Towards a biosensor based on Anti Resonant Reflecting Optical Waveguide fabricated from porous silicon.

International audienceRecently, we demonstrated that Anti Resonant Reflecting Optical Waveguide (ARROW) based on porous silicon (PS) material can be used as a transducer for the development of a new optical biosensor. Compared to a conventional biosensor waveguide based on evanescent waves, the ARROW structure is designed to allow a better overlap between the propagated optical field and the molecules infiltrated in the porous core layer and so to provide better molecular interactions sensitivity. The aim of this work is to investigate the operating mode of an optical biosensor using the ARROW structure. We reported here an extensive study where the antiresonance conditions were adjusted just before the grafting of the studied molecules for a given refractive index range. The interesting feature of the studied ARROW structure is that it is elaborated from the same material which is the porous silicon obtained via a single electrochemical anodization process. After oxidation and preparation of the inner surface of porous silicon by a chemical functionalization process, bovine serum albumin (BSA) molecules, were attached essentially in the upper layer. Simulation study indicates that the proposed sensor works at the refractive index values ranging from 1.3560 to 1.3655. The experimental optical detection of the biomolecules was obtained through the modification of the propagated optical field and losses. The results indicated that the optical attenuation decreases after biomolecules attachment, corresponding to a refractive index change Δnc of the core. This reduction was of about 2 dB/cm and 3 dB/cm for Transverse Electric (TE) and Transverse Magnetic (TM) polarizations respectively. Moreover, at the detection step, the optical field was almost located inside the core layer. This result was in good agreement with the simulated near field profiles

The engineering properties of glacial tills

Glacial tills are a product of the glacial processes of erosion, transportation and deposition and could have been subjected to several glacial cycles and periglacial processes to the extent that they are complex, hazardous soils that are spatially variable in composition, structure, fabric and properties, making them very difficult to sample, test and classify. An overview of the formation of glacial tills and their properties shows that they are composite soils which should be classified according to their lithology, their mode of deposition to link the glacial processes with the facies characteristics and their engineering behaviour. This enables representative design properties to be assigned using frameworks developed for composite soils

Studies of BSA interactions with gold nanoparticles deposited on functionalized porous silicon surface

International audienc

Planar ARROW biosensing structure based on functionalized pourous silicon material

International audienc

FTIR and Raman spectroscopy studies of functionalized oxidized porous silicon for label free bio-sensing applications

International audienc

Emission mechanisms in stabilized iron-passivated porous silicon: Temperature and laser power dependences

International audiencePhotoluminescence (PL) measurements of porous silicon (PS) and iron-porous silicon nanocomposites (PS/Fe) with stable optical properties versus temperature and laser power density have been investigated. The presence of iron in PS matrix is confirmed by Raman spectroscopy. The PL intensity of PS and PS/Fe increases at low temperature, the evolution of integrated PL intensity follows the modified Arrhenius model. The incorporation of iron in PS matrix reduces the activation energy traducing the existence of shallow levels related to iron atoms. Also, the temperature dependence of the porous silicon PL peak position follows a linear evolution at high temperature and a quadratic one at low temperature. Such evolution is due to the thermal carriers' redistribution and an energy transfer. Similarly, we have compared the laser power dependence of the PL in PS and PS/Fe layers. The results prove that the recombination process in PS is realised through the lower energy traps localised in the electronic gap. However, the observed emission in PS/Fe is essentially due to direct transitions. So, we can conclude that the presence of iron in PS matrix induces a strong modification of the PL mechanisms

Effects of silicon porosity on physical properties of ZnO films

International audienceWe report on structural and optical properties of ZnO thin films deposited on different Si-based substrates presenting different porosities. ZnO layers were prepared by sol gel method and deposited on crystalline silicon (ZnO/Si), mesoporous silicon (ZnO/PS+) and nanoporous silicon (ZnO/PS-) by spin coating. Several techniques such as scanning electron microscope (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence spectroscopy (PL) and spectroscopic ellipsometry (SE) were used to study the influence of the pore size of porous silicon (PS) on physical properties of ZnO films. SEM images revealed the formation of ZnO granular nanoparticles on Si, PS- and PS+ substrates. We show by the XRD analysis that hexagonal crystallized (002) ZnO is mainly obtained for ZnO/PS- system causing by a strong absorption of the capillary effect and high adhesion to PS- surface. An intense PL related to ZnO and PS- was demonstrated for ZnO/PS- in UV and visible ranges. Optical properties of ZnO were determined and analyzed by SE using Tanguy dispersion model. For each sample, a specific optical model was carried out. SE confirms a good physical properties of ZnO/PS- comparing to ZnO/Si and ZnO/PS+. For example, the good crystallinity is characterized by low damping factor value (Gamma). This value was found by SE to be low (29 meV) for the ZnO/PS-, while the damping factors of ZnO/Si and ZnO/PS+ are 47 meV and 70 meV, respectively. The amplitude of dielectric function of ZnO/PS- around 3.4 eV reveals an increase of grain size and crystallinity of ZnO layer

Energy Transfer and Emission Decay Kinetics in Mixed Microporous Lanthanide Silicates with Unusual Dimensionality

We have investigated the energy transfer dynamics in mixed lanthanide open-framework silicates, known as Ln-AV-20 materials, with the stoichiometric formula Na1.08K0.5Ln1.14Si3O8.5·1.78H2O (Ln = Gd3+, Tb3+, Eu3+), using steady-state and time-resolved luminescence spectroscopy. Energy transfer between donor and acceptor Ln3+ ions is extremely efficient, even at low molar ratios of the acceptor Ln3+ (<5%). The presence of two different Ln3+ environments makes the Ln-AV-20 intralayer structure intermediate between purely one-dimensional (1D) and two-dimensional (2D). The unusual dimensionality of the Ln-AV-20 layers prevents modeling of energy transfer kinetics by conventional kinetic models. We have developed a computer modeling program for the analysis of energy transfer kinetics in systems of unusual dimensions and show how it may be applied successfully to the AV-20 system. Using the program, nearest neighbor energy transfer rate constants are calculated as (5.30 ± 0.07) × 106 and (6.00 ± 0.13) × 106 s-1, respectively, for Gd/Tb- and Tb/Eu-AV-20 at 300 K. With increasing acceptor concentration, the energy transfer dynamics tend toward purely one-dimensional behavior, and thus, with careful selection of the ratio of individual Ln3+ ions, it is possible to tune the energy transfer dimensionality of the AV-20 layers from pure 1D to something intermediate between 1D and 2D