No description available.

The objective of this study is to develop a robust portable nano-calorimeter sensor for detection of energetic materials, primarily explosives, combustible materials and propellants. A micro-cantilever sensor array is actuated thermally using bi-morph structure consisting of gold (Au: 400 nm) and silicon nitride (Si3N4: 600 nm) thin film layers of sub-micron thickness. An array of micro-heaters is integrated with the microcantilevers at their base. On electrically activating the micro-heaters at different actuation currents the microcantilevers undergo thermo-mechanical deformation, due to differential coefficient of thermal expansion. This deformation is tracked by monitoring the reflected ray from a laser illuminating the individual microcantilevers (i.e., using the optical lever principle). In the presence of explosive vapors, the change in bending response of microcantilever is affected by the induced thermal stresses arising from temperature changes due to adsorption and combustion reactions (catalyzed by the gold surface). A parametric study was performed for investigating the optimum values by varying the thickness and length in parallel with the heater power since the sensor sensitivity is enhanced by the optimum geometry as well as operating conditions for the sensor (e.g., temperature distribution within the microcantilever, power supply, concentration of the analyte, etc.). Also, for the geometry present in this study the nano-coatings of high thermal conductivity materials (e.g., Carbon Nanotubes: CNTs) over the microcantilever surface enables maximizing the thermally induced stress, which results in the enhancement of sensor sensitivity. For this purpose, CNTs are synthesized by post-growth method over the metal (e.g., Palladium Chloride: PdCl2) catalyst arrays pre-deposited by Dip-Pen Nanolithography (DPN) technique. The threshold current for differential actuation of the microcantilevers is correlated with the catalytic activity of a particular explosive (combustible vapor) over the metal (Au) catalysts and the corresponding vapor pressure. Numerical modeling is also explored to study the variation of temperature, species concentration and deflection of individual microcantilevers as a function of actuation current. Joule-heating in the resistive heating elements was coupled with the gaseous combustion at the heated surface to obtain the temperature profile and therefore the deflection of a microcantilever by calculating the thermally induced stress and strain relationship. The sensitivity of the threshold current of the sensor that is used for the specific detection and identification of individual explosives samples - is predicted to depend on the chemical kinetics and the vapor pressure. The simulation results showed similar trends with the experimental results for monitoring the bending response of the microcantilever sensors to explosive vapors (e.g., Acetone and 2-Propanol) as a function of the actuation current.

This dissertation aims to advance the current state of use of silicon atomic force microscope (AFM) cantilevers with integrated heaters. To this end, the research consists of two primary thrusts - demonstrating new applications for the cantilevers, and advancing the current state of understanding of their thermal and mechanical behavior to enable further applications. Among new applications, two are described. In the first application, the cantilevers are used for nanoscale material deposition, using heat to modulate the delivery of material from the nanoscale tip. In the second application, the cantilever performs thermal analysis with nanoscale spatial resolution, enabling thermal characterization of near surface and composite interphase regions that cannot be measured with bulk analysis techniques. The second thrust of the research seeks to address fundamental questions concerning the precision use of heated cantilevers. Efforts to this end include characterizing the mechanical, electrical, and thermal behavior of the cantilevers, and optimizing calibration methodology. A technique is developed for calibrating the cantilever spring constant while operating at elevated temperature. Finally, an analytical model is developed for the heat flow in the cantilever tip and relevant dimensionless numbers that govern the relative importance of the various components of the thermal environment are identified. The dimensionless numbers permit exploration of the sensitivity of the tip-substrate interface temperature to the environmental conditions.

We developed new methods for controlling and studying microtubules (MTs) outside the complex workings of the living cell. Several surface treatments for preventing MT fouling on surfaces were analyzed and, for the first time, a self-assembled monolayer (SAM) was developed which prevented MT adsorption in the absence of passivating proteins. The morphology and thickness of the SAM was measured to determine the mechanism of formation and origin of the MT-resistant behavior. The SAM was integrated into electron beam lithography for patterning and manipulating MTs using electrophoresis. Reversible MT adsorption and patterning and alignment of single MTs were achieved. We characterized the mechanism for the MT migration under electric field with a focus on the electrodynamics of the flow cell and the forces acting on the MT, along with the time dependence of the process.

