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Natural photosynthetic photonic nanostructures can show sophisticated light–matter interactions including enhanced light absorption by slow light even for highly pigmented systems. Beyond fundamental biology aspects, these natural nanostructures are very attractive as blueprints for advanced photonic devices. But the soft‐matter biomimetic implementations of such nanostructures is challenging due to the low refractive index contrast of most organic photonic structures. Excitonic organic materials with near‐zero index (NZI) optical properties allow overcoming these bottlenecks. Here, it is demonstrated that the combination of NZI thin films with photonic multilayers like the ones found in nature enables broadband tunable strong reflectance as well as slow light absorption enhancement and tailored photoluminescence properties in the full VIS spectrum. Moreover, it is shown that this complex optical response is tunable, paving the way toward the development of active devices based on all‐polymer and near‐zero index materials photonic structures. [ABSTRACT FROM AUTHOR]

The refractive index of nanometric (<100 nm) chlorinated-silicon nitride films with embedded silicon quantum dots, prepared by remote plasma enhanced chemical vapor deposition was investigated by spectroscopic ellipsometry. The complex refractive indexes and thicknesses of the films were obtained from the ellipsometric measurements using the Cauchy model. The chemical composition of the bulk of the films, including the hydrogen, chlorine, and oxygen content, was measured by elastic forward analysis (EFA) and X-ray photoelectron spectroscopy (XPS). The EFA and XPS results indicate that the films are composed of nearly stoichiometric silicon nitride (Si3N4) with different amounts of hydrogen, chlorine, and oxygen, and that their top surface is oxidized. Based on the composition results the refractive index of the films was fitted using the effective medium approximation considering the system: Si substrate+Si3N4+Si+voids+top ultrathin oxidized surface layer. [ABSTRACT FROM AUTHOR]

The dielectric functions of Cu2ZnGeS4 bulk crystals grown by the Bridgman method were measured over the energy range 1.4 to 4.7 eV at room temperature using variable angle spectroscopic ellipsometry. The observed structures in the dielectric functions were adjusted using the Adachi's model and attributed to interband transitions E0, E1A, and E1B at Γ:(000), N(A):2π/a(0.5 0.5 0.5), and T(Z):2π/a(0 0 0.5) points of the first Brillouin zone, respectively. The model parameters (threshold energy, strength, and broadening) have been determined using the simulated annealing algorithm. The decrease in the first gap, E0, has been attributed to a higher Ge-S hybridization. The spectral dependence of the complex refractive index, the absorption coefficient, and the normal-incidence reflectivity were also derived. [ABSTRACT FROM AUTHOR]

Nanostructured films consisting of single Si nanoparticles (NPs) and Er3+ ions layers separated by nanometer-scale Al2O3 layers of controlled thickness have been prepared in order to tune the energy transfer between Si NPs and Er3+ ions. The amorphous Si NPs with an effective diameter of ∼4.5 nm are formed during growth and are able to sensitize the Er3+ ions efficiently with no postannealing treatments. The characteristic distance for energy transfer from Si NPs to Er3+ ions in Al2O3 is found to be in the 1 nm range. It is shown that in the nanostructured films, it is possible to achieve an optimized configuration in which almost all the Er3+ ions have the potential to be excited by the Si NPs. This result stresses the importance of controlling the dopant distribution at the nanoscale to achieve improved device performance. [ABSTRACT FROM AUTHOR]

Analysis of the optical properties of bulk Cu(In1-xGax)3Se5 mixed crystals synthesized from the elements as a function of the Ga content is presented. Measurements of the complex dielectric function [variant_greek_epsilon](ω)=[variant_greek_epsilon]1(ω)+i[variant_greek_epsilon]2(ω) were performed at room temperature in the photon energy range of 0.8–4.7 eV using a variable angle of incidence ellipsometer. The spectral dependence of the complex refractive index, the absorption coefficient, and the normal-incidence reflectivity were also derived. The structure observed in the dielectric functions attributed to the interband transitions E0, E1A, and E1B has been modeled using a modification of the Adachi’s model. The results are in excellent agreement with the experimental data over the entire range of photon energies. The model parameters, including the energies corresponding to the lowest direct gap and higher critical points, have been determined using the simulated annealing algorithm. The values of E0 and E1A are found to increase linearly with the increasing Ga content. [ABSTRACT FROM AUTHOR]

