A. Gagnaire

The effects of polarization of the incident light-modeling and analysis of a SPR multimode optical fiber sensor

A 3D skew ray modeling has been developed to consistently explain the experimental phenomena for an intrinsic SPR multimode optical fiber sensor. The effects of the polarization direction of the incident light at certain conditions have been clarified. This simulation is needed to accurately detect the variations of the refractive index of the bulk medium and of the thickness of the thin surface layer. More complete knowledge about light energy transmission by the skew ray in the multimode step-index fiber is obtained by this investigation.

Ellipsometric study of silicon nanocrystal optical constants

Samples of silicon nanocrystals on various substrates were prepared by cluster beam deposition of silicon nanoparticles, obtained by laser-induced pyrolysis of silane in a flow reactor. Using optical ellipsometry, the optical properties (refractive index and extinction coefficient) of the as-prepared silicon nanocrystal layers were determined in the wavelength range from 240 to 700 nm. Two dispersion models were used to describe the silicon nanocrystal optical properties: the Bruggeman effective medium approximation model and the Tauc–Lorentz model. The study showed that while a simple Bruggeman effective medium approximation model could not completely account for the silicon nanocrystal dispersion behavior, the optical response of the silicon nanocrystal layers could be satisfactorily described by a Tauc–Lorentz model. The present study also showed that, as for porous silicon, the silicon nanocrystal optical indexes significantly deviate from those of bulk crystalline and amorphous silicon. It confirms the special behavior of silicon under its nanoscale form.Samples of silicon nanocrystals on various substrates were prepared by cluster beam deposition of silicon nanoparticles, obtained by laser-induced pyrolysis of silane in a flow reactor. Using optical ellipsometry, the optical properties (refractive index and extinction coefficient) of the as-prepared silicon nanocrystal layers were determined in the wavelength range from 240 to 700 nm. Two dispersion models were used to describe the silicon nanocrystal optical properties: the Bruggeman effective medium approximation model and the Tauc–Lorentz model. The study showed that while a simple Bruggeman effective medium approximation model could not completely account for the silicon nanocrystal dispersion behavior, the optical response of the silicon nanocrystal layers could be satisfactorily described by a Tauc–Lorentz model. The present study also showed that, as for porous silicon, the silicon nanocrystal optical indexes significantly deviate from those of bulk crystalline and amorphous silicon. It confirms t...

Densification and aging of ZrO2 films prepared by sol-gel

The densification of ZrO2 films prepared by sol–gel synthesis has been investigated by stress measurements, infrared spectroscopy, and spectroscopic ellipsometry after annealing at 150–400°C. It is shown that the tensile stress is limited by viscous flow accompanying the densification, and that the main organic compounds reducing the rate of condensation reactions are acetate groups. The oxidation of these groups at 350°C induces a jump in both the stress and the refractive indices of the films. The effect of film aging in air on the stress has also been studied. The moisture-induced stress change follows a logarithmic time dependence, most likely due to hydration of ZrO2. The sign of stress change is determined by the amount of organic compounds in the gel.

Controlled spontaneous emission of a tri(8-hydroxyquinoline) aluminum layer in a microcavity

We report the fabrication of all-dielectric microcavities with a tri(8-hydroxyquinoline) aluminum (Alq3) organic layer as the emitting layer. In a first step, we characterized the materials used in the structures by ellipsometry, and ensured nondegradation of the organic material in the fabrication process. Then, by angular-resolved photoluminescence, we investigated changes in the angular emission pattern caused by the cavities and observed a sharply directed emission. We also investigated the influence of the position of the radiative layer in the cavity on normal spontaneous emission. We observed enhancements in spontaneous emission over 20 times higher than that of a single Alq3 layer. These are the highest reported for organic material based microcavities. They are mainly explained by the very small thickness of the Alq3 layer (20 nm≡0.06λ, λ being the resonant wavelength), by high-quality low-loss dielectric mirrors as well as by the narrow collecting angle of our experiment (±3°). This study corrob...

