Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / As plaquetas sÃo um grupo de cÃlulas que tÃm participaÃÃo fundamental nos processos hemostÃticos. Durantes estes eventos, tais cÃlulas passam por uma drÃstica transformaÃÃo de sua estrutura, o que inclui alteraÃÃo de forma, saindo de um perfil discÃide para um completamente amorfo. ConseqÃentemente, este fenÃmeno de reestruturaÃÃo da arquitetura celular està intimamente ligado a um rearranjo do citoesqueleto plaquetÃrio, estrutura localizada abaixo da membrana celular responsÃvel pela forma, estabilidade, maleabilidade, dentre outras caracterÃsticas mecÃnicas e fisiolÃgicas da membrana plasmÃtica. Neste contexto, a investigaÃÃo das caracterÃsticas elÃsticas de plaquetas ativadas, como sÃo denominadas ao iniciar o processo acima citado, apresenta-se como uma alternativa viÃvel ao aprofundamento no conhecimento da funÃÃo plaquetÃria no organismo. Para tanto, a microscopia de forÃa atÃmica (AFM), surge como uma tÃcnica de grande utilidade a este tipo de investigaÃÃo. Capaz de tocar a superfÃcie celular com forÃas da ordem de piconewtons, o microscÃpio de forÃa atÃmica pode ser utilizado como um nanoindentador, ou seja, de posse da geometria da sonda e da constante de mola do cantilever empregado, grandezas como elasticidade e viscosidade da amostra podem ser determinadas. Neste trabalho, duas subtÃcnicas de AFM foram empregadas no estudo de plaquetas humanas sadias ativadas, tais foram: Force Plot e Force Volume. A primeira fornece um grÃfico chamado de curva de forÃa, obtida com uma Ãnica indentaÃÃo na superfÃcie celular. Jà a segunda reÃne todas estas curvas numa imagem conhecida como imagem de volume de forÃa. Tais ferramentas provÃem informaÃÃes que, trabalhadas com um modelo matemÃtico adequado, no nosso caso o modelo de Hertz, tornam possÃveis a determinaÃÃo, nÃo apenas pontual, mas em todo o corpo da cÃlula, das propriedades mecÃnicas plaquetÃrias.

Nowadays, the assembly of small (<1mm) components has become an industrial reality. Many domains like MEMS, surgery, telecommunications, car industry, etc. now have large use of micro-parts. At this scale, predominant forces are different than in macroworld. The pieces often undergo adhesion problems. The adhesion forces can be splitted in different components : van der Waals, electrostatics and capillary condensation. This work focuses on capillary condensation as it often can be the major component of the adhesion force. The first part of this work details a review of literature of different fields involved in capillary condensation. A simulation tool is then implemented and theoretically validated in the second part of the work. Finally, a test bed is presented; this bed is then used to experimentally validate the simulation results. Experiments and simulation results are shown to concord. Therefore, the simulation tool can be used to model the force due to capillary condensation.

Controlling tribological interactions, such as friction and adhesion between contacting interfaces is critical for the advancement of technologies such as microelectromechanical systems (MEMS) devices. The challenge in MEMS device lubrication lies in the inherent nature of the material’s surface at the nanoscale as well as the nature of the surfaces typically used during experimentation. Device surfaces often display nanoscale roughness with surface asperities dictating the tribological properties between interfaces, yet the vast majority of past research has focused predominately on nanotribological studies of thin films on flat silicon substrates to model the behavior of these self-assembled wear-reducing coatings. New model surfaces have been manufactured and integrated into experiments in which surfaces with controlled asperity sizes act as more realistic models of MEMS surfaces. As friction and adhesion between real surfaces in sliding contact are dominated by the interactions of nanoscaled surface asperities, this research is an extension of previous work, moving beyond smooth surfaces by manufacturing and implementing new experimental platforms possessing controlled asperity sizes. The influence of asperity size on the tribological properties of these contacts is being studied for both native oxide and organosilane derivatized surfaces. These studies more readily mimic the conditions found at true asperity-asperity contacts. This research has aimed to develop new lubricant thin films that can effectively protect MEMS device surfaces during use with the long term goal of bringing MEMS devices out of the laboratory and into wide scale commercial use. This work investigates how self-assembled monolayers (SAMs) on curved surfaces can be utilized in manners that their analogs on flat surfaces cannot. SAMs on curved asperities can be used to trap short chain alcohols, which during contact may be released to function as an additional lubricant layer on the surface. Both atomic force microscopy and Fourier transform infrared spectroscopy have been employed to evaluate how chain disorder influences the protective function of these molecular lubricant layers on asperities. It was found that functionalized surfaces resisted wear and were able to operate under continuous scanning for longer time frames than unfunctionalized surfaces and that multicomponent films improved upon the performance of their base, single component analogs.

