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The dynamic properties of several rectangular and V-shaped microcantilevers were investigated. Particular attention was paid to the higher flexural eigenmodes of oscillation. The potential of the higher flexural modes was demonstrated through the use of cantilevers as standalone sensors for adsorbed mass. The mass adsorbed on the surface of a cantilever was in the form of a homogeneous water layer measured as a function of relative humidity. The minimum detectable water layer thicknesses were 13.7 Å, 3.2 Å, 1.1 Å, and 0.7 Å for the first four modes of a rectangular cantilever, clearly demonstrating enhanced accuracy for the higher eigenmodes of oscillation. These thicknesses correspond to minimum detectable masses of 33.5 pg, 7.8 pg, 2.7 pg and 1.7 pg for the first four modes. For quantitative applications the spring constants of each cantilever must be determined. Many methods exist but only a small number can calibrate the higher flexural eigenmodes. A method was developed to simultaneously calibrate all flexural modes of microcantilever sensors. The method was demonstrated for the first four eigenmodes of several rectangular and V-shaped cantilevers with nominal fundamental spring constants in the range of 0.03 to 1.75 N/m. The spring constants were determined with accuracies of 5-10 %. Spring constants of the fundamental mode were generally in agreement with those determined using the Sader method. The method is compatible with existing AFM systems. It relies on a flow of gas from a microchannel and as such poses no risk of damage to the cantilever beam, its tip, or any coating. A related method was developed for the torsional modes of oscillation. Preliminary results are shown for the fundamental mode of a rectangular cantilever. The method can be easily extended to the higher torsional modes, V-shaped cantilevers, and potentially, the flapping modes of the legs of V-shaped microcantilevers.

Devido à necessidade de caracterizar as armadilhas magneto-ópticas (AMO), as quais fornecem amostras densas de átomos frios, e de extrema importância o conhecimento dos valores das constantes mecânicas k e &#946 inerentes ao movimento harmônico super amortecido dos átomos nestas armadilhas. Neste trabalho, obtivemos estas constantes usando a técnica que aplica uma oscilação forçada aos átomos aprisionados através de um pequeno campo magnético oscilante adicional de forma a não perturbar o aprisionamento. Fizemos um estudo destas constantes como função de alguns parâmetros inerentes ao aprisionamento, como por exemplo: intensidade dos feixes laser, gradiente de campo magnético e dessintonia. A manipulação de átomos aprisionados, obtida através da observação de diversas estruturas espaciais dos mesmos, mostra um certo controle sobre estes átomos e a obtenção de valores para a temperatura dos átomos nestas estruturas, permite uma maior compreensão do mecanismo de aprisionamento. Nos detivemos então, na medida da temperatura dos átomos aprisionados em estrutura espacial do tipo anel além de propor um modelo teórico simples capaz de justificar os resultados obtidos. / In order to have precise characterization of magneto-optical traps (MOT), which are used to obtain a dense sample of cold atoms, it is important to measure the mechanical constants k and &#946 of the over-damped harmonic motion that rule the motion of the atoms inside the MOT. In this work, we obtain these constants by applying a small additional a.c. magnetic field that does not perturb the trap d.c. field but forces the trapped atoms to oscillate. We studied the variation of the constants by changing laser intensities, trapping field gradient and detuning. The manipulation of trapped atoms and the observation of several kinds of spatial structures allow one to have a better comprehension of the trapping mechanism. We measured the temperature of the atoms in the ring type structure and a simple theoretical model that explains the results is proposed.

