Transistors elettrochimici organici e la loro applicazione come sensori.

La presente tesi tratta della fabbricazione e del funzionamento di transistors elettrochimici organici (OECTs) composti da fi�lm sottili di poly(3,4-ethylenedioxythiophene) disperso con polystyrenesulfonic acid, o PEDOT:PSS, oltre che del loro possibile utilizzo come sensori. La trattazione si apre con una panoramica sui polimeri conduttivi, siano essi puri o drogati, e sulle loro caratteristiche chimiche ed elettriche: diversi metodi di drogaggio consentono il loro utilizzo come semiconduttori. Tra questi polimeri, il PEDOT �e uno dei pi�u utilizzati poich�e presenta accessibilit�a d'uso e ottima stabilit�a nel suo stato drogato, pur risultando insolubile in acqua; per ovviare a questo problema lo si polimerizza con PSS. Le propriet�a di questo composto sono poi ampiamente discusse, soprattutto in ambito di applicazioni tecniche, per le quali �e neccessario che il polimero in soluzione sia depositato su un substrato. A questo scopo vengono presentate le principali techiche che consentono la deposizione, permettendo di creare fil�lm sottili di materiale da utilizzarsi, nell'ambito di questa tesi, come gate e canale dei transistors elettrochimici. A seguire viene esposta la struttura degli OECTs e spiegato il loro funzionamento, modellizzando i dispositivi con un semplice circuito elettrico. Il confronto dei meno noti OECTs con i meglio conosciuti transistors a eff�etto campo semplifi�ca la comprensione del funzionamento dei primi, i quali sono rilevanti ai fi�ni di questa trattazione per il loro possibile funzionamento come sensori. In seguito alla spiegazione teorica, vengono illustrati i metodi seguiti per la deposizione di �film sottili di PEDOT:PSS tramite Spin Coating e per la fabbricazione degli OECTs su cui sono state eff�ettuate le misure, le quali sono state scelte e presentate in base ai risultati gi�a ottenuti in letteratura e a seconda dei dati ritenuti necessari alla caratterizzazione del transistor elettrochimico nell'ottica di un suo possibile utilizzo come sensore. Perci�o sono state eseguite misure amperometriche in funzione delle tensioni di gate e di drain, alternatamente tenendo costante una e variando l'altra, oltre che in funzione della concentrazione di elettrolita, dell'area del canale e del tempo. In conclusione sono presentati i dati sperimentali ottenuti ed una loro analisi.

Nanoscopic studies of conjugated polymer blends by (electric) scanning probe microscopy

Conjugated polymers and conjugated polymer blends have attracted great interest due to their potential applications in biosensors and organic electronics. The sub-100 nm morphology of these materials is known to heavily influence their electromechanical properties and the performance of devices they are part of. Electromechanical properties include charge injection, transport, recombination, and trapping, the phase behavior and the mechanical robustness of polymers and blends. Electrical scanning probe microscopy techniques are ideal tools to measure simultaneously electric (conductivity and surface potential) and dielectric (dielectric constant) properties, surface morphology, and mechanical properties of thin films of conjugated polymers and their blends.rnIn this thesis, I first present a combined topography, Kelvin probe force microscopy (KPFM), and scanning conductive torsion mode microscopy (SCTMM) study on a gold/polystyrene model system. This system is a mimic for conjugated polymer blends where conductive domains (gold nanoparticles) are embedded in a non-conductive matrix (polystyrene film), like for polypyrrole:polystyrene sulfonate (PPy:PSS), and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). I controlled the nanoscale morphology of the model by varying the distribution of gold nanoparticles in the polystyrene films. I studied the influence of different morphologies on the surface potential measured by KPFM and on the conductivity measured by SCTMM. By the knowledge I gained from analyzing the data of the model system I was able to predict the nanostructure of a homemade PPy:PSS blend.rnThe morphologic, electric, and dielectric properties of water based conjugated polymer blends, e.g. PPy:PSS or PEDOT:PSS, are known to be influenced by their water content. These properties also influence the macroscopic performance when the polymer blends are employed in a device. In the second part I therefore present an in situ humidity-dependence study on PPy:PSS films spin-coated and drop-coated on hydrophobic highly ordered pyrolytic graphite substrates by KPFM. I additionally used a particular KPFM mode that detects the second harmonic electrostatic force. With this, I obtained images of dielectric constants of samples. Upon increasing relative humidity, the surface morphology and composition of the films changed. I also observed that relative humidity affected thermally unannealed and annealed PPy:PSS films differently. rnThe conductivity of a conjugated polymer may change once it is embedded in a non-conductive matrix, like for PPy embedded in PSS. To measure the conductivity of single conjugated polymer particles, in the third part, I present a direct method based on microscopic four-point probes. I started with metal core-shell and metal bulk particles as models, and measured their conductivities. The study could be extended to measure conductivity of single PPy particles (core-shell and bulk) with a diameter of a few micrometers.

