As várias possibilidades de aplicações tecnológicas que o material de diamante permite na indústria de dispositivos impulsionou os avanços ele fabricação de amostras de diamante sintético de alta qualidade. O diamante sintético crescido pela técnica de alta. pressão e alta temperatura (HPHT - High Pressure-High Temperature) utiliza ligas de metais de transição corno solvente-catalizadores. Dentre as várias impurezas de metal de transição introduzidas no material resultante, as impurezas de níquel são as mais bem caraterizaclas, pois os centros relacionados com Ni apresentam características especiais nestas amostras sintéticas. Medidas ele absorção óptica e de ressonância pararnagnética eletrônica têm identificado vários centros relacionados com a impureza de níquel em diamante, tanto isolados como complexos envolvendo defeitos intrínsecos ou dopantes. Entretanto, existem ainda muitas dúvidas sobre a estrutura microscópica destes centros. Neste trabalho apresentamos uma investigação teórica das propriedades eletrônicas e estruturais de impurezas relacionadas com níquel em diamante. / High quality synthetic diamond can be grown from gmphite by high pressure-high temperate menthols, using transition metal (TM) alloys ( containing manganese, iron, nickel, and cobalt) as catalysts. Nickel is the only TM which has been unambiguously identified as present in the resulting synthetic material. Electron paramagnetic resonance (EPR) and optical absorption measurements have identified Ni-related active centers in diamond mostly isolate Ni and Ni-related complexos involving intrinsic defects or dopants. However, there is considerable controversy about the microscopic structure of those centers. We present a theoretical investigation on the structural and electronic properties of nickel impurities in diamond.

The rise of the Environmentalism in every sector of the Industry has lead the aircraft and engine manufacturing companies to develop new generations of more environmentally friendly engines. The companies, encouraged to this purpose, are in a constant research for new manufacturing and production techniques, in order to improve their products, from the environmental point of view, by gaining efficiency in the manufacturing techniques and reduce the fuel consumption and emissions in-flight. Having in mind this scenario, the sponsor of this Project is interested in understanding how changing the materials of the blades, titanium alloys currently, for other lighter materials, such as composites, is going to have an effect in the overall gas turbine efficiency. In the particular case of this Project, it will be studied the influence of the Stiffness and coating Thickness of those non-metallic materials suitable to be employed as coatings on gas turbine fan blades, from the icing point of view. The work procedure will be based on a study of Linear Elastic Fracture Mechanics of bi-material junctions and will extrapolate the general problem to the ice-coatings case, by getting experimental data from tests carried out in an Icing Tunnel. It will be observed that the coating Stiffness has an influence on the Adhesion Level of ice to less stiff materials, if compared with the Adhesion Level of ice to metals. Besides, it will be described how a 0.5 millimetres thin polymeric coating placed over a metallic substrate is enough to reduce the Adhesion Level of ice, hiding any effect that the underneath materials might have on the Adhesion Level.

The rise of the Environmentalism in every sector of the Industry has lead the aircraft and engine manufacturing companies to develop new generations of more environmentally friendly engines. The companies, encouraged to this purpose, are in a constant research for new manufacturing and production techniques, in order to improve their products, from the environmental point of view, by gaining efficiency in the manufacturing techniques and reduce the fuel consumption and emissions in-flight. Having in mind this scenario, the sponsor of this Project is interested in understanding how changing the materials of the blades, titanium alloys currently, for other lighter materials, such as composites, is going to have an effect in the overall gas turbine efficiency. In the particular case of this Project, it will be studied the influence of the Stiffness and coating Thickness of those non-metallic materials suitable to be employed as coatings on gas turbine fan blades, from the icing point of view. The work procedure will be based on a study of Linear Elastic Fracture Mechanics of bi-material junctions and will extrapolate the general problem to the ice-coatings case, by getting experimental data from tests carried out in an Icing Tunnel. It will be observed that the coating Stiffness has an influence on the Adhesion Level of ice to less stiff materials, if compared with the Adhesion Level of ice to metals. Besides, it will be described how a 0.5 millimetres thin polymeric coating placed over a metallic substrate is enough to reduce the Adhesion Level of ice, hiding any effect that the underneath materials might have on the Adhesion Level.