The human body is an intricate network of many highly regulated biochemical processes and cell adhesion is one of them. Cell adhesion is mediated by specific interactions between molecules on apposing cell surfaces and is critical to many physiological and pathological processes like inflammation and cancer metastasis. During inflammation, blood-borne circulating leukocytes regularly stick to and roll on the vessel walls, which consist in part, adhesive contacts mediated by the selectin family of adhesion receptors (P-, E- and L-selectin). This is the beginning of a multi-step cascade that ultimately leads to leukocyte recruitment in areas of injury or infection. In vivo, selectin-mediated interactions take place in a hydrodynamic milieu and hence, it becomes imperative to study these interactions under very similar conditions in vitro. The goal of this project was to characterize the kinetic and mechanical properties of selectin interactions with different physiologically relevant ligands and selectin-specific monoclonal antibodies (mAbs) under a mechanically stressful milieu, using atomic force microscopy (AFM). Elasticity studies revealed that bulk of the complex compliance came from the selectins, with the ligands or mAbs acting as relatively stiffer components in the stretch experiments. Furthermore, molecular elasticity was inversely related to selectin length with the Consensus Repeats (CRs) behaving as Hookean springs in series. Besides, monomeric vs. dimeric interactions could be clearly distinguished from the elasticity measurements. L-selectin dissociation studies with P-selectin Glycoprotein Ligand 1 (PSGL-1) and Endoglycan revealed that catch bonds operated at low forces while slip bonds were observed at higher forces. These results were consistent with previous P-selectin studies and suggested that catch bonds could contribute to the shear threshold for L-selectin-mediated rolling By contrast, only slip bonds were observed for L-selectin-antibody interactions, suggesting that catch bonds could be a common characteristic of selectin-ligand interactions. Force History studies revealed that off-rates of L-selectin-sPSGL-1 (or 2-GSP-6) interactions were not just dependent on applied force, as has been widely accepted but in fact, depended on the entire history of force application, thus providing a new paradigm for how force could regulate bio-molecular interactions. Characterizing selectin-ligand interactions at the molecular level, devoid of cellular contributions, is essential in understanding the role played by molecular properties in leukocyte adhesion kinetics. In this aspect, data obtained from this project will not only add to the existing body of knowledge but also provide new insights into mechanisms by which selectins initiate leukocyte adhesion in shear.

Devido à necessidade de caracterizar as armadilhas magneto-ópticas (AMO), as quais fornecem amostras densas de átomos frios, e de extrema importância o conhecimento dos valores das constantes mecânicas k e &#946 inerentes ao movimento harmônico super amortecido dos átomos nestas armadilhas. Neste trabalho, obtivemos estas constantes usando a técnica que aplica uma oscilação forçada aos átomos aprisionados através de um pequeno campo magnético oscilante adicional de forma a não perturbar o aprisionamento. Fizemos um estudo destas constantes como função de alguns parâmetros inerentes ao aprisionamento, como por exemplo: intensidade dos feixes laser, gradiente de campo magnético e dessintonia. A manipulação de átomos aprisionados, obtida através da observação de diversas estruturas espaciais dos mesmos, mostra um certo controle sobre estes átomos e a obtenção de valores para a temperatura dos átomos nestas estruturas, permite uma maior compreensão do mecanismo de aprisionamento. Nos detivemos então, na medida da temperatura dos átomos aprisionados em estrutura espacial do tipo anel além de propor um modelo teórico simples capaz de justificar os resultados obtidos. / In order to have precise characterization of magneto-optical traps (MOT), which are used to obtain a dense sample of cold atoms, it is important to measure the mechanical constants k and &#946 of the over-damped harmonic motion that rule the motion of the atoms inside the MOT. In this work, we obtain these constants by applying a small additional a.c. magnetic field that does not perturb the trap d.c. field but forces the trapped atoms to oscillate. We studied the variation of the constants by changing laser intensities, trapping field gradient and detuning. The manipulation of trapped atoms and the observation of several kinds of spatial structures allow one to have a better comprehension of the trapping mechanism. We measured the temperature of the atoms in the ring type structure and a simple theoretical model that explains the results is proposed.