Polimeri tiofenici funzionali e loro applicazioni nel fotovoltaico

Recentemente, sempre più attenzione è stata rivolta all' utilizzo di coloranti organici come assorbitori di luce per la preparazione di strati fotoattivi in celle solari organiche (OPV). I coloranti organici presentano un'elevata abilità nella cattura della luce solare grazie all'elevato coefficiente di estinzione molare e buone proprietà fotofisiche. Per questi motivi sono eccellenti candidati per l'incremento della conversione fotoelettrica in OPV. In questa tesi viene descritta una nuova strategia per l'incorporazione di derivati porfirinici in catena laterale a copolimeri tiofenici. Gli studi svolti hanno dimostrato che poli(3-bromoesil)tiofene può essere variamente funzionalizzato con idrossitetrafenilporfirina (TPPOH), per l'ottenimento di copolimeri utilizzabili come materiali p-donatori nella realizzazione di OPV. I copolimeri poli[3-(6-bromoesil)tiofene-co-(3-[5-(4-fenossi)-10,15,20-trifenilporfirinil]esil tiofene] P[T6Br-co-T6TPP] contenenti differenti quantità di porfirina, sono stati sintetizzati sia con metodi non regiospecifici che regiospecifici, con lo scopo di confrontarene le proprietà e di verificare se la strutture macromolecolare che presenta una regiochimica di sostituzione sempre uguale, promuove o meno il trasporto della carica elettrica, migliorando di conseguenza l'efficienza. E' stato inoltre effettuato un ulteriore confronto tra questi derivati e derivati simili P[T6H-co-T6TPP] che non contengono l'atomo di bromo in catena laterale con lo scopo di verificare se l'assenza del gruppo reattivo, migliora o meno la stabilità termica e chimica dei film polimerici, agendo favorevolmete sulle performance dei dispositivi fotovoltaici. Tutti i copolimeri sono stati caratterizzati con differenti tecniche: spettroscopia NMR, FT-IR e UV-Vis, analisi termiche DSC e TGA, e GPC. Le celle solari Bulk Heterojunction, preparate utilizzando PCBM come materiale elettron-accettore e i copolimeri come materilai elettron-donatori, sono state testate utilizzando un multimetro Keithley e il Solar Simulator.

Biological materials : Part A. tuning LCST of raft copolymers and gold/copolymer hybrid nanoparticles and Part B. biobased nanomaterials

The research described in this dissertation is comprised of two major parts. The first part studied the effects of asymmetric amphiphilic end groups on the thermo-response of diblock copolymers of (oligo/di(ethylene glycol) methyl ether (meth)acrylates, OEGA/DEGMA) and the hybrid nanoparticles of these copolymers with a gold nanoparticle core. Placing the more hydrophilic end group on the more hydrophilic block significantly increased the cloud point compared to a similar copolymer composition with the end group placement reversed. For a given composition, the cloud point was shifted by as much as 28 °C depending on the placement of end groups. This is a much stronger effect than either changing the hydrophilic/hydrophobic block ratio or replacing the hydrophilic acrylate monomer with the equivalent methacrylate monomer. The temperature range of the coil-globule transition was also altered. Binding these diblock copolymers to a gold core decreased the cloud point by 5-15 °C and narrowed the temperature range of the coil-globule transition. The effects were more pronounced when the gold core was bound to the less hydrophilic block. Given the limited numbers of monomers that are approved safe for in vivo use, employing amphiphilic end group placement is a useful tool to tune a thermo-response without otherwise changing the copolymer composition. The second part of the dissertation investigated the production of value-added nanomaterials from two biorefinery “wastes”: lignin and peptidoglycan. Different solvents and spinning methods (melt-, wet-, and electro-spinning) were tested to make lignin/cellulose blended and carbonized fibers. Only electro-spinning yielded fibers having a small enough diameter for efficient carbonization ( Peptidoglycan (a bacterial cell wall material) was copolymerized with poly-(3-hydroxybutyrate), a common polyhydroxyalkanoate produced by bacteria with the objective of determining if a useful material could be obtained with a less rigorous work-up on harvesting polyhydroxyalkanoates. The copolyesteramide product having 25 wt.% peptidoglycan from a highly purified peptidoglycan increased thermal stability by 100-200 °C compared to the poly-(3-hydroxybutyrate) control, while a less pure peptidoglycan, harvested from B. megaterium (ATCC 11561), gave a 25-50 °C increase in thermal stability. Both copolymers absorbed more moisture than pure poly-(3-hydroxybutyrate). The results suggest that a less rigorously harvested and purified polyhydroxyalkanoate might be useful for some applications.