The complex dielectric functions, [variant_greek_epsilon](ω)=[variant_greek_epsilon]1(ω)+i[variant_greek_epsilon]2(ω), of CuIn3Se5 and CuIn5Se8 crystals with different Cu contents have been determined in the 0.8–4.7 eV photon energy range by using spectroscopic ellipsometry. The spectral dependence of the real, [variant_greek_epsilon]1(ω), and imaginary, [variant_greek_epsilon]2(ω), parts of [variant_greek_epsilon](ω), as well as the complex refractive index, the absorption coefficient, and the normal-incidence reflectivity, has been modeled by using a modification of Adachi’s model. The results are in excellent agreement with the experimental data over the entire range of photon energies. The model parameters, including the energies corresponding to the lowest direct gap, E0, and to higher critical points, have been determined by using the simulated annealing algorithm. [ABSTRACT FROM AUTHOR]

Spectral dependence of the real [variant_greek_epsilon]1(ω) and imaginary [variant_greek_epsilon]2(ω) parts of the complex dielectric function, complex refractive index, absorption coefficient, and normal-incidence reflectivity of CuGa5Se8 crystals with slightly different Cu contents are modeled using Adachi’s model for interband transitions. The results are in good agreement with the experimental data over the entire range of photon energies. The model parameters are determined using the simulated annealing algorithm. [ABSTRACT FROM AUTHOR]

Er–Tm codoped a-Al2O3 thin films prepared by alternate pulsed laser deposition show a broad photoluminescence band with two characteristic peaks at 1540 and at 1640 nm, respectively, related to Er3+ and Tm3+ emissions. Two series of films have been prepared. For the first series, the Tm concentration [Tm] has been increased while keeping constant the Er concentration [Er]. The results show that the photoluminescence intensity at 1640 nm (I1640) to that at 1540 nm (I1540) decreases and that at 1640 nm (I1640) increases, i.e., the (I1640/I1540) ratio increases as [Tm] is increased. For [Tm]/[Er]=3, a fairly flat emission spectrum (I1640/I1540∼1) with a full width at half maximum of 230 nm is achieved. For the second series both [Tm] and [Er] are increased while keeping the [Tm]/[Er] ratio constant. The I1640/I1540 ratio tends to be constant with a full width at half maximum of 150 nm. The lifetime values decrease in all cases as [Tm] increases. The evolution of the I1640/I1540 and lifetimes as a function of [Tm] as well as the analysis of the latter considering Er as a donor and Tm as an acceptor evidence that there is an efficient energy transfer from Er3+ to Tm3+. These results suggest that enhanced performance with a flat broadband emission useful for planar integrated devices is achievable by further dopant engineering in the nanoscale. [ABSTRACT FROM AUTHOR]

Spectral dependence of the pseudodielectric function [variant_greek_epsilon](E)=[variant_greek_epsilon]1(E)+i[variant_greek_epsilon]2(E) as well as of the complex refractive index, extinction coefficient, absorption coefficient, and normal-incidence reflectivity of Cu2In4Se7 and CuGa3Se5 ordered vacancy compound crystals are modeled in the 0.8–4.4 eV photon energy range using a modification of Adachi’s model [T. Kawashima et al. J. Appl. Phys. 84, 5202 (1998)] for optical properties of semiconductors. Model parameters are determined using the acceptance-probability-controlled simulated annealing method. Excellent agreement with experimental data is obtained; the relative errors for the real [variant_greek_epsilon]1 and for imaginary [variant_greek_epsilon]2 part of the dielectric function are equal to 0.9%–1.5% and 3.2%–4.1% for the studied compounds. [ABSTRACT FROM AUTHOR]

