Imprint stamps DOI: 10.1002/smll.200600100 Wafer-Scale Ni Imprint Stamps for Porous Alumina Membranes Based on Interference Lithography** Woo Lee,* Ran Ji, Caroline A. Ross, Ulrich Gçsele, and Kornelius Nielsch In recent years, nanoporous anodic aluminum oxide (AAO) has been intensively exploited as a template material for the preparation of multifunctional nanostructures, which have applications in various scientific and technological fields. [1] In template-based materials synthesis, it is desirable to use a template with long-range order, so that structurally well-de- fined materials can be subsequently produced. In a typical anodization process, a self-ordered close-packed array of oxide nanopores forms with domain size (ordering length) on a scale of a few micrometers. [2] To achieve a long-range- ordered pore arrangement over a larger area, Masuda and co-workers first developed a pretexturing process that uses a SiC mold to produce ordered arrays of dimples on the Al substrate by nanoindentation prior to anodization. [3] Shallow indentations on an Al substrate initiate pore nucleation during anodization and lead to a long-range-ordered pore arrangement within the stamped area (e.g., 44 mm). This work has sparked considerable interest within the growing community of research groups using porous alumina, which is evident from the several hundred citations of these publi- cations within a few years. However, few groups have been able to fabricate large-area, long-range-ordered alumina membranes due to the high processing costs of the imprint stamps, which can be a few thousand US$ for a cm 2 pattern. Recently, alternative methods based on focused ion beams (FIB), [4] optical diffraction gratings, [5] and micro- ACHTUNGTRENNUNGbeads [6] were also used to achieve prepatterning of Al sub- strates, thus avoiding fabrication of the expensive SiC im- print stamp. More recently, Masuda and co-workers demon- strated the fabrication of ideally ordered AAO films with a sub-50-nm pore interval by employing metal molds, which were fabricated by replication from a resist pattern pre- pared by electron-beam lithography (EBL). [7] While each of these methods have their own advantages, most of them have limitations in scalability. Consequently, the simple and economic realization of long-range-ordered AAO over very large areas (cm 2 to wafer size) still presents challenges. Herein, we propose two inexpensive approaches for the development of large-scale metallic stamps, which can then be used to imprint Al (see Figure 1). The processes consist of two steps: the replication of Ni imprint stamps from a master pattern, and the subsequent fabrication of long- range-ordered AAO by anodization of Al prepatterned using the Ni stamps. In method I, the imprint stamp is repli- cated once by electrodeposition onto a large-scale periodic photoresist pattern, similar to the method described in ref. [7]. However, instead of using EBL, the periodic photo- resist patterns in the present work were fabricated by laser interference lithography (LIL), which allows the production of periodic nanostructures with a high throughput. [8] Pattern transfer by imprint lithography onto metallic substrates such as Al requires 50 to 2000 times higher pressures in compari- son to imprint lithography on polymer layers. [9] Due to the high mechanical stresses, damage to the imprint stamp often occurs after several uses, so it is advantageous to be able to make multiple imprint stamps from a single master. This has motivated the development of an alternative approach Figure 1. Schematic diagram of the fabrication of ideally ordered anodic alumina using Ni imprint stamps that can be replicated from a) a resist pattern (method I) and b) a silicon pattern (method II). [*] Dr. W. Lee, R. Ji, Prof. Dr. U. Gçsele, Dr. K. Nielsch Max Planck Institute of Microstructure Physics Weinberg 2, 06120 Halle (Germany) Fax: (+ 49)345-5511223 E-mail: woolee@mpi-halle.de Prof. Dr. C. A. Ross Department of Materials Science and Engineering 77 Massachusetts Avenue, Cambridge, MA 02139 (USA) [**] Financial support from the German Federal Ministry for Education and Research (BMBF, Project No. 03N8701) and the National Sci- ence Foundation are greatly acknowledged. We would like to thank Dr. Mato Knez for AFM investigations and Prof. H. I. Smith of MIT for the use of laboratory facilities and valuable discus- sions. Supporting information for this article is available on the WWW under http://www.small-journal.com or from the author. 978 # 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim small 2006, 2, No. 8-9, 978 – 982 communications