Terahertz (THz) technologies have numerous applications such as biological and medical imaging, security screening, remote sensing, and industrial process control. However, the lack of practical THz sources and detectors is still a significant problem limiting the impact of these applications. In this Thesis work, three novel THz radiation mechanisms are proposed and investigated, based on the distinctive electronic properties of charge carriers in 2D single-layer graphene and related 1D conductors (i.e., graphene nanoribbons and carbon nanotubes), combined with the use of nanoscale dielectric gratings. Numerical simulations as well as fabrication and characterization activities are carried out. The first proposed radiation mechanism is based on the mechanical corrugation of a single-layer sheet of graphene or 1D carbon conductor, deposited on a lithographically-defined sinusoidal grating. In the presence of a dc voltage, carriers will therefore undergo periodic angular motion and correspondingly radiate (similar to cyclotron emission but without the need for any external magnetic field). My numerical simulations indicate that technologically significant output power levels can correspondingly be obtained at geometrically tunable THz frequencies. Initial graphene samples on sinusoidal gratings were fabricated and found to undergo significant strain redistribution, which affects their structural quality. Charge carriers moving in a flat sheet of graphene or linear 1D carbon conductor parallel to a nanoscale grating can also produce THz radiation based on the Smith-Purcell effect. The role of the grating in this case is to diffract the evanescent electromagnetic fields produced by the moving electrons and holes so that THz light can be radiated. Once again, numerical simulations indicate that this approach is promising for the realization of ultra-compact THz sources capable of room-temperature operation. Initial experimental results with ultra-high-mobility graphene samples embedded in boron nitride films show promising THz electroluminescence spectra. The last approach considered in this Thesis involves graphene plasmons at THz frequencies, which can be excited through the decay of hot electrons injected with an applied bias voltage. A nearby grating can then be used to outcouple the guided electromagnetic fields associated with these collective charge oscillations into radiation. The excitation of these THz plasmonic resonances at geometrically tunable frequencies has been demonstrated experimentally via transmission spectroscopy measurements. / 2017-06-21T00:00:00Z

Die inhärenten elastomeren Eigenschaften von Gummiwerkstoffen sind im Vergleich zu Thermoplasten in vielen Spezialanwendungen vorteilhaft. Jedoch sind ihre schlechten Reibungs- und Verschleißeigenschaften ein wesentlicher Nachteil besonders bei tribologischen Anwendungen. In der vorliegenden Arbeit wurden Reibung, Verschleiß und mechanische Eigenschaften von Gummiwerkstoffen, die Polytetrafluorethylen(PFTE)-Pulver enthalten, untersucht. Hauptziel war dabei die Verbesserung der Reibungs- und Verschleißeigenschaften bei weiterer Erhöhung der mechanischen Eigenschaften der Elastomere. Es ist bekannt, dass sich Reibungs- und Verschleißeigenschaften gummiähnlicher Materialien in vielfältiger Weise von den Reibungseigenschaften der meisten anderen Festkörper unterscheiden. Die Gründe dafür sind das viskoelastische Verhalten und der sehr geringe elastische Modul von Gummi. Die Verwendung von mit Elektronen modifizierten PTFE-Pulvern in Ethylen-Propylen-Dien-Monomer (EPDM) Kautschuken führt zu einer signifikanten Reduzierung der Reibung, Erhöhung der Verschleißfestigkeit und gleichzeitig zu verbesserten mechanischen Eigenschaften in Folge einer speziellen chemischen Kopplung zwischen dem modifiziertem PTFE-Pulver und dem EPDM. Gummirezeptur, Vernetzungsmethode und die viskoelastischen Materialeigenschaften beeinflussen wesentlich die tribologischen und mechanischen Eigenschaften. Morphologie, Dispersion und die chemische Kopplung des PTFE-Pulvers haben einen signifikanten Einfluss auf die Reibungs- und Verschleißverhalten. Die viskoelastischen Materialeigenschaften, d.h. Härte, E-Modul und tan delta (Verlustfaktor) der Gummimischungen sind kritische Parameter und erfordern deshalb eine Optimierung. In dieser Arbeit wurden zwei Modellsysteme untersucht, die auf zwei unterschiedlichen Kautschuktypen basieren: a) Ethylen-Propylene-Diene-Monomer (EPDM) Kautschuk und b) Polychloropren Kautschuk (CR). / The inherent elastomeric properties of rubber compounds in comparison to thermoplastics are advantageous in many special purpose applications. However, their characteristic poor friction and wear properties are of prime concern especially in tribological applications. In the present work, friction, wear