Self-organization of colloidal particles on surfaces to form 2D or 3D nanofabrication templates has been explored actively in the past decade as an effective bottom-up method to produce a plethora of nanoarchitectures with diverse functionalities. Specifically, several elegant approaches to pattern surfaces with large-scale 2D arrays of nanosized structures through lateral self-assembly of colloidal spheres have been developed. These methods are commonly termed colloidal lithography (CL). A frequently used version of CL, nanosphere lithography (NSL) employs organized 2D colloidal crystals with a hexagonal close-packed motif as an evaporation mask, often in combination with reactive ion etching. Evaporation through the holes between close-packed nanospheres defines the resulting pattern, and in many applications material deposition conditions such as evaporation angle or specific deposition technique (e.g., sputtering, thermal deposition) are used to vary the achieved patterns. With this method facile production of vast planar arrays of diverse nanostructures has been accomplished. [1][2][3][4][5][6][7][8] In an alternative approach, referred to here as sparse colloidal lithography (SCL), charged colloidal beads are utilized in a similar manner as in NSL. [9,10] This method, developed in our group, enables facile production of large areas (several cm 2 ) of nanoscopic features like holes in thin films, disc-, ringand crescent-shaped structures with overall sizes currently down to 20 nm and which occupy 10 to 50 % of the total surface area. [11][12][13][14][15][16] The size distribution of SCL-fabricated nanostructures is largely determined by the size dispersions of the masking colloids and is typically less than 5 % for colloids with average diameters > 100 nm and up to 10 % for smaller colloids. In contrast to NSL, a sparse monolayer of colloidal particles defines the evaporation/etch mask in SCL. The convenience of this technique, employing charged polystyrene (PS) nanoparticles as etch and/or evaporation mask, has recently been demonstrated in a variety of applications such as investigation of fibroblast response to nanotopography, [17] model catalysts of Pt/alumina and Pt/ceria [18] and in the study of optical properties of macroscopic arrays of supported metallic nanostructures like discs, crescents, or rings or nanoholes in optically thin films. [11,13,14,16] In spite of the general advantage of facile bottom-up nanofabrication and a large variety of possible nanostructural motifs, SCL has so far been subject to limitations in producing nanostructures composed of materials with unfavourable etching selectivity, that is, where the substrate or polystyrene etch rates compete with the etch rate of the actual materials of the nanostructure. Examples of such systems are Pt on Au or Au-silica hybrid structures on glass. Another disadvantage of the method is the necessity of the reactive oxygen treatment for the PS mask removal so that nanostructures composed of the materials prone to oxidation (like Ag or Ru) rap...

No abstract

We present a straightforward method to double the refractive index sensitivity of surface-supported nanoplasmonic optical sensors by lifting the metal nanoparticles above the substrate by a dielectric nanopillar. The role of the pillar is to substantially decrease the spatial overlap between the substrate and the enhanced fields generated at plasmon resonance. Data presented for nanodisks and nanoellipsoids supported by pillars of varying heights are found to be in excellent agreement with electrodynamics simulations. The described concepts apply to multitude of plasmonic nanostructures, fabricated by top-down or bottom-up techniques, and are likely to further facilitate the development of novel nanooptical sensors for biomedicine and diagnostics.

No abstract