The field of Bioelectronics deals with the integration of electronics and biology, and possesses a tremendous potential regarding the improvement of the quality of life of millions of people. Thanks to their favorable properties, conjugated polymers have proven to be very suitable materials for the bridging of such diverse worlds. In particular, poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate), or PEDOT:PSS, is nowadays considered a benchmark material for bioelectronics applications. The aim of the present work is to give a detailed characterization of the physical and electrochemical properties of PEDOT:PSS thin films, and to prove the potentialities of this material both for the sensing of bioanalytes, through the development of innovative electrochemical sensors, and for tissue engineering applications, through the development of redox-active substrates that can control the replication of living cells. In this work, the development of all PEDOT:PSS-based organic electrochemical transistors (OECTs) is presented. The sensing efficiency of these devices was optimized in terms of sensitivity and limit of detection (LOD) through the investigation of the effect of device geometry, thickness, and operating voltages. An electrochemical characterization of these devices was carried out as well, in order to clarify the processes involved in the device operation. Furthermore, the operation of these devices as electrochemical sensors was tested on several analytes, obtaining in most cases a performance suitable for real applications. The development and characterization of a different kind of devices realized using the same material, redox-active substrates for applications in tissue engineering, is then presented. The effect of a change in the redox state of these PEDOT:PSS films on cell growth is assessed using two cell lines, human dermal fibroblasts (hDF) and human tumoral glioblastoma multiforme cells (T98G), finding that the cell proliferation rate has a clear dependence on the electrochemical state of its substrate.

In the field of Photovoltaic technologies the organic solar cells are particularly attractive because of their ease of processing, mechanical flexibility and potential low cost production techniques. So far, the reported efficiencies are not high enough to allow to be competitive in the market, however with the introduction of new photoactive materials, device architectures and light management structures, the power conversion efficiencies, at laboratory scale, has rapidly reached the 12%, showing a great potential and a bright future for organic solar cells. Nevertheless, in view of commercial products, two main problems are still unresolved: the relatively low performance of the modules and their lifetime. In sight of this, the present Ph.D thesis has a double goal: 1) a better understanding of the relationship between devices performance and photoactive materials structures 2) a deep investigation on device degradation processes, with particular attention on the effects induced by temperature and incident light. As a result, promising approaches to further optimize the polymer’s optoelectrial properties, and thus the corresponding device performance, are proposed. About the lifetime, first the thermal degradation mechanisms involved on the active layer was investigated and it has been demonstrated the role of the other layers and interfaces in the solar cell thermal stability. In this contest an innovative fast capacitance based thermal test has been developed in order to obtain information regarding the limit operating temperature above which the device becomes thermally unstable. In the end, a preliminary study on the photostability issue was carried out demostrating that the photodegradation of organic solar cells not depends just on the photostability of the donor polymer, but is connected also with the composition of the active layer solution and on the interaction with the adjacent layers. Solutions to limit or prevent the devices degradation processes are proposed.

The research reported in this manuscript concerns the structural characterization of graphene membranes and single-walled carbon nanotubes (SWCNTs). The experimental investigation was performed using a wide range of transmission electron microscopy (TEM) techniques, from conventional imaging and diffraction, to advanced interferometric methods, like electron holography and Geometric Phase Analysis (GPA), using a low-voltage optical set-up, to reduce radiation damage in the samples. Electron holography was used to successfully measure the mean electrostatic potential of an isolated SWCNT and that of a mono-atomically thin graphene crystal. The high accuracy achieved in the phase determination, made it possible to measure, for the first time, the valence-charge redistribution induced by the lattice curvature in an individual SWCNT. A novel methodology for the 3D reconstruction of the waviness of a 2D crystal membrane has been developed. Unlike other available TEM reconstruction techniques, like tomography, this new one requires processing of just a single HREM micrograph. The modulations of the inter-planar distances in the HREM image are measured using Geometric Phase Analysis, and used to recover the waviness of the crystal. The method was applied to the case of a folded FGC, and a height variation of 0.8 nm of the surface was successfully determined with nanometric lateral resolution. The adhesion of SWCNTs to the surface of graphene was studied, mixing shortened SWCNTs of different chiralities and FGC membranes. The spontaneous atomic match of the two lattices was directly imaged using HREM, and we found that graphene membranes act as tangential nano-sieves, preferentially grafting achiral tubes to their surface.

No description available.

