Deposition and growth of various nanomaterials at nanostructured interfaces

Abstract

The goal of this work is the deposition and growth of various nanoobjects on patterned surfaces. For this purpose, patterned surfaces function as a chemical template to direct the location and shape of the added nanoobjects. In particular, colloidal nanoparticles, viral particles and inorganic salts are used to assemble small structures along large areas of chemical surface patterns. The substrates for these assays are based on glass or silicon, which have been decorated with gold or platinum nanoparticles. These nanostructured substrates were obtained by block copolymer micelle nanolithography. The technology has been substantially improved for application to large-scale surface areas and optimum pattern quality. Here, the influence of trapped solvent vapor above the dipping solution on the thickness of the adsorbed polymer film was investigated. A higher amount of trapped vapor results in an increase of the lateral distance of the nanoparticles on the surface and a more reproducible pattern formation, which was shown by SEM analysis. Nanopatterned surfaces were then used as a chemical mosaic platform for the deposition and growth of different nanoobjects. CdSe-Au dumbbells, CoPt_3-Au heterodimers and Co-Au matchsticks were attached to gold nanoparticles which were deposited by block copolymer micelle nanolithography via a dithiol linker. The resulting patterns show a random orientation of the nanocrystals. The magnetic Co-Au matchsticks were additionally aligned in a magnetic field, resulting in an ordered surface. Furthermore, CdSe-Au dumbbells were immobilized by DNA assembly. Here, hybridization allowed for a controlled and reversible attachment of the nanocrystals on the surface. Direct assembly of spherical CdSe nanocrystals on a non-patterned surface was realized by block copolymer micelle nanolithography. Hydrophilic ligands enable the interaction between the nanocrystals as formed in organic solvents and the polar core of block copolymer micelles. Guided by the block copolymer micellar core the CdSe particles were hexagonally arranged on the substrate, with 3 or 4 particles being located in one micelle. The number of CdSe particles per micelle was investigated by electron and fluorescence microscopy and was found to be independent from the size of the polymer. In a solution-liquid-solid approach, CdSe rods and wires as well as Co rods were grown on the nanopatterned substrates. For the growth of the CdSe rods and wires, Au@Bi core shell particles on the surface were used as a catalyst. Interestingly, the Au@Bi core shell particles remained on the substrate while the tips of the wires were covered by the growth of bismuth. Layers of biotin modified cowpea mosaic viruses are formed on a biotin-doped lipid bilayer on a hydrophilic silicon oxide surface, connected by streptavidin. In quartz crystal microbalance studies, different biotin modifications were compared. The resulting films showed differences in their roughness and density. Thiol-modified streptavidin enabled the attachment of the virus nanoparticles to gold, where the resulting layer has the same density as on the lipid bilayer. In summary, nanostructured substrates are a versatile platform for the assembly of organic and inorganic nanoparticles as well as growth seeds for inorganic material. Several different methods to control the assembly of particles on a solid substrate were successfully investigated, demonstrating their potential for further application in nanotechnology.