Chemical and topographic surface patterning for the preparation of functional surfaces and particle arrays has been intensively investigated and widely applied in sensor technology, engineering of adhesion and wetting, catalysis, as well as nanobioanalytics. However, the parallel high-throughput functionalization of surfaces with microparticle arrays under ambient conditions by state-of-the-art surface patterning methods has remained challenging. The aim of this thesis is the parallel generation of microparticle arrays on surfaces to tailor the surface properties. Two strategies are studied for this purpose. The first strategy, inspired by the functional principles of adhesive secretion of insect feet’s hairy contact elements yielding tiny droplets as footprints onto contact substrates, involves the formation of microdot arrays by capillary submicron stamping using spongy continuous nanoporous block copolymer stamps with regular hexagonal arrays of contact elements. After infiltration of AgNO3 solution from the stamps’ backside, arrays of discrete two-dimensional AgNO3 microdots with an average diameter ~ 730 nm on silicon wafers extending several square millimetres were generated, while under higher pressure holey AgNO3 films were obtained. Subsequently, the patterns were transferred into Si wafers by surface-limited metal-assisted chemical etching (MACE). Topographically patterned silicon (tpSi) characterized by hexagonal arrays of wells resulted from MACE of Si wafers patterned with AgNO3 microdots, while MACE of Si wafers patterned with holey AgNO3 films yielded ordered Si pillar arrays. H2PtCl6, PdCl2 and HAuCl4 aqueous solutions were also employed as inks for preparation of tpSi by insect-inspired capillary sub-microstamping and MACE. Exploratory experiments suggest that inkjet printing of polymeric inks onto tpSi could yield persistent and scratch-resistant polymer blot patterns without coffee ring-like features for potential utilization as permanent identity labels or quick response codes. Hexagonal arrays of Au microparticles were rationally positioned by solid-state dewetting of thin gold films on tpSi at an elevated temperature under Ar atmosphere. The rationally positioned Au microparticles subsequently acted as seeds for the growth of dense, homogeneous layers of overlapping three-dimensional (3D) gold nanodendrites by templated galvanic displacement reactions. The obtained 3D gold nanodendrite layers on tpSi featuring high specific surfaces as well as abundance of sharp edges and vertices showed promising performances in SERS-based sensing and the heterocatalytic reduction of 4-nitrophenol to 4-aminophenol. The second example involves the functionalization of polymer surfaces with arrays of inorganic lubricant microparticles for friction management and the tailoring of tribological properties based on an imprint lithographic approach. For example, the tailoring of the interfacial shear behavior of a movable polymer part might be customized in this way by functionalizing the polymeric parts’ surfaces with MoS2 microparticle arrays. Monodomain monolayers of MoS2 microparticles were prepared on SiO2-coated Si wafers via thermal sulfurization arrays of ammonium tetrathiomolybdate microparticles obtained by imprint lithography. After transfer of the MoS2 microparticle arrays to poly(methyl methacrylate) (PMMA) monoliths (PMMA_MoS2) under conservation of the array order in such a way that the MoS2 microparticles were partially embedded into the PMMA and partially exposed, the obtained PMMA_MoS2 exhibited modified mechanical properties characterized by low friction coefficients half as that of non-modified PMMA monoliths. Therefore, the functionalization of surfaces with microparticle arrays is a viable and promising strategy to generate unprecedented surface functionalities.

In the last 15 years, an immense amount of research has gone into developing high efficiency Gallium Nitride based light emitting diodes (LED). These devices have become increasingly popular in LED displays and solid state lighting. Due to the large difference in refractive index between GaN and Air, a significant amount of light reflects at the boundary and does not escape the device. This drawback decreases external quantum efficiency (EQE) by minimizing light extraction. Scientists and engineers continue to develop creative solutions to enhance light extraction. Some solutions include surface roughening, patterned sapphire substrates, and reflective layers. This study proposes to increase external quantum efficiency and optimize light extraction efficiency of several LED structures using finite difference time domain analysis (FDTD). The structures under investigation include GaN based LEDs with nanoscale top gratings, patterned sapphire substrates in combination with SiO2 nanorod arrays, and reflective surfaces below and above the sapphire substrate. First, we optimize GaN based nanoscale top gratings and increase light extraction by 17.8%. Next, we simulate ITO based top gratings and enhance light extraction by 40%. Third, we optimize patterned sapphire substrate period and width and the vertical position of a SiO2 nanorod array. We achieve as high as 51.8% improvement in light extraction. Finally, we increase light extraction by 160% with the use of a silver reflection layer.

