How to make single small holes with large aspect ratios

In many areas of research a need for single small holes with diameters from a few nm to several μm and large aspect ratios exists that is hard to meet with existing technologies. In a proof of principle it is shown that suitable single holes or specific arrays of some single holes can be made by first etching a very large number of small and deep holes or pores into semiconductors like Si or InP by established electrochemical means, followed by masking the desired holes and filling all others with, e.g., a metal in a galvanic process. The potential and limitations of this technique is briefly discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)