The dielectric function ε(ω) of polycrystalline bulk samples of the quaternary chalcopyrite semiconductors Ag1-xCuxInSe2 with x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0 has been determined by spectroscopic ellipsometry in the energy range from 0.5 to 4.7 eV at room temperature. Accurate values of refractive indices n and extinction coefficients k representative of bulk materials are obtained from the data. The value of the main energy gap is very sensitive to the composition and varies from 1.225 to 1.009 eV as x increases (Cu content). The structures observed in ε(ω) have been analyzed by fitting the numerically differentiated experimental spectrum ssecond derivatived to analytical line shapes. As a result, the energies corresponding to different electronic transitions have been determined as a function of the composition, and they have been identified within the electronic band structure of chalcopyrites. [ABSTRACT FROM AUTHOR]

Real time reflectivity measurements with ps time resolution at the wavelength λ=514.5 nm have been used to analyze the rapid melting and solidification dynamics of Sb thin films on glass substrates irradiated with a visible laser pulse (λ=583 nm) of duration either 30 ps or 2 ns. Significant differences in the solidification dynamics have been obtained for the three different film thickness investigated (25, 50, and 200 nm) as well as between ps and ns laser pulse excitation. Bulk solidification is the dominant mechanism observed at high laser fluence in the thinner films, no matter the pulse duration used, while interfacial solidification is the only mechanism observed in the thicker film for both pulse durations. These results have been interpreted in terms of the differences of the effective thermal conductivity of the films. The comparison of the behavior of these films with the case of Sb-rich GeSb ones makes it clear that relatively minor changes in the film composition can lead to big changes in the solidification dynamics under similar heat flow conditions that are beneficial for the application of such films in phase change optical recording with ultrashort pulses. The optical properties of molten phase of Sb and of the solid material at the melting temperature have been also been determined at 514.5 nm. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Nanocomposite thin films formed by Ag nanocrystals embedded in an amorphous aluminum oxide (Al[sub 2]O[sub 3]) host were prepared by alternating-target pulsed laser deposition. Spectroscopic ellipsometry was used to determine the effective refractive index (n=n+ik). When the Ag volume fraction is over 2%, the linear optical properties of the nanocomposite films differ from those of the pure dielectric host. The extinction coefficient shows a maximum around 435 nm that is related to the surface plasmon resonance. Near this wavelength, the real part of the refractive index undergoes anomalous dispersion, leading to a significant increase of the n value of the composite compared to that of the matrix. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Structured nanocomposite films consisting of five Fe layers embedded in an amorphous Al[sub 2]O[sub 3] matrix (Fe:Al[sub 2]O[sub 3]) have been grown by sequential pulsed laser deposition. The formation of well isolated quasispherical nanocrystals is observed for samples with Fe content per layer close to 6.5 × 10[sup 15] atoms/cm². Increasing the Fe content leads first to the formation of elongated nanocrystals and then to quasicontinuous layers. The evolution in the shape and size of the nanocrystals is reflected in the magnetic behavior of these systems. A crossover from a low temperature ferromagnetic regime to a high temperature superparamagnetic regime is observed at a temperature of 23 K in the samples containing isolated quasi-spherical nanocrystals. In this case, a reduced moment per Fe atom (1.4 µ[sub B]/atom) with respect to the value for α-Fe (2.2 µ[sub B]/atom) is estimated. This behavior is attributed to the presence of a Fe-oxide surface shell on the nanocrystals. The large values of the estimated effective magnetic anisotropy (1.4 × 10[sup 6] J/m³) and the low temperature coercivity in these samples are attributed to a strong surface contribution to anisotropy, whereas the temperature dependence of coercivity is attributed to thermal activation. [ABSTRACT FROM AUTHOR]

