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.

In this paper we report on a spectroscopic study on CH observables including laser inducedfluorescence (LIF) on CH and emission spectroscopy on the CH Ger¨o band. Directobservation by LIF has been found to be very difficult, both because of technical difficultiesand an overall low CH density in the discharge. Analysis of CH(A) emission shows that it isdue to CH4 dissociative excitation processes, by He(23S) in He-based mixtures, and byelectron impact in N2-CH4. The analysis of spectra evidences the need for more preciseknowledge on the collision quenching of electronically excited states and on the electronenergy distribution function.

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.

Evolution of N2(A, v = 0-3) metastable species produced by triggered single filamentary streamer discharge was investigated utilizing emission spectrometry and laser-induced fluorescence techniques. Triggered streamers were produced repeatedly in point-to-plane DBD electrode geometry in pure nitrogen at 200 Torr and metastable species were monitored in the centre of the discharge gap. Populations of all four monitored vibronic levels increase during streamer channel decay phase, reaching local maximum in a microsecond timescale and decreasing afterwards. Maximum population of an individual , v) vibronic level occurs with a certain delay after streamer onset ?d(v), which decreases with increasing vibrational number. The longest delay ?d = 5 ± 0.5 µs was fixed for the lowest metastable level v = 0, whereas ?d values of 4.4 ± 0.5, 1.75 ± 0.25 and 0.85 ± 0.25 µs were fixed for v = 1, 2 and 3, respectively. Coupled evolution of the two lowest , v = 0, 1) levels was monitored independently by applying an indirect method based on emission intensity of the N2 Herman infrared system. Very good agreement between emission and fluorescence based diagnostics was achieved for later post-discharge times t > ?d. A simple 0-D model of , v) post-discharge kinetics based on vibrational relaxation and electronic quenching of individual vibronic levels reproduces experimental observations fairly well. According to the model, observed maxima likely occur due to the collisional cascade that transfers metastable species from higher even/odd vibrational levels towards v = 0/v = 1 terminal levels through the ?v = 2 vibrational relaxation mechanism.

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.

Time-resolved images of a single-surface dielectric barrier micro-discharge were obtained by employing ICCD microscopy with high spatial and time resolution. The micro-discharge was repetitively produced using amplitude-modulated ac high voltage waveforms applied to the coplanar electrode geometry in a reactor, fed either with high-purity Ar or N2 at atmospheric pressure. The driving high-voltage amplitude was set to initiate just one single micro-discharge per one ac half-cycle. Images recorded within the two successive ac cycles provided evidence that the track left by the first micro-discharge influenced the propagation trajectory of consecutive streamers. Images of individual micro-discharges allowed evaluation of the luminous streamer channel diameter and its evolution along the streamer's propagationtrajectory. Minimum luminous streamer channel diameters of 30±6µm and 50±10µm were fixed in Ar and N2, respectively. Furthermore, direct comparison between a single micro-discharge image and an image integrating many micro-discharges allowed the estimation of potential errors associated with methods based on accumulating optical emission produced by many micro-discharge events.

In this paper we present laser induced fluorescence (LIF) measurements of OH relative density in a He-H2Oatmospheric pressure dielectric barrier discharge, with an estimation of the absolute density based on thequantitative analysis of the LIF signal and on the decay of OH density in the post-discharge. The possibleinterference of H2O2 photo-dissociation is discussed and finally excluded. Densities of the order of1013 cm3 have been estimated in mixtures with water vapour content ranging from 2.3 to 23 Torr partialpressure. LIF diagnostic characteristics and sensitivity in theOH case at atmospheric pressure are discussedin comparison with absorption techniques.

Laser induced fluorescence by one (LIF) and two photon (TALIF) excitation has been employed to characterize NO, O species in the expanded stream of N(2)-O(2) air like low pressure plasma jet. The gas, excited in a coaxial RF capacitive discharge at pressure P(1), expands through a de Laval nozzle into a vessel at P(2)=0.25 Ton at expansion ratio P(1)/P(2) of about 35. The multiple expansion compression waves of the jet are traced by laser induced fluorescence of NO and O dissociation products expanding through the nozzle. The quantitative O and NO densities, obtained by in-situ calibration of TALIF and LIF signals are discussed.

The evolution of individual v = 0-10 vibrational levels of N2(A3$\Sigma_{\text{u}}^{+}$ ) metastable species produced by filamentary streamer discharge was investigated by the laser-induced fluorescence technique. Triggered single streamer filament was periodically produced in pure nitrogen at a pressure of 200 torr and metastable species were monitored during the streamer channel decay in the centre of the discharge gap. The observed dynamics of N2(A3$\Sigma_{\text{u}}^{+}$ ) vibrational levels follow two very different scenarios: while higher (v > 6) vibronic levels decay exponentially in hundreds of nanoseconds, the populations of lower levels (v <= 6) definitely increase, first reaching a local maximum on a microsecond timescale and then decreasing afterwards. Population maxima of N2(A3$\Sigma_{\text{u}}^{+}$ , v <= 6) levels occur after the streamer onset with a certain delay, which decreases with increasing vibrational number. Interpretation of experimental observation based on a 0D kinetic model of the post-discharge period takes into account the most important processes redistributing populations between the N2(A3$\Sigma_{\text{u}}^{+}$ ), N2 $\left({{\text{B}}^{3}}{{\Pi}_{\text{g}}}\right)$ and N2$\left({{\text{C}}^{3}}{{\Pi}_{\text{u}}}\right)$ vibronic levels. The model reproduces experimental observations fairly well, including observed maxima delays occurring due to the collisional cascade, which transfers metastable species from higher even/odd vibrational levels towards v = 0/v = 1 terminal levels through the ?v = 2 vibrational relaxation mechanism. A calibration procedure based on the rate of energy-pooling processes was used to determine absolute populations of the v = 0 and 1 levels from LIF data, and the model results were utilized to place on an absolute scale all the higher (v > 1) measured vibronic levels. Vibrational distributions obtained from calibrated LIF data at selected instants show a reasonable qualitative agreement with model predictions. Population maxima exceeding 3 × 1014 cm-3 were fixed for v = 2 and 3 vibrational levels, while the lowest v = 0 level reaches only 8-9 × 1013 cm-3. Lastly, we show that the observed rate of the v = 2 level decay is not compatible with published rate constants for the v = 2 -> v = 0 vibrational relaxation.

