Engineering the Growth of Germanium Nanowires by Tuning the Supersaturation of Au/Ge Binary Alloy Catalysts

Abstract

Access to the full text of the published version may require a subscription. Rights AbstractThe synthesis of Ge nanowires with very high-aspect ratios (greater than 1000) and uniform crystal growth directions is highly desirable, not only for investigating the fundamental properties of nanoscale materials, but also for fabricating integrated functional nanodevices. In this article, we present a unique approach for manipulating the supersaturation, and thus the growth kinetics, of Ge nanowires using Au/Ge bilayer films. Ge nanowires were synthesized on substrates consisting of two parts: a Au film on one half of a Si substrate and a Au/Ge bilayer film on the other half of the 2 substrate. Upon annealing the substrate, Au and Au/Ge binary alloy catalysts were formed on the Au-side and Au/Ge-side of the substrates respectively, under identical conditions. The mean lengths of Ge nanowires produced were found to be significantly longer on the Au/Ge bilayer side of the substrate compared to the Au-coated side, as a result of a reduced incubation time for nucleation on the bi-layer side. The mean length and growth rate on the bilayer side (with a 1 nm Ge film) was found to be 5.5 ± 2.3 µm and 3.7 × 10 -3 µm s -1 respectively, and 2.7 ± 0.8 µm and 1.8 × 10 -3 µm s -1for the Au film. Additionally, the lengths and growth rates of the nanowires further increased as the thickness of the Ge layer in the Au/Ge bilayer was increased. In-situ TEM experiments were performed to probe the kinetics of Ge nanowire growth from the Au/Ge bilayer substrates.Diffraction contrast during in-situ heating of the bilayer films clarified the fact that thinner Ge films,i.e. lower Ge concentration, take longer to alloy with Au than thicker films. Phase separation was also more significant for thicker Ge films upon cooling. The use of binary alloy catalyst particles, instead of the more commonly used elementary metal catalyst, enabled the supersaturation of Ge during nanowire growth to be readily tailored, offering a unique approach to producing very long high aspect ratio nanowires.

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Diameter-Controlled Germanium Nanowires with Lamellar Twinning and Polytypes

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Recent advances in the growth of germanium nanowires: synthesis, growth dynamics and morphology control

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