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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Abstract:We present the fabrication of silicon dioxide (SiO 2 ) coated silicon nanopillar array structures and demonstrate their application as sensitive optical biosensors. Colloidal lithography, plasma dry etching and deposition processes are used to fabricate SiO 2 coated Si nanopillar arrays with two different diameters and periods. Proof of concept bio recognition experiments are carried out with the bovine serum albumin (BSA)/antiBSA model system using Fourier transform visible and IR spectrometry (FT-VIS-IR) in reflection mode. A limit of detection (LoD) value of 5.2 ng/ml is estimated taking in to account the wavenumber uncertainty in the measurements.

We present experimental demonstration and analysis of enhanced surface second harmonic generation (SHG) from hexagonal arrays of silicon pillars. Three sets of Si pillar samples with truncated cone-shaped pillar arrays having periods of 500, 1000, and 2000 nm, and corresponding average diameters of 200, 585 and 1550 nm, respectively, are fabricated by colloidal lithography and plasma dry etching. We have observed strong dependence of SHG intensity on the pillar geometry. Pillar arrays with a 1000 nm period and a 585 nm average diameter give more than a one order of magnitude higher SHG signal compared to the other two samples. We theoretically verified the dependence of SHG intensity on pillar geometry by finite difference time domain simulations in terms of the surface normal E-field component. The enhanced surface SHG light can be useful for nonlinear silicon photonics, surface/interface characterization, and optical biosensing.

Radial junction nanopillar Si solar cells are interesting for cost effective efficiency improvement. Here, we address a convenient top-down fabrication of Si nanopillar solar cells using spin-on doping and rapid thermal annealing (RTA) for conformal PN junction formation. Broadband suppressed reflection as low as an average of 5% in the 300-1100 nm wavelength range and un-optimized cell efficiency of 7.3% are achieved. The solar cell performance can be improved by optimization of spin-on-doping and suitable surface passivation. Overall, the all RTA processed, spin-on doped nanopillar radial junction solar cell shows a very promising route for low cost and high efficiency thin film solar cell perspectives.