The object of this thesis is to apply scanning probemicroscopy (SPM) to the field of advanced powder processing.Measurement of interparticle surface forces at conditionsrelevant to ceramic processing has been performed together withthorough studies of powder friction. Surface force measurements between silicon nitride andsilica surfaces in 1-bromonaphtalene and diiodomethane resultedin an attractive van der Waals force in both media for thesymmetric systems and a repulsive van der Waals force for theasymmetric systems. This agreed well with theoreticalpredictions from Lifshitz theory. Measurements in electrolytesolutions between silicon nitride surfaces with a varyingdegree of oxidation showed that silanol groups dominated theinteractions at a high degree of oxidation, whereas theinfluence of amine species became stronger after surfaceetching. Surface charge, surface potential and density ofsurface groups have been extracted from DLVO computer modellingof the experimental force curves. Surface force measurementshave been carried out using a nitrided silica sphere as acolloidal probe, representative for commercial silicon nitridepowders. Adsorption of poly(acrylic acid) above the isoelectricpoint generated a thin polymer layer of an essentially flatconformation. Friction force measurements were attainable via novelcalibration procedures of both the lateral photodetectorresponse and the cantilever torsional spring constant.Combining the method for detector calibration with evaluationof static friction slopes simplified the choice of appropriatecontact mechanics theory to evaluate the friction measurements.Applying the method on friction measurements between ironsurfaces coated with commercial lubricants showed a substantialsurface deformation not seen from the friction force alone. Thenanorheological properties of silica surfaces coated with twodifferent stearic acids have been evaluated from friction forcemeasurements. Steady sliding motion was replaced by highlyregular stick-slip motion at a critical load and velocity. Thestick-slip motion was successfully described and fitted to aphenomenological model. The contact area evaluated fromMaugis-Dugdale theory revealed the contact diameter to be veryclose to the stick-slip periodicity. Friction measurements were carried out between individualspray-dried ceramic granules as a function of binderconcentration and relative humidity. The hygroscopic nature ofthe binder resulted in a higher adhesion force but lowerfriction coefficient with increasing humidity. This effect wasascribed to softening of the binder and a lowering of the shearstrength of the binder rich surface layer on the granules.Comparison of the friction force between two granules and agranule and a hard metal surface confirmed that resistance toflow during the initial stages of powder pressing is dominatedby granule-wall friction and adhesion. Keywords: Atomic force microscope, AFM, SPM, van der Waalsinteraction, DLVO-theory, surface forces, colloidal probe,force curve, friction, adhesion, stick-slip, cantilever,calibration, spring constant, silicon nitride, iron,silica.

<p>The object of this thesis is to apply scanning probemicroscopy (SPM) to the field of advanced powder processing.Measurement of interparticle surface forces at conditionsrelevant to ceramic processing has been performed together withthorough studies of powder friction.</p><p>Surface force measurements between silicon nitride andsilica surfaces in 1-bromonaphtalene and diiodomethane resultedin an attractive van der Waals force in both media for thesymmetric systems and a repulsive van der Waals force for theasymmetric systems. This agreed well with theoreticalpredictions from Lifshitz theory. Measurements in electrolytesolutions between silicon nitride surfaces with a varyingdegree of oxidation showed that silanol groups dominated theinteractions at a high degree of oxidation, whereas theinfluence of amine species became stronger after surfaceetching. Surface charge, surface potential and density ofsurface groups have been extracted from DLVO computer modellingof the experimental force curves. Surface force measurementshave been carried out using a nitrided silica sphere as acolloidal probe, representative for commercial silicon nitridepowders. Adsorption of poly(acrylic acid) above the isoelectricpoint generated a thin polymer layer of an essentially flatconformation.</p><p>Friction force measurements were attainable via novelcalibration procedures of both the lateral photodetectorresponse and the cantilever torsional spring constant.Combining the method for detector calibration with evaluationof static friction slopes simplified the choice of appropriatecontact mechanics theory to evaluate the friction measurements.Applying the method on friction measurements between ironsurfaces coated with commercial lubricants showed a substantialsurface deformation not seen from the friction force alone. Thenanorheological properties of silica surfaces coated with twodifferent stearic acids have been evaluated from friction forcemeasurements. Steady sliding motion was replaced by highlyregular stick-slip motion at a critical load and velocity. Thestick-slip motion was successfully described and fitted to aphenomenological model. The contact area evaluated fromMaugis-Dugdale theory revealed the contact diameter to be veryclose to the stick-slip periodicity.