si-nc and in the thermally induced evolution of the deposited films.

Complementary metal-oxide-semiconductor-compatible tunable Fabry-Perot microcavities filled with liquid crystals (LCs) are realized and studied in the near-infrared region. Electric-field-induced shifts of the second-order cavity modes of 127 and 49 nm are obtained for Merck-E7 and Merck-6608 LC, with driving potentials of 5 and 10 V, respectively.

Quantum confined Ge nanocrystals embedded in high bandgap and high-k Al2O3 dielectric matrix have been synthesized to demonstrate dual functional devices using Si-compatible fabrication technology. Transmission electron microscopy has shown the formation of Ge nanocrystals of varying diameter from 2.5 to 7.5 nm, much lower than the excitonic Bohr radius of Ge. A broad visible electroluminescence band at room temperature has been observed, which is attributed to the recombination of injected electrons and holes in Ge nanocrystals. An anti-clockwise hysteresis in the capacitance-voltage measurement of these devices indicates the charge storage in nanocrystals, useful for floating gate memory devices. [ABSTRACT FROM AUTHOR]

We report a spectroscopic study about the energy transfer mechanism among silicon nanoparticles (Si-np), both amorphous and crystalline, and Er ions in a silicon dioxide matrix. From infrared spectroscopic analysis, we have determined that the physics of the transfer mechanism does not depend on the Si-np nature, finding a fast (<200 ns) energy transfer in both cases, while the amorphous nanoclusters reveal a larger transfer efficiency than the nanocrystals. Moreover, the detailed spectroscopic results in the visible range here reported are essential to understand the physics behind the sensitization effect, whose knowledge assumes a crucial role to enhance the transfer rate and possibly employing the material in optical amplifier devices. Joining the experimental data, performed with pulsed and continuous-wave excitation, we develop a model in which the internal intraband recombination within Si-np is competitive with the transfer process via an Auger electron-'recycling' effect. Posing a different light on some detrimental mechanism such as Auger processes, our findings clearly recast the role of Si-np in the sensitization scheme, where they are able to excite very efficiently ions in close proximity to their surface. [ABSTRACT FROM AUTHOR]

Optical properties of directly excited erbium (Er3+) ions have been studied in silicon rich silicon oxide materials codoped with Er3+. The spectral dependence of the direct excitation cross section (σdir) of the Er3+ atomic 4I15/2→4I11/2 transition (around 0.98 μm) has been measured by time resolved μ-photoluminescence measurements. We have determined that σdir is 9.0±1.5×10-21 cm2 at 983 nm, at least twice larger than the value determined on a stoichiometric SiO2 matrix. This result, in combination with a measurement of the population of excited Er3+ as a function of the pumping flux, has allowed quantifying accurately the amount of optically active Er3+. This concentration is, in the best of the cases, 26% of the total Er population measured by secondary ion mass spectrometry, which means that only this percentage could provide optical gain in an eventual optical amplifier based on this material. [ABSTRACT FROM AUTHOR]

Linear and nonlinear optical properties of silicon suboxide SiOx 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 (n2∼-10-8 cm2/W) and nonlinear absorption coefficient (β∼10-6 cm/W). Under femtosecond excitation conditions, a smaller nonlinear refractive index is found (n2∼10-12 cm2/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. [ABSTRACT FROM AUTHOR]

We report on the study and modeling of the structural and optical properties of rib-loaded waveguides working in the 600–900-nm spectral range. A Si nanocrystal (Si-nc) rich SiO2 layer with nominal Si excess ranging from 10% to 20% was produced by quadrupole ion implantation of Si into thermal SiO2 formed on a silicon substrate. Si-ncs were precipitated by annealing at 1100 °C, forming a 0.4-μm-thick core layer in the waveguide. The Si content, the Si-nc density and size, the Si-nc emission, and the active layer effective refractive index were determined by dedicated experiments using x-ray photoelectron spectroscopy, Raman spectroscopy, energy-filtered transmission electron microscopy, photoluminescence and m-lines spectroscopy. Rib-loaded waveguides were fabricated by photolithographic and reactive ion etching processes, with patterned rib widths ranging from 1 to 8 μm. Light propagation in the waveguide was observed and losses of 11 dB/cm at 633 and 780 nm were measured, modeled and interpreted. [ABSTRACT FROM AUTHOR]

