Nikolaos Vainos

Development and Nonlinear Optical Properties of Block Copolymers Micelles Encapsulating Metal Nanoparticles

Hybrid materials, consisting of an amphiphilic block copolymer matrix incorporating metal nanoparticles, have attracted great attention due to their unique properties, such as the catalytic behavior or the optical properties, making them potential candidates for photonic devices. High purity block copolymers, such as poly(isoprene‐b‐acrylic acid) (PI‐b‐PAA) and poly[(sodium sulfamate‐carboxylate‐isoprene)‐b‐tert‐butylstyrene] (BS‐SCI), have been synthesized by anionic polymerization and dissolved in selective solvents for the formation of well defined micelles. These block copolymers have been used as matrices for the in situ synthesis of gold nanoparticles either inside the dense core or at the periphery of the corona of their micelles. The systems were investigated by dynamic light scattering (DLS), UV‐visible and ATR‐IR spectroscopy, atomic force microscopy (AFM) and transmission electron microscopy (TEM). Additionally, the third non linear optical response of the hybrid materials synthesized has been ...

Near-IR organic light emitting diodes based on porphyrin compounds

Here we report on organic light-emitting diodes incorporating two porphyrin compounds exhibiting red to near infra-red (IR) emission. Especially, the compound with the long side groups (porphyrin II) has a red-shifted emission (λPLmax = 793 nm) compared to the compound with the single porphyrin ring (porphyrin I, (λPLmax = 723 nm) as a consequence of its extended π-conjugation. We studied the electroluminescence of blends with poly(9-vinyl carbazole) (PVK), achieving high color purity near-infrared electroluminescence.

Enhancing spectral response of organic photodetectors through surface modification of metal oxide electrodes

For bulk heterojunction (BHJ) organic photodetectors (OPDs), it was found that the direct contact between the deposited electrode and the photoactive organic layer leads to severe quenching of excitons. Improved device architectures hence involve the incorporation of charge transport layers, such as metal oxide layers, between electrodes and the active layer, allowing substantially higher internal efficiencies to be achieved. We show here that through appropriate surface modification of the underlying metal oxide layer, i.e. through hydrogen annealing, a novel light trapping scheme for the photoactive layer deposited on top of the metal oxide layer is developed. This is achieved via optimization of polymer morphology and chain alignment in OPD devices through the formation of an extended interfacial hydrogen bonding network acting as nucleation site for enhanced chain alignment within the bulk material.

Direct ArF excimer laser microfabrication methods for polymer photonics

Direct laser ablative microfabrication methods are exploited in the development of polymer photonic structures. A dedicated experimental microfabrication facility using ArF excimer laser radiation at λ = 193 nm has been developed. It operates, in conjunction with soft-lithography, chemical post-processing and laser deposition methods, aiming to high quality materials processing. The flexibility of the alternative techniques developed here is demonstrated through the fabrication of exemplar photonic structures, including surface relief holograms, planar optical waveguide and polymer fiber structures. The versatility of the technique is verified by patterning geometrically complex and non-planar surfaces, towards a complete suite of alternative and flexible tools for fabricating polymer photonics.

Polymer photonic technologies for optical communications

The impact of photonics in telecommunications is indisputably massive; however it relies on efficient cost reduction which is in turn only possible if significant cost savings are made at all steps in the development of the photonic device from the material to packaging. The PHOTOPOLIS consortium has identified polymer technology as the ideal solution for producing low-cost devices. The paper aims to discuss the status of polymer photonic components and subsystems able to generate, transmit and manage optical information in a cost effective manner.

Numerical simulation and design of organic integrated optical circuits: The PHOTOPOLIS approach

Organic materials may provide an interesting alternative to integrated optics on either a stand-alone or a hybrid approach where they are combined with conventional material platforms. The development of accurate numerical tools is of paramount importance for designing these structures for telecommunication applications. In this paper, we demonstrate how standard computational electromagnetic methods can be applied in such designs, highlighting the device features that are important from a telecommunications point-of-view. Our analysis focuses on integrated optical waveguides, waveguide couplers, microring resonators and other passive structures. To analyze these devices we make use of analytical methods, such as coupled mode theory and numerical tools such as the finite difference frequency domain method. The tools outlined here form the basis for designing the structures that will be studied within the PHOTOPOLIS initiative.

Laser-induced soft matter organization and microstructuring of photonic materials

Abstract: Laser radiation forces applied in fully transparent, highly entangled semi-dilute polymer solutions generate freestanding, threedimensional, micro- and, potentially, nano-solids. The underlying phenomena are attributed to a synergy of effects involving the radiation forces exerted by milliwatt laser beams on polymer chains and the entanglement of macromolecules. Most importantly, since the primary stages of formation, the incident optical field is structured and guided by the induced microstructures. This self-confinement enhances the effect and results in great compression of the material, osmotic solvent extraction and, eventually, materials solidification in free space. Structural reversibility verifies the absence of any chemical modification of the material. These innovative concepts are demonstrated through the fabrication of microstructures, including among others plasmonic and fluorescent semiconductor quantum–dot hybrid structures, as well as polymer fibers also drawn by laser radiation forces. The phenomenology of the involved effects is plausibly explained here and further research will resolve the fundamental aspects and lead the way forward to new and emerging concepts for future microfabrication technologies.