The considerable interest in nanomaterials and nanotechnology over the last decade is attributed to Industry's desire for lower cost, more sophisticated devices and the opportunity that nanotechnology presents for scientists to explore the fundamental properties of nature at near atomic levels. In pursuit of these goals, researchers around the world have worked to both perfect existing technologies and also develop new nano-fabrication methods; however, no technique exists that is capable of producing complex, 2D and 3D nano-sized features of arbitrary shape, with smooth walls, and at low cost. This in part is due to two important limitations of current nanofabrication methods. First, 3D geometry is difficult if not impossible to fabricate, often requiring multiple lithography steps that are both expensive and do not scale well to industrial level fabrication requirements. Second, as feature sizes shrink into the nano-domain, it becomes increasingly difficult to accurately maintain those features over large depths and heights. The ability to produce these structures affordably and with high precision is critically important to a number of existing and emerging technologies such as metamaterials, nano-fluidics, nano-imprint lithography, and more. Summary To overcome these limitations, this study developed a novel and efficient method to etch complex 2D and 3D geometry in silicon with controllable sub-micron to nano-sized features with aspect ratios in excess of 500:1. This study utilized Metal-assisted Chemical Etching (MaCE) of silicon in conjunction with shape-controlled catalysts to fabricate structures such as 3D cycloids, spirals, sloping channels, and out-of-plane rotational structures. This study focused on taking MaCE from a method to fabricate small pores and silicon nanowires using metal catalyst nanoparticles and discontinuous thin films, to a powerful etching technology that utilizes shaped catalysts to fabricate complex, 3D geometry using a single lithography/etch cycle. The effect of catalyst geometry, etchant composition, and external pinning structures was examined to establish how etching path can be controlled through catalyst shape. The ability to control the rotation angle for out-of-plane rotational structures was established to show a linear dependence on catalyst arm length and an inverse relationship with arm width. A plastic deformation model of these structures established a minimum pressure gradient across the catalyst of 0.4 - 0.6 MPa. To establish the cause of catalyst motion in MaCE, the pressure gradient data was combined with force-displacement curves and results from specialized EBL patterns to show that DVLO encompassed forces are the most likely cause of catalyst motion. Lastly, MaCE fabricated templates were combined with electroless deposition of Pd to demonstrate the bottom-up filling of MaCE with sub-20 nm feature resolution. These structures were also used to establish the relationship between rotation angle of spiraling star-shaped catalysts and their center core diameter. Summary In summary, a new method to fabricate 3D nanostructures by top-down etching and bottom-up filling was established along with control over etching path, rotation angle, and etch depth. Out-of-plane rotational catalysts were designed and a new model for catalyst motion proposed. This research is expected to further the advancement of MaCE as platform for 3D nanofabrication with potential applications in thru-silicon-vias, photonics, nano-imprint lithography, and more.

No description available.

Printing of 3-dimensional nanostructures with high-resolution by two-photon polymerization has gained significant attention recently. Isopropyl thioxanthone (ITX) has been studied and used as a photoinitiator because of its unique property in initiating and depleting polymerization, but to further improve the resolution of 3D structures, new photoinitiating materials are necessary to decrease the power requirements especially in industrial world. In this dissertation, different new types of thioxanthone-based photoinitiators were synthesized and our new initiators possessed a clear enhancement in terms of excitation over ITX. To clearly reveal the writing mechanism behind it, the behavior of the initiators was evaluated by several methods such as low temperature phosphorescence spectroscopy and density functional theory (DFT) calculations. The first type of new molecules with alkyne bridge will be discussed in chapter 2 and the further developed initiators with electron donating and withdrawing groups will be discussed in chapter 3. By modifying the structure of ITX, we have revealed and proposed an important pathway to guide future development of photoinitiators in direct laser writing.

Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / Dissertation presented for the degree of Doctor of Philosophy in Engineering at the University of Stellenbosch / ENGLISH ABSTRACT: Planar weak link structures, such as micro-bridges, variable thickness bridges and nanobridges, have always attracted a lot of attention. Their potential to behave as real Josephson elements make them useful devices, with numerous applications. Powerful techniques, such as focused ion-beam and electron-beam lithography, were successfully used and are well understood in planar weak link structure fabrication. In this dissertation the results of an experimental study on planar weak link structures are presented. For the first time these structures have been successfully fabricated using AFM nanolithography on hard high-temperature superconducting YBCO tracks, where diamond coated silicon tips were used as a ploughing tool. Superconducting YBCO thin films were deposited on different substrates, using inverted cylindrical magnetron sputtering. The films were used to fabricate micro-bridges, variable thickness bridges and nano-bridges, by using conventional photolithography, argon ion-beam milling and AFM nanolithography. The measured I-V characteristics of the fabricated micro-bridges (width down to 1.9 µm), variable thickness bridges (thickness down to 15 nm) and nano-bridge (width down to 490 nm) showed well defined DC and AC Josephson effect characteristics. For better understanding of the behaviour of these types of weak links, critical current versus temperature measurements, and magnetic field modulation of the critical current measurements, were also performed, with the results and discussions given inside the chapters. The major challenges that were experienced in the laboratory during the fabrication processes and the operation of the fabricated devices are also discussed, with the solutions given where appropriate. / AFRIKAANSE OPSOMMING: Swak-skakel vlakstrukture, soos mikrobr.ue, br.ue met veranderlike dikte en nanobr.ue, het nog altyd baie aandag getrek. Hul het die potensiaal om soos werklike Josephson-elemente te kan funksioneer en is, as gevolg hiervan, nuttige toestelle met veelvuldige toepassings. Kragtige tegnieke, soos gefokuste ioonstraal- en elektronstraal litografie, is suksesvol gebruik en word goed verstaan in die vervaardiging van swak-skakel vlakstrukture. In hierdie proefskrif word die resultate van ¡¦n eksperimentele studie van swak-skakel vlakstrukture voorgel.e. Vir die eerste keer is hierdie strukture suksesvol vervaardig, deur gebruik te maak AFMnanolitografie op harde, ho¡Le-temperatuur supergeleier YBCO (Yttrium Barium Koperoksied) spore, waar diamantbedekte silikonpunte gebruik is as ploeginstrument. ¡¦n Dun lagie van supergeleidende YBCO is op verskillende substrate gedeponeer, deur gebruik te maak van omgekeerde silindriese magnetron verstuiwing. Die dun lagies is gebruik in die vervaardiging van mikrobr.ue, br.ue met veranderlike dikte en nanobr.ue, deur die gebruik van gewone fotolitografie, argon-ioonstraal frees en AFM nanolitografie. Die gemete I-V eienskappe van die vervaardigde mikrobr.ue (met breedte so laag as 1.9 µm), veranderlike-dikte br.ue (dikte tot 15 nm) en nanobr.ue (breedte so min as 490 nm) toon goed gedefinieerde GS en WS eienskappe van die Josephson-effek. Ten einde die gedrag van hierdie tipes swak-skakels beter te kan verstaan, is metings gedoen van kritieke stroom teenoor temperatuur, asook magnetiese veld modulasie van die kritieke stroom. Hierdie resultate en besprekings daarvan word binne die toepaslike hoofstukke aangebied. Die grootste uitdagings wat in die laboratorium, sowel as met die toetsing van die vervaardigde toestelle ondervind is, word ook bespreek. Waar moontlik, word toepaslike oplossings voorgestel.

