The charge trapping effect due to the exposure of alumina surfaces to plasma has been studied in a volume dielectric barrier discharge (DBD) in Ar and He noble gases. The long lasting charge trapping of alumina dielectric plates, used as barriers in DBDs, is evidenced by an ex situ thermoluminescence (TL) experiment performed with a standard and a custom two-dimensional (2D)-TL apparatus. The spatial density of trapped surface charges is found to be strongly correlated to the plasma morphology, and the surface spatial memory lasted for several minutes to hours after plasma exposure. In the case of Ar, the plasma channel impact signature on the surface shows a higher equivalent radiation dose with respect to the surface plasma wave and the post-discharge species signature. As a consequence, for the development of discharges, inside the dielectric surface the availability of lower energy trapped electrons is larger in the first region of plasma impact. The reported spatial memory increases the likelihood of the occurrence of plasma filaments in the same position in different runs. In He plasmas, the dielectric barrier shows an almost uniform distribution of trapped charges, meaning that there is no preferred region for the development of the discharge. In all cases a slight asymmetry was shown in the direction of the gas flow. This can be interpreted as being due to the long-living species moving in the direction of the gas flow, corresponding with the TL side experiment on the sample exposed to the plasma afterglow. The maximum values and the integral of the 2D-TL images showed a linear relation with the total charge per ac cycle, corresponding with findings for the TL glow curve. In conclusion, 2D-TL images allow the retrieval of information regarding the plasma surface interaction such as the plasma morphology, trap sites and their activation temperature.

Inspired by the powerful photosensitizing properties of the red hair pigments pheomelanins, a photoresponsive cysteine-containing variant of the adhesive biopolymer polydopamine (pDA) is developed via oxidative copolymerization of dopamine (DA) and 5-S-cysteinyldopamine (CDA) in variable ratios.Chemical and spectral analysis indicate the presence of benzothiazole/benzothiazine units akin to those of pheomelanins. p(DA/CDA) copolymers displayimpedance properties similar to those of biological materials and a marked photoimpedance response to light stimuli. The use of the p(DA/CDA) copolymerto implement a solution-processed hybrid photocapacitive/resistive metalinsulator- semiconductor (MIS) device disclosed herein is the fi rst example oftechnological exploitation of photoactive, red-hair-inspired biomaterials as soft enhancement layer for silicon in an optoelectronic device. The bio-inspiredmaterials described herein may provide the active component of new hybrid photocapacitive sensors with a chemically tunable response to visible light.

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.

Two simple small molecules are designed and successfully implemented here as hole-transporting material (HTM) in perovskite-based solar cells (PSCs). With the aim of elucidating the interconnection between molecular structure, properties, and their role in the working devices, these HTMs are implemented in both thin planar direct (n-i-p) and inverse (p-i-n) geometries. It is observed how the HTM layer morphology influences the photovoltaic performance. Moreover, from analysis of the different devices, fundamental information is retrieved on the factors influencing small molecule hole extracting/transporting functionality in PSCs. Specifically, two main roles are identified: When HTMs are introduced as growing substrate (p-i-n), there is a positive impact on the device performance via influence of perovskite formation; meanwhile, their efficacy in transporting the holes governs the performance of direct configurations (n-i-p). These findings can be extended to a wide family of small molecule HTMs, providing general rules for refining the design of novel and more efficient ones.

Modification  of  the  electrical  transport  of  arandom  network  of  silicon  nanowires  assembled  on  n-silicon  support,  after  silicon  nanowires  functionalization by  chlorination/alkylation  procedure  ,  is  here  described and  discussed.  We  show  that  the  organic  functionalities induce  charge  transfer  at  single  SiNW  and  produce doping-like effect that is kept in the random network too. The  SiNWs  network  also  presents  a  surface recombination  velocity  lower  than  that  of  bulk  silicon. Interestingly,  the  functionalized  silicon  nanowires/n-Si junctions  display  photo-yield  and  open  circuit  voltages higher  than  those  including  oxidized  silicon  nanowire networks.  Electrical  properties  stability  in  time  of junctions  embedding  propenyl  terminated  siliconnanowires  network  and  transport  modification  aftersecondary  functionalization  is  also  shown.  These  results suggest  a  possible  route  for  the  integration  of functionalized  Si  nanowires,  although  randomly distributed,  in stable  large  areasensitive based 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 p-conjugating aromatic amines to tailor functionality.

