DOI: 10.1002/adma.200601945 Etching Masks Based on Miniemulsions: A Novel Route Towards Ordered Arrays of Surface Nanostructures** By Achim Manzke, Christian Pfahler, Oliver Dubbers , Alfred Plettl,* Paul Ziemann, Daniel Crespy , Eyk Schreiber, Ulrich Ziener, and Katharina Landfester Among the many phenomena revealed and provided by nanoscience, the functionalization of a surface by nanopat- terning certainly holds promise for a large number of attrac- tive applications. A prominent example is the deposition of self-assembled monolayers by microcontact printing in order to control wettability, adhesion, friction, and wear. [1,2] In this context, the well-known lotus effect should be mentioned. This effect is based on a strong reduction of the adhesion of water droplets by nanopatterning a surface with, for example, dense arrays of statistically distributed nanopillars. [3,4] A further application of such nanopillars is their use as effective electron field emitters, as has been demonstrated for Si, [5,6] a material which is also at the focus of the present work, or, more recently, for diamond. [7] Moreover, highly ordered ar- rays of nanopillars are extremely helpful for the characteriza- tion of individual emitters by scanning tunneling microscopy (STM) or scanning tunneling spectroscopy (STS). For an inverted pattern of nanopillars, that is, ordered ar- rays of cylindrical nanopores with a high aspect ratio, a similar wealth of possible applications can be thought of. For in- stance, they can serve as contact holes in semiconductors. Ac- cording to the present semiconductor technology roadmap, they should exhibit diameters well below 80 nm for the “65 nm node generation”. [8] Similarly, applications in nano- optics appear attractive; nanopores based on colloidal masks were fabricated into Si with a diameter of 60 nm. [9] Smaller di- ameters of the order of 30 nm should be obtainable by nano- machining a poly(methyl methacrylate) PMMA resist with an atomic force microscope and subsequent metal-coating and lift-off, thereby accepting the disadvantage of a nonparallel process. [10] Note that the recently developed technique of con- trolling the diameter of nanopores in ultrathin Si/SiO 2 mem- branes by the electron beam of a transmission electron micro- scope is still a nonparallel procedure. [11] Another approach to preparing nanoholes in Si is based on self-organized porous alumina masks in combination with anisotropic Cl 2 reactive- ion etching (RIE). [12] In this way, holes with diameters > 13 nm and an aspect ratio of 3 could be obtained. Similar diameters are obtained by a recently reported tech- nique based on the self-organization of inverse spherical mi- celles formed from diblock copolymers dissolved in an apolar solvent, such as toluene, and selectively loaded in the micellar core with a metal salt, such as HAuCl 4 . [13–16] By dip-coating such solutions onto practically any sufficiently flat substrate, hexagonally ordered arrays of Au nanodots can be prepared by an ashing process. [17] They can be used as nanomasks in a subsequent anisotropic etching step, resulting in correspond- ing arrays of nanopillars. In this way, hexagonally ordered pil- lars with a diameter of 14 nm and an aspect ratio of 5 were obtained in Si. This micellar preparation technique offers a number of impressive advantages, such as the control of the resulting particle size within the range of ca. 1–12 nm as well as of the interparticle distance, ranging between 10 and 150 nm. However, this technique also exhibits some inherent drawbacks: First, the maximum interparticle distance, as ap- proximately given by the diameter of the micelles, is limited to a maximum of 200 nm. For larger block lengths of the in- volved polymer chains, a spherical shape of the resulting mi- celles is no longer guaranteed. Larger distances between indi- vidual nanostructures such as pillars are, however, desirable for many applications. Again, field emitters with a large as- pect ratio are an example, exhibiting optimal performance when distance between emitters is approximately twice the emitter height. [18] Another, even more important, characteris- tic difficulty with the micellar approach is related to the prep- aration of alloy particles. This is only possible for a few mate- rial systems because of the problem of selectively ligating different alloy components within a single micellar core. Thus, an alternative preparation method that overcomes the two main problems related to the micellar approach is highly desirable. For this purpose, a novel technique based on miniemulsions loaded with a metal precursor complex and stabilized in water by surfactants is introduced in this Com- munication. After direct polymerization, solutions of colloidal particles are obtained, which, as in the micellar approach, self-assemble into hexagonally ordered arrays after a corre- sponding drop is deposited onto a substrate. This first strongly COMMUNICATION Adv. Mater. 2007, 19, 1337–1341 © 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1337 – [*] Dr. A. Plettl, A. Manzke, C. Pfahler, O. Dubbers, Prof. P. Ziemann Institut für Festkörperphysik, Universität Ulm Albert-Einstein-Allee 11, 89069 Ulm (Germany) E-mail: alfred.plettl@uni-ulm.de D. Crespy, E. Schreiber, Dr. U. Ziener, Prof. K. Landfester Institut für Organische Chemie III, Universität Ulm Albert-Einstein-Allee 11, 89069 Ulm (Germany) [**] We thank Prof. P. Walther (ZE Electron Microscopy, Ulm) for advis- ing us in the use of HRSEM. Support by the Deutsche Forschungs- gemeinschaft (DFG) within the Cooperative Research Center SFB 569 as well as by the Landesstiftung Baden-Württemberg is grateful- ly acknowledged.