The work presented in the thesis is focused on the synthesis of diverse colloidal semiconductor NCs in organic media, their surface design with tiny inorganic and hybrid capping species in solution phase, and subsequent assembling of these NC building units into two-dimensional close-packed thin-films and three-dimensional non-ordered porous superstructures.

Durch Multiskalensimulationen wird der Ladungstransport in nanodrahtbasierten Schottky-Barrieren-Feldeffekt-Transistoren im Materialsystem Ni2Si/Si untersucht. Die Bedingungen an die Genauigkeit der verwendeten Eingangsparameter werden bestimmt und Vorhersagen über optimale Material- und Geräteparameter werden getroffen. Es wird die Frage beantwortet, ob die Bestimmung von physikalischen Parametern aus einzelnen gemessenen Strom-Spannungs-Kennlinie möglich ist. Der Feldeffekt wird durch Berechnungen auf Basis der Finiten-Elemente-Methode und die resultierenden Stromflüsse durch ein quantenmechanisches Transportmodell ermittelt. In der Untersuchung der geometrischen Eingangsparameter wird gezeigt, dass bis auf den Radius des Nanodrahtes die in einem Experiment zu erwartenden Messfehler keinen drastischen Einfluss auf die Strom-Spannungs-Kennlinie haben. Signifikant ist hingegen der Einfluss der Temperatur, der effektiven Ladungsträgermassen und der Höhe der Schottky-Barriere. Da diese drei Eingangsparameter des betrachteten Systems mit relativ großen Ungenauigkeiten behaftet sind, ist die Bestimmung von physikalischen Parametern aus einzelnen gemessenen Strom-Spannungs-Kennlinien auf die erhoffte Weise nicht möglich. Die Arbeit zeigt auch, dass bereits moderate Veränderungen der Arbeitstemperatur einen bedeutenden Einfluss auf die Strom-Spannungs-Kennlinie haben. Für die Konstruktion von Transistoren mit hoher Stromdichte kann anhand der ermittelten Daten die Verkleinerung der aktiven Region durch Oxidation vorgeschlagen werden.:Kurzfassung/Abstract I Verwendete Symbole IV Verwendete Parameter VI Verwendete Abkürzungen VII 1 Motivation 8 2 Grundlagen 9 2.1 Modellbildung und Simulation 9 2.2 Schottky-Diode 10 2.3 Feldeffekt-Transistor 12 2.4 Feldeffekt-Transistor auf der Basis von Silizium-Nanodrähten 13 3 Methoden 17 3.1 Simulationsmodell 17 3.2 Finite-Elemente-Methode 20 3.3 Landauer-Büttiker-Formalismus 21 3.4 Hamiltonoperator 22 3.5 Transmissionsfunktion 23 3.6 Büttiker Sonde 24 4 Ergebnisse und Diskussion 26 4.1 Implementierung des Simulationsprogrammes 26 4.2 Berechnung der Basis-Strom-Spannungs-Kennlinie 31 4.3 Wahl der Simulationsparameter 35 4.4 Abhängigkeit von geometrischen Parametern 41 4.5 Abhängigkeit von physikalischen Parametern 49 5 Zusammenfassung, Schlussfolgerungen und Ausblick 55 Abbildungsverzeichnis 59 Literatur 62 / Charge transport in nanowire-based Schottky-barrier field-effect transistors in the material system Ni2Si/Si is examined by multi-scale simulations. The requirements for the accuracy of the input parameters are determined and predictions about optimum material and device parameters are made. The question is answered, whether the determination of physical parameters from