Teresa Ligonzo

Melanin Layer on Silicon: an Attractive Structure for a Possible Exploitation in Bio-Polymer Based Metal- Insulator-Silicon Devices

Dr. M. Ambrico , Dr. P. F. Ambrico CNR-Istituto di Metodologie Inorganiche e dei Plasmi-UOS di Bari70125 Bari, Italy E-mail: marianna.ambrico@ba.imip.cnr.it Dr. A. Cardone , Dr. S. R. Cicco CNR-Istituto di Chimica dei Composti OrganoMetallici-UOS di Bari70125 Bari, Italy Ligonzo , Dr. . T Prof. Augelli . V Dipartimento Interateneo di FisicaUniversita degli Studi di Bari “Aldo Moro”70125 Bari, Italy Dr. R. Di Mundo , Prof. G. M. arinola F Dipartimento di ChimicaUniversita degli Studi di Bari “Aldo Moro”70125 Bari, Italy

Optical characterization of CdSxSe1−x films grown on quartz substrate by pulsed laser ablation technique

Abstract CdS x Se 1− x alloys have been deposited on quartz substrates by means of pulsed laser ablation, a relatively new technique for growing semiconductor films. We obtained high quality polycrystalline films which present photoluminescence efficiency up to at room temperature. The dependence of the band gap on the x composition, measured by absorption spectra at 10 K, shows an upwards band gap bowing. The real part of the refractive index in the transparent region at room temperature is well described by the Sellmeier relation.

Engineering polydopamine films with tailored behaviour for next-generation eumelanin-related hybrid devices

Eumelanin-type biopolymers have attracted growing interest in the quest for soft bioinspired functional materials for application in organoelectronics. Recently, a metal-insulator-semiconductor device with a good quality interface was produced by spin coating of a commercial synthetic eumelanin-like material on a dry plasma-modified silicon surface. As a proof-of-concept step toward the design and implementation of next-generation eumelanin-inspired devices, we report herein an expedient chemical strategy to bestow n-type performance to polydopamine, a highly popular eumelanin-related biopolymer with intrinsic semiconductor behaviour, and to tune its electrical properties. The strategy relies on aerial co-oxidation of dopamine with suitable aromatic amines, e.g. 3-aminotyrosine or p-phenylenediamine, leading to good quality black polymeric films. Capacitance–voltage experiments on poly(dopamine/3-aminotyrosine) and poly(dopamine/p-phenylenediamine)-based metal insulator semiconductor devices on p-Si indicated a significant increase in flat band voltage with respect to polydopamine and previous synthetic eumelanin-based diodes. Variations of the flat band voltage under vacuum were observed for each device. These results point to polydopamine as a versatile eumelanin-type water-dependent semiconductor platform amenable to fine tuning of its electronic properties through incorporation of π-conjugating aromatic amines to tailor functionality.

Contacting organic molecules by metal evaporation

Reproducible electrical contacts to organic molecules are created non-destructively by indirect electron beam evaporation of Pd onto molecular films on cooled substrates. In contrast, directly evaporated contacts damage the molecules seriously. Our conclusions are based on correlating trends in properties of a series of molecules with systematically varying, exposed functional groups, with trends in the electrical behaviour of Pd/molecule/GaAs junctions, where these same molecules are part of the junctions.

Organic–inorganic dielectric multilayer systems as high reflectivity distributed Bragg reflectors

Unprecedentedly high reflectivity distributed Bragg reflectors consisting of fluorocarbon polymer (CFx) and high refractive index inorganic oxide multilayers have been fabricated by means of assisted ion-beam sputtering at room temperature. Multilayer stacks consisting of a CFx/TiOx and CFx/HfOx pairs exhibit reflectivities larger than 98% in the infrared and ultraviolet spectral region, respectively. The superior wide tunability and the high efficiency, with respect to inorganic–inorganic multilayers is due to the exceptionally low refractive index of the fluorcarbon polymer (n≃1.35) on a very large spectral region (300–2000 nm).