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Les travaux élaborés dans cette thèse ont pour objectif de caractériser les propriétés magnétiques et structurales de nanostructures magnétiques obtenues par une nouvelle méthode de synthèse mixte physique/chimique, dite croissance hybride. La première partie du travail réalisé consiste en l’élaboration de films minces métalliques sur substrats par pulvérisation cathodique. Sur ces films minces, la synthèse chimique par voie organométallique aboutit à des réseaux de nanofils de Co monocristallins hcp, ultra-denses, ou des films nanostructurés de Fe. Les observations MEB/MET et les mesures de diffraction de rayons X réalisées sur les substrats montrent le fort impact induit par la cristallinité de la couche mince sur la morphologie et la direction de croissance des nanostructures magnétiques.Les mesures magnétiques réalisées sur des réseaux de nanofils de Co montrent une forte anisotropie magnétique perpendiculaire au substrat. Cela est obtenu grâce à l’anisotropie magnétocristalline du Co hcp (avec l’axe c parallèle à l’axe du fil) qui s’ajoute à l’anisotropie de forme. L’aimantation thermiquement stable, semble suivre un régime de retournement cohérent, régime non observé dans les structures polycristallines. L’organisation de ces nanostructures, leur grande densité et la stabilité de leur aimantation font de ce réseau un bon candidat aux applications de médias d’enregistrement magnétique à forte densité. / The elaboration of this thesis aims to characterize the magnetic and structural properties of magnetic nanostructures obtained by a new mixed physical / chemical synthesis method, called hybrid growth. The first part of the work consists in the development of thin metal films on substrates by cathode sputtering. Furthermore, the chemical synthesis conducted by organometallic chemistry on those thin films, results in an array of ultra-dense Co monocristallins hcp nanowires, or nanostructured Fe films. Additionally, The SEM/TEM observations and the X-ray diffraction measurements conducted on the substrates and induced by the crystlalline structure of the thin film, show the high impact on the magnetic nanostructures morphology and growth direction.Moreover, the magnetic measurements executed on the Co nanowires array show a strong magnetic anisotropy perpendicular to the substrate. This observation is obtained due to the magnetocrystalline anisotropy acting along the nanowire axis (Co hcp structure with the c axis parallel to the nanowire axis) in the same direction of the nanowires shape anisotropy. The magnetization within these structures is thermally stable. It follows a coherent magnetization reversal mode that has not been observed in the polycrystalline structures up to now. Finally, the self-organization of the nanowires as well as their high density and stable magnetization nominate this system for their application in high density magnetic storage devices.

This dissertation investigates the influence of surface heterogeneities on colloid deposition. First, deposition of colloidal particles on a nanofiltration membrane during cross flow membrane filtration was studied under different operating pressures and solution chemistries. An atomic force microscope (AFM) was then used to observe the deposit morphology formed on the membrane. At the initial stages of fouling, more particles preferentially accumulate near the peaks than in the valleys of the rough nanofiltration membrane surface. This study demonstrates that it is difficult to isolate, correlate and assess the effects that physical (roughness) heterogeneity and chemical heterogeneity has on colloid deposition based on experiments involving surfaces where the physical and chemical heterogeneities are uncorrelated or randomly distributed. In the second phase of the study, the deposition of model colloidal particles onto patterned charge-heterogeneous surfaces was studied both experimentally and theoretically. Controlled charge heterogeneity was created experimentally employing self assembled monolayers of alkanethiols patterned onto gold substrates using a soft lithographic technique. Model colloidal particles and fluorescent nanoparticles were sequentially deposited onto the patterned substrate under no flow (quiescent) conditions, and the deposited structures and the micro-patterns were imaged in situ using a combination of phase contrast and fluorescence microscopy. This study indicates that particles tend to preferentially deposit at the edges of the chemically favourable stripes. The theoretical investigation involved the formulation of a mathematical model based on Random Sequential Adsorption (RSA). This study showed that a simple binary probability distribution assumed in the model is able to predict the experimental deposit morphology adequately, particularly the periodicity of the underlying patterns on the substrate. Furthermore, the effect of charge heterogeneity on the electrostatic double layer interaction between a particle and a charge heterogeneous planar surface was studied numerically employing a 3D finite element model. In this system, significant lateral forces at close separation distances were observed, and found to be appreciably higher when the particle is near the edge of a heterogeneous region of the substrate. From the above studies, it can be concluded that by altering/controlling the chemical heterogeneity of the substrate, it is possible to achieve significant control on the resulting deposit morphology.

Interfacial features of polymers are a complex, fascinating topic, and industrially very important. There is clearly a need to understand interactions between polymer layers as they can be used for controlling surface properties, colloidal stability and lubrication. The aim of my Ph.D study was to investigate fundamental phenomena of polymers at interfaces, covering adsorption, interactions between polymer layers and surfactants, surface forces and friction between adsorbed layers. A branched brush layer with high water content was formed on silica surfaces by a diblock copolymer, (METAC)m-b-(PEO45MEMA)n, via physisorption. The adsorption properties were determined using several complementary methods. Interactions between pre-adsorbed branched brush layers and the anionic surfactant SDS were investigated as well. Surface forces and friction between polymer layers in aqueous media were investigated by employing the Atomic Force Microscopy (AFM) colloidal probe technique. Friction forces between the surfaces coated by (METAC)m-b-(PEO45MEMA)n in water are characterized by a low friction coefficient. Further, the layers remain intact under high load and shear, and no destruction of the layer was noted even under the highest pressure employed, about 50 MPa. Interactions between polymer layers formed by a temperature responsive diblock copolymer, PIPOZ60-b-PAMPTMA17 (phase transition temperature of 46.1 °C), was investigated in the temperature interval 25-50 °C by using the AFM colloidal probe technique. Friction between the layers increases with increasing temperature (25-45 °C), while at 50 °C friction was found to be slightly lower than that at 45 °C. We suggest that this is due to decreased energy dissipation caused by PIPOZ chains crystallizing in water above the phase transition temperature. The structure of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayers was determined by X-ray reflectometry. Surface forces and friction between DPPC bilayer-coated silica surfaces were measured utilizing the AFM colloidal probe technique. Our study showed that DPPC bilayers are able to provide low friction forces both in the gel (below ≈ 41°C) and in the liquid crystalline state (above ≈ 41°C). However, the load bearing capacity is lower in the gel state. This is attributed to a higher rigidity and lower self-healing capacity of the DPPC bilayer in the gel state. Friction forces in single asperity contact acting between a micro-patterned silicon surface and an AFM tip was measured in air. We found that both nanoscale surface heterogeneities and the µm-sized depressions affect friction forces, and considerable reproducible variations were found along a particular scan line. Nevertheless, Amontons’ first rule described average friction forces reasonably well. Amontons’ third rule and Euler’s rule were found to be less applicable to our system. / <p>QC 20141209</p>

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