individual measured current-voltage curves is possible? The field effect is described by calculations based on the finite element method and the resulting currents are calculated with a quantum mechanical transport model. In the study of the geometric input parameters it is shown that experimental uncertainties do not drastically affect the current-voltage characteristic, except from the nanowire radius. However, significant is the influence of the temperature, the effective charge carrier mass and the height of the Schottky-barrier. Since these three input parameters are known only with low experimental accuracy for the considered system, the determination of physical parameters from individual measured current-voltage curves is not possible in the expected way. The results also show that moderate changes of the working temperature have a significant influence on the current-voltage characteristic. For the construction of transistors with high current density the reduction of the active region by oxidation is proposed.:Kurzfassung/Abstract I Verwendete Symbole IV Verwendete Parameter VI Verwendete Abkürzungen VII 1 Motivation 8 2 Grundlagen 9 2.1 Modellbildung und Simulation 9 2.2 Schottky-Diode 10 2.3 Feldeffekt-Transistor 12 2.4 Feldeffekt-Transistor auf der Basis von Silizium-Nanodrähten 13 3 Methoden 17 3.1 Simulationsmodell 17 3.2 Finite-Elemente-Methode 20 3.3 Landauer-Büttiker-Formalismus 21 3.4 Hamiltonoperator 22 3.5 Transmissionsfunktion 23 3.6 Büttiker Sonde 24 4 Ergebnisse und Diskussion 26 4.1 Implementierung des Simulationsprogrammes 26 4.2 Berechnung der Basis-Strom-Spannungs-Kennlinie 31 4.3 Wahl der Simulationsparameter 35 4.4 Abhängigkeit von geometrischen Parametern 41 4.5 Abhängigkeit von physikalischen Parametern 49 5 Zusammenfassung, Schlussfolgerungen und Ausblick 55 Abbildungsverzeichnis 59 Literatur 62

L'introduction d'une contrainte mécanique dans le canal de MOSFETs sur SOI est indispensable pour les noeuds technologiques sub-22 nm. Son efficacité dépend de la géométrie et des règles de dessin du dispositif. L'impact des étapes du procédé de fabrication des transistors (gravure des zones actives, formation de la grille métallique, implantation des Source/Drain (S/D)) sur la contrainte du silicium contraint sur isolant (sSOI) a été mesuré par diffraction des rayons X en incidence rasante (GIXRD). Parallèlement, le gain en performances de MOSFETs sur sSOI a été quantifié par rapport au SOI (100% de gain en mobilité pour des nMOS longs et larges (L=W=10 μm), 35% de gain en courant de drain à saturation (IDsat) pour des nMOS courts et étroits (L=25 nm, W=77 nm)). Des structures contraintes innovantes ont aussi été étudiées. Un gain en IDsat de 37% (18%) pour des pMOS sur SOI (sSOI) avec des S/D en SiGe est démontré par rapport au sSOI avec des S/D en Si, pour une longueur de grille de 60 nm et des films de 15 nm d'épaisseur. Des mesures GIXRD, couplées à des simulations mécaniques, ont permis d'étudier et d'optimiser des structures originales avec transfert de contrainte d'une couche enterrée précontrainte (en SiGe ou en nitrure) vers le canal.

