Stabilizing organic photocathodes by low temperature atomic layer deposition of TiO2

Low-temperature atomic layer deposition forms a compact TiO2 film atop a polymer light absorber for stable and efficient organic–inorganic photo-driven H2 evolution.</p

Organic semiconductors for artificial vision

Organic semiconductors have emerged in the past two decades as promising materials for many technological applications. Thanks to their unique optoelectronic properties, they represent an ideal system to mimic natural photoreceptor functioning. This similarity has been exploited, on one hand, to realize organic-based devices for image detection, taking advantage of typical features of natural visual systems, such as trichromatic sensing; on the other hand, these materials can be interfaced with biological tissues for cell photo-stimulation, with the main goal of restoring light sensitivity in the case of retinas affected by photoreceptor degeneration

Bio-organic interfaces for cellular photo-excitation

The most common strategies to control electrical activity in living cells are based on electrical or chemical stimulation. However, in recent years, techniques relying on optical stimuli are emerging as promising alternatives with peculiar advantages, particularly for the high degree of temporal and spatial resolution that can be achieved. Here we describe the technique of cell stimulation by polymer photo-excitation (CSP), which takes advantage of the unique optoelectronic properties of the interface between organic semiconducting thin films and an ionic liquid environment. Due to their intrinsic bio-affinity with biological systems, conjugated polymers have been demonstrated as functional substrates for the growth of different types of cellular systems. CSP exploits their ability to generate electrical stimuli following photoexcitation. In particular, we demonstrate that thin films of poly(3-hexylthiophene) (P3HT) are able to elicit electrical activity in different types of cells, from primary neurons to cellular lines. An interesting result is that the stimulation is equally effective with films obtained by blending the donor polymer with an electron acceptor, but also with single component P3HT layers; this allows us to shed light on the actual photoexcitation mechanism, which is based on a capacitive coupling of the active interface with the cellular membrane, as corroborated by further physico-chemical analysis. Other developments of the technique with important consequences for neuroscientific experimentation will also be presented. These results open the way to a new generation of neuronal communication and photo-manipulation tools

New experiments on color in context and organic-based artificial photoreceptors

In recent years, organic semiconductors have been used to develop a new generation of photodetectors; in some cases their outstanding properties, especially in terms of spectral tuning, have been exploited in order to reproduce human cone sensitivities. To date, however, it is still not clear if the spectral differences between real and artificial cone responses, unavoidable at a certain extent, may lead to real, corresponding differences in the final color perception. As a matter of fact, one should note that perception is the final result of a complex analysis and elaboration made by our visual system at a superior level respect to the color sensation, as detected in the retinal photoreceptors layer. Therefore, aiming at the development of an artificial retina, the way how human perception actually works can not be disregarded. In this paper, we focus in detail on the role and effect of spatial normalization, when applied to a set of tristimulus values obtained using different integration curves, derived by different organic semiconducting materials. In a recent work, we proposed an experimental setup to investigate this issue. We used a multispectral rendering of a virtual scene as a simulation of incoming light spectra, and a set of artificial cone sensitivities to obtain different tristimulus values for each combination of integrating curves. Finally, we applied different computational models with and without spatial color computation to partially simulate human perception. A preliminary analysis of the values showed that the application of a spatial color algorithm leads to a normalization of the differences in artificial cones spectral sensitivities. In this paper we present the results of a new session of experiments, based on the same experimental setup, but using new multispectral test images of real scenes, and a different selection of organic active materials. We analyze the values obtained after the application of the processing methods, trying to define some latex in the selection, among the many available organic semiconductors, of their most effective combination. Moreover, we introduce some hypothesis regarding the effect of different frequency cut points and overlapping areas between the photore-sponsivity curves

Electronic nanofeatures in epitaxial ferroelectric oxide heterostructures

We report on ferroelectric field effect experiments in epitaxial oxide heterostructures consisting of the ferroelectric oxide Pb(Zr,Ti)O₃ and the metallic oxides GdBa₂Cu₃O₇ and SrRuO₃. To perform the experiments, we used conventional capacitor structures, as well as a scanning probe approach that allows one to control the local ferroelectric polarization without the use of permanent electrical contacts. In the case of the scanning probe approach, nanometer scale control of the ferroelectric domain structure can be achieved over large areas of up to 2500 μm². Nonvolatile, reversible electronic nanofeatures were written in Pb(Zr₀.₅₂Ti₀.₄₈)O₃ / SrRuO₃ heterostructures by switching the local polarization field of the ferroelectric layer, inducing a field effect in the thin (30 Å) SrRuO₃ layer that changes its sheet resistance by 7%. This doping technique permits one to write reversible, nonvolatile electronic structures without requiring traditional lithographic processing or permanent electrical contacts