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Atomic gold–enabled three-dimensional lithography for silicon mesostructures

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Science  26 Jun 2015:
Vol. 348, Issue 6242, pp. 1451-1455
DOI: 10.1126/science.1257278

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Complex shapes from chemical lithography

Lithographic printing of semi-conductors builds up complex patterns one layer at a time. The process involves multiple steps to mask, print, and etch each layer. Luo et al. tweaked the same process used to grow silicon nanowires to pattern them into complex three-dimensional (3D) shapes. Gold acted as a catalyst to grow and elongate silicon nanowires from the vapor phase. Varying the pressure of the growth process altered the rate of gold diffusion along the surface of the wire. Upon etching the wires, the non-uniform coating of gold acted as a lithographic mask. The authors were thus able to make complex-shaped silicon spicules with a series of ridges and notches by strictly chemical means.

Science, this issue p. 1451

Abstract

Three-dimensional (3D) mesostructured semiconductors show promising properties and applications; however, to date, few methods exist to synthesize or fabricate such materials. Metal can diffuse along semiconductor surfaces, and even trace amounts can change the surface behavior. We exploited the phenomena for 3D mesoscale lithography, by showing one example where iterated deposition-diffusion-incorporation of gold over silicon nanowires forms etchant-resistant patterns. This process is facet-selective, producing mesostructured silicon spicules with skeletonlike morphology, 3D tectonic motifs, and reduced symmetries. Atom-probe tomography, coupled with other quantitative measurements, indicates the existence and the role of individual gold atoms in forming 3D lithographic resists. Compared to other more uniform silicon structures, the anisotropic spicule requires greater force for detachment from collagen hydrogels, suggesting enhanced interfacial interactions at the mesoscale.

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