Marianna Ambrico

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

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.

STRUCTURAL PROPERTIES AND PHOTOLUMINESCENCE STUDY OF CDSE/SI EPILAYERS DEPOSITED BY LASER ABLATION

Structural and optical characterization of CdSe thin films deposited by laser ablation technique on silicon (100)- and (111)-oriented substrates are reported. The effect of the substrate orientation on the growth and luminescence features of the two types of epilayers are investigated. Photoluminescence spectra of CdSe films measured from 10 up to 300 K and as a function of the laser excitation intensity give detailed information on the extrinsic levels localized in the forbidden gap. Temperature dependence of the energy of the n=1 exciton line has been fitted by the Varshni’s equation and by an expression containing the Bose–Einstein occupation factor for phonons. Parameters related to the electron-phonon interaction have been obtained. Temperature dependence of the broadening of exciton linewidth has been studied in terms of an expression containing both exciton-optical phonon and exciton-acoustic phonons coupling constants. Evaluated fitting parameters have shown the dominant contribution of optical ph...

Thermoluminescence study of the trapped charge at an alumina surface electrode in different dielectric barrier discharge regimes

In this study, the charge trapping effect in alumina dielectric surfaces has been deeply investigated by means of a dedicated dielectric barrier discharge apparatus in different discharge regimes and gas mixtures. This work further validates our previous findings in the case of air discharges in a filamentary regime. Long lasting charge trapping has been evidenced by ex situ thermoluminescence characterizations of alumina dielectric barrier plates exposed to a plasma. The density of trapped surface charges was found to be higher in the glow discharge with respect to pseudo-glow and filamentary regimes, and for all regimes the minimum trap activation temperature was 390 K and the trap energy was less than or around 1 eV. This implies that in the case of glow discharges a higher reservoir of electrons is present. Also, the effect was found to persist for several days after running the discharge.

Dielectric function and electric properties of germanium thin films prepared by gold mediated crystallization

Crystallization of hydrogenated amorphous germanium (a‐Ge:H) thin films deposited by plasma enhanced chemical vapor deposition using the GeH4 and H2 precursors has been investigated. A comparative analysis of the kinetics of the thermal crystallization by annealing to 650°C and of the gold-mediated crystallization (Au-MMC) is carried out. The impact of the Au-MMC on the microcrystalline Ge film microstructure and electrical properties is discussed. The Au thin layer results in a more dense and ordered structure with lower roughness of the microcrystalline Ge films. In order to describe the Ge crystallization kinetics, the dielectric functions of a‐Ge:H and microcrystalline germanium μc‐Ge have also been determined by spectroscopic ellipsometry in the range of 0.75−6.0eV and parametrized using the Tauc-Lorentz dispersion equation.

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.

A water-soluble eumelanin polymer with typical polyelectrolyte behaviour by triethyleneglycol N-functionalization

N-functionalization of 5,6-dihydroxyindole with a hydrophilic triethyleneglycol (TEG) chain provides access to a new class of water-soluble eumelanin-like materials with relatively high dielectric constant and polyelectrolyte behaviour, reflecting enhanced charge transport by in-depth incorporation of hydration networks.

Memory-like behavior as a feature of electrical signal transmission in melanin-like bio-polymers

The memory-like behavior of melanin biopolymer under electrical stimuli is shown through electrical transport characterization performed on melanin based metal insulator semiconductor structures on silicon. The presence of a memory window and retention behavior is verified by capacitance-voltage read outs before and after the application of voltage pulses. Interestingly, these phenomena occur without the presence of metallic nanoclusters enclosed in the melanin matrix. Charge trapping is considered the main mechanism responsible for the melanin memory-like character. The inability to erase the memory window has been ascribed to the permanent polarization effect during the application of the voltage pulse.

Laser triggered single streamer in a pin-to-pin coplanar dielectric barrier discharge

The effect of laser light interaction with alumina surface of a single filament coplanar dielectric barrier discharge has been investigated. It has been found that for laser photon energy lower than the pure alumina photoelectron emission threshold, the laser beam was effective in triggering single streamer discharge below regular ignition voltage threshold. This work demonstrates that triggering of the filamentary discharge occurs due to the laser induced extraction of electrons originally trapped by the plasma radiation at the dielectric surface; the trap energy levels lower than the dielectric band gap explain the easier electron detrapping due to incident laser photons.