We present a study of the metal sites of different proteins through X-ray Absorption Fine Structure (XAFS) spectroscopy. First of all, the capabilities of XAFS analysis have been improved by ab initio simulation of the near-edge region of the spectra, and an original analysis method has been proposed. The method subsequently served ad a tool to treat diverse biophysical problems, like the inhibition of proton-translocating proteins by metal ions and the matrix effect exerted on photosynthetic proteins (the bacterial Reaction Center, RC) by strongly dehydrate sugar matrices. A time-resolved study of Fe site of RC with μs resolution has been as well attempted. Finally, a further step aimed to improve the reliability of XAFS analysis has been performed by calculating the dynamical parameters of the metal binding cluster by means of DFT methods, and the theoretical result obtained for MbCO has been successfully compared with experimental data.

No description available.

Nowadays alternative energies are an extremely important topic and the possibility of using hydrogen as an energy carrier must be explored. Many problems infer the technological application of this abundant and powerful resource, one of them the possibility of storage. In the framework of suitable materials for hydrogen storage, magnesium has been the center of this study because it is cheap and the amount of stored hydrogen that it achieves (7.6 wt%) is extremely appealing. Nanostructure helps to overcome the slow hydrogen diffusion and the functionalization of surfaces with transition metals or oxides favors the hydrogen molecule dissociation/recombination. The aim of this research is the investigation of the metal-hydride transformation in magnesium nanoparticles synthesized by inert-gas condensation, exploiting the fact that they are a simple model system. The so produced nanostructured powder has been analyzed in response to nanoparticles surface functionalization by transition metal clusters, specifically palladium, nickel and titanium, chosen on the basis of their completely different Mg-related phase diagrams. The role of the intermetallic phases formed upon heating and hydrogenation treatments will be presented to provide a comprehensive picture of hydrogen sorption in this class of nanostructured storage materials.

No description available.

The possibility of combining different functionalities in a single device is of great relevance for further development of organic electronics in integrated components and circuitry. Organic light-emitting transistors (OLETs) have been demonstrated to be able to combine in a single device the electrical switching functionality of a field-effect transistor and the capability of light generation. A novel strategy in OLET realization is the tri-layer vertical hetero-junction. This configuration is similar to the bi-layer except for the presence of a new middle layer between the two transport layers. This “recombination” layer presents high emission quantum efficiency and OLED-like (Organic Light-Emitting Diode) vertical bulk mobility value. The key idea of the vertical tri-layer hetero-junction approach in realizing OLETs is that each layer has to be optimized according to its specific function (charge transport, energy transfer, radiative exciton recombination). Clearly, matching the overall device characteristics with the functional properties of the single materials composing the active region of the OFET, is a great challenge that requires a deep investigation of the morphological, optical and electrical features of the system. As in the case of the bi-layer based OLETs, it is clear that the interfaces between the dielectric and the bottom transport layer and between the recombination and the top transport layer are crucial for guaranteeing good ambipolar field-effect electrical characteristics. Moreover interfaces between the bottom transport and the recombination layer and between the recombination and the top transport layer should provide the favourable conditions for the charge percolation to happen in the recombination layer and form excitons. Organic light emitting transistor based on the tri-layer approach with external quantum efficiency out-performing the OLED state of the art has been recently demonstrated [Capelli et al., Nat. Mater. 9 (2010) 496-503] widening the scientific and technological interest in this field of research.

Many studies on the morphology, molecular orientation, device performance, substrate nature and growth parameter dependence have been carried out since the proposal of Sexithiophene (6T) for organic electronics [ ] However, these studies were mostly performed on films thicker than 20nm and without specifically addressing the relationship between morphology and molecular orientation within the nano and micro structures of ultrathin films of 0-3 monolayers. In 2004, the observation that in OFETs only the first few monolayers at the interface in contact with the gate insulator contribute to the charge transport [ ], underlined the importance to study submonolayer films and their evolution up to a few monolayers of thickness with appropriate experimental techniques. We present here a detailed Non-contact Atomic Force Microscopy and Scanning Tunneling Microscopy study on various substrates aiming at the investigation of growth mechanisms. Most reported similar studies are performed on ideal metals in UHV. However it is important to investigate the details of organic film growth on less ideal and even technological surfaces and device testpatterns. The present work addresses the growth of ultra thin organic films in-situ and quasi real-time by NC-AFM. An organic effusion cell is installed to evaporate the organic material directly onto the SPM sample scanning stage.