This thesis describes the development and application of condensed-phase cavity-based spectroscopic techniques - namely cavity ring-down spectroscopy (CRDS); cavity enhanced absorption spectroscopy (CEAS); broadband cavity enhanced absorption spectroscopy (BBCEAS) and evanescent wave (EW) variants of all three. The recently-developed cavity technique of EW-broadband cavity enhanced absorption spectroscopy (EW-BBCEAS) has been used—in combination with a supercontinuum source (SC) and a sensitive, fast readout CCD detector—to record of the full visible spectrum (400–700 nm) of a silica-liquid interfacial layer (with an effective thickness ca. 1 µm), at rapid acquisition rates (> 600 Hz) that are sufficient to follow fast kinetics in the condensed phase, in real time. The sensitivity achieved (A_min= 3.9 x 10^-5) is comparable with previous EW-CRDS and EW-CEAS studies, but the spectral region accessed in this broadband variant is much larger. The study of liquid|air interfaces using EW cavity-based techniques is also illustrated for the first time. The first application of BBCEAS to the analysis of microfluidic samples, flowing through a microfluidic chip, is illustrated. Proof-of-principle experiments are presented, demonstrating the technique’s ability to provide full visible broadband spectral measurements of flowing microfluidic droplets, with both high detection sensitivity (α_min < 10^-2 cm^-1) and excellent spatial and temporal resolution: an SC light source and sensitive, fast readout CCD allowed measurement repetition rates of 273 Hz, whilst probing a very small sample volume (ca. 90 nL). A significant portion of this thesis is devoted to demonstrating the powerful capabilities of CEAS, CRDS and BBCEAS in monitoring radical recombination reactions and associated magnetic field effects (MFEs) in solution. The efficacy of CEAS as a high-sensitivity MFE detection method has been established in a proof-of-principle study, using narrow band CEAS in combination with phase-sensitive detection: MFE-induced absorbance changes of ca. 10^-6 could be detected using the modulated CEAS technique and the data are shown to be superior to those obtained using conventional transient absorption (TA) methods typically employed for MFE measurements. The powerful capabilities of CRDS in monitoring radical recombination reactions and associated MFEs are also demonstrated. In particular, a pump-probe CRDS variant allows not only high sensitivity (A_min on the order 10^-6), but also sub-microsecond time-resolution. Combined, these features represent significant advantages over TA. Finally, SC-BBCEAS is used to measure full visible spectra of photoinduced reactions and their MFEs. The applicability of this approach to in vitro MFE studies of Drosophila cryptochrome is demonstrated—the results mark the first in vitro observation of a magnetic field response in an animal cryptochrome, a key result supporting the hypothesis that cryptochromes are involved in the magnetic sense in animals.

Electrically detected magnetic resonance (EDMR) is a sensitive spectroscopic technique, which can be used to readout few to single electron spins in semiconductor and carbon nanodevices for applications in solid state quantum information processing (QIP). Since only electrically active defects contribute to the EDMR signal, this technique can be used further to investigate defects and impurities in photovoltaic devices, in which they limit the sunlight-to-energy conversion efficiency significantly. Here, I employ X-band EDMR for semiconductor defect analysis and identify the most important recombination centres in Czochralski silicon with oxide precipitates, which can be intentionally grown to confine detrimental metallic impurities to inactive regions of the wafer in order to serve as a defect-free substrate for modern silicon photovoltaic devices. Those experiments show that oxide precipitation is accompanied by the formation of silicon dangling bonds. Furthermore, I describe a very promising route towards the fabrication and readout of few to single electron spins in carbon nanotube devices, which can be characterised structurally via transmission electron microscopy in order to relate their electrical and spin properties with their structure. Finally, I employ EDMR to read out electron spin states in donor-doped silicon field-effect transistors as a prerequisite for their application in QIP. I report on a novel cryogenic probe head for EDMR experiments in resonant microwave cavities operating at 0.35 T (9.7 GHz, X-band) and 3.34 T (94 GHz, W-band). This approach overcomes the inherent limitations of conventional X-band EDMR and permits the investigation of paramagnetic states with a higher spectroscopic resolution and signal intensity. Both advantages are demonstrated and discussed. I further report on a novel mechanism giving rise to the EDMR effect in donor-doped silicon field-effect transistors, which is capable of explaining why the EDMR signal intensities of the conduction electrons are enhanced by a factor of ∼100, while the donor resonance signals increase by a factor of ∼20 from X- to W-band only. The spin-relaxation and dephasing times are extracted from a series of pulsed-EDMR measurements and confirm this model. The author gratefully acknowledges funding from Trinity College Oxford, Department of Materials, EPSRC DTA, and Konrad-Adenauer-Stiftung e.V. (Begabtenförderung).