Erbium doped Al[sub 2]O[sub 3] films with concentrations up to 6×10[sup 20] Er cm[sup -3] have been prepared in a single step process by pulsed-laser deposition. Alternate ablation of Al[sub 2]O[sub 3] and Er targets has been used to control the in-depth distribution and in-plane concentration of Er[sup 3+] ions independently. The characteristic Er[sup 3+] photoluminescence response at 1.53 μm has been studied as a function of the Er[sup 3+] distribution. It is found that lifetime values can be greatly increased by increasing the Er[sup 3+]–Er[sup 3+] in-depth separation above 3 nm. This result can be related to a reduced Er[sup 3+]–Er[sup 3+] energy migration process. The in-plane Er[sup 3+] concentration was increased by either increasing the number of pulses on the Er target or the laser energy density for ablation. By the latter method in-plane concentrations as high as 1.1×10[sup 14] Er cm[sup -2] per layer (corresponding to 2×10[sup 20] Er cm[sup -3]) were achieved, while keeping lifetime values as high as 6 ms. This result is explained in terms of shallow Er[sup 3+] implantation during deposition. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We demonstrate that optical extinction spectroscopy can be used to determine the effective shape of Cu nanocrystals (NCs) embedded in a transparent amorphous Al[sub 2]O[sub 3] host both produced by pulsed laser deposition. The axial ratio of the NCs was extracted from the positions of the surface plasmon modes of the optical extinction spectra of the nanocomposite film. Comparison to the results obtained by grazing incidence small angle x-ray scattering shows excellent agreement. Thus, optical spectroscopy can be used as a simple, easily accessible, and versatile tool for the characterization of the NCs that form nanocomposite films. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study reporting on the optical characterization by spectroscopic ellipsometry (SE), of composite films with Bi nanocrystals in Ge (Bi:Ge films) and Al2O3 (Bi:Al2O3 films) hosts produced by pulsed laser deposition (PLD) in vacuum. Methodology used to conduct the study; Details on Bi:Ge films; Findings of the study.

Provides information on a study that used of molecular beam epitaxy in the incorporation and optical activation of erbium in silicon to focus on the effect of oxygen on the erbium-related luminescence.

Presents a study that examined optical activation, excitation and concentration limits of erbium (Er) in crystal silicon (Si). Background on erbium doping of silicon; Factors required for attaining efficient luminescence from Er in Si.

Presents a study which examined the crystallization kinetics of amorphous germanium films under nanosecond laser irradiation. Analysis of the presence of relaxation processes in the amorphous phase; Implications of real time reflectivity measurements and Raman spectroscopy for amorphous regrowth; Reflectivity transients obtained at increasing pulse energy densities.

Studies the room-temperature luminescence from erbium-implanted oxygen-doped silicon epitaxial films grown by molecular beam epitaxy. Purpose of the optical doping of silicon with erbium; Details on the experiment; Discussion on the results of the study.

The linear optical properties of Cu2ZnSnS4 bulk poly-crystals have been investigated using spectroscopic ellipsometry in the range of 1.2–4.6 eV at room temperature. The characteristic features identified in the optical spectra are explained by using the Adachi analytical model for the interband transitions at the corresponding critical points in the Brillouin zone. The experimental data have been modeled over the entire spectral range taking into account the lowest E0 transition near the fundamental absorption edge and E1A and E1B higher energy interband transitions. In addition, the spectral dependences of the refractive index, extinction coefficient, absorption coefficient, and normal-incidence reflectivity values have been accurately determined and are provided since they are essential data for the design of Cu2ZnSnS4 based optoelectronic devices. [ABSTRACT FROM AUTHOR]

The implantation of bismuth during pulsed laser deposition (PLD) has been directly observed and investigated. Bi was deposited on amorphous aluminum oxide (Al[SUB2]O[SUB3]) and the laser energy density on the Bi target was varied by one order of magnitude (0.4 to 5 J cm[SUP-2]). Cross-sectional transmission electron micrographs reveal that, for laser energy densities above 2 J cm[SUP-2], in addition to the formation of Bi nanocrystals, there is a dark and apparently continuous layer in the Al[SUB2]O[SUB3] underneath them. From previous velocity measurements, the kinetic energy of the Bi species in the plume generated at laser energy densities above 2 J cm[SUP-2] has been estimated to be around 200 eV, which gives a calculated implantation range of 1.8 nm in Al[SUB2]O[SUB3]. This is in good agreement with the position of the Bi-rich layer. [ABSTRACT FROM AUTHOR]

Presents information pertaining to the production of the active rare-earth Er3+ -Yb3+ co-doped phosphate glass films using pulsed laser deposition in a single step. Description of the films; Reference to the density of the films obtained under the conditions of photoluminescence intensity; How luminescent emission can be excited.

