Ripalta Stabile

Patterning of light-emitting conjugated polymer nanofibres

Organic materials have revolutionized optoelectronics by their processability, flexibility and low cost, with application to light-emitting devices for full-colour screens, solar cells and lasers. Some low-dimensional organic semiconductor structures exhibit properties resembling those of inorganics, such as polarized emission and enhanced electroluminescence. One-dimensional metallic, III-V and II-VI nanostructures have also been the subject of intense investigation as building blocks for nanoelectronics and photonics. Given that one-dimensional polymer nanostructures, such as polymer nanofibres, are compatible with sub-micrometre patterning capability and electromagnetic confinement within subwavelength volumes, they can offer the benefits of organic light sources to nanoscale optics. Here we report on the optical properties of fully conjugated, electrospun polymer nanofibres. We assess their waveguiding performance and emission tuneability in the whole visible range. We demonstrate the enhancement of the fibre forward emission through imprinting periodic nanostructures using room-temperature nanoimprint lithography, and investigate the angular dispersion of differently polarized emitted light.

Laser emission from electrospun polymer nanofibers

althoughelectrospinning (ES), based on the stretching of a polymersolution under electrostatic forces, represents a practicallyunique technology that combines low cost and high through-put. Moreover, the addition of active components (i.e.,nanoparticles or molecular species) to the ES polymersolution allows one to obtain composite nanofibers withspecific functionalities.

Nanotopographic Control of Neuronal Polarity

We employ simple geometrical rules to design a set of nanotopographies able to interfere with focal adhesion establishment during neuronal differentiation. Exploiting nanoimprint lithography techniques on cyclic-olefin-copolymer films, we demonstrate that by varying a single topographical parameter the orientation and maturation of focal adhesions can be finely modulated yielding independent control over the final number and the outgrowth direction of neurites. Taken together, this report provides a novel and promising approach to the rational design of biocompatible textured substrates for tissue engineering applications.

Electrospun dye-doped polymer nanofibers emitting in the near infrared

The authors report on the fabrication and characterization of near infrared fluorescent nanofibers. The nanofibers are composed by an organic dye dispersed in a poly(methylmethacrylate) inert matrix and realized by electrospinning. They exhibit diameters down to 70nm, with average values in the range of 170–480nm, depending on the process parameters, and photoluminescence emission peaked at 865nm. The temporal behavior of the emission under ultraviolet excitation in air can be described by an oxygen diffusion model with a characteristic time τ in the range of 400–1200s, depending on the fiber size, which correspond to a photostability longer than (0.4–1.2)×105 excitation laser pulses. These results open the way for large volume and cost-effective realization of infrared-emitting nanofibers, which are promising candidates as nanoscale infrared light sources.

Near-infrared imprinted distributed feedback lasers

The authors report on the fabrication and characterization of an organic distributed feedback laser operating in the near infrared. The device, fabricated by room-temperature nanoimprint lithography, is based on an organic dye hosted by a poly(methylmethacrylate) matrix. The laser emission from an imprinted 620nm period grating is peaked at 918nm with a linewidth of 8A and a pumping threshold of 37μJ∕cm2, and it is strongly polarized with a polarization contrast as high as 0.99. The lasing wavelength is tunable in the range of 890–930nm by adjusting the grating period, and the operational lifetime is up to 6×103 excitation pulses in vacuum environment. These results demonstrate the possibility of realizing imprinted organic-based near-infrared lasers, thus approaching spectral regions relevant for optical communication applications.

Monolithic active-passive 16 × 16 optoelectronic switch

We present what is to our knowledge the first active-passive monolithically integrated 16×16 switch. The active InP/InGaAsP elements provide semiconductor optical amplifier gates in a multistage rearrangeably nonblocking switch design. Thirty-two representative connections, including the shortest, longest, and comprehensive range of intermediate paths have been assessed across the switch circuit. The 10 Gb/s signal routing is demonstrated with an optical signal-to-noise ratio up to 28.3 dB/0.1 nm and a signal extinction ratio exceeding 50 dB.

Collagen-functionalised electrospun polymer fibers for bioengineering applications

Polymer electrospun fibers are gaining increasing importance in nanobiotechnology, due to their intrinsic three-dimensional topography and biochemical flexibility. Here we present an in-depth study of protein functionalisation for polymethylmethacrylate fibers. We compare different coating approaches for type I collagen, including physisorption and covalent binding methods relying on functional linkers. The biofunctionalised fibers are investigated by scanning electron and confocal laser scanning microscopy, wettability measurements, Fourier-transform infrared spectroscopy, and protein quantification assays. We demonstrate that the largest amount of proteins adsorbed on fibers does not determine the best performance in terms of cell attachment and proliferation in vitro, which is instead related to the type of linking and the relevant role played by adsorption of serum biomolecules on the three-dimensional nanostructures. This study is relevant for designing and engineering novel biomaterials and scaffold architectures based on electrospun nanofibers.

Polymeric distributed feedback lasers by room-temperature nanoimprint lithography

Room temperature nanoimprinting lithography is used to realize a distributed feedback laser by direct dry pressing of the conjugated polymer (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]). The laser device exhibits emission at 630nm with a pump threshold of 25μJ∕cm2 and a polarization contrast of the emitted light as large as 0.91. Therefore, room temperature nanoimprint lithography turns out to be very effective for producing stable patterns on light-emitting polymers for the one-step fabrication of nanopatterned optoelectronic devices.

CdS-polymer nanocomposites and light-emitting fibers by in situ electron-beam synthesis and lithography.

A straightforward, electron-beam induced synthesis and patterning approach to the in situ generation of CdS nanocrystals in nanocomposite films and light-emitting electrospun nanofibers is used. Smartly combining room-temperature nanoimprinting, electrospinning, and electron-beam decomposition of nanocrystal precursors and subsequent nucleation of nanoparticles in a polymer matrix allows exploitation of the most favorable flow conditions of organics to produce various nanocomposite nanostructures.

Monolithically Integrated 8 × 8 Space and Wavelength Selective Cross-Connect

The first monolithically integrated InGaAsP/InP active-passive 8 × 8 cross-connect is designed, fabricated and demonstrated. The selection functionalities in the space and wavelength domain are implemented simultaneously on a single chip. Eight broadband inputs connect to an array of 1 × 8 broadband space selection switches. Wavelength domain selection is subsequently performed with an array of eight 8 × 8 gated cyclic routers. The on-chip fan-outs and fan-ins allow the integration of 136 semiconductor optical amplifier gates and eight cyclic routers within a chip area of 14.6 × 6.7 mm2 . Circuit connectivity is evaluated for the full range of paths with optical and electronic connections for 84% of the paths in this first prototype. Good spectral uniformity for the cyclic routers and loss compensation from the semiconductor optical amplifier gates allow for operation across a broad spectral range. Data routing studies are performed for a representative range of paths to show optical signal to noise ratios of greater than 30 dB/0.1 nm. Dynamically reconfigurable routing is also demonstrated for four simultaneously routed wavelengths. Switch rise and fall times are measured to be 3.8 and 3.2 ns respectively.