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NANO LETTERS

Extended Arrays of Vertically Aligned Sub-10 nm Diameter [100] Si Nanowires by Metal-Assisted Chemical Etching
Zhipeng Huang,† Xuanxiong Zhang,† Manfred Reiche,† Lifeng Liu,† Woo Lee,*,†,‡ Tomohiro Shimizu,† Stephan Senz,† and Ulrich Gosele*,† ¨
Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120 Halle Germany, and Korea Research Institute of Standards and Science, Yuseong, 305-340 Daejon, Korea
Received July 31, 2008

2008 Vol. 8, No. 9 3046-3051

ABSTRACT
Large-area high density silicon nanowire (SiNW) arrays were fabricated by metal-assisted chemical etching of silicon, utilizing anodic aluminum oxide (AAO) as a patterning mask of a thin metallic film on a Si (100) substrate. Both the diameter of the pores in the AAO mask and the thickness of the metal film affected the diameter of SiNWs. The diameter of the SiNWs decreased with an increase of thickness of the metal film. Large-area SiNWs with average diameters of 20 nm down to 8 nm and wire densities as high as 1010 wires/cm2 were accomplished. These SiNWs were single crystalline and vertically aligned to the (100) substrate. It was revealed by transmission electron microscopy that the SiNWs were of high crystalline quality and showed a smooth surface.

In recent years silicon nanowires (SiNWs) have attracted much attention1,2 due to their many unique properties and potential applications as building blocks for advanced electronic devices,3,4 biological sensors,5,6 and optoelectronic devices,7,8 as well as for renewable energy devices.9 As in many applications of nanostructured materials, it is important not only to synthesize SiNWs with a high degree of regularity and uniformity in terms of diameter and length, but also to accurately position them in arrays. Fabrication of spatially well-resolved two-dimensional (2D) periodic arrays of vertically aligned epitaxial SiNWs with controlled density is of utmost importance for many practical applications, such as in field-effect

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