The influence of the surface migration of gold on the growth of silicon nanowires

Abstract

Interest in nanowires continues to grow, fuelled in part by applications in nanotechnology. The ability to engineer nanowire properties makes them especially promising in nanoelectronics. Most silicon nanowires are grown using the vapour-liquid-solid (VLS) mechanism, in which the nanowire grows from a gold/silicon catalyst droplet during silicon chemical vapour deposition. Despite over 40 years of study, many aspects of VLS growth are not well understood. For example, in the conventional picture the catalyst droplet does not change during growth, and the nanowire sidewalls consist of clean silicon facets. Here we demonstrate that these assumptions are false for silicon nanowires grown on Si(111) under conditions where all of the experimental parameters (surface structure, gas cleanliness, and background contaminants) are carefully controlled. We show that gold diffusion during growth determines the length, shape, and sidewall properties of the nanowires. Gold from the catalyst droplets wets the nanowire sidewalls, eventually consuming the droplets and terminating VLS growth. Gold diffusion from the smaller droplets to the larger ones (Ostwald ripening) leads to nanowire diameters that change during growth. These results show that the silicon nanowire growth is fundamentally limited by gold diffusion: smooth, arbitrarily long nanowires cannot be grown without eliminating gold migration.

In Situ Atomic‐Scale Study of Particle‐Mediated Nucleation and Growth in Amorphous Bismuth to Nanocrystal Phase Transformation

“…However, the size of the bottom smaller nanocrystal reduces from ≈12.0 to ≈3.6 nm in length and from ≈8.5 to ≈5.0 nm in width (Figure 3s–w). This implies that the coalescence of two nanocrystals with a large rotation angle takes a surface migration‐driven coalescence pathway 41, 42, 43. The remaining smaller bottom nanocrystal shows a rapid atomic rearrangement mechanism (Figure 3w,x) similar to the one in Figure 3g–l,q,r.…”

In-situ TEM Observation of Repeating Events of Nucleation in Epitaxial Growth of Nano CoSi2 in Nanowires of Si

“…36,37 The Si nanowires were detached from the wafer in ethanol solution by ultrasonic vibration. Polycrystalline Co nanowires were synthesized by electroplating Co into a porous anodic aluminum oxide (AAO) template structure and then the AAO template was etched away to obtain Co nanowires.…”

Growth of one-dimensional Si/SiGe heterostructures by thermal CVD

“…This was also observed on high magnification SEM images of pure Si nanowires, with sometimes new catalytic growth of very slender nanowires (figure S1 available at stacks.iop.org/Nano/19/335603). Despite some recent investigation on the surface migration of gold during the synthesis, this phenomenon remains unclear, and it is undoubtedly experimental conditions dependent [26][27][28][29]. However, for electronic or thermoelectric applications, gold can be easily removed from the nanowires by chemical gold removers [30].…”