<div>Silicon based semiconductor technology is facing more and more challenges to continue the Moore's law due to its fundamental scaling limitations. To continue the pace of progress of device performance for both logic and memory devices, researchers are exploring new low-dimensional materials, e.g. nanowire, nanotube, graphene and hexagonal boron nitride. Transition metal dichalcogenides (TMDs) are attracted considerable attention due their atomically thin nature and proper bandgap at the initial study. Recently, more and more interesting properties are found in these materials, which will bring out more potential usefulness for electronic applications. Competing with the silicon device performance is not the only goal in the potential path finding of beyond silicon. Low-dimensional materials may have other outstanding performances as an alternative materials in many application realms. </div><div><br></div><div>This thesis explores the potential of TMD based devices in memory and logic applications. For the memory application, TMD based vertical devices are fully studied. Two-terminal vertical transition metal dichalcogenide (TMD) based memory selectors were firstly built and characterized, exhibiting better overall performance compared with some traditional selectors. Polymorphism is one of unique properties in TMD materials. 2D phase engineering in TMDs attracted great attention. While electric switching between semiconductor phase to metallic phase is the most desirable. In this thesis, electric field induced structural transition in MoTe₂ and Mo_1-xW_xTe₂ is firstly presented. Reproducible bipolar resistive random access (RRAM) behavior is observed in MoTe₂ and Mo_1-xW_xTe₂ based vertical devices. Direct confirmation of a phase transition from a 2H semiconductor to a distorted 2H_d metallic phase was obtained after applying an electric field. Set voltage is changed with flake thickness, and switching speed is less than 5 ns. Different from conventional RRAM devices based on ionic migration, the MoTe₂-based RRAMs offer intrinsically better reliability and control. In comparison to phase change memory (PCM)-based devices that operate based on a change between an amorphous and a crystalline structure, our MoTe₂-based RRAM devices allow faster switching due to a transition between two crystalline states. Moreover, utilization of atomically thin 2D materials allows for aggressive scaling and high-performance flexible electronics applications. Both of the studies shine lights on the new application in the memory field with two-dimensional materials.<br></div><div><br></div><div>For the logic application, the ultra thin body nature of TMDs allows for more aggressive scaling compared with bulk material - silicon. Two aspects of scaling properties in TMD based devices are discussed, channel length scaling and channel width scaling. A tunability of short channel effects in MoS₂ field effect transistor (FET) is reported. The electrical performance of MoS₂ flakes is governed by an unexpected dependence on the effective body thickness of the device which in turn depends on the amount of intercalated water molecules that exist in the layered structure. In particular, we observe that the doping stage of a MoS₂ FET strongly depends on the environment (air/vacuum). For the channel width scaling, the impact of edge states in three types of TMDs, metallic T_d-phase WTe₂ as well as semiconducting 2H-phase MoTe₂ and MoS₂ were explored, by patterning thin flakes into ribbons with varying channel widths. No obvious charge depletion at the edges is observed for any of these three materials, which is different from what has been observed in graphene nanoribbon devices. </div>

Esta Tese aborda o estudo de transistores por efeito de campo orgânicos (OFETs do inglês, Organic Feld-Effect Transistors). Entender o comportamento da carga acumulada no canal do OFET, a qual é responsável pelo processo de condução elétrica no dispositivo, é de grande importância para ajudar a melhorar sua eficiência ou a propor um modelo teórico que descreva o comportamento do transistor em todos os seus regimes de operação. Vários trabalhos na literatura investigam o campo elétrico na camada semicondutora do transistor (ao longo do canal) gerado pela acumulação de cargas, porém nenhum investiga o campo na camada dielétrica de OFETs, que é diretamente proporcional à carga acumulada no canal. Investigou-se inicialmente o campo elétrico na camada dielétrica do dispositivo por meio da espectroscopia vibracional por Geração de Soma de Frequências (espectroscopia SFG do inglês, Sum-Frequency Generation). Espectros SFG obtidos nos dispositivos polarizados exibiram uma banda em ~1720 cm-1, devido ao grupo carbonila da camada dielétrica orgânica (PMMA &#8211; poli(metil metacrilato)), cuja a amplitude foi proporcional à voltagem de porta aplicada, indicando que esses grupos polares foram orientados sob ação do intenso campo elétrico no dispositivo. Esse sinal SFG induzido pelo campo pode ser devido a duas contribuições, um termo não linear de segunda ordem (devido à reorientação molecular) e outro de terceira ordem (interação entre os campos ópticos e o campo