Topographically Patterned Surfaces as Substrates for Functional Particle Arrays

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Title: Topographically Patterned Surfaces as Substrates for Functional Particle Arrays
Authors: Han, Weijia
Thesis advisor: Prof. Dr. Martin Steinhart
Thesis referee: Prof. Dr. Wolfgang Harneit
Abstract: 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.
Subject Keywords: Stamping; Topographically patterned Si; Inkjet-printing; SERS; particle-arrays
Issue Date: 30-Oct-2019
License name: Attribution-NonCommercial-ShareAlike 3.0 Germany
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Type of publication: Dissertation oder Habilitation [doctoralThesis]
Appears in Collections:FB05 - E-Dissertationen

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