No description available.

As várias possibilidades de aplicações tecnológicas que o material de diamante permite na indústria de dispositivos impulsionou os avanços ele fabricação de amostras de diamante sintético de alta qualidade. O diamante sintético crescido pela técnica de alta. pressão e alta temperatura (HPHT - High Pressure-High Temperature) utiliza ligas de metais de transição corno solvente-catalizadores. Dentre as várias impurezas de metal de transição introduzidas no material resultante, as impurezas de níquel são as mais bem caraterizaclas, pois os centros relacionados com Ni apresentam características especiais nestas amostras sintéticas. Medidas ele absorção óptica e de ressonância pararnagnética eletrônica têm identificado vários centros relacionados com a impureza de níquel em diamante, tanto isolados como complexos envolvendo defeitos intrínsecos ou dopantes. Entretanto, existem ainda muitas dúvidas sobre a estrutura microscópica destes centros. Neste trabalho apresentamos uma investigação teórica das propriedades eletrônicas e estruturais de impurezas relacionadas com níquel em diamante. / High quality synthetic diamond can be grown from gmphite by high pressure-high temperate menthols, using transition metal (TM) alloys ( containing manganese, iron, nickel, and cobalt) as catalysts. Nickel is the only TM which has been unambiguously identified as present in the resulting synthetic material. Electron paramagnetic resonance (EPR) and optical absorption measurements have identified Ni-related active centers in diamond mostly isolate Ni and Ni-related complexos involving intrinsic defects or dopants. However, there is considerable controversy about the microscopic structure of those centers. We present a theoretical investigation on the structural and electronic properties of nickel impurities in diamond.

No description available.

<p>   Organic electronics has been a highly researched field owing to the low cost, biocompatibility, mechanical flexibility, and superior performance relative to their inorganic counterparts in some applications. Significant advancement has been achieved across various device platforms including organic light-emitting diodes (OLEDs), organic field effect transistors (OFETs), and organic solar cells, for instance. Recently, soft materials that can conduct both charge and ions simultaneously (i.e., organic mixed conductors) have been a major catalyst in the fields of biosensors and energy storage. Extensive research efforts in the organic electronics field are being invested to establish the relevant structure-property relationships to design and develop higher performing organic mixed conductors. Simultaneously, these materials are utilized in developing prototype biosensors with the aim of superior performance, lower cost, and better patient comfort and outcomes than currently available technologies. Following suit, this dissertation is dedicated to furthering organic electronics on both fundamental and applied fronts. Specifically, this work examines a novel class of redox-active macromolecules, radical polymers, as the organic electrochemical transistor (OECT) active layer. In addition, wearable ocular biosensors utilizing soft materials to realize design innovation are presented.</p> <p>   For the first part of the present dissertation, radical polymer-based blends are evaluated for mixed electron and ion conduction in OECTs. Traditional macromolecular design motifs for OECT active layer materials have been a closed-shell macromolecular backbone for electron conduction with charge-neutral hydrophilic side chains (e.g., triethylene glycol) for ion conduction. When poly(4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl) (PTEO) is blended with poly(3-hexylthiophene) (P3HT), 2,2,6,6-tetramethylpiperidin-N-oxy (TEMPO) radicals in PTEO act as an independent voltage regulator that modulates the ionic and hence electronic transport of the OECT devices. Electrochemical analysis of the blend films reveals that the ionic transport and hence electrochemical doping of the P3HT phase occur when the applied bias matches the onset oxidation potential of TEMPO radicals in PTEO even though that of P3HT is lower than that of TEMPO oxidation. By optimizing the blend ratio, figure-of-merit (i.e., μC*) values over 150 F V–1 cm–1 s–1 at loadings as low as 5% PTEO (by weight) are achieved, placing the performance on the same order as top-performing conjugated polymers despite the mediocre performance of pristine P3HT (<10 F V–1 cm–1 s–1). These findings suggest that introduction of open-shell moieties in the OECT active layer as a secondary redox-active species may significantly improve OECT performance metrics and offer a new paradigm for future macromolecular designs.</p> <p>   In the second part of the dissertation, novel design strategies for wearable ocular electroretinography (ERG) sensors are presented. Typically, wearable sensors are custom-made contact lenses fabricated in a bottom-up fashion where the pre-fabricated sensor component is either embedded in the contact lens body or sandwiched between two. The present work instead utilizes commercially available contact lenses, and the corneal electrode is integrated via electropolymerization of poly(3,4-ethylenedioxythiophene):iron(III) p-toluenesulfonate (PEDOT:Tos) on the lens surface. Electrochemical analysis of the PEDOT:Tos reveals that the measured impedance is several orders of magnitude lower than that of noble metals (e.g., Au) used as the working electrode in commercial electrodes. The mechanical and chemical stability along with the soft form factor of the present design strategy enables high-fidelity recording of ERG signals in human subjects without the need for topical anesthesia.</p> <p>   Following the similar strategy, a new seamless wearable ocular sensor integration strategy utilizing polydopamine (PDA) conformal coating is demonstrated. In this work, we utilize its strong adhesive property originating from the van der Waals interactions between catechol moieties of PDA and various hydrophilic functional groups (e.g., hydroxy, ether, etc.) already present in commercial contact lens materials. The facile integration demonstrates high peeling strength (> 55 J m-2), chemical and mechanical stability. A series of <em>in vivo</em> assessments demonstrates high accuracy, reliability, and user comfort of the fabricated wearable sensor in both animal and human subjects. The findings suggest that the PDA-assisted integration strategy may be applied in designing various future-generation wearable ocular electrophysiological sensors.</p>

