Microwave-Assisted Ge_1–xSn_x Nanowire Synthesis: Precursor Species and Growth Regimes

This study illustrates the different stages of Ge 1– x Sn x nanowire formation with high Sn content in solution and also the molecular precursors involved in the synthesis. We can identify homometallic Ge(II) as well as heterometallic Ge(II) and Sn(II) containing imido cubane derivatives being involved in the growth process. Two different scenarios are described for the initiation of the nanowire growth: a random seeding and a prenucleation step. Both scenarios can lead to constant diameter growth under continuous replacement of tin being consumed for the crystal formation from the Sn growth promoter. Once the growth medium is depleted from the Sn containing molecular species, the Sn growth seed is consumed resulting in diameter shrinkage. Most interestingly, the tin content increases with diminishing nanowire diameter from 10.7% to 28.4% at the very tip (270 to 10 nm). Similar results are obtained in Raman studies along a nanowire with shrinking diameter, while the Raman shift remains constant along nanowires of similar diameter. The nanowires are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), and μ-Raman spectroscopy.