Template-induced colloidal deposition during solvent evaporation is a promising technique for extending the possibilities of nanosphere lithography and the creation of photonic band gap materials. We investigated the influence of the parameters that determine the surface topography of templates on colloidal crystal structure. On pillar-shaped templates, large defect-free square symmetric monolayers, ordered vacancy arrays, and body-centered cubic (bcc) and simple cubic (sc) colloidal crystals could be grown. Close-packed crystals displayed defects and large defect grains. Our results indicate that this may be avoided when the direction of gravity with respect to the substrate is changed.The ability of colloids to self-assemble into 2D and 3D crystalline structures lies at the heart of many studies in nanoand micrometer-scale materials science. 1 Especially in the field of photonic band gap materials, colloidal crystals are being routinely used.2 Furthermore, 2D and thin 3D colloidal crystals can be used as a mask for creating regular arrays of nanometer-sized features with a technique called nanosphere lithography.3-5 One of the simplest and most frequently used techniques for assembling 2D and 3D colloidal crystals is colloidal crystallization during solvent evaporation. [6][7][8][9] Apart from its simplicity and low cost, the main advantages of the technique are (i) the possibility to grow millimeter-sized single crystals with a hexagonal (111) orientation of the top surface and (ii) the possibility to control the thickness of the deposited crystal by varying the initial particle volume fraction. 7 A major limitation is that the crystal symmetry and 3D orientation of the crystal cannot be influenced. The use of a patterned substrate, or template, provides the possibility to direct colloidal crystallization epitaxially. 10 Recent experiments on colloidal epitaxy under equilibrium conditions have shown the growth of crystal structures that are metastable in bulk crystallization and thus would not grow without the use of the template. 11,12 Several papers have reported results on template-induced colloidal assembly during solvent evaporation, but the systems consisted of (repeated 13 ) 2D deposits of micrometer-scale particles 14 or showed the frequent occurrence of defects and a lack of long-range order. 15In this letter, we demonstrate the templated growth of 100-nm-radius particles in colloidal crystals with close-packed and non-close-packed symmetry. The crystals were grown by convective assembly on a substrate placed in a vertical setup (i.e., parallel to gravity). We will address the influence of various parameters that determine the template topography on 2D and 3D colloidal crystal structure. Our results indicate that the direction of the gravitational field plays a crucial role in template-directed convective assembly.Silica particles with diameters of d ) 202 and 220 nm (polydispersity σ ≈ 0.005) were deposited onto a substrate that was vertically placed in a slowly evaporating dispersion in eth...

A metal film perforated by a regular array of subwavelength holes shows unexpectedly large transmission at particular wavelengths, a phenomenon known as the extraordinary optical transmission (EOT) of metal hole arrays. EOT was first attributed to surface plasmon polaritons, stimulating a renewed interest in plasmonics and metallic surfaces with subwavelength features. Experiments soon revealed that the field diffracted at a hole or slit is not a surface plasmon polariton mode alone. Further theoretical analysis predicted that the extra contribution, from quasi-cylindrical waves, also affects EOT. Here we report the experimental demonstration of the relative importance of surface plasmon polaritons and quasi-cylindrical waves in EOT by considering hole arrays of different hole densities. From the measured transmission spectra, we determine microscopic scattering parameters which allow us to show that quasi-cylindrical waves affect EOT only for high densities, when the hole spacing is roughly one wavelength. Apart from providing a deeper understanding of EOT, the determination of microscopic scattering parameters from the measurement of macroscopic optical properties paves the way to novel design strategies.

We present the implementation of tailored trapping potentials for ultracold gases on an atom chip. We realize highly elongated traps with box-like confinement along the long, axial direction combined with conventional harmonic confinement along the two radial directions. The design, fabrication and characterization of the atom chip and the box traps is described. We load ultracold ( 1 µK) clouds of 87 Rb in a box trap, and demonstrate Bose-gas focusing as a means to characterize these atomic clouds in arbitrarily shaped potentials. Our results show that box-like axial potentials on atom chips are very promising for studies of one-dimensional quantum gases.

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