Nonlattice Substrates Research Articles

SIMULATION FOR RAMIFIED AGGREGATES ON NONLATTICE SUBSTRATES WITH IMPURITIES

A growth mechanism of ramified aggregates on nonlattice substrates with fixed impurities is studied systematically. Based on the experimental observations of Au atomic aggregates on molten glass surfaces, an Improved Restricted Cluster-Cluster Aggregation (IRCCA) model is established. In this model, fixed impurities are distributed randomly on a nonlattice substrate, and all the aggregates with different sizes are allowed to diffuse and rotate. The influence of the liquid substrate and impurity on the structure of the ramified aggregates is studied systematically. The simulation results are in good agreement with the experimental findings.

Distribution of impurities on nonlattice substraes influence for fractal aggregates

According to the experimental observation of Au atomic aggregations on a molten glass surface, we established a computational model to simulate Improved Restricted Cluster-Cluster Aggregation (IRCCA) on nonlattice substrates with regularly and randomly distributed impurities. In the model, the random diffusion step and rigidity rotation around the mass center of cluster were considered. The aggregation process was simulated and the influence of the distribution of impurity on the properties of aggregations was systemically investigated. The results show that regularly distributed impurities play a more important role in restricting the aggregation of clusters than randomly distributed impurities, resulting in a higher number density of fractal aggregates with smaller radius of gyration and fractal dimension.

Studies on a nonequilibrium atomic cluster system with repulsive interactions

A simulation model for diffusion and aggregation of atomic clusters with repulsi ve interactions on nonlattice substrates is established, and the aggregation pro cess of the silver atoms on charged silicone oil surfaces has been studied. It w as found that after the stable atomic clusters form, due to the repulsive intera ction among the clusters, the number density of the atomic clusters decays with time exponentially and the time constant is Oaa; statistically, the relative speed V between two clusters increases linearly with their distance L according to V=HL, where the constant H≈Oaa after deposition and then approaches zero with time. With the increase of the viscosity coefficient o f liquid substrates, the friction force increases and H decreases. A linear relation between the friction force and H is found with the slope k≈0 10±001 We show that the critical radius r11 of the clusters, abo ve which the atomic clusters start to carry charges, is related nearly to the at omic affinity, i.e., the energy needed for the cluster to carry an extra electro n. It is found that H and Oaa increase slowly with r11 and their slopes are 12±03s-1-1μm-1-1 and 16±06s-1-1μm-1-1, respectively. Our simulation results are in agreement w ith the previous experimental findings.

Computer simulation for ramified aggregates on nonlattice substrates with impurities

According to the experimental results of Au atomic aggregaties on molten glass surfaces with impurities, based on the characteristic assumption that clusters diffuse with random diffusion steps and rigid rotation angles, an improved restri cted cluster_cluster aggregation model for nonlattice substrates with impurities is established. Then the whole diffusion，rotation and aggregation processes of the clusters are simulated. The impurities are distributed on the nonlattice su bstrate ramdomly, and its influence on the properties of the ramified aggregates is studied systematically .The simulation data are in good agreement with the e xperimental results.

Formations of fractal islands aggregated with discs in Gaussian distribution on nonlattice substrates

The growth mechanism of fractal islands on a two-dimensional nonlattice substrate with periodic boundary conditions has been investigated by using Monte Carlo technique. Results show that the fractal dimension df of the final ramified islands is almost independent of the diffusion step length, mobility and rigid rotation of the islands. The characteristics of the size distribution of the discs in an island do not change the dimension df of the island. However, we find that df increases linearly with the surface coverage ρ of the system and its slope decreases with the increase of the mean diameter of the discs.

Formation of fractal islands on nonlattice substrates

A Monte Carlo study on the formation of fractal islands on nonlattice substrates is presented. The islands, including disc aggregates and single discs, perform two-dimensional diffusion along four directions with different diffusion step lengths and rigid rotation about their centers of mass on a nonlattice square with periodic boundary conditions. It is found that the fractal dimension of the ramified islands is almost independent of the diffusion step length, rigid rotation angle, and disc size. However, the fractal dimension increases linearly with the surface coverage. Our simulation results are in good agreement with the previous experimental findings of the aggregation of the silver atomic islands on silicone oil surfaces.