Presents a study which analyzed the solid-liquid transition induced in antimony by laser irradiation by means of real time reflectivity measurements. Principle behind the real time reflectivity procedure; Materials and methods used; Results.

The optical transmission at a fixed visible wavelength of Bi nanoparticles embedded in a dielectric is known to show a sharp hysteretic evolution as a function of the temperature due to the reversible melting-solidification of the nanoparticles. In this work, we explore the temperature-dependent optical response of Bi nanoparticles embedded in a doped germanate glass (GeO2-Al2O3-Na2O) in a broad range from the visible to the near infrared. The transmission contrast induced by melting of the nanoparticles is shown to be strongly wavelength-dependent and evolves from positive to negative as the wavelength increases. This behaviour is well modelled using effective medium calculations, assuming that the nanoparticles size, shape, and distribution are unmodified upon melting, while their dielectric function turns from that of solid Bi to that of liquid Bi thus modifying markedly their optical response. These results open a route to the spectral tailoring of the thermo-optical response of Bi nanoparticles-based materials, which can be profitable for the engineering of wavelength-selective thermo-optical modulators and filters with optimized amplitude of modulation and wavelength dependence. [ABSTRACT FROM AUTHOR]

Using spectroscopic ellipsometry we investigated and analyzed the pseudo-optical constants of Cu2ZnSnSe4 bulk crystals, grown by the Bridgman method, over 0.8-4.5 eV photon energy range. The structures found in the spectra of the complex pseudodielectric functions were associated to E0, E1A, and E1B interband transitions and were analyzed in frame of the Adachi's model. The interband transition parameters such as strength, threshold energy, and broadening were evaluated by using the simulated annealing algorithm. In addition, the pseudo-complex refractive index, extinction coefficient, absorption coefficient, and normal-incidence reflectivity were derived over 0.8-4.5 eV photon energy range. [ABSTRACT FROM AUTHOR]

This work shows the influence of conditioning the Bi target previous to the pulsed laser deposition of Bi nanocomposite films on their optical and thermo-optical properties. The nanostructured films prepared by alternate pulsed laser deposition at room temperature in vacuum consist of Bi nanostructures (NSs) with different characteristic sizes that are organized in layers and embedded in an amorphous AlO host. Preablation of the Bi target prior to deposition leads to higher Bi concentration and Bi NSs with larger average sizes. As a result a lower optical transmission and an enhanced thermo-optical contrast are observed. [ABSTRACT FROM AUTHOR]

The reflectivity variations of a dielectric thin film during the deposition of a disordered monolayer of metallic nanoparticles are studied. We present experimental results and provide theoretical physical insight into the behavior of the reflectivity signal and its dependence on the dielectric thin-film thickness and structural features of the monolayer of nanoparticles. A closed-form expression is used to describe the reflectivity of a disordered monolayer of particles on a flat substrate within the frame of a coherent-scattering model approach. It is shown that the model reproduces qualitatively the behavior of the reflectivity signal during the experiment. Finally we study the optical response in the limit of small particles for low surface coverage fractions of the monolayer to evidence the main parameters that dictate the evolution of the reflectivity signal during the growth of a monolayer of nanoparticles. [ABSTRACT FROM AUTHOR]

In this work, we report on the production of Ge nanoparticles (NPs) in an inert Ar gas atmosphere by pulsed laser deposition (PLD) at room temperature (RT). The direct deposition of energetic particles/droplets resulting from the ablation process of the target material has been avoided by using an original and customized off-axis shadow mask ( shadowed off-axis) deposition set-up where the NPs deposition on the substrate takes place by means of scattering between the NPs formed in the vapor phase and the background Ar atoms. It is found that the Ar gas pressure parameter has a relevant role in the crystallization process, with better crystallinity obtained as the background Ar pressure is raised for the given experimental conditions. [ABSTRACT FROM AUTHOR]