Abstract The interaction between the multilayer of Antiferromagnetic(AFM)/ Ferromagnetic(FM) film have been one of the focal point in scientific and technology. In our preliminary result the enhancement on the low field magnetoresistance of AFM-La0.67Sr1.33MnO4 and FM-La0.67Ca0.33MnO3 mixture is obvious. It is, therefore, worthwhile to make it into a form of multilayer as the tunneling magnetoresistance (TMR) structure. This project was planed to start at a bilayer film of AFM-La0.67Sr1.33MnO4/ FM-La0.67Ca0.33MnO3 on SrTiO3(100) substrate by an off-axis RF sputtering system. Experiment at high temperature region (T¡Ö70K) exhibits normal colossal magnetoresistance (CMR) behavior. A small cusp appears in R-T curve between 50~70K which is believed due to the quantum fluctuation initiated from AFM layer acted on the AFM/FM interface. However, the MR properties at this region shows abnormal phenomenon. The MR curve strongly depends on the sample posture during measurement when the relative geometry between the applied field, the applied current and the sample surface is fixed. The reason of this abnormal phenomenon is not clear yet and worth for further study .

Discotic liquid crystal (LC) molecules have a structure that is comprised of a rigid aromatic core with side-chain molecules. Intermolecular £k-£k interactions force the tube to orient and form one-dimensional columnar structures which can act as molecular wires. In recent years, discotic LC molecules have been deposited on surfaces from solution to create the solid-state electronic elements used widely in solar cells, organic light-emitting diodes (OLED), organic photovoltaic, field-effect transistors (FET), and molecular wires. Different stacking morphologies can change the behavior of the material and thus will have potential for different applications. Hence, effective control over the stacking of the LC molecules on surfaces is important for optimizing the performance and effectiveness of LC-based electronic components and devices. This study has focused on LC molecules with acid and ester containing functional groups, and how these groups influence the stacking behavior on surfaces. Here, the self-aggregation behavior of the discotic LC ester in solution was investigated quantitatively by determining the concentration dependence of the 1H NMR chemical shifts. Our results showed that discotic LC ester has different self-aggregation behavior in CH2Cl2, THF and Benzene organic solvents. THF solvent showed the highest degree of aggregation, followed by CH2Cl2, and then benzene. We also studied the effects of (i) different solvents (THF, CH2Cl2, and Benzene), (ii) different surface functional groups (OH, CH3, NH2, SH, and diphenyl), and (iii) temperature, on the stacking phenomenon of discotic LCs on silicon surfaces. In part (i) our results showed that discotic LC ester had different morphologies on silicon surfaces due to differences in solvent polarity and evaporation rate. In part (ii), we observed that different surface functional groups did not affect the intermolecular interaction between either the ester- or acid-type LC molecules. For the acid-type LC, strong hydrogen bonding interactions with the surface caused the crystals to form rod-like fiber structures. However, the ester-type LC molecules formed ribbon-like stacks on the surfaces. For functional groups containing CH3 (more hydrophobic surfaces), we observed no LC molecules on the surface, which was likely due to the poor wettability of the solvents on OTS. In part (iii), we observed that both acid and ester discotic LCs formed large aggregates on the surfaces due to a ¡§ripening effect¡¨. With increased temperature, the molecules were able to overcome the wetting interaction with the surface and self-aggregate into three-dimensional clusters.