estático no volume do material). Observamos uma redução quase completa do sinal SFG em altas temperaturas (próximas da Tg do polímero dielétrico), indicando que o mecanismo de reorientação molecular é o responsável pelo sinal SFG gerado. Foram realizadas então medidas preliminares de microscopia SFG para mapear esse sinal SFG ao longo do canal de OFETs a base dos polímeros N2200 (semicondutor) e PMMA (dielétrico). Os resultados conseguem demonstrar a variação da densidade de carga acumulada no canal quando o dispositivo está polarizado e próximo à saturação. Usando Microscopia por Modulação de Carga (microscopia CMM do inglês, Charge Modulation Microscopy), que é outro método não invasivo para investigar a acumulação de cargas em um dispositivo operando, mapeamos a distribuição de carga no canal desses OFETs com alta resolução espacial (sub-micrométrica). Além disso, uma simulação da densidade de carga esperada e dos perfis de CMM foi realizada usando um modelo ambipolar para OFETs. Com base nessas simulações, propusemos uma modulação de onda quadrada do OFET, que permite uma comparação mais direta dos perfis de CMM com o perfil de densidade de carga ao longo do canal do transistor. Usando o esquema proposto, esses perfis foram medidos e comparados com o esperado com base no modelo ambipolar. Em geral os perfis de densidade de carga obtidos concordam bem com o modelo, usando apenas um único parâmetro global ajustável, exceto muito próximo do eletrodo de dreno e no regime de saturação profunda, quando os experimentos apresentam um artefato devido à eletro-absorção e não permitem uma comparação precisa com o modelo. Portanto, espera-se que esta Tese tenha contribuído para o avanço de técnicas de caracterização da distribuição de carga em OFETs, e assim melhorar o entendimento de seus mecanismos de funcionamento. / This Thesis deals with the study of Organic Field Effect Transistors (OFETs). Understanding the behavior of the accumulated charge along the OFET channel, which is responsible for the electrical conduction process in the device, is of great importance for improving its efficiency or proposing a theoretical model that describes the behavior of the transistor in all its operating regimes. Several studies in the literature investigate the electric field in the semiconductor layer of the transistor (along the channel) generated by the charge accumulation, but none investigates the field in the OFET dielectric layer, which is directly proportional to the charge accumulated in the channel. The electric field in the dielectric layer of the device was initially investigated by Sum-Frequency Generation (SFG) vibrational spectroscopy. SFG spectra obtained in the polarized devices exhibited a band at ~ 1720 cm-1, due to the carbonyl group of the organic dielectric layer (PMMA - poly (methyl methacrylate)), whose amplitude was proportional to the applied gate voltage, indicating that these polar groups were oriented by the intense electric field in the device. This field-induced SFG signal may be due to two contributions, a second order non-linear term (due to molecular reorientation) and a third order term (interaction between the optical fields and the static field in the material volume). We observed an almost complete reduction of the SFG signal at high temperatures (close to the Tg of the dielectric polymer), indicating that the molecular reorientation mechanism is responsible for the generated SFG signal. Preliminary SFG microscopy measurements were performed to map this SFG signal along the channel of OFET fabricated with N2200 (semiconductor) and PMMA (dielectric) polymers. The results demonstrate the variation of the accumulated charge density along the channel when the device is polarized and close to saturation. Using Charge Modulation Microscopy (CMM), which is another noninvasive method to investigate the accumulation of charges in an operating device, we mapped the charge distribution in the channel of these OFETs with high spatial resolution (sub-micrometer). In addition, a simulation of the expected charge density and CMM profiles was performed using an ambipolar model for OFETs. Based on these simulations, we proposed a square-wave modulation of the OFET, which allows a more direct comparison of the CMM profiles with the charge density profile. Using the proposed scheme, these profiles along the transistor channel were measured and compared with those expected from the ambipolar model. In general, the obtained charge density profiles agree well with the model, using only a single global adjustable parameter, except very close to the drain electrode and in the deep saturation regime, when the experiments have an artifact due to the electro-absorption and do not allow a precise comparison with the model. Therefore, it is expected that this Thesis has contributed to the advancement of techniques to characterize the charge distribution in OFETs, and thus improve the understanding of its operating mechanisms. Keywords: Field-effect transistors. Organic electronics. Nonlinear optics. Sum-frequency generation. Polarization of dielectrics. Charge modulation microscopy. Metal-insulator-semiconductor capacitor.