The near-infrared emission from calcium boroaluminate (CABAL) glasses codoped with Er3+ and Tm3+ has been investigated. It is shown that by controlling the [Tm]/[Er] concentration ratio a fairly flat emission with a bandwidth of 370 nm can be achieved in the wavelength range from 1.4 to 2.0 μm. The broadband emission is formed by three bands centered at 1.4, 1.5 and 1.8 μm, which are related to the emission from the Tm3+: 3 H4→3 F4, Er3+: 4 I13/2→4 I15/2 and Tm3+: 3 F4→3 H6 transitions, respectively. Compared to Er-only doping and Tm-only doping at the same concentration, codoping with both ions leads to a reduction of the intensity and lifetime of the Er-related band at 1.53 μm and to an intensity enhancement of the two Tm-related emission bands at 1.46 and 1.80 μm. This is a result of energy transfer (ET) processes between Er3+ and Tm3+ ions that are relevant when determining the emission spectrum shape. Two dominant ET processes are identified, both consisting of transferring the energy of the Er3+ first excited level (4 I13/2) in the first case to the Tm3+ first excited level (3 F4), which is excited to the third excited level (3 H4), and in the second case to the Tm3+ ground state (3 H6) which is excited to the first excited level (3 F4). [ABSTRACT FROM AUTHOR]

Landraces and bean (Phaseolus vulgaris L.) cultivars grown in Mexico are diverse, as are consumer preferences and agroecological production environments. Mexican common bean cultivars were analyzed using amplified fragment length polymorphism (AFLP) finger-printing to examine the genetic relationships within and among races, based on the genotyping of 112 bred cultivars developed in Mexico. Molecular analysis of dry bean germplasm will be useful to corroborate previous cultivar characterizations and establish the genetic basis of improved germplasm, to facilitate the use of that diversity, and to implement the use of markers in selection. Germplasm included 111 cultivars belonging to Mesoamerica (25), Jalisco (39), Durango (28), and Nueva Granada (19) races, which are commonly cultivated throughout the bean-producing areas of Mexico. A Mexican P. coccineus species cultivar (Blanco Tlaxcala) was also included for comparison. Broad genetic diversity was found within bean races, and diversity values between races were similar. Most of the Nueva Granada germplasm was clearly different from that of alt other races, whereas the P. coccineus cultivar was distinct from all P. vulgaris cultivars. A based on the AFLP analysis did not clearly match with that made on the basis of racial classification. This mismatch was probably due to genetic recombination between Andean (Nueva Granada) and Mesoamerican (Jalisco, Durango, and Mesoamerica) gene pools. Utilization of contrasting parents for specific crosses has also contributed to broadening the genetic basis of common bean. [ABSTRACT FROM AUTHOR]

The synthesis by pulsed laser deposition of a bismuth nano-plane embedded in an amorphous germanium matrix is reported. The structural changes were studied by Raman spectroscopy as a function of temperature. Upon heating, the Bi nano-plane melts and, as the sample is cooled, it re-crystallizes at a temperature well below the melting point. The results show a broad melting–solidification hysteresis cycle (170 K) that is compared to the ones obtained earlier on nanoparticles. Furthermore, a metal-induced crystallization effect was also observed in the germanium matrix. [ABSTRACT FROM AUTHOR]

Thin films of Zn have been prepared by pulsed laser deposition with a KrF excimer laser (248 nm). The laser energy density (E.D.) on the target has been varied in the 1 to 5 J/cm2 range. The results show that as the E.D. increases the material distribution changes. For low E.D.(≤ 1.6 J/cm2) the maximum of the distribution is at the substrate center, for intermediate E.D. it is displaced to the side, and a clear minimum appears at the center of the substrate for the higher E.D. (≥4.5 J/cm2). The growth velocity at the center of the substrate reaches a maximum value for E.D. of 2.8 J/cm2, and decreases for higher E.D. as a result of the competition between deposition and self-sputtering. Virtually a zero growth velocity is obtained for E.D. above 4.5 J/cm2. The self-sputtering process is most likely responsible for the increase of the film surface roughness as a function of the laser E.D. The low cohesive energy for metal Zn, compared to other metals (Fe, Ag, Cu) is correlated with the high efficiency of the self-sputtering for this material. [ABSTRACT FROM AUTHOR]