No description available.

Spin-polarized two-dimensional electron states (2DESs) at surfaces and interfaces of magnetically active materials attract immense interest because of the idea of exploiting fermion spins rather than charge in next generation electronics. Applying angle-resolved photoelectron spectroscopy, we show that the silicon surface of GdRh2Si2 bears two distinct 2DESs, one being a Shockley surface state, and the other a Dirac surface resonance. Both are subject to strong exchange interaction with the ordered 4f-moments lying underneath the Si-Rh-Si trilayer. The spin degeneracy of the Shockley state breaks down below ~90 K, and the splitting of the resulting subbands saturates upon cooling at values as high as ~185 meV. The spin splitting of the Dirac state becomes clearly visible around ~60 K, reaching a maximum of ~70 meV. An abrupt increase of surface magnetization at around the same temperature suggests that the Dirac state contributes significantly to the magnetic properties at the Si surface. We also show the possibility to tune the properties of 2DESs by depositing alkali metal atoms. The unique temperature-dependent ferromagnetic properties of the Si-terminated surface in GdRh2Si2 could be exploited when combined with functional adlayers deposited on top for which novel phenomena related to magnetism can be anticipated.

<p> In an era of advancing printed electronics, solution-processable organic semiconductors continue to make significant strides in electronic and optoelectronic applications. Electrochromic (EC) technology, which encompass reversible optical modulation under electrochemical biasing, has progressed rapidly over the past half-century and developed into niche commercial-scale devices for auto-tinting glasses as well as low-power, non-emissive displays. To utilize the advantages of organic electrochromic materials in next-generation devices, it is imperative to understand their fundamental material properties, interactions with other device components, and the underlying electrochemistry that governs the overall optical and electrochemical response of the complete electrochromic device. This dissertation presents a discussion on the synergistic role of organic electrochromes, charge-balancing layers and electrolytes in determining two key performance metrics, namely the optical contrast and operational stability, of an electrochromic device (ECD). The absorption features of colored-to-transmissive switching conjugated polymers have been investigated by exploring material design strategies in conjunction with analytical approaches to optimize and enhance the optical contrast. In parallel, transmissive redox-active radical polymer counter electrodes have been developed as compatible charge-balancing layers and integrated into devices by pairing with electrochromic polymers (ECPs) to achieve stable and high-contrast optical modulation. Electrochemical activity of both conjugated and radical polymer electrodes in different ionic and solvent environments have been further examined to understand material-electrolyte interactions governing mixed ionic-electronic conduction. Finally, a small molecular approach to realizing transparent-to-colored electrochromism is discussed, where distinct substituent-induced degradation pathways of conjugated radical cations were revealed. Overall, this research aims to assist future development of robust, ultra-high contrast organic electrochromic platforms.  </p>