When does a nanoparticle become a cluster?

Area of Science:

• Materials Science
• Physical Chemistry
• Computational Physics

Background:

• Distinguishing between nanoparticles and clusters is crucial for understanding material properties.
• Existing definitions lack clear physical criteria, leading to ambiguity in terminology.
• Finite aggregates exhibit unique behaviors influenced by size and surface effects.

Purpose of the Study:

• To establish clear physical criteria for differentiating nanoparticles and clusters.
• To investigate the behavior of finite Lennard-Jones spherical aggregates across different size regimes.
• To provide a unified understanding of size-dependent properties in small material systems.

Main Methods:

• Molecular dynamics simulations of finite Lennard-Jones spherical aggregates (N = 73 to 4235 atoms).
• Analysis under both equilibrium and non-equilibrium (sublimation) conditions.
• Introduction of energetic (local potential energy profiles) and structural (pair distance distribution) criteria.

Main Results:

• Identification of two distinct size regimes: scalable (nanoparticles) and non-scalable (clusters).
• Scalable regime shows linear property variations and homogeneous interiors.
• Non-scalable regime exhibits abrupt changes, steep potential energy gradients, and surface atom dominance.
• Non-equilibrium sublimation simulations reveal a size threshold correlating with the transition between regimes.

Conclusions:

• Three independent criteria (energetic, structural, non-equilibrium) consistently identify a universal size threshold.
• This threshold separates nanoparticle and cluster behaviors, governed by local potential energy.
• Findings emphasize treating clusters as finite systems dominated by surface atoms and interactions.