No description available.

This thesis describes the characterization of the particle size distribution of cellulose nanocrystals (CNC), the synthesis and characterization of fluorescent CNCs, and the development of a fluorescence microscopy method to probe the distribution of fluorescent CNCs in polymer composites. In this thesis, several methods are used to characterize the size of CNC particles. Size distribution measurements by single particle counting methods (Transmission electron microscopy, Atomic force microscopy) are compared to an ensemble method, Dynamic lighting scattering (DLS) and differences between the various methods will be discussed. The effect of sonication on the CNC size distributions measured by AFM and DLS is examined. Furthermore, a reliable and reproducible method for re-dispersing dry CNC powder will be explored in this chapter since CNC is often stored in a dry environment due to its stability. Rhodamine B isothiocyanate (RBITC) and 5-(4,6-dichlorotriazinyl) amino fluorescein (DTAF) were selected for labelling CNCs. These dyes have the advantage of being cheap and readily available and compatible with relatively simple synthetic chemistry. The photophysical properties of all dye labeled CNCs were studied in more detail than in previous studies. The focus is on understanding the most appropriate labeling efficiency to maximize the ability to detect individual CNCs while minimizing the amount of dye used to avoid modifying the CNC properties. The characterization methods include ensemble methods such as UV-Vis absorption and scattering measurements, fluorescence spectroscopy and single molecule methods such as Total internal reflection fluorescence microscopy (TIRFM), Atomic force microscopy (AFM) and correlated TIRFM/AFM measurements. All of these methods have their advantages and disadvantages. After characterization, the most suitable dye labeled CNC sample was selected for development of a fluorescence microscopy method to characterize CNC distribution in CNC/polymer composites. The dye labeled CNC has been incorporated into polyvinyl alcohol (PVA) films and studied by fluorescence microscopy. These experiments demonstrated that the level of CNC agglomeration varies significantly for different film preparation methods, indicating that fluorescence microscopy is a useful and easily accessible method for optimizing film preparation. The self-quenching of the dye in the film was also measured and discussed and is an important consideration for choice of the dye loading and CNC content in the films.

To study the effect of the substrate support on the nanoscale contact, three different regimes, i.e., graphene on rigid (ultra-crystalline diamond) and on elastic (Polydimethylsiloxane) supports and free-standing graphene, were considered. The contribution of the graphene support to the mechanical and electrical characteristics of the graphene/metal contact was studied using the conductive atomic force microscopy (AFM) technique.The results revealed that the electrical conductivity of the graphene/metal contact highly depends on the nature of the graphene support. The conductivity increased when transitioning from suspended to elastic and then to rigid substrates, which is attributed to the changes in the contact area being higher for the suspended graphene and lower for the rigid substrate. The experimental observations showed good agreement with theoretical results obtained from modeling of the studied material systems. Further, the results indicated that in addition to the substrate support, the nature of the contact, static or dynamic, results in large variations of the electrical conductivity of the graphene/metal contacts. In case of the static mode, the contact made with supported graphene was very stable for a wide range of applied normal loads. Transitioning to the dynamic mode led to instability of the graphene/metal contact as demonstrated by lowering in the electrical conductivity values. This transition was even more pronounced for free-standing graphene which is attributed to graphene sagging during rapid scanning of the tip over the graphene surface. This study creates a new knowledge on understanding of the nanoscale contacts forming with 2D materials thus enabling further advances in the applications of 2D materials in highly stable and reliable electronic devices.