A oxidação anódica local utilizando o Microscópio de Força Atômica (AFM - Atomic Force Microscopy) foi investigada aplicando-se uma tensão negativa entre sonda de nitreto de silício e superfícies de Si. Todas as amostras foram limpas em uma solução de 1 NH4OH (30%): 1H2O2 (38%): 4H2O(DI) a 80ºC conhecida na literatura como SC1 (Standard Cleaning 1) ou, alternativamente, uma imersão em solução diluída de ácido hidrofluorídrico seguido de SC1 ou fervura em álcool isopropílico. As nano-oxidações consistiram de padrões quadrados localizados de óxido com área de 0,25 µm² e foram obtidos através do crescimento de linhas paralelas com espaço e comprimento interlinear constante (<2 nm) e várias varreduras dos quadrados em uma mesma área. Das análises de AFM, foram obtidos perfis transversais e 3D, os quais foram empregados na obtenção da espessura do óxido como função da tensão aplicada, número de varreduras e intervalo de tempo após a limpeza SC1. Foi observado que a espessura aumenta com a tensão negativa aplicada e com o número de varreduras. Também foram realizadas simulações para levantar as distribuições de tensão e de campo elétrico no sistema sonda-ar-silício ou sonda-ar-óxido-silício(substrato). Observou-se uma oxidação local assistida por um alto campo elétrico capaz de induzir difusão iônica local finita na extremidade da sonda. Foi simulado também o efeito das diferentes terminações de sonda do AFM, circular ou pontiaguda, no campo elétrico e na queda de tensão. Foram também realizadas oxidações com sondas recobertas com ouro em superfícies de Si precedidas de imersão simples em solução de ácido hidrofluorídrico seguido ou não do procedimento de limpeza SC1. Por fim, análises de absorção por infravermelho (FTIR) foram realizadas em superfícies de Si oxidadas por AFM para analisar a estrutura dos óxidos anódicos obtidos. A oxidação anódica utilizando sondas de nitreto de silício ocorre apenas após pré-limpeza terminada com SC1, sendo catalisada pelos altos campos elétricos (_ 106 V/cm), tendo como elementos reagentes, as espécies H2O adsorvidas e o óxido nativo hidrolisado na superfície após a etapa de limpeza SC1. / Local anodic oxidation of silicon using Atomic Force Microscopy (AFM) was investigated by applying a negative voltage between silicon nitride tip and Si surfaces. All samples were cleaned with an ammonium-based solution known in literature as standard cleaning 1 (SC1) or a dip in a diluted hydrofluoric acid solution followed by SC1 or, also, boiling in isopropyl alcohol. Localized squares patterns of oxide, 0.25 µm² in area, were formed by growing parallel lines with constant interlinear spacing and length and several scans in the same area. From AFM analysis with non-biased tip, it was obtained 3D and section profiles, which were used to obtain the oxide thickness as a function of the applied voltage, number of scans and interval of time after SC1 cleaning. It was noteworthy that thickness increases with the applied negative voltage and with the number of scans. Simulations were performed in order to model voltage and electric field distributions of the system tip-air-silicon or tip-air-oxide-silicon(substrate) indicating a local oxidation assisted by high electrical field and local ionic diffusion of species. It was simulated the effect of tip termination, circular or sharpen, on the electric field and voltage distributions. In addition, oxidations were performed using Au coated tips onto Si surfaces previously dipped in diluted hydrofluoric acid solution followed or not by SC1 cleaning process. Finally, infrared absorption analysis (FTIR) were performed in order to analise the structure of the obtained anodic oxides. The anodic oxidation using silicon nitride tips has occurred only after SC1 precleaning step, being catalized by high electric field (_ 106 V/cm), having as reagents, the adsorbed water species and hydrolized native oxide on the surface after the SC1 cleaning step.

