One-Step Fabrication of GeSn Branched Nanowires

We report for the first time the self-catalyzed, single-step growth of branched GeSn nanostructures by a vapor-liquid-solid mechanism. These typical GeSn nanostructures consist of < 111 >-oriented, Sn-rich (similar to 8 atom %) GeSn branches grown epitaxially on GeSn trunks, with a Sn content of similar to 4 atom %. The trunks were seeded from Au0.80Ag0.20 nanoparticles followed by the catalytic growth of secondary branches (diameter similar to 50 nm) from the excess of Sn on the sidewalls of the trunks, as determined by high-resolution electron microscopy and energy-dispersive X-ray analysis. The nanowires, with < 111 >-directed GeSn branches oriented at similar to 70 degrees to the trunks, have no apparent defects or change in crystal structure at the trunk-branch interface; structural quality is retained at the interface with epitaxial crystallographic relation. The electrochemical performance of these highly ordered GeSn nanostructures was explored as a potential anode material for Li-ion batteries, due to their high surface-to-volume ratio and increased charge carrier pathways. The unique structure of the branched nanowires led to high specific capacities comparable to, or greater than, those of conventional Ge nanowire anode materials and Ge1-xSnx nanocrystals.