Bio-based PLA_PHB plasticized blend films: Processing and structural characterization

Bio-based films formed by poly(lactic acid) (PLA) and poly(3-hydroxybutyrate) (PHB) plasticized with an oligomer of the lactic acid (OLA) were used as supporting matrices for an antibacterial agent (carvacrol). This paper reports the main features of the processing and physico-chemical characterization of these innovative biodegradable material based films, which were extruded and further submitted to filmature process. The effect of the addition of carvacrol and OLA on their microstructure, chemical, thermal and mechanical properties was assessed. The presence of these additives did not affect the thermal stability of PLA_PHB films, but resulted in a decrease in their crystallinity and in the elastic modulus for the active formulations. The obtained results showed the effective presence of additives in the PLA or the PLA_PHB matrix after processing at high temperatures, making them able to be used in active and bio-based formulations with antioxidant/antimicrobial performance.

Processing and characterization of plasticized PLA/PHB blends for biodegradable multiphase systems

Blends of poly(lactic acid) (PLA) and poly(3-hydroxybutyrate) (PHB) plasticized with a lactic acid oligomer (OLA) added at three different concentrations (15, 20 and 30 wt% by weight), were prepared by an optimized extrusion process to improve the processability and mechanical properties of these biopolymers for flexible film manufacturing. Morphological, chemical, thermal, mechanical, barrier and migration properties were investigated and formulations with desired performance in eco-friendly films were selected. The efficiency of OLA as plasticizer for PLA_PHB blends was demonstrated by the significant decrease of their glass transition temperatures and a considerable improvement of their ductile properties. The measured improvements in the barrier properties are related to the higher crystallinity of the plasticized PLA_PHB blends, while the overall migration test underlined that all the proposed formulations maintained migration levels below admitted levels. The PLA_PHB blend with 30 wt% OLA was selected as the optimum formulation for food packaging, since it offered the best compromise between ductility and oxygen and water vapor barrier properties with practically no migration.

Synthesis and evaluation of novel polymer modifiers for biodegradable polymers

The effects of ester plasticizers and copolymers on the mechanical properties of the natural biodegradable polymers, poly(3-hydroxybutyrate) [PHB] and poly(lactic acid) [PLA] have been studied after subjecting to melt processing conditions. Ester plasticizers were synthesized from citric, tartaric and maleic acids using various alcohols. A variety of PLA copolymers have also been prepared from poly(ethylene glycol) derivatives using stannous octanoate catalysed ring opening polymerisations of DL-lactide. A novel PLA star copolymer was also prepared from an ethoxylated pentaerythritol. The structures of these copolymers were determined by NMR spectroscopy. The plasticizing effect of the synthesised additives at various concentrations was determined. While certain additives were capable of improving the mechanical properties of PLA, none were effective in PHB. Moreover, it was found that certain combinations of additives exhibited synergistic effects. Possible mechanisms are discussed. Biotic and abiotic degradation studies showed that the plasticizers (esters and copolymers) did not inhibit the biodegradability of PHB or PLA in compost at 60°C. Simple toxicity tests carried out on compost extract and its ability to support the growth of cress seeds was established. PLA was found to be susceptible to limited thermal degradation under melt processing conditions. Conventional phenolic antioxidants showed no significant effect on this process, suggesting that degradation was not predominantly a free radical process. PLA also underwent photo-oxidative degradation with UV light and the process could be accelerated in the presence of a photoactivator such as iron (III) diisononyl dithiocarbamate. The mechanisms for the above processes are discussed. Finally, selected compounds were prepared on a pilot plant scale. Extruded and blown films were prepared containing these additives with conventional polymer processing equipment. The mechanical properties were similar to those obtained with laboratory produced compression moulded films.

