Can Nanowires Coalesce?

Area of Science:

• Materials Science
• Crystallography
• Nanotechnology

Background:

• Coalescence of nanowires and 3D structures into continuous films is essential for growing high-quality III-nitride and III-V materials on mismatched substrates.
• Understanding this process is also fundamental for materials science and nanotechnology.

Purpose of the Study:

• To develop a growth model for vertical nanowire coalescence.
• To establish a morphological diagram for substrate surface coverage based on key growth parameters.
• To analyze the conditions necessary for full nanowire coalescence.

Main Methods:

• Utilized the Kolmogorov crystallization theory for modeling the solid-like coalescence process.
• Developed a growth model for vertical nanowires.
• Defined coverage as a function of material collection efficiency (a) and normalized surface diffusion flux (b).

Main Results:

• Full nanowire coalescence into a continuous film is achieved only when material collection efficiency (a) equals 1, irrespective of surface diffusion (b).
• When a > 1, common in vapor-liquid-solid growth, nanowires only partially merge, never forming a continuous film.
• Vapor phase epitaxy results in partial merging, while directional molecular beam epitaxy allows full coalescence at a=1.

Conclusions:

• The study provides a predictive model for nanowire and 3D island surface coverage.
• Results enable control over coalescence by tuning parameters like surface density, droplet size, diffusivity, and initial geometry.
• Applicable to various epitaxy techniques including vapor-liquid-solid, selective area, and self-induced growth.