Physicochemical characterization of covalently bonded alkyl monolayers on silica surfaces

Abstract The physicochemical properties of silica surfaces covalently bonded with alkyl monolayers, in a chain length range from C6 to C22, are investigated by using chromatographic, ellipsometric and capacitance measurements. A compact structure is found with an interchain distance of about 0.67 nm; the experimental thickness is very close to the theoretical chain length value. The hydrophobic character of such chemically modified silica surfaces increases with the chain length.

Ellipsometric study of anodic oxide growth: Application to the titanium oxide systems

Abstract A method is given for obtaining the optical indices of a thin film together with those of the substrate from an analysis of ellipsometric measurements on a set of samples with different film thicknesses. This method has been applied to the particular case of an anodic oxide film on titanium. The optical indices are compared with previous results quoted in the literature.

Fabrication and characterization of organic semiconductor-based microcavities

Abstract Structures confining light along one or two directions (microcavities) are of prime importance for the construction of opto-electronic devices based on luminescent semiconductor materials. Our work is devoted to the making of microcavities centered at 2.4 eV (515 nm) formed by two TiO 2 /SiO 2 distributed Bragg reflectors, surrounding an emitting layer. The emitting layer is an organic semiconductor (tri-hydroxyquinoline-aluminum, Alq 3 ) chosen for its strong luminescent efficiency. For the fabrication of such complex structure, the layer optical path length is an determining parameter to obtain a high quality microcavity. First, a particular attention has been paid to the characterization of the optical properties of the active layer and the mirror layers. Optical indices have been obtained by means of spectroellipsometry. Alq 3 and TiO 2 dispersion laws were successfully modeled with a model developed by Forohoui and Bloomer. Secondly, we applied in situ ellipsometry to control the mirror layer deposition. Finally, we show that this method allows microcavity fabrication with good accuracy.

Characterization of graded refractive index silicon oxynitride thin films by spectroscopic ellipsometry

Layers with a continuous variation in the optical index with thickness were characterized by spectroscopic ellipsometry. These oxynitride films were grown by electron cyclotron resonance plasma-enhanced chemical vapor deposition using silane as a silicon precursor and oxygen and nitrogen as plasma gases. Specific linear and parabolic index profiles were fabricated by computer-controlled gas flow. Reduction of ellipsometry data measured ex situ on these films was performed with polynomial analysis. The validity of this approach was checked by a depth analysis via chemical etching. An investigation of the limits of the method is presented.

GROWTH AND STRUCTURE OF RAPID THERMAL SILICON OXIDES AND NITROXIDES STUDIED BY SPECTROELLIPSOMETRY AND AUGER ELECTRON SPECTROSCOPY

Rapid thermal oxidation of Czochralski‐grown silicon in either O2 or N2O atmospheres have been studied using spectroellipsometry and Auger electron spectroscopy. Multiwavelength ellipsometric data were processed in order to separately derive the thicknesses and refractive indexes of rapid thermal dielectrics. Results revealed a significant increase of the mean refractive index as the film thickness falls below 20 nm for both O2 or N2O oxidant species. A multilayer structure including an about 0.3‐nm‐thick interfacial region of either SiOx or nitroxide in the case of O2 and N2O growth, respectively, followed by a densified SiO2 layer, was found to accurately fit the experimental data. The interfacial region together with the densified state of SiO2 close to the interface suggest a dielectric structure in agreement with the continuous random network model proposed for classical thermal oxides. Auger electron spectroscopy analysis confirmed the presence of noncrystalline Si—Si bonds in the interfacial region...

Optical properties of native oxides on InP

Abstract The optical properties of anodically, thermally, and chemically grown oxides on InP have been studied using a spectroellipsometric method. The dielectric functions of the main compounds have been obtained in the spectral range 1.8–5.2 eV. The interface properties of these native oxides have been studied.