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...

The plasmonic properties of arrays of supported Al nanodisks, fabricated by hole-mask colloidal lithography (HCL), are analyzed for the disk diameter range 61-492 nm at a constant disk height of 20 nm. Strong and well-defined (UV-vis-NIR) localized surface plasmon resonances are found and experimentally characterized with respect to spectral peak positions, peak widths, total cross sections, and radiative and nonradiative decay channels. Theoretically, the plasmon excitations are described by electrostatic spheroid theory. Very good qualitative and quantitative agreement between model and experiment is found for all these observables by assuming a nanoparticle embedded in a few nanometer thick homogeneous (native) aluminum oxide shell. Other addressed aspects are: (i) the role of the strong interband transition in Al metal, located at 1.5 eV, for the plasmonic excitations of Al nanoparticles, (ii) the role of the native oxide layer, and (iii) the possibility of using the plasmon excitation as an ultrasensitive, remote, real-time probe for studies of oxidation/corrosion kinetics in metal nanoparticle systems.

We report the first observation of non-Fermi-liquid (NFL) effects in a clean Yb compound at ambient pressure and zero magnetic field. The electrical resistivity and the specific-heat coefficient of high-quality single crystals of YbRh(2)Si(2) present a linear and a logarithmic temperature dependence, respectively, in more than a decade in temperature. We ascribe this NFL behavior to the presence of (presumably) quasi-2D antiferromagnetic spin fluctuations related to a very weak magnetic phase transition at T(N) approximately 65 mK. Application of hydrostatic pressure induces anomalies in the electrical resistivity, indicating the stabilization of magnetic order.

Localized surface plasmon resonances (LSPR) are collective electronic excitations in metallic nanoparticles. The LSPR spectral peak position, as a function of nanoparticle size and material, is known to depend primarily on dynamic depolarization and electron structure related effects. The former gives rise to the well-known spectral red shift with increasing nanoparticle size. A corresponding understanding of the LSPR spectral line width for a wide range of nanoparticle sizes and different metals does, however, not exist. In this work, the radiative and nonradiative damping contributions to the LSPR line width over a broad nanoparticle size range (40-500 nm) for a selection of three metals with fundamentally different bulk dielectric properties (Au, Pt, and Al) are explored experimentally and theoretically. Excellent agreement was obtained between the observed experimental trends and the predictions based on electrostatic spheroid theory (MLWA), and the obtained results were successfully related to the specific band structure of the respective metal. Moreover, for the first time, a clear transition from a radiation damping dominated to a quenched radiation damping regime (subradiance) in large nanoparticles was observed and probed by varying the electron density through appropriate material choice. To minimize inhomogeneous broadening (commonly present in ensemble-based spectroscopic measurements), a novel, electron-beam lithography (EBL)-based nanofabrication method was developed. The method generates large-area 2D patterns of randomly distributed nanodisks with well-defined size and shape, narrow size distribution, and tunable (minimum) interparticle distance. In order to minimize particle-particle coupling effects, sparse patterns with a large interparticle distance (center-to-center ≥6 particle diameters) were considered.

The plasmonic properties of nanodisk arrays of Pt, Pd, and, for comparison, Ag are studied over a large size and spectral range and analyzed theoretically by an electrostatic model. Pt and Pd nanodisks exhibit broad localized surface plasmons with a higher sensitivity of the plasmon to the disk aspect ratio compared to Ag. Extinction cross-sections are generally about 50% smaller for Pt and Pd. The spectral plasmon positions, line-widths, and extinction cross-sections are well reproduced by the model.