and mechanical properties of rubber compounds based on PTFE powder have been investigated. The main aim was to improve the friction and wear properties while further enhancing the mechanical properties of rubber compounds. As known, friction and wear behaviour of rubber-like materials differ in many ways from the frictional properties of most other solids. The reason for this is the high viscoelasticity and very low elastic modulus of rubber. The use of electron-modified PTFE powder in EPDM results in significant improvement in reducing friction, enhancing wear resistance and simultaneously improving mechanical properties due to specific chemical coupling between modified PTFE powder and EPDM. The rubber formulation, crosslinking mode and bulk viscoelastic properties strongly influences friction, wear and mechanical properties. The morphology, dispersion, and specific chemical coupling of PTFE powder play a significant role on friction and wear behaviour. The bulk viscoelastic properties, i.e. hardness, modulus and tan delta (loss factor) of the compounds are critical parameters and therefore, requires optimization. In this work two model systems based on two different rubber matrixes i.e. Ethylene-Propylene-Diene-Monomer (EPDM) and Chloroprene (CR) rubber have been investigated.

Die inhärenten elastomeren Eigenschaften von Gummiwerkstoffen sind im Vergleich zu Thermoplasten in vielen Spezialanwendungen vorteilhaft. Jedoch sind ihre schlechten Reibungs- und Verschleißeigenschaften ein wesentlicher Nachteil besonders bei tribologischen Anwendungen. In der vorliegenden Arbeit wurden Reibung, Verschleiß und mechanische Eigenschaften von Gummiwerkstoffen, die Polytetrafluorethylen(PFTE)-Pulver enthalten, untersucht. Hauptziel war dabei die Verbesserung der Reibungs- und Verschleißeigenschaften bei weiterer Erhöhung der mechanischen Eigenschaften der Elastomere. Es ist bekannt, dass sich Reibungs- und Verschleißeigenschaften gummiähnlicher Materialien in vielfältiger Weise von den Reibungseigenschaften der meisten anderen Festkörper unterscheiden. Die Gründe dafür sind das viskoelastische Verhalten und der sehr geringe elastische Modul von Gummi. Die Verwendung von mit Elektronen modifizierten PTFE-Pulvern in Ethylen-Propylen-Dien-Monomer (EPDM) Kautschuken führt zu einer signifikanten Reduzierung der Reibung, Erhöhung der Verschleißfestigkeit und gleichzeitig zu verbesserten mechanischen Eigenschaften in Folge einer speziellen chemischen Kopplung zwischen dem modifiziertem PTFE-Pulver und dem EPDM. Gummirezeptur, Vernetzungsmethode und die viskoelastischen Materialeigenschaften beeinflussen wesentlich die tribologischen und mechanischen Eigenschaften. Morphologie, Dispersion und die chemische Kopplung des PTFE-Pulvers haben einen signifikanten Einfluss auf die Reibungs- und Verschleißverhalten. Die viskoelastischen Materialeigenschaften, d.h. Härte, E-Modul und tan delta (Verlustfaktor) der Gummimischungen sind kritische Parameter und erfordern deshalb eine Optimierung. In dieser Arbeit wurden zwei Modellsysteme untersucht, die auf zwei unterschiedlichen Kautschuktypen basieren: a) Ethylen-Propylene-Diene-Monomer (EPDM) Kautschuk und b) Polychloropren Kautschuk (CR). / The inherent elastomeric properties of rubber compounds in comparison to thermoplastics are advantageous in many special purpose applications. However, their characteristic poor friction and wear properties are of prime concern especially in tribological applications. In the present work, friction, wear and mechanical properties of rubber compounds based on PTFE powder have been investigated. The main aim was to improve the friction and wear properties while further enhancing the mechanical properties of rubber compounds. As known, friction and wear behaviour of rubber-like materials differ in many ways from the frictional properties of most other solids. The reason for this is the high viscoelasticity and very low elastic modulus of rubber. The use of electron-modified PTFE powder in EPDM results in significant improvement in reducing friction, enhancing wear resistance and simultaneously improving mechanical properties due to specific chemical coupling between modified PTFE powder and EPDM. The rubber formulation, crosslinking mode and bulk viscoelastic properties strongly influences friction, wear and mechanical properties. The morphology, dispersion, and specific chemical coupling of PTFE powder play a significant role on friction and wear behaviour. The bulk viscoelastic properties, i.e. hardness, modulus and tan delta (loss factor) of the compounds are critical parameters and therefore, requires optimization. In this work two model systems based on two different rubber matrixes i.e. Ethylene-Propylene-Diene-Monomer (EPDM) and Chloroprene (CR) rubber have been investigated.

