(e) Example of pore array obtained when only one third of the pores are localised using nanoimprint lithography. (f) Example of non-cylindrical pore array obtained with non-equilateral triangular lattice. In the case of thermal NIL presented here, holes are pre-patterned in a triangular array on the surface of a thin aluminium layer deposited on a P+ conductive Si wafer. As described in Figure 1c, a thermoplastic Ensartinib cell line resin (NEB22 from Sumitomo Chemicals, Tokyo, Japan) is coated on an aluminium layer. A silicon mould, treated with an anti-sticking layer [31] and presenting a triangular

array of pits, is then pressed on the sample in an EVG520 hot embossing tool (EV Group, St. Florian an Inn, Austria) at 0.2 kN.cm−2 and 125°C. Mould patterns are www.selleckchem.com/products/Belinostat.html reproduced in the polymer since the applied temperature is higher than the resin’s glass transition temperature. After removal from the mould at room temperature, the pattern is transferred into the surface of the Al layer using a conventional plasma dry etching technique. In a Centura 5200 reactive ion etching chamber (Applied Materials, Santa Clara, CA, USA), a Cl2/Ar/O2 plasma is used to remove the residual resin layer and a Cl2/BCl3 plasma is used for etching the Al surface. The final structure consists of a 2 × 2-cm2 surface of aluminium structured with holes of few nanometres depth in

a triangular array of different periods according to the initial mould design. During the anodization, these holes will act as surface defects, initiating the pore growth as described in Figure 1a. The layer is so directly anodized at the voltage corresponding to the period given by the

NIL and according to Equation 1. Samples are anodized in a home-made cell under a constant voltage, in an orthophosphoric or oxalic acid bath at constant temperature (T = 8°C). The electrolyte is stirred during the process of anodization to facilitate the flow of the species in the electrolyte and to remove the bubbles of H2 gas from the platinum electrode. A Parstat 2273 potentiostat (Princeton Applied Research, Oak Ridge, TN, USA) is used to apply a constant voltage and to follow the I-V curve in situ between a platinum circular electrode and the sample. In order to obtain second defect-free triangular arrays of pores, the voltage has to be adjusted so that the natural period of the porous alumina corresponds to the NIL-fabricated guiding pattern. The anodizing time does not differ significantly from the classical anodization time of a simple anodization: with 3% oxalic acid under 40 V at 8°C, simple anodization of 1 μm of Al takes 1,750 s and anodization after nanoimprint lasts 1,700 s. Furthermore, under these experimental conditions, the ratio between the thickness of Al layer deposited and the final thickness of highly organised alumina is evaluated at 1.25. Figure 1b shows an array of 2 × 2 cm2 of highly organised porous alumina.