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.

Early diagnosis of plant virus infections before the disease symptoms appearance may represent a significant benefit in limiting disease spread by a prompt application of appropriate containment steps. We propose a label-free procedure applied on a device structure where the electrical signal transduction is evaluated via impedance spectroscopy techniques. The device consists of a droplet suspension embedding two representative purified plant viruses i.e.,Tomato mosaic virus and Turnip yellow mosaic virus,put in contact with a highly hydrophobic plasma textured silicon surface. Results show a high sensitivity of the system towards the virus particles with an interestingly low detection limit,from tens to hundreds of attomolar corresponding to pg/mL of sap,which refers,in the infection time-scale,to a concentration of virus particles in still-symptomless plants. Such a threshold limit,together with an envisaged engineering of an easily manageable device,compared to more sophisticated apparatuses,may contribute in simplifying the in-field plant virus diagnostics.

Hysteresis behaviour of the current-voltage characteristics collected on spin coated synthetic eumelanin layer embedded in the Au/eumelanin/ITO/glass structure is shown. The effect has been observed under dark both in air and vacuum environment and its magnitudehas been found related to the eumelanin hydration state. Moreover, in vacuum and under white light illumination, enhancement of the hysteresis loop area respect to those collected under dark has been observed. Space charge storage and charge trapping/detrapping as possible mechanisms responsible of the observed current-voltage behaviour are discussed. Preliminary experimental results have evidenced the possible integration of eumelanin layers in electro-optical charge storage based memory devices.

Synthetic melanin based metal-insulator-semiconductor devices are fabricated for the first time thanks to silicon surface wettability modification by using dielectric barrier discharge plasma. Ambipolar charge trapping in air and ion drift mechanisms under vacuum are identified by capacitance-voltage hysteresis loops. These results aim to foresee the possible integration of synthetic melanin layers as a novel capacitor in organic polymer based devices.

The electrical transport across a biomimetic interface made up of spin coated melanin layers on nanotextured silicon surfaces with different texturing features and wetting properties is discussed. Nanotexturing allows, under certain conditions, the melanin to anchor better on a hydrophobic silicon surface, overcoming the hydrophilic melanin-hydrophobic silicon interface issue. The feature of the electrical signal transduction across such a structure was studied by impedance spectroscopy and found to be influenced by the nano-texturing chemistry and surface morphology. The effects of a voltage pulse, as external stimulus modifying the electrical transport mechanisms, and retention of the subsequently achieved carrier transport conditions have been elucidated. The results suggest a possible exploiting of this circuit element for bio and environmental molecules' sensing.

The memory-like behavior of melanin biopolymer under electrical stimuli is shown throughelectrical transport characterization performed on melanin based metal insulator semiconductorstructures on silicon. The presence of a memory window and retention behavior is verified bycapacitance-voltage read outs before and after the application of voltage pulses. Interestingly, thesephenomena occur without the presence of metallic nanoclusters enclosed in the melanin matrix.Charge trapping is considered the main mechanism responsible for the melanin memory-likecharacter. The inability to erase the memory window has been ascribed to the permanentpolarization effect during the application of the voltage pulse.

Sub-micron Al2O3 powders with a surface activated by dielectric barrier discharge exhibit improved performance in wet deposition of ceramic layers. In addressing the possible mechanisms responsible for the observed improvement, a comprehensive thermoluminescence (TL) study of plasma-activated powders was performed. TL offers the unique possibility of exploring the population of intrinsic electrons/holes in the charge trapping states. This study covers a wide range of experimental conditions affecting the TL of powders: treatment time, plasma working gas composition, change of discharge configuration, step-annealing of powder, exposure to laser irradiation and aging time. Deconvoluted TL spectra were followed for the changes in their relative contributions. The TL spectra of all tested gases (air, Ar, N-2 and 5% He in N-2) consist of the well-known main dosimetric peak at 450 K and a peak of similar magnitude at higher temperatures, centered between 700 and 800 K depending on the working gas used. N-2 plasma treatment gave rise to a new specific TL peak at 510 K, which exhibited several peculiarities. Initial thermal annealing of Al2O3 powders led to its significant amplification (unlike the other peaks); the peak was insensitive to optical bleaching, and it exhibited slow gradual growth during the long-term aging test. Besides its relevance to the ceramic processing studies, a comprehensive set of data is presented that provides a useful and unconventional view on plasma-mediated material changes.

