Surface Patterning with Colloidal Monolayers

Abstract

This thesis focuses on the controlled assembly of monodisperse polymer colloids into ordered two-dimensional arrangements. These assemblies, commonly referred to as colloidal monolayers, are subsequently used as masks for the generation of arrays of complex metal nanostructures on solid substrates.The motivation of the research presented here is twofold. First, monolayer crystallization methods were developed to simplify the assembly of colloids and to produce more complex arrangements of colloids in a precise way. Second, various approaches to colloidal lithography are designed with the aim to include novel features or functions to arrays of metal nanostructures.The air/water interface was exploited for the crystallization of colloidal monolayer architectures as it combines a two-dimensional confinement with a high lateral mobility of the colloids that is beneficial for the creation of high long range order. A direct assembly of colloids is presented that provides a cheap, fast and conceptually simple methodology for the preparation of ordered colloidal monolayers. The produced two-dimensional crystals can be transformed into nonclose-packed architectures by a plasma-induced size reduction step, thus providing valuable masks for more sophisticated lithographic processes. Finally, the controlled co-assembly of binary colloidal crystals with defined stoichiometries on a Langmuir trough is introduced and characterized with respect to accessible configurations and size ratios.Several approaches to lithography are presented that aim at introducing different features to colloidal lithography. First, using metal-complex containing latex particles, the synthesis of which is described as well, symmetric arrays of metal nanoparticles can be created by controlled combustion of the organic material of the colloids. The process does not feature an inherent limit in nanoparticle size and is able to produce complex materials as will be demonstrated for FePt alloy particles. Precise control over both size and spacing of the particle array is presented.Second, two lithographic processes are introduced to create sophisticated nanoparticle dimer units consisting of two crescent shaped nanostructures in close proximity; essentially by using a single colloid as mask to generate two structures simultaneously. Strong coupling processes of the parental plasmon resonances of the two objects are observed that are accompanied by high near-field enhancements. A plasmon hybridization model is elaborated to explain all polarization dependent shifts of the resonance positions. Last, a technique to produce laterally patterned, ultra-flat substrates without surface topographies by embedding gold nanoparticles in a silicon dioxide matrix is applied to construct robust and re-usable sensing architectures and to introduce an approach for the nanoscale patterning of solid supported lipid bilayer membranes.

Electrolyte solutions at heterogeneously charged substrates

“…The linear nature of the Euler-Lagrange equations (5) and (6) tells that the quadratic (Gaussian) approximation of the underlying density functional in Eqs. (1) and (2) corresponds to a linear response approach.…”

“…Detailed knowledge of the structure of electrolyte solutions close to solid substrates is of great importance to numerous research areas and fields of application, ranging from electrochemistry [1,2] and wetting phenomena [3,4] via coating [5] and surface patterning [6,7] to colloid science [8,9] and microfluidics [10,11]. The vast majority of models describing fluids in contact with substrates consider the latter as uniform with respect to the wall-fluid interaction.…”

Fabrication of Periodic Nanostructure Assemblies by Interfacial Energy Driven Colloidal Lithography

“…As evident from Figure b, the colloidal spheres assemble in a hexagonal‐close‐packed (hcp) pattern, which is the most commonly observed pattern in self‐assembled monolayers of colloidal spherical particles . Wetting properties of the substrate also plays an important role in the self‐assembly process on a solid substrate . A good hydrophilic surface is necessary so that the colloidal suspension can homogenously spread on the substrate .…”

“…Wetting properties of the substrate also plays an important role in the self‐assembly process on a solid substrate . A good hydrophilic surface is necessary so that the colloidal suspension can homogenously spread on the substrate . In our experiment, the Si substrates were first subjected to RCA 1 standard cleaning, which improves the hydrophilicity of the silicon oxide surface.…”

Composite Nanogels Based on Zeolite-Poly(ethylene glycol) Diacrylate for Controlled Drug Delivery

“…Moreover, in order to gain insight into the polymerization mechanism, and to confirm that the process corresponds to a mini-emulsion (also known in the literature as a nanoemulsion), mean size measurements were carried out for the PEGDA 700 specimen before the start of the reaction, after 24 h of polymerization, and at the end of the reaction (42 h) (see Figure 4). Given the sizes were roughly similar, the measurement indicated that the reaction is characteristic of an inverse mini-emulsion system, in which each water droplet acts as a nanoreactor where the polymerization takes place in bulk [33]. Important parameters of mini-emulsion, such as the hydrophilic-lipophilic balance of the surfactant (HLB), the surfactant/aqueous and the solvent/aqueous medium ratio, the monomer concentration, the molecular weight of the PEGDA oligomer, and the blending ratio of the two different macromers (PEGDA 700 and PEGDA 2000 ) were previously studied for their effects upon the particle size, size distribution, and morphology of these advanced NGs [34].…”