2-(Methacryloyloxy) ethylacetoacetate (MEEAH) was used as stabilyzing agent to control the chemical reactivity of Ti and Zr monomeric alkoxides in a Si—Ti—Zr sol. The organic and inorganic polymerizations were carried out simultaneously. The organic polymerization was performed using benzoyl peroxide as the initiator. The inorganic polymerization was done via the sol-gel process. The polymerization was studied by several spectroscopic techniques, including Fourier Transform Infrared (FTIR), UV-Vis, 29Si NMR, Small Angle X-ray Scattering (SAXS) and X-ray diffraction (XRD). Theoretical calculation and experimental results showed that MEEAH acted as a monodentate ligand, mainly. This led to a high condensation extent of the Si species in the sol. A short range order gel was obtained, according to the SAXS results. The Si—O—Ti and Si—O—Zr bonds were detected by FTIR. The bonds remained stable, because a sample calcined at 1173 K was amorphous according to the XRD results, indicating structural homogeneity. [ABSTRACT FROM AUTHOR]

A Si-Ti-Zr polymeric system containing hybrid Si species was prepared, using Tetraethyl orthosilicate (TEOS) and Methyl triethoxysilane (MTES) as the Si sources. The TEOS-MTES molar ratio was 60-40, respectively. Monomeric Ti and Zr alkoxides were used. The final molar ratios Si-Ti-Zr were 82-7-11, respectively. The samples were characterized by 29Si NMR, SAXS, FTIR and UV-Vis spectroscopies. The NMR results showed that the hybrid Si species were produced to a very low extent and that the kinetics of the polymerization was controlled by Ti and Zr. According to the SAXS results, linear oligomers were obtained. The Si—O—Ti and Si—O—Zr bonds were detected by FTIR. In the latter case, the bonds are stable, as the corresponding vibrations were detected in the oxide calcined at 773 K. A microporous structure was obtained, where the average pore diameter was 1.4 nm. [ABSTRACT FROM AUTHOR]

An experimental strategy was developed to obtain Si–Ti–Zr transparent sols via the sol-gel process. The chelating agents isoeugenol (2-methoxy-4-propenylphenol, isoH), salicylaldehyde (2-hydroxybenzaldehyde, salH), and itaconic anhydride (2-methylenesuccinic anhydride, anhH) were employed separately to stabilize monomeric Ti and Zr precursors, in order to control their chemical reactivity, avoiding precipitation. In all cases a prehydrolyzed tetraethyl orthosilicate (TEOS) sol was the Si source. The sols were polymerized at room temperature (293 K) to obtain gels and these were dried and calcined at 873 K in air. The radial distribution functions (RDF) of the gels were obtained at room temperature. The solids were studied by scanning electron microscopy (SEM). The porosity and surface area of solids were determined by N2 adsorption. The surface area results obtained range between 83–198 m2/g. The average pore diameters are 1.44–1.61 nm. [ABSTRACT FROM AUTHOR]

Nanocomposite thin films formed by Cu nanocrystals (NCs) embedded in an amorphous aluminium oxide (Al[sub 2] O[sub 3] ) host have been prepared by alternate pulsed laser deposition. Spectroscopic ellipsometry is used to determine the effective refractive index (n=n+ik). The extinction coefficient is non-negligible and shows a broad absorption band related to the surface plasmon resonance. In the neighbourhood of this wavelength, the real part of the refractive index undergoes an anomalous dispersion, leading to a significant increase of the n value of the composite compared to that of the host. When the Cu content is low enough, about 2 at. %, the use of an effective medium approach combined with a regression method allows us to determine the metal content and film thickness from the ellipsometric measurements. For larger concentrations this approach is no longer valid. [ABSTRACT FROM AUTHOR]