Les transistors ayant un faible niveau de bruit à basse fréquence, une faible puissance de dissipation et fonctionnant à basse température (≤ 4.2 K) sont actuellement inexistants alors qu’ils sont très demandés pour la réalisation de préamplificateurs à installer au plus près des détecteurs ou des dispositifs à la température de quelques dizaines de mK, dans le domaine de l’astrophysique, de la physique mésoscopique et de l’électronique spatiale. Une recherche menée depuis de nombreuses années au LPN vise à réaliser une nouvelle génération de HEMTs (High Electron Mobility Transistors) cryogéniques à haute performance pour répondre à ces demandes. Cette thèse, dans le cadre d’une collaboration entre le CNRS/LPN et le CEA/IRFU, a pour but la réalisation de préamplificateurs cryogéniques pour des microcalorimètres à 50 mK.Les travaux de cette thèse consistent en des caractérisations systématiques des paramètres électriques et des bruits des HEMTs (fabriqués au LPN) à basse température. En se basant sur les résultats expérimentaux, l’une des sources de bruit à basse fréquence dans les HEMTs a pu être identifiée, c’est-à-dire la part du courant tunnel séquentiel dans le courant de fuite de grille. Grâce à ce résultat, les hétérostructures ont été optimisées pour minimiser le courant de fuite de grille ainsi que le niveau de bruit à basse fréquence. Au cours de cette thèse, différentes méthodes spécifiques ont été développées pour mesurer de très faibles valeurs de courant de fuite de grille, les capacités du transistor et le bruit 1/f du transistor avec une très haute impédance d’entrée. Deux relations expérimentales ont été observées, l’une sur le bruit 1/f et l’autre sur le bruit blanc dans ces HEMTs à 4.2 K. Des avancées notables ont été réalisées, à titre d’indication, les HEMTs avec une capacité de grille de 92 pF et une consommation de 100 µW peuvent atteindre un niveau de bruit en tension de 6.3 nV/√Hz à 1 Hz, un niveau de bruit blanc de 0.2 nV/√Hz et un niveau de bruit en courant de 50 aA/√Hz à 10 Hz. Enfin, une série de 400 HEMTs, qui répondent pleinement aux spécifications demandées pour la réalisation de préamplificateurs au CEA/IRFU, a été réalisée. Les résultats de cette thèse constitueront une base solide pour une meilleure compréhension du bruit 1/f et du bruit blanc dans les HEMTs cryogéniques afin de les améliorer pour les diverses applications envisagées. / Transistors with low noise level at low frequency, low-power dissipation and operating at low temperature (≤ 4.2 K) are currently non-existent, however, they are widely required for realizing cryogenic preamplifiers which can be installed close to sensors or devices at a temperature of few tens of mK, in astrophysics, mesoscopic physics and space electronics. Research conducted over many years at LPN aims to a new generation of high-performance cryogenic HEMTs (High Electron Mobility Transistors) to meet these needs. This thesis, through the collaboration between the CNRS/LPN and the CEA/IRFU, aims for the realization of cryogenic preamplifiers for microcalorimeters at 50 mK.The work of this thesis consists of systematic characterizations of electrical and noise parameters of the HEMTs (fabricated at LPN) at low temperatures. Based on the experimental results, one of the low-frequency-noise sources in the HEMTs has been identified, i.e., the sequential tunneling part in the gate leakage current. Thanks to this result, heterostructures have been optimized to minimize the gate leakage current and the low frequency noise. During this thesis, specific methods have been developed to measure very low-gate-leakage-current values, transistor’s capacitances and the 1/f noise with a very high input impedance. Two experimental relationships have been observed, one for the 1/f noise and other for the white noise in these HEMTs at 4.2 K. Significant advances have been made, for information, the HEMTs with a gate capacitance of 92 pF and a consumption of 100 µW can reach a noise voltage of 6.3 nV/√ Hz at 1 Hz, a white noise voltage of 0.2 nV/√ Hz, and a noise current of 50 aA/√Hz at 10 Hz. Finally, a series of 400 HEMTs has been realized which fully meet the specifications required for realizing preamplifiers at CEA/IRFU. The results of this thesis will provide a solid base for a better understanding of 1/f noise and white noise in cryogenic HEMTs with the objective to improve them for various considered applications.