</p><p>Friction measurements were carried out between individualspray-dried ceramic granules as a function of binderconcentration and relative humidity. The hygroscopic nature ofthe binder resulted in a higher adhesion force but lowerfriction coefficient with increasing humidity. This effect wasascribed to softening of the binder and a lowering of the shearstrength of the binder rich surface layer on the granules.Comparison of the friction force between two granules and agranule and a hard metal surface confirmed that resistance toflow during the initial stages of powder pressing is dominatedby granule-wall friction and adhesion.</p><p>Keywords: Atomic force microscope, AFM, SPM, van der Waalsinteraction, DLVO-theory, surface forces, colloidal probe,force curve, friction, adhesion, stick-slip, cantilever,calibration, spring constant, silicon nitride, iron,silica.</p>

Neste trabalho foram produzidas molas cerâmicas através do processo de moldagem por injeção em baixa pressão, utilizando-se como matéria-prima alumina submicrométrica, aditivada com ligantes a base de ceras. Dentro do tanque de uma injetora Pelstman, estes materiais foram homogeneizados e resultaram em uma suspensão de baixa viscosidade. Entre os objetivos deste trabalho estão a produção de molas cerâmicas helicoidais com perfil circular, a extração dos ligantes orgânicos utilizados durante a moldagem, a pré-sinterização das molas a 1000°C, o acabamento e a sinterização das molas em diferentes temperaturas e a medida de algumas de suas propriedades. A mudança na temperatura de sinterização é uma maneira simples de alterar as propriedades das molas cerâmicas, sem alterar sua composição ou suas dimensões. Foram produzidos três lotes de molas de alumina, que foram sinterizadas a 1550°C, 1600°C e 1650°C, com o objetivo de verificar os efeitos da temperatura sobre a constante de mola e a tensão de fratura. As molas de alumina sinterizada foram obtidas com densidades variando de 94,0% para 97,5% do limite teórico. As constantes de mola foram medidas desde a temperatura ambiente até 1100°C. Os dados obtidos nos ensaios de fratura sob compressão foram analisados de acordo com a estatística deWeibull e o método da máxima verossimilhança. Com o aumento da temperatura de sinterização, de 1550°C até 1650°C, foi observado que a constante de mola e a resistência característica de Weibull das molas de alumina aumentaram em 15% e 32%, respectivamente. Por outro lado, a temperatura de sinterização não teve muita influência sobre o módulo de Weibull. Isso acontece porque as bolhas internas e os defeitos superficiais introduzidos na fase de conformação das molas cerâmicas, possuem um efeito pronunciado na fratura das molas, mais importante do que a redução da porosidade com o aumento da temperatura de sinterização, e são fundamentais para determinar a resistência à compressão das molas cerâmicas. / Submitted by Marcelo Teixeira (mvteixeira@ucs.br) on 2014-06-05T16:49:28Z No. of bitstreams: 1 Dissertacao Rodrigo Antonio Barbieri.pdf: 4044147 bytes, checksum: 645abe8dc3f878007d2ac1715ded418e (MD5) / Made available in DSpace on 2014-06-05T16:49:28Z (GMT). No. of bitstreams: 1 Dissertacao Rodrigo Antonio Barbieri.pdf: 4044147 bytes, checksum: 645abe8dc3f878007d2ac1715ded418e (MD5) / In this work, ceramic coil springs was prepared by low-pressure injection molding using alumina submicrometer-sized powder. The powder are mixed with organic binders in the Pelstman machine tank for several hours resulting in a mixture with low viscosity. This work include the production of helical ceramic springs, thermal debinding, sintering in different temperatures and measure some properties. Sintering temperature was shown to be a simple way to change the spring constant and resistence to compression of ceramics without having a significant impact in the spring´s physical dimensions. Three sets of springs were sintered at different temperatures, from 1550°C to 1650°C, in order to observe the effects on spring constant and fracture stress. Sintered alumina springs were obtained with densities ranging from 94.0% to 97.5% of the theoretical limit. Springs constants were measured from room temperature up to 1100°C. Fracture stress data was analyzed according to Weibull statistics and the maximum likelihood method. Upon increase of sintering temperature from 1550°C to 1650°C, the spring constant and the Weibull characteristic strength of the alumina springs increases by 15% and 32%, respectively. On the other hand, sintering temperature has a negligible influence on Weibull modulus. This is because internal bubbles and surface defects introduced in the production stage of the ceramic springs - more than the reduction in porosity with increasing sintering temperature - are critical in determining the compression resistance of the ceramic springs.