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.

Optical, electrical and discharge product measurements were performed in order to reveal thebehaviour of N2(A 3
+u ) metastables in a surface dielectric barrier discharge (DBD) driven inN2 with small NO admixtures in a modulated ac regime. Metastable species were detectedboth in a thin surface plasma layer and in the space afterglow through plasma induced emissionand optical-optical double resonance laser induced fluorescence, respectively. Basically, theobserved N2(A 3
+u ) species follow the discharge current oscillations in the plasma layer,while they evolve on a millisecond time scale due to diffusion through the space afterglow.Emission spectrometry provides a rough estimation of average metastable concentration in athin surface plasma layer ~ 9 × 1013 cm-3. Fluorescence measurements then allow an upperestimation of metastable concentration in the space afterglow
1 × 1012 cm-3.

We report results of a novel time-resolved broad-band absorption spectroscopy experiment for OH density measurement applied to a pulsed dielectric barrier discharge in Ar/H2O mixtures. The measurement is aimed at the calibration of our previous OH LIF measurements in the same discharge. The apparatus is simple and cheap, being based on a UV LED light source and a non-intensified, non-cooled, gateable linear CCD array as a detector. The set-up is capable of ruling out both medium/long-term drifts of the UV source and of the discharge, and discharge emission from the measurement. Performances of the set-up are discussed, together with possible improvements for its use as a standalone technique.

Laser induced fluorescence measurements of the rate coefficients of N+2 (B 2
+u , v = 0)collision quenching by N2 and O2 are presented. The values of (8.84 ± 0.37) × 10-10 cm3 s-1and (10.45 ± 0.45) × 10-10 cm3 s-1 have been found for N2 and O2, respectively. The presentresults agree well with the literature data obtained by selective methods for ion B stateexcitation. The data are discussed in the framework of the spectroscopic evaluation of thereduced electric field in electrical discharges at high pressure, which makes use of the secondpositive system and first negative system emissions of nitrogen.

Optical emission produced by streamers is determined by spatial distribution of electronically excited atomic and diatomic species within the streamer head and streamer channel. Peculiarities of emission and LIF diagnostics dedicated to investigating the basic structure of streamers with high spatio-temporal resolution are discussed. Possible strategies based on the 2D projections of cylindrically symmetric streamers to determine radial distributions of excited species within the streamer channel are illustrated for streamers produced in volume or on the dielectric surface at atmospheric and low pressures.

Our recent work on optical emission spectroscopy (OES) and laser-induced fluorescence (LW) applied to dielectric barrier discharge (DBD) at atmospheric pressure (ATP) is reported. The interplay of discharge kinetics and diagnostic techniques features is evidenced, with emphasis on collision processes that, with their variety of state-to-state characteristics and rate constants, determine the observation of a peculiar collision-dominated non-equilibrium system.

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.

Radial distributions of electronically excited species produced during surface streamer propagation were obtained by applying the Abel inverse transform to projected luminosities of single streamers. The streamers were generated in an argon and nitrogen surface coplanar dielectric barrier discharge at atmospheric pressure and their magnified microscopic images were registered with high time resolution. Selected regions of the projected luminosities were processed by the Abel inverse transform procedure based on the Hankel-Fourier method assuming cylindrical symmetry of the streamer channel. Projected as well as Abel-inverted profiles were fitted by Gaussian functions. It is shown that the projected profiles, in addition to the Abel-inverted ones, can be well approximated by the sum of two coaxial Gaussians with two different half-widths and weights. The sharper Gaussian component with higher weight characterizes the radial dependence of the primary cathode-directed streamer-channel luminosity. The second (broader) Gaussian component probably originates either from the pre-breakdown Townsend phase or from the second wave propagating towards the anode.

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.

In this article a study of chemiresistor sensors based on Single and Multi Wall Carbon Nanotube films deposited at low temperature by means of a spray technique is presented. A dispersion of nanotube powder in a non-polar 1,2-Dichloroethane solvent was used as starting solution. Electron Microscopy in Scanning and Transmission mode were used in order to verify the morphological properties of the deposited films. The conductivity of carbon nanotubes (CNTs) was measured in two organic solvent vapors environments: 2-propanol and carbon-tetrachloride. The solvents used are characterized by different polarities. The results show that the electrical resistance of the sensors increases when exposed to solvent vapors. Finally the effect of Teflon-like and Melanin coatings on the sensitivity yield is presented and discussed.

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.

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.