Trapping light with micro lenses in thin film organic photovoltaic cells.

We demonstrate a novel light trapping configuration based on an array of micro lenses in conjunction with a self aligned array of micro apertures located in a highly reflecting mirror. When locating the light trapping element, that displays strong directional asymmetric transmission, in front of thin film organic photovoltaic cells, an increase in cell absorption is obtained. By recycling reflected photons that otherwise would be lost, thinner films with more beneficial electrical properties can effectively be deployed. The light trapping element enhances the absorption rate of the solar cell and increases the photocurrent by as much as 25%. (C) 2008 Optical Society of Americ

Atomic force spectroscopy-based essay to evaluate oocyte postovulatory aging

Postovulatory aging is a process occurring in the mature (MII) oocyte leading the unfertilized ones to apoptosis. The optimal time window of fertility for different mammalian species after oocytes maturation depends on its timeliness: the higher the time elapsed from the accomplishment of the MII stage, the lower are the chances of fertilization and of development of a viable embryo. In the in vitro fertilization, the selection of competent oocytes for intracytoplasmic sperm injection (ICSI) is mostly made by the visual inspection of the MII oocyte morphology, which does not allow to determine the oocyte postovulatory age. On the other hand, more specific tests usually involve some kind of staining, thus compromising the viability of the oocyte for reproductive purposes. Hence, the need of a noninvasive analysis of oocyte aging to improve the success rate of in vitro fertilization procedures. Here, we exploit atomic force microscopy to examine the evolution of the mechanical properties of mouse oocytes during in vitro postovulatory aging. Three hours before the occurrence of any visual morphological feature related to degradation, we observe a sudden change of the mechanical parameters: the elastic modulus doubles its initial value, while the viscosity decreases significantly. These mechanical variations are temporally correlated with the release of the cortical granules, investigated by fluorescence microscopy. Interestingly, the oocyte mechanics correlates as well with the yield of embryo formation, evaluated up to the blastocyst formation stage. These results demonstrate that minimally invasive mechanical measurements are very sensitive to the aging of the oocyte and can be used as a label-free method to detect the age of the postovulatory oocytes

Glucose is a key driver for GLUT1-mediated nanoparticles internalization in breast cancer cells

The mesenchymal state in cancer is usually associated with poor prognosis due to the metastatic predisposition and the hyper-activated metabolism. Exploiting cell glucose metabolism we propose a new method to detect mesenchymal-like cancer cells. We demonstrate that the uptake of glucose-coated magnetic nanoparticles (MNPs) by mesenchymal-like cells remains constant when the glucose in the medium is increased from low (5.5 mM) to high (25 mM) concentration, while the MNPs uptake by epithelial-like cells is significantly reduced. These findings reveal that the glucose-shell of MNPs plays a major role in recognition of cells with high-metabolic activity. By selectively blocking the glucose transporter 1 channels we showed its involvement in the internalization process of glucose-coated MNPs. Our results suggest that glucose-coated MNPs can be used for metabolic-based assays aimed at detecting cancer cells and that can be used to selectively target cancer cells taking advantage, for instance, of the magnetic-thermotherapy

Timing methodologies and studies at the FERMI free-electron laser.

Time-resolved investigations have begun a new era of chemistry and physics, enabling the monitoring in real time of the dynamics of chemical reactions and matter. Induced transient optical absorption is a basic ultrafast electronic effect, originated by a partial depletion of the valence band, that can be triggered by exposing insulators and semiconductors to sub-picosecond extreme-ultraviolet pulses. Besides its scientific and fundamental implications, this process is very important as it is routinely applied in free-electron laser (FEL) facilities to achieve the temporal superposition between FEL and optical laser pulses with tens of femtoseconds accuracy. Here, a set of methodologies developed at the FERMI facility based on ultrafast effects in condensed materials and employed to effectively determine the FEL/laser cross correlation are presented