O uso de materiais orgânicos em dispositivos eletrônicos, além de menor custo e facilidade de processamento, permite obter flexibilidade e transparência. Entretanto, para que a aplicação comercial desses materiais seja viável, os processos que ocorrem nos dispositivos ainda precisam ser mais bem compreendidos, visando maior eficiência e tempo de vida. É de grande importância o estudo das interfaces entre o semicondutor orgânico e os contatos metálicos, onde ocorre transferência de portadores de carga, e a interface com o dielétrico em transistores orgânicos (OFETs), onde se forma o canal de condução. As interfaces de dispositivos eletrônicos poliméricos foram estudadas, utilizando-se Espectroscopia SFG (do inglês Sum Frequency Generation). Esta técnica obtém um sinal com a soma das frequências de dois feixes incidentes sobrepostos, em um processo seletivo a meios onde não há simetria de inversão, como no caso de interfaces. Com aplicação de um feixe de excitação na região visível e outro sintonizável no infravermelho médio, a espectroscopia SFG fornece um espectro vibracional da interface e permite o estudo do ordenamento e da orientação dos grupos moleculares. Foram construídos e analisados OFETs de poli-3-hexiltiofeno (P3HT) preparados sobre substrato de vidro ou silício, utilizando como isolante óxido de silício e/ou poli-metil-metacrilato (PMMA). Foram obtidos espectros in situ do canal de OFETs em operação, observando pequenas alterações na forma de linha, porém a baixa relação sinal/ruído não permitiu obter conclusões detalhadas. Foi constatada a manifestação de bandas da camada isolante de PMMA como consequência da aplicação de campo elétrico. Este fenômeno foi considerado como uma nova ferramenta para estudar a distribuição de cargas e campo elétrico no canal de transistores. Não foram detectados sinais de degradação irreversível no polímero semicondutor a curto prazo, e a mudança de comportamento elétrico foi atribuída majoritariamente a dopagem por oxigênio absorvido no material. / The usage of organic materials in electronic devices allows not only low cost and ease of processing but also flexibility and transparency. However, to achieve viable commercial application, the processes involved on the devices operation must still be better comprehended, aiming for improved efficiency and life time. There is great importance in the study of the interfaces between organic semiconductors and metallic contacts, where charge transfer takes place, and between the dielectric and semiconductor layers of organic transistors (OFETs), where the conducting channel is formed. The interfaces in polymeric electronic devices were studied by SFG spectroscopy (Sum Frequency Generation). In this technique, a signal with frequency that equals the sum of those of two incident beams is generated in a process only allowed in media without inversion symmetry, such as interfaces. Using a visible excitation beam and a tunable infrared one, SFG spectroscopy yields a vibrational spectrum of the interface and provides information about the conformation and orientation of molecular groups. Poly-3-hexylthiophene (P3HT) OFETs were fabricated using glass or silicon substrates and silicon oxide and/or poly-methyl-methacrylate (PMMA) for the dielectric layer. SFG spectra were acquired in situ from the channel region of operating OFETs, observing small changes in lineshape, but low signal-to-noise ration did not allow a detailed interpretation. It was found that PMMA vibrational bands appeared when polarizing the device. This phenomenon was considered a new tool for studying the electric field and charge distribution along transistor channels. It was not noted any sign of short term irreversible degradation of the semiconducting polymer, and the change in the electrical behavior was attributed mainly to doping of the polymer by oxygen absorbed in the material.

