Elsevier

Microelectronic Engineering

Volume 88, Issue 8, August 2011, Pages 2444-2446
Microelectronic Engineering

Large area nanopatterning by combined anodic aluminum oxide and soft UV–NIL technologies for applications in biology

https://doi.org/10.1016/j.mee.2011.02.013Get rights and content

Abstract

Combining the nanoporous anodic aluminum oxide (AAO) technique with soft lithography constitutes a highly reproducible and quick method for large-area nanopatterning, with increasing potential for applications in biology. The AAO templates were used as master-molds to fabricate large areas (several square centimeters) of nanostructured and ordered tapered PDMS-bumps. The master-molds were filled using hexane-diluted PDMS of reduced viscosity compared to standard one. Viscosity evolution study for different current agent and hexane concentrations was achieved. The as-obtained stamps served subsequently to create large-area highly ordered nanostructured silicon substrates using UV assisted Nanoimprint Lithography (UV–NIL).

Introduction

Soft lithography is well known to be useful for biological applications since it is compatible with an insulating support and the requirement of large-area samples for the easy observation and manipulation of nano-objects. The present work concerns the elaboration of new templates by UV assisted Nanoimprint Lithography (UV–NIL) [1], [2] for different applications in biology including: (i) detection of biomolecules with Localized Surface Plasmon Resonance (LSPR) [3], (ii) imaging of living cells [4] and (iii) AFM studies of membrane proteins [5]. For these topics, soft UV–NIL is used for the fabrication of large-area arrays of either gold nanodisks, nanopillars or nanoholes on an insulating substrate. In our previous works [3], [5], [6], PDMS master-molds were fabricated using e-beam lithography and reactive ion etching (RIE) on silicon wafers. This very time consuming procedure can now be replaced by the use of self-organized nanoporous alumina as molds. Furthermore, the advantage of the alumina substrate compared to silicon dioxide is the easier demolding from the PDMS stamp after curing. This is related to a lower surface energy compared to that of SiO2 and to the natural, conical shape of the holes close to the surface. This particular shape is inherent to the electrochemical fabrication process. It is also possible to remove the alumina membrane by dissolution in acids without attacking the PDMS stamp. Preliminary works of Zhou et al. have been published using PDMS with toluene as a solvent [7]. In the present work, we study the influence of hexane as a solvent and the imprint in the AMONIL is shown. Are also presented, the nanoholes etching in silicon, the deposition of gold and lift-off for the fabrication of nanodisks, which can subsequently be used for bioplasmonic applications.

Section snippets

Master-mold fabrication

Nanoporous alumina substrates exhibit an arrangement of parallel nanometric pores, organized in a hexagonal lattice and extending on surfaces of a few square centimeters. The pores are vertical and their diameter and aspect ratio can easily be controlled. The pore diameter can vary from 10 to 200 nm and the aspect ratio can be larger than 500. Their synthesis is carried out electrochemically from aluminum wafers. After polishing, an anodic potential is applied at a controlled temperature to an

Viscosity

In pure PDMS, the viscosity is around 4500 mPa s. The curves reported on Fig. 2 show the evolution of the viscosity of PDMS versus time for different curing agent and hexane concentrations. The hexane diluted PDMS contains 1/10 curing agent concentration. Viscosities between 100 and 1800 Pa s were obtained. The viscosity decreases while increasing the dilution in hexane. A small enhancement of the viscosity was observed as a function of time. The same effects were observed for the dilution with the

Conclusion and perspectives

Regular nanofeature arrays were manually patterned by soft UV–NIL in Si wafers over large areas (few cm2) demonstrating the advantages of using AAO in order to realize inexpensive and efficient hexane-diluted PDMS stamps. Effects of curing agent and hexane dilution on the resulting PDMS viscosity were measured allowing adapting the included quantities in stamps preparation to the imprint process and confirming that the system AAO and hexane-diluted PDMS is a good candidate for soft UV–NIL stamp

Acknowledgments

We would like to thank the CNRS-LPN researchers for helpful discussions and PRES UniverSud who gave the grant for these studies.

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