A totally innovative electrolyte-gated field effect transistor, embedding a phospholipid filmat the interface between the organic semiconductor and the gating solution, is described.The electronic properties of OFETs including a phospholipid film are studied in both purewater and in an electrolyte solution and compared to those of an OFET with the organicsemiconductor directly in contact with the gating solution. In addition, to investigate therole of the lipid layers in the charge polarization process and quantify the field-effectmobility, impedance spectroscopy was employed. The results indicate that the integrationof the biological film minimizes the penetration of ions into the organic semiconductorthus leading to a capacitive operational mode as opposed to an electrochemical one. TheOFETs operate at low voltages with a field-effect mobility in the 103 cm2 V1 s1 rangeand an on/off current ratio of 103. This achievement opens perspectives to the developmentof FET biosensors potentially capable to operate in direct contact with physiological fluids.

In this paper, a spray technique is used to perform low temperature deposition of multi-wall carbon nanotubes on semi-insulating gallium arsenide in order to obtain photodectors. A dispersion of nanotube powder in non-polar 1,2-dichloroethane is used as starting material. The morphological properties of the deposited films has been analysed by means of electron microscopy, in scanning and transmission mode. Detectors with different layouts have been prepared and current-voltage characteristics have been recorded in the dark and under irradiation with light in the range from ultraviolet to near infrared. The device spectral efficiency obtained from the electrical characterization is finally reported and an improvement of the photodetector behavior due to the nanotubes is presented and discussed.

The integration of biopolymers into hybrid electronics is one of the up to date issues in view of the achievement of fully bio-compatible devices. Among 'hot topics' in bio-polymer research, synthetic melanin or, briefly, "melanin", has been recently recognized as a quite intriguing macromolecule thanks to its multifunctional optoelectronic properties. To date, melanin transport properties have been mainly enlightened on pellets, while optical absorption and conductivity properties have been investigated on melanin layers deposited on quartz and indium tin oxide/glass. The unavailability of suitable procedures to improve or promote adequate self assembling of melanin layer deposition onto substrate of interest in organic and solid state electronics (hybrid) like silicon substrates, prevent interesting studies on such structures. The reason stems basically on the difference between the hydrophilic nature of the melanin and the hydrophobic one of the supports (mostly of silicon). However, our group solved this issue and was able to tailor a melanin based metal/insulator/metal and metal/insulator/silicon structures, where synthetic melanin was embedded as the insulating part. This allowed to disclose interesting features related to data storage capabilities of melanin layers deposited on indium tin oxide/glass and silicon never investigated so far. In this work we show an overview on our recent mentioned results, and particular attention is paid on structures on silicon substrates. The use of pSi and nSi substrates and measurements under different environment conditions has enabled to gain insight into ambipolar electrical transport mechanisms, still unexplored. These results constitute a first important basic insight into melanin-based bio inspired structures and represent a significant step towards their integration in several kinds of hybrid organic polymer-based devices.

Naturally contaminated basil seeds were treated by a surface dielectric barrier discharge driven in the humid air by an amplitude modulated AC high voltage to avoid heat shock. In order to avoid direct contact of seeds with microdischarge filaments, the seeds to be treated were placed at sufficient distance from the surface discharge. After treatment, the seeds were analyzed in comparison with control samples for their microbial contamination as well as for the capability of germination and seedling growth. Moreover, chemical modification of seed surface was observed through the elemental energy dispersive x-ray analysis and wettability tests. We found that treatment applied at 20% duty cycle (effective discharge duration up to 20 s) significantly decreases microbial load without reducing the viability of the seeds. On the other side, seedling growth was considerably accelerated after the treatment, and biometric growth parameters of seedlings (total length, weight, leaf extension) considerably increased compared to the controls. Interestingly, scanning electron microscopy images taken for the different duration of treatment revealed that seed radicle micropylar regions underwent significant morphological changes while the coat was substantially undamaged. Inside the seed, the embryo seemed to be well preserved while the endosperm body was detached from the epithelial tegument. A total of 9 different genera of fungi were recovered from the analyzed seeds. Scanning electron microscopy images revealed that conidia were localized especially in the micropylar region, and after plasma treatment, most of them showed substantial damages. Therefore, the overall effect of the treatment of naturally contaminated seeds by reactive oxygen and nitrogen species produced by plasma and the consequent changes in surface chemistry and microbial load can significantly improve seed vigor.