O uso de materiais orgânicos em dispositivos eletrônicos, além de menor custo e facilidade de processamento, permite obter flexibilidade e transparência. Entretanto, para que a aplicação comercial desses materiais seja viável, os processos que ocorrem nos dispositivos ainda precisam ser mais bem compreendidos, visando maior eficiência e tempo de vida. É de grande importância o estudo das interfaces entre o semicondutor orgânico e os contatos metálicos, onde ocorre transferência de portadores de carga, e a interface com o dielétrico em transistores orgânicos (OFETs), onde se forma o canal de condução. As interfaces de dispositivos eletrônicos poliméricos foram estudadas, utilizando-se Espectroscopia SFG (do inglês Sum Frequency Generation). Esta técnica obtém um sinal com a soma das frequências de dois feixes incidentes sobrepostos, em um processo seletivo a meios onde não há simetria de inversão, como no caso de interfaces. Com aplicação de um feixe de excitação na região visível e outro sintonizável no infravermelho médio, a espectroscopia SFG fornece um espectro vibracional da interface e permite o estudo do ordenamento e da orientação dos grupos moleculares. Foram construídos e analisados OFETs de poli-3-hexiltiofeno (P3HT) preparados sobre substrato de vidro ou silício, utilizando como isolante óxido de silício e/ou poli-metil-metacrilato (PMMA). Foram obtidos espectros in situ do canal de OFETs em operação, observando pequenas alterações na forma de linha, porém a baixa relação sinal/ruído não permitiu obter conclusões detalhadas. Foi constatada a manifestação de bandas da camada isolante de PMMA como consequência da aplicação de campo elétrico. Este fenômeno foi considerado como uma nova ferramenta para estudar a distribuição de cargas e campo elétrico no canal de transistores. Não foram detectados sinais de degradação irreversível no polímero semicondutor a curto prazo, e a mudança de comportamento elétrico foi atribuída majoritariamente a dopagem por oxigênio absorvido no material. / The usage of organic materials in electronic devices allows not only low cost and ease of processing but also flexibility and transparency. However, to achieve viable commercial application, the processes involved on the devices operation must still be better comprehended, aiming for improved efficiency and life time. There is great importance in the study of the interfaces between organic semiconductors and metallic contacts, where charge transfer takes place, and between the dielectric and semiconductor layers of organic transistors (OFETs), where the conducting channel is formed. The interfaces in polymeric electronic devices were studied by SFG spectroscopy (Sum Frequency Generation). In this technique, a signal with frequency that equals the sum of those of two incident beams is generated in a process only allowed in media without inversion symmetry, such as interfaces. Using a visible excitation beam and a tunable infrared one, SFG spectroscopy yields a vibrational spectrum of the interface and provides information about the conformation and orientation of molecular groups. Poly-3-hexylthiophene (P3HT) OFETs were fabricated using glass or silicon substrates and silicon oxide and/or poly-methyl-methacrylate (PMMA) for the dielectric layer. SFG spectra were acquired in situ from the channel region of operating OFETs, observing small changes in lineshape, but low signal-to-noise ration did not allow a detailed interpretation. It was found that PMMA vibrational bands appeared when polarizing the device. This phenomenon was considered a new tool for studying the electric field and charge distribution along transistor channels. It was not noted any sign of short term irreversible degradation of the semiconducting polymer, and the change in the electrical behavior was attributed mainly to doping of the polymer by oxygen absorbed in the material.