In vitro hydrolytic degradation of centrifugally spun polyhydroxybutyrate-pectin composite fibres

BACKGROUND: Centrifugal spinning is a novel fibre-forming process that readily permits the incorporation of additives while avoiding the thermal damage often associated with conventional melt spinning. Centrifugal spinning of a viscous solution of poly(3-hydroxybutyrate) (PHB) mixed with pectin was used to fabricate a range of fibres containing different concentrations of this biologically active agent. The influence of this blending on fibre morphology and in vitro degradation in an accelerated hydrolytic model at 70 ?C and pH of 10.6 is reported. RESULTS: Blending influenced the physiochemical properties of the fibres, andthis significantly affected thedegradation profile of both the fibre and its PHB constituent. A greater influence on degradation was exerted by the type of pectin and its degree of esterification than by variations in its loading. CONCLUSION: Centrifugal spinning permits the fabrication of composite fibrous matrices from PHB and pectin. Incorporation of the polysaccharide into the fibres can be used to manipulate degradation behaviour and demonstrates a model for doping of matrices with active biological constituents. The unique features of the centrifugal spinning process, as illustrated by the structure of the fibres and the degradation profiles, suggest possible applications of centrifugally spun biopolymers as wound scaffolding devices and in tissue engineering.

Controlled RAFT polymerization and zinc binding performance of catechol-inspired homopolymers

Incorporation of catechols into polymers has long been of interest due to their ability to chelate heavy metals and their use in the design of adhesives, metal-polymer nanocomposites, antifouling coatings, and so on. This paper reports, for the first time, the reversible addition-fragmentation chain transfer (RAFT) polymerization of a protected catechol-inspired monomer, 3,4-dimethoxystyrene (DMS), using commercially available trithiocarbonate, 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT), as a chain transfer agent. Our identified RAFT system produces well-defined polymers across a range of molecular weights (5-50 kg/mol) with low molar mass dispersities (Mw/Mn < 1.3). Subsequent facile demethylation of poly(3,4-dimethoxystyrene) (PDMS) yields poly(3,4-dihydroxystyrene) (PDHS), a catechol-bearing polymer, in quantitative yields. Semiquantitative zinc binding capacity analysis of both polymers using SEM/EDXA has demonstrated that both PDMS and PDHS have considerable surface binding (65% and 87%, respectively), although the films deposited from PDMS are of a better quality and processability due to solubility and lower processing temperatures. © 2014 American Chemical Society.

Synthesis and characterisation of interfacial layers in organic solar cells

The quest for renewable energy sources has led to growing attention in the research of organic photovoltaics (OPVs), as a promising alternative to fossil fuels, since these devices have low manufacturing costs and attractive end-user qualities, such as ease of installation and maintenance. Wide application of OPVs is majorly limited by the devices lifetime. With the development of new encapsulation materials, some degradation factors, such as water and oxygen ingress, can almost be excluded, whereas the thermal degradation of the devices remains a major issue. Two aspects have to be addressed to solve the problem of thermal instability: bulk effects in the photoactive layer and interfacial effects at the photoactive layer/charge-transporting layers. In this work, the interface between photoactive layer and electron-transporting zinc oxide (ZnO) in devices with inverted architecture was engineered by introducing polymeric interlayers, based on zinc-binding ligands, such as 3,4-dihydroxybenzene and 8-hydroxyquinoline. Also, a cross-linkable layer of poly(3,4-dimethoxystyrene) and its fullerene derivative were studied. At first, controlled reversible addition-fragmentation chain transfer (RAFT) polymerisation was employed to achieve well-defined polymers in a range of molar masses, all bearing a chain-end functionality for further modifications. Resulting polymers have been fully characterised, including their thermal and optical properties, and introduced as interlayers to study their effect on the initial device performance and thermal stability. Poly(3,4-dihydroxystyrene) and its fullerene derivative were found unsuitable for application in devices as they increased the work function of ZnO and created a barrier for electron extraction. On the other hand, their parental polymer, poly(3,4-dimethoxystyrene), and its fullerene derivative, upon cross-linking, resulted in enhanced efficiency and stability of devices, if compared to control. Polymers based on 8-hydroxyquinoline ligand had a negative effect on the initial stability of the devices, but increased the lifetime of the cells under accelerated thermal stress. Comprehensive studies of the key mechanisms, determining efficiency, such as charge generation and extraction, were performed by using time-resolved electrical and spectroscopic techniques, in order to understand in detail the effect of the interlayers on the device performance. Obtained results allow deeper insight into mechanisms of degradation that limit the lifetime of devices and prompt the design of better materials for the interface stabilisation.

