Arnaud Brioude

Preparation and characterization of sol–gel Y2O3 planar waveguides

Abstract Y2O3 thin film waveguides were prepared using a sol–gel method and a dip-coating procedure. Multicoating operations were necessary to produce multimode and low attenuation coefficient waveguides. Thickness and refractive index were determined by m-lines spectroscopy. X-ray diffraction (XRD) and conventional transmission electron microscopy (CTEM) were used for structural investigations and nanocrystals size determination as a function of the annealing temperature. The Y2O3 amorphous phase was observed at low heat-treatment temperature (300°C) and the layers turn to cubic nanocrystalline form when the annealing temperature reached 400°C. An annealing treatment at 600°C was necessary to provide more densified and good optical planar waveguides exhibiting an attenuation coefficient lower than 2 dB/cm.

Sol–gel fabrication of thick multilayers applied to Bragg reflectors and microcavities

Abstract We discuss attractive potentialities of the sol–gel process applied to planar microcavities with distributed Bragg reflectors (DBRs). This method is well known for its good flexibility and the optical quality of the thin films obtained. The DBRs are composed of alternated TiO2 and SiO2 thin films. One of the main problems of the sol–gel process is the stresses induced during the layers heat treatment leading to defects and cracks in the films. The study of these stresses shows that with the appropriate annealing temperature and duration of the firing process, the stress in the SiO2 layers partially compensates the stress in the TiO2 layers. DBRs and microcavities formed by 60 stacked layers have been elaborated in these conditions. The reflectivity of such sol–gel DBRs reaches 99.7%. The sol–gel DBRs are used to fabricate microcavities containing Eu3+ rare earth ions with a quality factor of approximately 1000.

Spectral properties of LuBO3 powders and thin films processed by the sol-gel technique

Abstract Powders and thin films of LuBO3:Eu3+ have been prepared using an original synthesis route, the sol–gel (SG) technique. The derived compounds have been structurally and morphologically characterized confirming the good quality of the synthesized materials obtained by such a process. Both modifications of the structure, from amorphous to the vaterite form for the films and from the vaterite to the calcite for the powders, with the thermal processing have been controlled by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Spectral repartition of the laser-induced luminescence of Eu3+ in each form correlates well with the structural descriptions.

Natural superhydrophilicity and photocatalytic properties of sol–gel derived ZnTiO3-ilmenite/r-TiO2 films

The additive free heteronucleation and nanocrystallization of ternary Zn(x)Ti(y)O(z) sols and coatings is presented. A proper adjustment of the Zn/Ti ratio in the sol allows the formation of elaborate superhydrophilic cubic spinel-like Zn(2)TiO(4), c-ZnTiO(3) or h-ZnTiO(3)-ilmentite/r-TiO(2)-rutile films. Their morphology and natural superhydrophilicity can be fine-tuned by the inclusion of 5% silica. This doping step delivers high dye intake capacities and water contact angle values below 3°. XPS analysis indicates that Zn and Si enrichment enables greater surface hydroxylation and thus improved water wetting behaviour. The transparent h-ZnTiO(3)-ilmenite/r-TiO(2) nanocomposite coatings deposited on glass and Si-wafers show a remarkable activity in the photomineralization of fatty-acids.

Elaboration and characterization of bimetallic gold–silver nanoparticles supported on mesostructured silica films

Silver–gold nanoparticles are grown inside mesostructured silica films obtained from block copolymers, using two successive steps: the first one involves silver nanoparticle growth. The second step consists of the replacement of the silver with gold. Using two commercial block copolymers, containing polyethylene oxide and polypropylene oxide blocks, mesostructured silica films are suitable “soft” templates for elaborating either spherical gold nanoparticles or nanorods array. Then, a third step involving soft silver reduction allows the preparation of core–shell gold–silver nanostructures. Grazing incidence small-angle X-ray scattering (GISAXS) and Anomalous GISAXS (AGISAXS) analysis are performed using synchrotron radiation on a bimetallic nanoparticles-containing film.

Resonant Raman effect enhanced by surface plasmon excitation of CdSe nanocrystals embedded in thin SiO2 films

In this article, the Raman signal of CdSe nanocrystals well dispersed in a very thin SiO2 film (20 nm) has been investigated by surface plasmon excitation in a resonant Raman spectroscopy experiment. In order to perform the excitation, the thin SiO2 layer containing nanocrystals is deposited on a well-defined silver layer. The surface plasmon excitation increases the sensitivity of the Raman experiment, compared to the conventional setup, and allows the observation of a small number of nanocrystals (around 5000). The luminescence has also been measured and its dependence with the separation between the metal layer and CdSe nanocrystals is analyzed. In particular the quenching of the luminescence for thin film has been used to obtain only the Raman signal in resonant configuration.

Growth of Nanocrystalline Translucent h-BN Films Deposited by CVD at High Temperature on SiC Substrates

h-BN layers were deposited on α-SiC substrates by CVD at high temperature (1500-1900°C) using B2H6 and NH3 diluted in Ar. Growth rates were in the 6-10 µm/h range. In all the conditions studied, the BN as deposited layers were found to be translucent to light, some having a light whitish aspect and other a more yellowish one. It was also observed that the deposit was not always adhesive. µ-Raman and TEM characterization showed that the layers were nano-crystalline with crystallite size < 10 nm. The growth rate was found temperature and N/B ratio dependent due to an N limited growth regime which is more pronounced above 1700°C.

Reversible multi polyelectrolyte layers on gold nanoparticles

Gold nanoparticles surface can be easily modified by different molecules such as polyelectrolytes. In a typical multilayer system made of polyethyleneimine and poly(styrene sulfonate)sodium alternated layers around gold nanoparticles, we have evaluated the interactions between the different layers and the relative strength of interfacial properties. By means of UV–Visible and FTIR spectroscopies, we have shown that due to its amine functionalities, the bonding of polyethyleneimine to gold particles is stronger than the one implied with the sulfonate anion in the PSS inducing a clean removal of this latter after the last polyethyleneimine deposition. Considering that polyethyleneimine is cytotoxic and that only weak covalent bonds are concerned in polyelectrolyte multilayer, this last point is of main importance since external degradation thus exposing polyethyleneimine sub-layer of multilayer films to in vivo tissue cells can occur by many ways.