Selective coupling of Whispering Gallery Modes in film coated micro-resonators.

Whispering Gallery Mode (WGM) micro-resonators like microspheres or microtoroids are typically used as high-Q cavity substrate on which a functional film coating is deposited. In order to exploit the coating properties a critical step is the efficient excitation of WGMs mainly contained inside the deposited layer. We developed a simple method able to assess whether or not these modes are selectively excited. The method is based on monitoring the thermal shift of the excited resonance, which uniquely depends on the thermo-optic coefficient and on the thermal expansion coefficient of the material in which the mode is embedded.

Modelling of organic field effect transistors with inkjet printed poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) electrodes: study of the annealing effects.

In the present work, the transport mechanism of organic transistors with bottom-gate/top-contact structure, manufactured by employing traditional and inkjet printing techniques, was studied. Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) conductive polymer was used for realizing printed source, drain and gate electrodes. The influence of the printing parameters (substrate temperature, drop overlapping degree, drop emission frequency) on the uniformity and morphology of the PEDOT:PSS layer was investigated. Polymethyl methacrylate (PMMA) was used as organic dielectric and pentacene, deposited by thermal evaporation, was employed as p-type semiconductor. Organic field effect transistors (OFETs) were fabricated and electrically characterized before and after the thermal annealing process at 120 degrees C for 1 h in nitrogen ambient. The effect of the annealing on the performances of the OFETs was investigated by modelling the measured electrical characteristics and analyzing them in terms of mobility, characteristic temperature and energy distribution of the density of localized states (DOS). In addition, the OFET working under electrical stress in ambient conditions was observed and discussed.

Study of the interference effects in an optical cavity for organic light-emitting diode applications.

The interference effects generated in a bottom-emitting electroluminescent device fabricated on a polymer underlayer introduced with the aim of improving the anode roughness have been studied. The analysis of the interference fringes at different detection angles and the spatial coherence demonstrates that this phenomenon is due to multiple internal reflections that propagate in the polymer layer. This effect can be eliminated by modifying the polymer thickness and the incidence angle of the electromagnetic radiation at the anode-polymer interface. Inkjet etching technology is adopted for microcavities-shaped polymer structuring to destroy the resonator effect of the optical cavity.

Plasma functionalization procedure for antibody immobilization for SU-8 based sensor.

In this paper, we report the study on a new protocol for the immobilization process of antigen/antibody assay on SU-8 layers by oxygen plasma treatment. Plasma treatments, at different plasma powers and for different duration times, are performed and their effects on immobilization efficiency are studied. The chemical properties and the surface morphology of SU-8 before and after the functionalization and immobilization of (IgG) are then verified by Raman spectroscopy and atomic force microscopy (AFM). An increase of the surface roughness of SU-8 layers is observed after the oxygen plasma treatment and an intensity variation of functional groups is also evidenced. To demonstrate the validity of the process the distribution of IgG immobilized on SU-8 surfaces is detected by fluorescence microscopy measurement after incubation with fluorescein isothiocyanate (FITC)-tagged anti-human IgG. An increase of the amount of the adsorbed protein of about 20% and a good repeatability on antigen/antibody distribution on the surface are detected for IgG on plasma treated substrates. Finally, label free measurements are performed by SU-8 optical ring resonators reaching detection limits of 0.86ngcm(-2). The proposed approach offers a smart protocol for IgG immobilization on SU-8 substrate that can be easily extended to different antigen/antibody assay and polymeric materials for the realization of high performance immunosensors.