Template-Induced Growth of Close-Packed and Non-Close-Packed Colloidal Crystals during Solvent Evaporation

Abstract

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...

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