Fabrication of Periodic Nanostructure Assemblies by Interfacial Energy Driven Colloidal Lithography

Abstract

4577www.MaterialsViews.com wileyonlinelibrary.com particles with diameters ranging from tens of nanometers to several micrometers are commercially available; thus, a wide variety of patterns can be fabricated by colloidal lithography. The colloidal lithography technique has been extensively used to fabricate various periodic structures including nanowire/nanopillar arrays of different materials such as Si, ZnO, InP. [6][7][8] Despite being a very successful technique, [ 9 ] the use of colloidal lithography in case of wetchemical synthesis has been very limited. The main limitation in using colloidal lithography in combination with solutionbased synthesis is that the masked region, that is, the contact area between the colloidal sphere and the substrate is very small while the rest of the substrate remains accessible for the solution. So, in a normal approach involving drop casting of solution on a monolayer of colloidal particles, the solution easily penetrates through the interstices between the colloidal spheres and settles down on the substrate making a continuous layer with periodic holes.With respect to pattern fabrication using liquids, superhydrophilic-superhydrophobic micropatterns is a unique and rapidly developing fi eld, which is based on extreme differences in wettability between superhydrophilic and superhydrophobic regions on the same substrate. [ 10,11 ] Enormous research effort is being devoted to understand and control the wettability of the solid surface in order to uniquely and precisely control the geometry, position and the shape of the liquid droplets on the solid surface. In addition to the fabrication of periodic microdroplets, [ 10 ] this technique is also widely used in various other applications such as surface tension confi ned micro channels, [ 12 ] fi lling micro patterns, [ 13,14 ] passive dispensing by dewetting, [ 15 ] controlling bioadhesion, [ 16 ] cell encapsulation droplet arrays [ 17 ] and fabrication of complex micropatterns. [ 18 ] However, this technique is only suitable for large (>50 µm) structures.Here, we combine colloidal lithography with generation of hydrophobic-hydrophilic regions and demonstrate a novel interfacial energy driven colloidal lithography technique to fabricate periodic micron and submicron-size patterns from solution phase. We utilize self-developed periodic wettability of a Si substrate in the presence of self-assembled colloidal silica spheres. The feasibility and the versatility of the concept are demonstrated by fabricating periodically arranged ZnO nanowire (NW) ensembles on sol-gel derived ZnO seed pattern

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