Neste trabalho foram produzidas molas cerâmicas através do processo de moldagem por injeção em baixa pressão, utilizando-se como matéria-prima alumina submicrométrica, aditivada com ligantes a base de ceras. Dentro do tanque de uma injetora Pelstman, estes materiais foram homogeneizados e resultaram em uma suspensão de baixa viscosidade. Entre os objetivos deste trabalho estão a produção de molas cerâmicas helicoidais com perfil circular, a extração dos ligantes orgânicos utilizados durante a moldagem, a pré-sinterização das molas a 1000°C, o acabamento e a sinterização das molas em diferentes temperaturas e a medida de algumas de suas propriedades. A mudança na temperatura de sinterização é uma maneira simples de alterar as propriedades das molas cerâmicas, sem alterar sua composição ou suas dimensões. Foram produzidos três lotes de molas de alumina, que foram sinterizadas a 1550°C, 1600°C e 1650°C, com o objetivo de verificar os efeitos da temperatura sobre a constante de mola e a tensão de fratura. As molas de alumina sinterizada foram obtidas com densidades variando de 94,0% para 97,5% do limite teórico. As constantes de mola foram medidas desde a temperatura ambiente até 1100°C. Os dados obtidos nos ensaios de fratura sob compressão foram analisados de acordo com a estatística deWeibull e o método da máxima verossimilhança. Com o aumento da temperatura de sinterização, de 1550°C até 1650°C, foi observado que a constante de mola e a resistência característica de Weibull das molas de alumina aumentaram em 15% e 32%, respectivamente. Por outro lado, a temperatura de sinterização não teve muita influência sobre o módulo de Weibull. Isso acontece porque as bolhas internas e os defeitos superficiais introduzidos na fase de conformação das molas cerâmicas, possuem um efeito pronunciado na fratura das molas, mais importante do que a redução da porosidade com o aumento da temperatura de sinterização, e são fundamentais para determinar a resistência à compressão das molas cerâmicas. / In this work, ceramic coil springs was prepared by low-pressure injection molding using alumina submicrometer-sized powder. The powder are mixed with organic binders in the Pelstman machine tank for several hours resulting in a mixture with low viscosity. This work include the production of helical ceramic springs, thermal debinding, sintering in different temperatures and measure some properties. Sintering temperature was shown to be a simple way to change the spring constant and resistence to compression of ceramics without having a significant impact in the spring´s physical dimensions. Three sets of springs were sintered at different temperatures, from 1550°C to 1650°C, in order to observe the effects on spring constant and fracture stress. Sintered alumina springs were obtained with densities ranging from 94.0% to 97.5% of the theoretical limit. Springs constants were measured from room temperature up to 1100°C. Fracture stress data was analyzed according to Weibull statistics and the maximum likelihood method. Upon increase of sintering temperature from 1550°C to 1650°C, the spring constant and the Weibull characteristic strength of the alumina springs increases by 15% and 32%, respectively. On the other hand, sintering temperature has a negligible influence on Weibull modulus. This is because internal bubbles and surface defects introduced in the production stage of the ceramic springs - more than the reduction in porosity with increasing sintering temperature - are critical in determining the compression resistance of the ceramic springs.

Die Arbeit befasst sich mit der Erforschung und Anwendung der Kelvinsonden-Rasterkraftmikroskopie. Die Technik wird bezüglich der Quantität der gemessenen Werte und der erzielbaren lateralen Auflösung untersucht und auf diverse Probensysteme angewandt. Die so erhaltenen nanoskopischen Werte werden mit markoskopischen Messergebnissen verglichen. Sowohl die elektrostatische Kraft zwischen der Messspitze und der Probenoberfläche als auch deren Gradienten können zur Minimierung der elektrostatischen Wechselwirkung herangezogen werden. Die Detektion des Kraftgradienten zum Aufbau eines Regelkreises erweist sich gegenüber der Kraftdetektion überlegen. Die experimentell ermittelten Befunde werden durch eine Rechnersimulation bestätigt. Diese zeigt die Möglichkeit von quantitativen Ergebnissen für laterale Objektgrößen im Bereich von einigen Nanometern. Im Experiment kann dies gezeigt werden. Es folgt die Anwendung der Kelvinsonden-Rasterkraftmikroskopie: Nanoskopisch ermittelte Werte der Austrittsarbeitsänderung von Metalleinkristall-Oberflächen durch die Adsorption von C_60 entsprechen Literaturwerten, die mit makroskopisch messenden Methoden ermittelt wurden. Sich zeitlich ändernde Oberflächenpotentiale von einer organischen Solarzelle und von lateral unterschiedlich dotiertem Silizium lassen sich quantitativ messen. Der sich bei der Adsorption von Oktadezyl-Phosphonsäure auf Glimmer und Graphit bildende elektrostatische Dipol wird untersucht und abgebildet. Das Wachstumsverhalten und die Austrittsarbeit der organischen Moleküle PTCDA und Alq_3 auf den teilweise mit KBr bedeckten Metallsubstraten Au und Ag wird untersucht. Schlussendlich wird gezeigt, dass mit der Kelvinsonden-Rasterkraftmikroskopie sogar der molekülinterne Dipol der vier Butyl-Gruppen von Tetra-3,5-di-ter-butyl-phenyl-Porphyrinen aufgelöst werden kann.