Orientation dependence of heterogeneous nucleation at the Cu-Pb solid-liquid interface

Area of Science:

• Materials Science
• Computational Materials Science
• Crystallization

Background:

• Surface structure significantly influences heterogeneous nucleation.
• Previous work showed distinct Cu/Pb interface structures: Cu(100) exhibited surface alloying, while Cu(111) showed a prefreezing layer.
• Interface behavior differs at elevated temperatures (750 K).

Purpose of the Study:

• To investigate the effect of copper (Cu) surface structure on lead (Pb) heterogeneous nucleation from the melt.
• To compare nucleation behavior on Cu(111) and Cu(100) surfaces using molecular-dynamics (MD) simulations.
• To quantify nucleation barriers and understand wetting phenomena.

Main Methods:

• Molecular-dynamics (MD) simulations were employed to study the Cu/Pb solid-liquid interface.
• Undercooling simulations were performed to induce heterogeneous nucleation of Pb crystals.
• Quantitative analysis of nucleation barriers and qualitative observation of critical nucleus geometry were conducted.

Main Results:

• Heterogeneous nucleation of Pb occurred readily on the Cu(111) surface at 592 K (26 K undercooling), forming a nearly planar critical nucleus.
• Nucleation barriers on Cu(111) were over two orders of magnitude lower than homogeneous nucleation barriers.
• Nucleation on the Cu(100) surface required substantial undercooling (~170 K) due to poor wetting (contact angle > 90°), attributed to surface alloying.

Conclusions:

• The Cu(111) surface, with its prefreezing layer, promotes efficient heterogeneous nucleation of Pb.
• The surface-alloyed Cu(100) surface hinders nucleation due to poor wetting, requiring significant undercooling.
• MD simulations provide quantitative insights into surface-mediated nucleation phenomena, aligning with classical nucleation theory predictions.