Molecular dynamics (MD) simulations provide a powerful computational approach to investigate nanomaterial synthesis at the atomic scale, offering insights into dynamic processes that are challenging to observe experimentally. This article focuses on MD modeling of vapor deposition and colloidal growth mechanisms, emphasizing substrate interactions, diffusion-limited aggregation, and oriented attachment. The discussion includes temperature and precursor concentration effects on morphology, with examples from nanowire and 2D material growth.

Vapor deposition processes, such as chemical vapor deposition (CVD), involve the adsorption and reaction of precursor molecules on a substrate, followed by nucleation and growth. MD simulations capture these processes by modeling atomic interactions using empirical potentials or reactive force fields. Substrate interactions play a critical role in determining the growth mode—whether it follows a layer-by-layer (Frank-van der Merwe), island-forming (Volmer-Weber), or mixed (Stranski-Krastanov) mechanism. For instance, in graphene growth on copper substrates, simulations reveal that carbon adatoms exhibit higher mobility on Cu(111) surfaces compared to Cu(100), leading to differences in nucleation density and domain size. The binding energy between adatoms and the substrate, typically ranging from 0.5 to 2.0 eV depending on the material system, influences the critical nucleus size and growth kinetics.

Diffusion-limited aggregation (DLA) is a key mechanism in colloidal growth and vapor-phase synthesis, where particle morphology depends on the balance between adatom diffusion and attachment rates. MD simulations of gold nanoparticle growth show that low precursor concentrations favor fractal structures due to limited adatom availability, while higher concentrations promote compact morphologies. Temperature modulates diffusion coefficients, following an Arrhenius relationship with activation energies between 0.1 and 0.5 eV for most metallic systems. For example, in nanowire growth, temperatures above 500 K enhance surface diffusion, enabling the formation of elongated structures via atomic attachment at kink sites.

Oriented attachment (OA) is another growth mechanism observed in nanocrystals, where primary particles align crystallographically before merging to form larger structures. MD simulations of TiO2 nanoparticles demonstrate that OA occurs when particles approach within 1–2 nm, with misorientation angles below 15 degrees enabling coherent attachment. The process is driven by a reduction in surface energy, often exceeding 1 J/m² for high-energy facets. In CdSe nanowire growth, OA leads to single-crystalline structures despite initial polycrystalline aggregation, as simulated by tracking the reorientation dynamics of adjacent nanoparticles.

Temperature effects on morphology are particularly evident in 2D material synthesis. MD studies of MoS2 growth reveal that temperatures below 800 K result in incomplete sulfurization and defective layers, while optimal growth occurs between 900–1100 K, where precursor decomposition and adatom mobility are balanced. Excess precursor concentrations at these temperatures can lead to multilayer formation, with simulations showing a transition from monolayer to bilayer growth at precursor partial pressures above 10⁻³ atm.

Colloidal growth simulations highlight the role of ligand stabilization in shaping nanoparticles. For example, MD models of platinum nanoparticle synthesis in oleylamine demonstrate that ligand coverage above 50% suppresses uncontrolled aggregation, yielding monodisperse particles. The ligand binding strength, typically 0.3–0.8 eV, determines the equilibrium particle size, with stronger ligands favoring smaller diameters due to increased surface stabilization.

In nanowire growth, MD simulations of vapor-liquid-solid (VLS) mechanisms reveal how catalyst composition affects morphology. For silicon nanowires grown using gold catalysts, the eutectic alloy composition (19% Si at 363°C) governs the liquid droplet size and, consequently, the nanowire diameter. Deviations from this composition, as modeled by varying the Si/Au ratio, lead to diameter fluctuations or kinking. Similarly, in colloidal nanowire synthesis, the aspect ratio is controlled by the precursor-to-ligand ratio, with simulations showing a linear increase in length for ratios up to 1:1, beyond which branching occurs.

Substrate lattice mismatch also influences nanomaterial growth, as seen in MD studies of GaN nanowires on sapphire. A mismatch of 16% induces strain, but simulations show that nanowires adopt a tilted growth mode to minimize dislocation formation. The tilt angle, calculated to be 5–10 degrees, matches experimental observations, validating the model’s predictive capability.

Precursor dissociation kinetics are another critical factor. In MD simulations of ZnO growth from zinc acetate, the dissociation barrier of 1.2 eV correlates with experimental decomposition temperatures around 300°C. Faster dissociation at higher temperatures increases the zinc adatom population, promoting vertical growth of nanorods. Conversely, low temperatures favor lateral growth due to slower adatom generation.

The solvent environment in colloidal synthesis also affects growth pathways. MD models of CdSe quantum dot formation in octadecene show that solvent viscosity above 3 cP suppresses Brownian motion, reducing collision frequencies and yielding smaller particles. The solvent-nanoparticle interaction energy, typically 0.1–0.3 eV, further modulates growth rates by altering the desorption energy of monomers.

In summary, MD simulations elucidate atomic-scale processes in nanomaterial synthesis, linking experimental conditions to morphological outcomes. By quantifying energy barriers, diffusion rates, and interfacial interactions, these models enable predictive design of nanomaterials with tailored properties. Future advancements in computational power and force field accuracy will further enhance the resolution and predictive capability of such simulations.