O Brasil ocupa posição de destaque no mercado de açúcar a granel e consumo elevado deste ingrediente na forma líquida, em especial pelas indústrias de bebidas e alimentos. O açúcar líquido apresenta vantagens em relação ao açúcar a granel como facilidade do manuseio e dosagem, espaço reduzido para a armazenagem, redução das perdas, custos e mão-de-obra, melhora na sanitização e grande variação possível nas proporções de diferentes misturas de açúcares. O açúcar Uquido invertido é uma solução de sacarose, glicose e frutose em água e recebe esse nome porque durante a sua produção há a inversão do poder óptico de rotação da solução. No processo produtivo do açúcar invertido existem alguns pontos que podem gerar a contaminação por microrganismos, dessa forma torna-se importante o desenvolvimento de técnicas que propiciem a sanitização eficiente desta matéria-prima. Este trabalho estudou duas técnicas alternativas de controle microbiano: a radiação gama com fonte de cobalto-60 e a radiação com feixe de elétrons. O estudo foi conduzido nas doses de 5, 10, 20, 30 e 50 kGy. O teor de sacarose apresentou decréscimo com a radiação indicando que ocorreu a quebra da ligação glicosídica com a formação de glicose e fioitose, gerando o aumento do teor de sólidos solúveis. Ocorreu a formação de compostos ácidos, confirmado pela redução de pH, que foi proporcional ao aumento da dose de radiação. As maiores doses provocaram alterações na cor do xarope pela formação de polímeros com cadeia molecular longa. A viscosidade nas amostras irradiadas com radiação gama aumentou em relação ao controle, indicando a prevalência de polimerização das moléculas, enquanto que na radiação com feixe de elétrons a polimerização foi observada somente na amostra que recebeu a dose de 50 kGy. Na análise sensorial, os julgadores apontaram diferença significativa (5%) no sabor entre o controle e as amostras irradiadas com 5 kGy, nas duas técnicas de processamento. Não foi possível identificar o efeito da radiação gama no controle de bolores e leveduras. / Brazil occupies position of prominence in the sugar market and high consumption of this ingredient in the liquid form, in special for the beverages and food industries. The liquid sugar presents advantages in relation to the bulk granulated system such as easiness of the handling and dosage, reduced space for the storage, reduction of the losses, costs and hand of workmanship, improvement of the sanitizing and great possible variation in the ratios of different mixtures of sugars. The inverted liquid sugar is a solution of sucrose, glucose and fructose in water. This ingredient receives this name because during its production it has an inversion of the optic power of rotation of the solution. In the productive process of the inverted sugar some points occur that can generate contamination by microorganisms, so its become important the development of techniques that propitiate the efficient sanitizing of this raw material. This work aims at to consider two alternative techniques of microbiologic control: gamma radiation with source of cobalto-60 and radiation with electron beam. The study was lead in the doses of 5, 10, 20, 30 and 50 kGy. Concentration of sucrose presented in syrup decreased with the radiation indicating the scission of glicosidic linkage in addition with the glucose and fiaictose formation, generating the increase in solids soluble. The acid compounds formation occurred, confirmed by the reduction of pH, that it was proportional with the increase of the radiation dose. The biggest doses had provoked change of color in the syrup by the long molecular chain polymers formation. Viscosity in the samples processed by gamma radiation increased in relation to the control, indicating the prevalence of polymerization of molecules, whereas in the radiation with electron beam the polymerization was only observed in the sample that received the dose of 50 kGy, In the sensorial analysis, the judges had pointed significant difference (5%) in the flavor among control and the samples radiated with 5 kGy in the two techniques of processing. The alterations provoked for the irradiation had not been enough to provide significant changes in the inverted sugar, even in the highest dose of 50 kGy. It was not possible to identify the effect of gamma radiation in the control of molds and yeasts.