Stimulated emission from silicon-nanocrystal planar waveguides grown via phase separation and thermal crystallization of SiO/SiO2 superlattices is presented. Under high power pulsed excitation, positive optical gain can be observed once a good optical confinement in the waveguide is achieved and the silicon nanocrystals have proper size. A critical tradeoff between Auger nonradiative recombination processes and stimulated emission is observed. The measured large gain values are explained by the small size dispersion in these silicon nanocrystals. [ABSTRACT FROM AUTHOR]

The energy transfer mechanism among silicon nanoparticles (Si-np), both amorphous and crystalline, and Er ions in a silicon dioxide matrix is analyzed. A model is developed in which the internal intraband recombination within Si-np is competitive with the transfer process via an Auger electron-erecyclingE process and the studies have recast the role of Si-np in the sensitization scheme, where they are able to excite very efficiently ions in close proximity to their surface.

Optical properties of directly excited erbium ([Er.sup.3+]) ions are analyzed in silicon rich silicon oxide materials codoped with [Er.sup.3+]. Time resolved [micro]-photoluminescence measurements are used for measuring the spectral dependence of the direct excitation cross section of the [Er.sup.3+] atomic transition.

A systematic study of the linear and nonlinear optical properties of Si[O.sub.x] films deposited on silica by plasma-enhanced chemical-vapor deposition (PECVD) technique is presented. The contribution per nanocrystal to the electronic third-order nonlinear susceptibility is found to increase with reduction in the size of the Si nanoparticles due to the appearance of electronic transitions between discrete levels induced by quantum confinement.

The study and modeling of the structural and optical properties of rib-loaded waveguides working in the 600-900-nm spectral range is presented. A Si nanocrystal rich SiO2 layer with nominal Si excess ranging from 10% to 20% is produced by quadrupole ion implantation of Si into thermal SiO2 formed on a silicon substrate.

Porous silicon (pSi) is a sponge-like material obtained by electrochemical etching of a crystalline silicon wafer. Due to quantum confinement effects, this material is photoluminescent and this is a fundamental property from the perspective of bioimaging applications. Limitations in nanomedicine to the use of photoluminescent pSi structures are mainly due to optical quenching in an aqueous environment and to the adverse effects of reactive groups introduced by etching procedures. In this work, we exploited an inorganic TiO2 coating of pSi microparticles by Atomic Layer Deposition (ALD) that resulted in optical stability of pSi particles in a biological buffer (e.g. PBS). The use of a rotary reactor allows deposition of a uniform coating on the particles and enables a fine tuning of its thickness. The ALD parameters were optimized and the photoluminescence (PL) of pSi–TiO2 microparticles was stabilized for more than three months without any significant effect on their morphology. The biocompatibility of the coated microparticles was evaluated by analyzing the release of cytokines and superoxide anion (O2−) by human dendritic cells, which play an essential role in the regulation of inflammatory and immune responses. We demonstrated that the microparticles per se are unable to significantly damage or stimulate human dendritic cells and therefore are suitable candidates for nanomedicine applications. However, a synergistic effect of the microparticles with bacterial products, which are known to stimulate immune-response, was observed, indicating that a condition unfavorable to the use of inorganic nanomaterials in biological systems is the presence of infection diseases. These results, combined with the proved PL stability in biological buffers, open the way for the use of pSi–TiO2 microparticles as promising materials in nanomedicine, but their ability to increase immune cell activation by other agonists should be considered and even exploited. [ABSTRACT FROM AUTHOR]