Reactive ion etching (RIE) plasma processes fed with CF4 have been investigated as single-step maskless method for nanotexturing the surface of crystalline silicon. Variation of surface topography under different plasma conditions has been evaluated with scanning electron microscopy and correlated with total, diffuse, and specular reflectance. Chemical features have been evaluated by X-ray photoelectron spectroscopy and current-voltage characteristics have been measured under dark and illuminated conditions. Results indicate that a widely tunable nanoscale texture can be generated onto silicon surface leading to a reduced total reflectance. A significant uptake of carbon and fluorine is detected onto treated silicon with fluorine mainly in ionic form. Further, the plasma modification is per se capable, without further doping procedures, to generate a photovoltaic behavior onto treated silicon, with higher short circuit current in less reflective samples.

This work enlighten on the modification of the electrical and optoelectronic properties at metal/silicon interface, where the silicon surface is nanostructured by single step mask-less CF4 plasmain reactive ion etching mode. The electrical transport across metal/nanotextured silicon/siliconstructure has been correlated with morphological variations of surface topological features andchemistry. The results evidence that such nanostructures enhance the photovoltaic behavior andaffect electrical and optoelectronic transport to a different extent, depending not only on surfacetexturing but also on surface chemistry.

Temperature variation of indirect band gap of Tl2In2S3Se layered single crystals were obtained by means of absorption and photoconductivity measurements. The temperature coefficient of -7.1× 10-4 eV/K from absorption measurements in the temperature range of 10-300 K in the wavelength range of 520 -1100 nm and -5.0 × 10-4 eV/K from PC measurements in the temperature range of 132-291 K in the wavelength range of 443-620 nm upon supplying voltage V = 80 V were obtained. From the analysis of dark conductivity measurements in the temperature range of 150-300 K, conductivity activation energy was obtained as 0.51 eV above 242 K. The degree of the disorder, the density of localized states near Fermi level, the average hopping distance and average hopping energy of Tl2In2S3Se crystals were found as, 1.9×105 K and Nf = 4×1020 cm-3eV-1, 29.1 Å and 24.2 meV in the temperature range of 171-237 K, respectively. Activation energy of hopping conductivity at T = 171 K was obtained as 41.3 meV, the concentration of trapping states was found as 1.6 × 1019 cm-3.

Polycrystalline diamond films with a thickness of about 2 mu m were deposited by chemical vapour deposition on silicon substrates in continuous and pulsed wave regimes with duty cycle between 25% and 100%. The thermoluminescent behaviour of these films was analysed in the temperature range 323-723 K after beta irradiation with doses in the range 7-107 Gy. All the films exhibit a dosimetric peak centred at about 592 K, showing a good linearity in the whole investigated dose range. The thermoluminescence analyses show that the intensity of the dosimetric peak is maximum for the continuous wave film, while it decreases for the pulsed wave samples. The variation of the crystalline quality and the purity of the films with the employed duty cycle, investigated via micro-Raman spectroscopy and room-temperature photoluminescence, indicates that the continuous wave (duty cycle = 100%) film has the best quality, corresponding to the highest thermoluminescence efficiency.

In this study, the charge trapping effect in alumina dielectric surfaces has been deeplyinvestigated by means of a dedicated dielectric barrier discharge apparatus in differentdischarge regimes and gas mixtures. This work further validates our previous findings in thecase of air discharges in a filamentary regime. Long lasting charge trapping has beenevidenced by ex situ thermoluminescence characterizations of alumina dielectric barrier platesexposed to a plasma. The density of trapped surface charges was found to be higher in theglow discharge with respect to pseudo-glow and filamentary regimes, and for all regimes theminimum trap activation temperature was 390K and the trap energy was less than or around1 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.

Nanofluids are nowadays representing an exciting tool with significant impact and tremendous potential in several industrial applications. In the present paper, we focus our attention on the tunability of the electrical and dielectric properties of alumina nanoparticle-based nanofluids achieved by preliminary modifying the particle surface charging by a diffuse coplanar dielectric barrier discharge plasma treatment. We produced a parametric study on the tuning of the plasma-treatedalumina-based nanofluid electrical response as a function of the selected discharge feeding gases.