Carbon nanotubes (CNTs) and graphene (G) are the two (semi-)conducting allotropes of carbon offering a very high surface to bulk ratio. When combined with electrochemistry and using the principles of molecular self-assembling, many new applications of CNTs and graphene have become feasible, e.g. in the field of molecular electronics, as energy storage materials and for drug delivery. In this work scanning probe microscopy techniques (STM, AFM and EC-AFM) are used to understand the structure of self-assembled organic and electroactive molecules, oligomers and polymers on the surface of CNTs and graphene, and to rationalize their function as supramolecular system in the macroscopic world. It was found that there is a strong tendency for self-assembling in solution of aromatic electrophores with HOMO/LUMO levels close to the semiconducting CNT frontier orbitals. The tunneling currents through the aromatic guest molecules on CNT are much higher than for the same molecule on highly oriented pyrolytic graphite (HOPG). In the 1st chapter of this thesis the different microscopic techniques used with special emphasis on the electrochemical atomic force microscopy (EC-AFM), a relatively new combination technique which plays an important role in this work, are presented. It is followed by the structural analysis of stiff, semi-flexible and flexible oligo-viologen on CNTs. Using a large set of molecules with well defined small structural differences allowed to study how the superstructure (guests@CNT) is determined by the tiny changes in the guest structure. Mostly helical super structures of guests around the CNT host were observed. The guest’s rod length, its side chain length and its flexibility translate unambiguously into the corresponding STM images. A non-linear, star shaped oligo-viologen cannot wrap CNT without overlapping star branches, as expected from model considerations. In collaboration with a Korean research group we were able to build an n-doped FET using a reduced rigid oligo-viologen@CNT. Along with the oligomer the formation of stiff poly-viologens@CNT and poy-imides@CNT are studied. As compared to the oligomers@CNT, the polymers@CNT have less conformational freedom when wrapping a CNT. Thus, exclusively double to multi stranded helical wrapping was observed. An interesting new phenomenon was discovered with stiff poly-viologen or poly-naphthaline tetracarboxylic acid diimide with purely sp2 configured atoms, i.e. an outer, large diameter helical structure of “the guest” polymer and a CNT “host” sitting inside the spiral. The spiral diameter was simulated using PM7 calculations. The CNT can be moved within the large spiral by voltage pulse application. Subsequently, the conformation of flexible poly-viologens and poly-TEMPO on host materials such as CNTs and vapor grown carbon fibers (VGCF) was studies. Again, helical wrapping is observed, but the diameter adapts here to the CNT diameter. Monomer subunit resolution was achieved in case of polyTEMPO. The practical importance in energy storage is discussed in the corresponding original paper. The next chapter of thesis focuses on AFM imaging of a new battery material, i.e. poly-ferrocene on graphene oxide (PVF@GO) and on reduced graphene oxide (PVF@rGO), as well as poly-viologen as PV@GO and PV@rGO. A highlight is definitely the visualization of the so-called ion-breathing, i.e. the reversible counter ion movement from solution into the battery material composite upon electrochemical reduction/oxidation. To the best of my knowledge, this phenomenon is for the first time visualized here by a combination of electrochemistry and AFM. STM analysis of electrically conductive rGO allows for subunit resolution of polyviologen@rGO sitting in partially 2D crystalline structure on rGO. In the last chapter, my publication on the drug delivery system doxorubicin at carbon nanotubes is described. Dox@CNT is already used as drug delivery system in animal tests, but little is known on the structure of the drug on the carrier, and a reductive release trigger has so far not been identified. Rich structural variations of the drug on the CNT (helical strands of monomers and dimers) were found. It is possible to get the drug loading efficiency from STM image analysis. Reductive release of Dox@CNT was also unknown so far. Electron injection into Dox@CNT from an electrode or from the biological reducing agent glutathione (GSH) leads to irreversible release of Dox. Experimental results are in excellent agreement with semi-empirical simulations.