The present thesis entitled “Construction of versatile biomolecule nano-platforms via Dip-pen Nanolithography and their application in bio-sensing and cell differentiation” aims at contributing to the field of Nanobiotechnology, best defined as miniaturized biotechnology where nanofabrication technology is used for biological purposes. To this end, this research work employs the relatively novel nanofabrication technique called Dip-pen Nanolithography (DPN) for direct patterning of biologically relevant molecules at the micro- and nanoscale, both for biosensor applications and cell differentiation studies. - The first chapter deals with the challenges encountered when working with Dip-pen Nanolithography and so called multi-pens. In order to facilitate the levelling of the tips with respect to the substrate and also to obtain a constant feedback of the force exerted from the tips to the substrate, a device was developed and fabricated together with a collaboration. The resulting piezoresistive device could be implemented successfully and was used to pattern two different molecules on gold substrates. An improved sensitivity at detecting the touching point could be shown when compared to conventional tips. - The second chapter deals with the miniaturization of an already in-house developed biosensor platform. Therefore, several different approaches were evaluated for the DPN patterning of oligonucleotides on gold or chemically modified glass in order to ensure a covalent attachment. The most successful strategy was the click chemistry route, where an azide bearing oligonucleotide was coupled to an alkyne bearing glass substrate, using a copper catalyst (1,3-dipolar cycloaddition) yielding an triazole. This way, a sensor platform could be established and the sensitivity could be assessed. - The third chapter deals with the development and fabrication of DPN patterned substrates for cell differentiation experiments. A biotin-thiol was chosen for patterning because it allows derivatization with streptavidin and any type of biotinylated molecule. The patterning was accomplished, using a lipid as a carrier molecule. This way, the feature size of the pattern was around 5 µm and the overall pattern area was bigger than 1 mm². The substrates were applied successfully in cell differentiation experiments, having a biotinylated BMP-2 immobilized on the substrates. / La presente tesis titulada "Construcción de nanoplataformas biomoleculares versátiles vía Nanolitografía Dip-pen y su aplicación en bio-sensing y diferenciación celular" pretende contribuir al campo de la nanobiotecnología, definida como la biotecnología en miniatura donde se utiliza la tecnología de nanofabricación con fines biológicos. Con este objectivo, este trabajo de investigación emplea la relativamente novedosa técnica de nanofabricación llamada Dip-Pen Nanolitografía (DPN) para obtener un patrón de moléculas biológicamente relevantes a micro y nanoescala, tanto para aplicaciones de biosensores como para los estudios de diferenciación celular. - El primer capítulo trata de los desafíos encontrados al trabajar con Dip-Pen Nanolitografía y los llamados multi-pens. Con el fin de facilitar la nivelación de la punta con respecto al sustrato y obtener un control constante de la fuerza ejercida desde las puntas al sustrato, se desarrolló y fabricó un dispositivo. El dispositivo piezo-resistivo resultante se pudo aplicar con éxito y se utilizó para la fabricación de patrones de dos moléculas diferentes en sustratos de oro. Se obtuvo una mejora de la sensiblidad en la detección del punto de contacto en comparación con puntas convencionales - El segundo capítulo trata de la miniaturización de una plataforma biosensora que ya se había desarollado previamente en el laboratorio. Se evaluaron varios métodos diferentes para la fabricación de un patrón de oligonucleótidos mediante DPN sobre oro o sobre vidrio modificado químicamente con el fin de asegurar una unión covalente. La estrategia más exitosa resultó ser la ruta de química click, donde un oligonucleótido con un grupo azida se acopla a un sustrato de vidrio que presenta un grupo alquino, utilizando un catalizador de cobre (cicloadición 1,3-dipolar) y produciendo un triazol. De esta manera, se pudo establecer una plataforma sensora y se pudo evaluar su sensibilidad - El tercer capítulo trata del desarrollo y la fabricación sustratos con patrón mediante DPN para experimentos de diferenciación celular. Una molécula de biotina-tiol fue elegida como patrón, ya que permite la derivatización con estreptavidina y, en un segundo paso, cualquier tipo de molécula de biotina. El patrón se llevó a cabo usando un lípido como molécula para facilitar el transporte de la tinta. De esta manera, el tamaño de la característica del patrón fue de alrededor de 5 micras y el área de patrón general más grande que 1 mm ². Los sustratos se aplicaron con éxito en experimentos de diferenciación celular, usando la proteína BMP-2 biotinilada inmovilizada sobre los sustratos.