Innovative solution in organic photovoltaic devices

New technologies for photovoltaic energy generation can contribute to environmentally friendly, renewable energy production and may lead to the reduction of carbon dioxide liberated by burning fossil fuels and biomasses. Besides the established silicon based solar cells new photovoltaic technology has gained a lot of interest during the last decade. Among them organic solar cells (OSC) based on conjugated molecules or polymers are promising candidates for the manufacturing of environmentally safe, flexible, lightweight, and inexpensive photovoltaic devices which can be used in low cost applications. Particularly attractives are in photovoltaic (PV) elements based on thin plastic films. The flexibility offered through the chemical tailoring of desired properties, as well as the cheap technology already well developed for all kinds of plastic thin film applications would make such an approach widely adopted. Unfortunately a main bottleneck is to be solved before industrial production could become economically viable, particularly represented by the still low conversion efficiency. In organic semiconductors the primary photo-excitations do not directly and quantitatively lead to free charge carriers but to coulombically bound electron-hole pairs, called excitons, that need strong electric fields to generated free charge carriers, present for example at the discontinuous potential drops at the interfaces between donors and acceptors as well as between semiconductors and metals. The exciton diffusion lengths in polymers and in organic semiconductors is usually around 10-20 nm: for efficient photovoltaic devices, the excitons have to split before recombining and the free electrons and holes must be transported towards the electrodes to produce the photocurrent. Major problem derives from loss mechanism, such as exciton decay, charge recombination and low mobility, resulting in reduced photocurrent extraction at the electrodes and low power conversion efficiency. The improvement of the efficiency is one of the most important aspect in which is concentrated the research in OSC, our too. Two different routes going towards this objective focalized in this aspect have been explored, in order to contribute to realize a novel and effective technology in the photovoltaic field. The first concerns the development of a novel light trapping system bases on microlenses, The second, on which we are still working, regards the fabrication of nanostructured solar cells by top-down techniques, particularly nanoimprinting (NIL).Il problema energetico sta destando negli ultimi anni sempre maggior interesse e preoccupazione, per il ridursi delle risorse fossili e dal conseguente acuirsi dei problemi d’inquinamento derivanti dal loro quasi esclusivo utilizzo per la produzione di energia elettrica. Non è sorprendente quindi che dal mondo della ricerca un grande sforzo sia dedicato allo sviluppo della tecnologia fotovoltaica. Attualmente, il silicio possiede una posizione centrale nel panorama delle celle fotovoltaiche: l’elevato costo di questo tipo di tecnologia, derivato dall’alto costo del materiale e dei processi fabbricativi, ha incoraggiato lo sviluppo di soluzioni alternative che si basino su materiali innovativi. Tra queste, grande risalto è stato dato negli ultimi anni alle cosiddette "organic solar cell", basate sull’impiego di semiconduttori organici. Il loro vantaggio risiede nel fatto che questi possono essere depositati, su larghe aree e a costi molto ridotti, in fase liquida, utilizzando quindi metodi tipici dell’industria della stampa nel campo del fotovoltaico ed eliminando così alti costi di materiale e di processo tipici dell’industria a semiconduttore inorganico. L’impiego di film sottili e conseguentemente di poco materiale, contribuisce a rendere il fotovoltaico organico uno dei più quotati candidati per lo sviluppo di una tecnologia solare a basso costo. Una tipologia di celle solari organiche utilizza come materiali foto attivi i polimeri coniugati; evidenti progressi sono stati compiuti, col raggiungimento di efficienze ragguardevoli, dell’ordine del 4-5%. Purtroppo però, questo non è ancora sufficiente perché la tecnologia possa essere trasferita su scala industriale. Molti sforzi si stanno facendo nell’ambito della ricerca per migliorare l’efficienza di queste celle. Sullo sviluppo e l’impiego di soluzioni alternative e innovative applicabili al campo del fotovoltaico organico, e in particolare polimerico, è concentrata la nostra attività di ricerca. Due percorsi in particolare sono stati investigati, basate sull’impiego di un nuovo sistema per l’intrappolamento in cavità della luce e sull’impiego delle nanotecnologie fabbricative

Low-cost and fast wet-based technique to generate nanostructured organic materials layers and its application to chemiresistive gassensing devices

4noNanostructured materials for sensors and transducers are of great interest to the scientific community due to several advantages that these materials can provide (e.g., integration with large scale manufacturing technologies, enhanced performances, etc.). Nonetheless, large-area, low-cost and fast processing technologies for creating effective sensing nanostructures are still sought for. In this work, a recently described technique called Auxiliary Solvent-Based Sublimation-Aided NanoStructuring (ASB-SANS) has been used to generate poly(3-hexylthiophene) (P3HT, a well known semiconducting polymer) nanofilamentary structures onto interdigitated electrodes. These have been tested as gas sensing layers for volatile organic compounds, delivering promising results.openopenViviani, Emanuele; Bertoni, Cristina; Dal Zilio, Simone; Fraleoni-Morgera, AlessandroViviani, Emanuele; Bertoni, Cristina; DAL ZILIO, Simone; FRALEONI MORGERA, Alessandr

Nanostructured P3HT layers fabricated by self-assembly as promising gas sensors

Poly(3-hexylthiophene) (P3HT) nanofibers fabricated by self-assemby have been used as active sensing layers in chemiresistive gas sensors for acetone, ammonia and water. Their response has been compared to that of analogous devices in which P3HT was present as a plain, nonnanostructured layer. The results of this comparison show that nanofiber-based sensors have faster signal decay times and complete baseline recovery even after being exposed to saturated vapors of the analytes. Moreover, the current response of nanofiber-based devices increases by one order of magnitude or more upon exposure to the analyte, while for plain layers this increase is about 50% at maximum. Finally, on the basis of the collected data, a correlation between the analyte polarizability and the 90% baseline recovery times seems to exist, likely due to the occurrence of just physical adsorption (and not also of vapor penetration) of the analyte onto the polymer surface

Controlled self-organization of polymer nanopatterns over large areas

Abstract Self-assembly methods allow to obtain ordered patterns on surfaces with exquisite precision, but often lack in effectiveness over large areas. Here we report on the realization of hierarchically ordered polymethylmethacrylate (PMMA) nanofibres and nanodots over large areas from solution via a fast, easy and low-cost method named ASB-SANS, based on a ternary solution that is cast on the substrate. Simple changes to the ternary solution composition allow to control the transition from nanofibres to nanodots, via a wide range of intermediate topologies. The ternary solution includes the material to be patterned, a liquid solvent and a solid substance able to sublimate. The analysis of the fibres/dots width and inter-pattern distance variations with respect to the ratio between the solution components suggests that the macromolecular chains mobility in the solidified sublimating substance follows Zimm-like models (mobility of macromolecules in diluted liquid solutions). A qualitative explanation of the self-assembly phenomena originating the observed nanopatterns is given. Finally, ASB-SANS-generated PMMA nanodots arrays have been used as lithographic masks for a silicon substrate and submitted to Inductively Coupled Plasma-Reactive Ion Etching (ICP-RIE). As a result, nanopillars with remarkably high aspect ratios have been achieved over areas as large as several millimeters square, highlighting an interesting potential of ASB-SANS in practical applications like photon trapping in photovoltaic cells, surface-enhanced sensors, plasmonics