Neste trabalho foram obtidos nanotubos de carbono de paredes múltiplas (MWNT). O crescimento apresentou alta densidade de nanotubos orientados perpendicularmente à superfície do substrato, com cerca de 20 m de comprimento e diâmetros entre cerca de 20 e 60 nm. Foram utilizados filmes catalisadores contendo ferro, depositados a partir de solução de nitrato de ferro (Fe(NO3)3.9H2O) em álcool etílico com concentrações que variaram entre 37 mmol/L e 1,2 mmol/L. Não foram notadas diferenças significativas entre os nanotubos crescidos com diferentes concentrações, com exceção da solução de 0,6 mmol/L onde não foi observado o crescimento de nanotubos. Os crescimentos de nanotubos de carbono foram efetuados em um reator CVD a plasma de microonda. Os resultados de espectroscopia Raman sugerem que os nanotubos de carbono obtidos neste trabalho correspondem a MWNT, apresentando alto grau de desordem estrutural. Foram realizados crescimentos diretos de nanotubos de carbono sobre as pontas comerciais de AFM, utilizando filmes de nitrato de ferro. Os nanotubos crescidos nas pontas apresentaram tendência em formarem aglomerados. Não foram obtidas pontas de AFM satisfatórias com este método. Outro método consistiu no crescimento de nanotubos de carbono em amostras planas de silício, utilizando filme catalisador de nitrato de ferro com posterior captura de nanotubos na extremidade da ponta, utilizando um microscópio AFM. Foram realizados 26 procedimentos, onde a maioria dos resultados não foi satisfatória. Apenas em dois dos procedimentos foram obtidos resultados muito bons com nanotubos de carbono retos e protuberantes emergindo das pontas. Ainda neste trabalho foi desenvolvido um método de reciclagem das pontas. O processo é de grande valia, pois a obtenção de pontas de AFM com nanotubos apresenta sucesso em apenas uma fração do número de tentativas, levando a inutilização de um número representativo de pontas. A reciclagem das pontas foi realizada por meio da corrosão dos nanotubos de carbono em plasma de hidrogênio. O equipamento utilizado para essa finalidade foi o próprio reator CVD a plasma de microonda, também utilizado para o crescimento dos nanotubos. / In this work multi walled carbon nanotubes (MWCNT) were obtained. The growth presented high density nanotubes oriented perpendicularly to the substrate, with about 20 m length and diameters between 20 and 60 nm. Catalytic films containing iron were used. These films were deposited from solution of iron nitrate (Fe(NO3)3.9H2O) in ethyl alcohol with concentrations that varied between 37 mmol / L and 1.2 mmol / L. It was not observed significant difference among the grown nanotubes obtained with different concentrations, except from the solution of 0.6 mmol / L, where the nanotubes growth was not observed. The growths of carbon nanotubes were obtained in a microwave plasma CVD reactor. The Raman spectroscopy suggests that the carbon nanotubes obtained in this work correspond to MWCNT, presenting high degree of structural disorder. Direct growths of carbon nanotubes on commercial AFM tips were performed, using films of iron nitrate. The nanotubes grown directly on the tips presented tendency in forming agglomerates. They were not obtained satisfactory AFM tips with this method. Another method consisted of carbon nanotubes growth on flat silicon substrates, using catalytic film of iron nitrate, with subsequent nanotubes capture at the extremity of the tip, using a microscope AFM. Altogether 26 procedures were performed, where most of their results were not satisfactory. In just two of these procedures were obtained very good results with straight and protuberant carbon nanotubes emerging of the tips. Still in this work a method of tip recycling was developed. The process is valuable, since the success in obtaining AFM tips with nanotubes occurs in just a fraction of the attempts, generating a representative number of lost tips. The tips recycling were performed through the corrosion of the carbon nanotubes in hydrogen plasma. The equipment used for this purpose was the microwave plasma CVD reactor, also used for carbon nanotubes growth.