O Brasil ocupa posição de destaque no mercado de açúcar a granel e consumo elevado deste ingrediente na forma líquida, em especial pelas indústrias de bebidas e alimentos. O açúcar líquido apresenta vantagens em relação ao açúcar a granel como facilidade do manuseio e dosagem, espaço reduzido para a armazenagem, redução das perdas, custos e mão-de-obra, melhora na sanitização e grande variação possível nas proporções de diferentes misturas de açúcares. O açúcar Uquido invertido é uma solução de sacarose, glicose e frutose em água e recebe esse nome porque durante a sua produção há a inversão do poder óptico de rotação da solução. No processo produtivo do açúcar invertido existem alguns pontos que podem gerar a contaminação por microrganismos, dessa forma torna-se importante o desenvolvimento de técnicas que propiciem a sanitização eficiente desta matéria-prima. Este trabalho estudou duas técnicas alternativas de controle microbiano: a radiação gama com fonte de cobalto-60 e a radiação com feixe de elétrons. O estudo foi conduzido nas doses de 5, 10, 20, 30 e 50 kGy. O teor de sacarose apresentou decréscimo com a radiação indicando que ocorreu a quebra da ligação glicosídica com a formação de glicose e fioitose, gerando o aumento do teor de sólidos solúveis. Ocorreu a formação de compostos ácidos, confirmado pela redução de pH, que foi proporcional ao aumento da dose de radiação. As maiores doses provocaram alterações na cor do xarope pela formação de polímeros com cadeia molecular longa. A viscosidade nas amostras irradiadas com radiação gama aumentou em relação ao controle, indicando a prevalência de polimerização das moléculas, enquanto que na radiação com feixe de elétrons a polimerização foi observada somente na amostra que recebeu a dose de 50 kGy. Na análise sensorial, os julgadores apontaram diferença significativa (5%) no sabor entre o controle e as amostras irradiadas com 5 kGy, nas duas técnicas de processamento. Não foi possível identificar o efeito da radiação gama no controle de bolores e leveduras. / Brazil occupies position of prominence in the sugar market and high consumption of this ingredient in the liquid form, in special for the beverages and food industries. The liquid sugar presents advantages in relation to the bulk granulated system such as easiness of the handling and dosage, reduced space for the storage, reduction of the losses, costs and hand of workmanship, improvement of the sanitizing and great possible variation in the ratios of different mixtures of sugars. The inverted liquid sugar is a solution of sucrose, glucose and fructose in water. This ingredient receives this name because during its production it has an inversion of the optic power of rotation of the solution. In the productive process of the inverted sugar some points occur that can generate contamination by microorganisms, so its become important the development of techniques that propitiate the efficient sanitizing of this raw material. This work aims at to consider two alternative techniques of microbiologic control: gamma radiation with source of cobalto-60 and radiation with electron beam. The study was lead in the doses of 5, 10, 20, 30 and 50 kGy. Concentration of sucrose presented in syrup decreased with the radiation indicating the scission of glicosidic linkage in addition with the glucose and fiaictose formation, generating the increase in solids soluble. The acid compounds formation occurred, confirmed by the reduction of pH, that it was proportional with the increase of the radiation dose. The biggest doses had provoked change of color in the syrup by the long molecular chain polymers formation. Viscosity in the samples processed by gamma radiation increased in relation to the control, indicating the prevalence of polymerization of molecules, whereas in the radiation with electron beam the polymerization was only observed in the sample that received the dose of 50 kGy, In the sensorial analysis, the judges had pointed significant difference (5%) in the flavor among control and the samples radiated with 5 kGy in the two techniques of processing. The alterations provoked for the irradiation had not been enough to provide significant changes in the inverted sugar, even in the highest dose of 50 kGy. It was not possible to identify the effect of gamma radiation in the control of molds and yeasts.