PEDOT:PSS thin films: Applications in Bioelectronics

Owing to their capability of merging the properties of metals and conventional polymers, Conducting Polymers (CPs) are a unique class of carbon-based materials capable of conducting electrical current. A conjugated backbone is the hallmark of CPs, which can readily undergo reversible doping to different extents, thus achieving a wide range of electrical conductivities, while maintaining mechanical flexibility, transparency and high thermal stability. Thanks to these inherent versatility and attracting properties, from their discovery CPs have experienced incessant widespread in a great plethora of research fields, ranging from energy storage to healthcare, also encouraging the spring and growth of new scientific areas with highly innovative content. Nowadays, Bioelectronics stands out as one of the most promising research fields, dealing with the mutual interplay between biology and electronics. Among CPs, the polyelectrolyte complex poly (3,4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS), especially in the form of thin films, has been emphasized as ideal platform for bioelectronic applications. Indeed, in the last two decades PEDOT:PSS has played a key role in the sensing of bioanalytes and living cells interfacing and monitoring. In the present work, development and characterization of two kinds of PEDOT:PSS-based devices for applications in Bioelectronics are discussed in detail. In particular, a low-cost amperometric sensor for the selective detection of Dopamine in a ternary mixture was optimized, taking advantage of the electrocatalytic and antifouling properties that render PEDOT:PSS thin films appealing tools for electrochemical sensing of bioanalytes. Moreover, the potentialities of this material to interact with live cells were explored through the fabrication of a microfluidic trapping device for electrical monitoring of 3D spheroids using an impedance-based approach.

Ruptura celular, extração e encapsulamento de Astaxantina de Haematococcus pluvialis (Volvocales, Chlorophyta)

O interesse na produção de astaxantina de fontes naturais vem aumentando significativamente, devido principalmente à sua capacidade como potente agente antioxidante. Na obtenção da astaxantina por via biotecnológica, a microalga Haematococcus pluvialis é um dos micro-organismos industrialmente mais interessantes. Entretanto, como a maioria dos carotenoides, a astaxantina é uma molécula altamente insaturada que pode ser facilmente degradada por processos térmicos. Em função desta instabilidade, uma possibilidade que se abre, a fim de proteger sua atividade biológica de fatores ambientais e reforçar a sua estabilidade física, é o encapsulamento. Neste sentido, este trabalho vem contribuir em inovações relacionadas ao desenvolvimento de tecnologia para ruptura celular, extração e nanoencapsulamento de astaxantina produzida por via biotecnológica, mais especificamente de astaxantina obtida através do cultivo de H. pluvialis. Neste estudo, os cultivos foram realizados em meio BBM e acetato de sódio e conduzidos a temperatura constante de 25±1 ºC em fotobiorreatores de 1 L com aeração por borbulhamento de ar de 300 mL.min-1 , agitação manual diária e sob iluminância constante de 444 µmol fótons.m-2 s -1 durante 15 dias, sendo inoculados com suspensão de microalgas previamente preparada, na proporção de 10%, e pH ajustado em 7,0. A biomassa foi recuperada dos cultivos por centrifugação e seca a 35 °C por 48 h. Em seguida, foram empregadas diferentes técnicas de ruptura celular (química, mecânica e enzimática). Após a ruptura, foi realizada a extração dos carotenoides e a quantificação dos carotenoides totais (µg.g-1 ) e da extratibilidade (%). Entre os solventes testados no método de ruptura química, o diclorometano foi o selecionado para a extração dos pigmentos carotenoides. Dentre as técnicas mecânicas de ruptura celular, a maceração da biomassa congelada com terra diatomácea resultou na maior extratibilidade e carotenoides totais (66,01% e 972,35 μg.g-1 ). A melhor condição de lise da parede celular de H. pluvialis, utilizando o preparado enzimático Glucanex® , ocorreu em pH do meio reacional de 4,5 a 55 ºC, com atividade inicial de β-1,3-glucanase de 0,6 U.mL-1 e um tempo de reação de 30 min, alcançando-se 17,73% de atividade lítica relativa. Nestas condições, com a reação enzimática assistida por ultrassom sem congelamento prévio da biomassa, atingiu-se 83,90% e 1235,89 µg.g -1 , respectivamente, para extratibilidade e carotenoides totais. Dentre as técnicas combinadas testadas, a maceração com terra diatomácea associada à lise enzimática apresentou valores de extratibilidade e carotenoides totais de, respectivamente, 93,83% e 1382,12 µg.g-1 . No encapsulamento do extrato contendo astaxantina obtido por lise enzimática associada por ultrassom, envolvendo a coprecipitação com PHBV (poli(3-hidroxibutirato-cohidroxivalerato)) em fluidos supercríticos, o aumento da pressão tendeu a reduzir o diâmetro da partícula formada, enquanto que o aumento da relação biomassa contendo astaxantina:diclorometano usada na etapa de extração incrementou o percentual de encapsulamento e a eficiência de encapsulamento para ambas pressões testadas (80 e 100 bar). Os maiores valores de percentual de encapsulamento (17,06%) e eficiência de encapsulamento (51,21%) foram obtidos nas condições de 80 bar e relação biomassa:diclorometano de 10 mg.mL -1 . Nestas condições, o diâmetro médio de partícula foi de 0,228 µm. Com base nos resultados obtidos, técnicas para a obtenção de astaxantina de H. pluvialis e seu encapsulamento foram desenvolvidas com sucesso, podendo ser extendidas a outros produtos intracelulares de microalgas.