Synthesis of silicon carbide thin films by ion beam sputtering

Synthesis of silicon carbide (SiC) films has been obtained by means of ion beam sputtering. The films have been grown by co-sputtering Si and C targets by means of two Ar-ion beams at substrate temperatures ranging between 30 and 700°C. Chemical, structural and optical analysis have been performed on the samples. The change from amorphous to polycrystalline phase and the relative improvement of the chemical and optical properties have been observed on films grown at 700°C.

A reverberation chamber to investigate the possible effects of "in vivo" exposure of rats to 1.8 GHZ electromagnetic fields: A preliminary study

A system generating 1.8GHz electromagnetic fields for bio-medical and behavioral study on laboratory animals was designed and implemented. The system is based on a reverberation chamber. An input power up to 5W can be sent to an indoor transmitting antenna and an electric field strength (E) more than 90V/m can be reached inside the chamber. The system was characterized at different input powers measuring E in different points by means of a miniature sensor. Then, boxes with 300cc of physiological liquid inside were realized as simple phantoms simulating laboratory animals (rats) and E inside the liquid was measured, performing several simulations by moving the phantoms (1,2) in the chamber and/or putting them still in different positions. On the basis of these measurements, the SAR (Specific Absorption Rate) and the Pe (power efficiency = SAR/input power) were determined at different powers. The actual system is characterized by a low power efficiency with respect to the in vivo exposition systems based on transversal electromagnetic (TEM) cells. Its advantage is to have inside the chamber a habitat similar to the usual one for the laboratory animals.

Electrical properties of gold–polymer composite films

Electrical conductivity measurements in the range 50–300 K have been carried out on gold–fluorocarbon–polymer composite films. Such measurements have been performed on samples with different percentages in volume of gold, before and after thermal annealing up to 450 K. The experimental temperature dependence of conductivity, in the range 50–300 K, follows the exponential law σ=σ0u200aexp[−(T0/T)γ], where T0 and γ are constants. Best fit analyses carried out on experimental conductivity data, before and after thermal annealing, give values of γ that can be related to the gold content of the film and to the size of grains embedded in the polymeric matrix. Such results suggest that grain redistribution can take place after thermal annealing and that the grains tend to coalesce. Dependence of conductivity on temperature during heating and cooling processes is also discussed.

From Commercial Tyrosine Polymers to a Tailored Polydopamine Platform: Concepts, Issues and Challenges En Route to Melanin-Based Bioelectronics

Over the past decade synthetic melanins, melanin-like polymers and melanin-based copolymers have been the focus of growing attention as soft biocompatible functional materials for engineering high performance, low cost optoelectronic devices, such as memory devices, light emitting diodes and field effect transistors. The unique combination of physicochemical properties of melanins, such as broad band absorption in the UV-visible range, intrinsic free radical character, water-dependent hybrid ionic–electronic conductor behaviour and excellent biocompatibility, have inspired use of melanic polymers as valuable functional materials for organic bioelectronics. However, several gaps and issues still hinder rapid progress of melanin-based organic electronics and bioelectronics, including in particular the limited contribution of electronic conductivity and current decay with time under biasing. The aim of this paper is to provide an overview of the structural and optoelectronic properties of melanins and to bring to focus current gaps and challenges in the development of melanin-based materials for bioelectronics. Starting from commercial samples, the paper surveys different melanin-type materials with special emphasis on the potential of polydopamine (pDA), a highly adhesive mussel-inspired melanin-type platform, for incorporation in optoelectronic devices. Simple chemical tailoring procedures for engineering pDA-based n-type polymers and photoresponsive materials for photocapacitive sensors are eventually illustrated.

Charge trapping induced by plasma in alumina electrode surface investigated by thermoluminescence and optically stimulated luminescence

The plasma of a dielectric barrier discharge can fill traps in the alumina that cover the electrode. Trap energies and lifetimes are estimated by thermoluminescence and optically stimulated luminescence. Comparison with similar results for traps created by other radiation sources clarifies the mechanisms regulating this effect. Alumina’s trap energies are approximately 1 eV, and the traps remain active for several days after plasma exposure. These results could be important to keep dielectric barrier discharge plasmas uniform since a trapped charge can be an electron reservoir.