The Effect of Package Geometry on Moisture Driven Degradation of Polymer Aluminum Capacitors

Polymer aluminum electrolytic capacitors were introduced to provide an alternative to liquid electrolytic capacitors. Polymer electrolytic capacitor electric parameters of capacitance and ESR are less temperature dependent than those of liquid aluminum electrolytic capacitors. Furthermore, the electrical conductivity of the polymer used in these capacitors (poly-3,4ethylenedioxithiophene) is orders of magnitude higher than the electrolytes used in liquid aluminum electrolytic capacitors, resulting in capacitors with much lower equivalent series resistance which are suitable for use in high ripple-current applications. The presence of the moisture-sensitive polymer PEDOT introduces concerns on the reliability of polymer aluminum capacitors in high humidity conditions. Highly accelerated stress testing (or HAST) (110ºC, 85% relative humidity) of polymer aluminum capacitors in which the parts were subjected to unbiased HAST conditions for 700 hours was done to understand the design factors that contribute to the susceptibility to degradation of a polymer aluminum electrolytic capacitor exposed to HAST conditions. A large scale study involving capacitors of different electrical ratings (2.5V – 16V, 100µF – 470 µF), mounting types (surface-mount and through-hole) and manufacturers (6 different manufacturers) was done to determine a relationship between package geometry and reliability in high temperature-humidity conditions. A Geometry-Based HAST test in which the part selection limited variations between capacitor samples to geometric differences only was done to analyze the effect of package geometry on humidity-driven degradation more closely. Raman spectroscopy, x-ray imaging, environmental scanning electron microscopy, and destructive analysis of the capacitors after HAST exposure was done to determine the failure mechanisms of polymer aluminum capacitors under high temperature-humidity conditions.

DLTS investigation of acceptor states in P3MeT Schottky barrier diodes

Deep Level Transient Spectroscopy (DLTS) has been used to investigate hole traps in the depletion region of Schottky barrier diodes formed from electropolymerised poly(3-methylthiophene). The capacitance transients appear to be composed of a fast and a slow component. Analysis of the slower component using the ''rate window'' technique yields isochronal differential capacitance curves that depend on temperature in the manner predicted by theory.

Influence of fabrication conditions on the electrical behaviour of polymer Schottky diodes

Evidence is presented which shows that anomalies in the I-V characteristics of Schottky diodes formed from electrodeposited poly(3-methylthiophene) are related to the time films are held under vacuum prior to deposition of the rectifying aluminium electrode. For short times (similar to 15 mins) a plateau appears in the forward bias characteristic which disappears leading to a significant voltage offset as the device ages or is driven into high forward bias.