Atomic Diffusion, Configuration Evolution And Dielectric Pulsed Deposition Of Cu (100) Surface

To investigate the microscopic dynamics associated with the early deposition process of Cu films on Cu (100) surface, this dissertation has focused on the diffusion of Cu adatoms, the evolution of Cu atomic islands and the pulsed deposition of Cu thin films on Cu(100) substrate surface through computational simulation.A supercell which consists of4×4×5Cu atoms with periodic boundary conditions is constructed to approximate Cu(100) substrate surface. On the basis of calculations of energy barriers for active adatoms hopping in various configurations, a novel method for classifying configurations on Cu(100) surface is conceived and the impacts of other atoms on the active adatom are analyzed, including breaking or forming a Cu-Cu bond, its corresponding type and the ledge lying in the diffusion path. A regression is also carried out to analyze energy barriers of all the subcategories. Simulations and calculations show that the novel method is concise and intuitional and can distinguish different impacts of atoms on the energy barriers of the active adatom.The impacts of electronic and elastic relaxations on the energy of supercell are studied and calculations show that more impacts could be attributed to electronic relaxation. Displacements of atoms from perfect crystal lattice are analyzed by considering the relaxation of a typical0-0configuration and results show that the displacement of an atom is relevant to its distance to the active adatom. The nearer the atom is to the active adatom, the larger displacement it would be.Evolution and stability analysis of various configurations at300K displays that even though all atoms with coordination number less than four can diffuse, however, only those type with larger probability to diffuse can happen. Those diffusion types control the evolved configuratons. Analysis of evolution also shows that the active Cu adatom is more possible to hop to high-coordinated sites and triangle trimers and compact tetramers are very stable at300K.Several configurations of atomic islands with their sizes range between2and30are constructed to simulate Cu atomic island diffusion on a Cu(100) surface with10000x10000sites. Diffusion coefficients and other diffusion parameters are calculated with the temperature ranges between300K and600K. It is found that for those islands with the same atom number, evolved configurations are almost independent on their initial configurations. Diffusion coefficients lie in the same order of magnitude and logarithmic diffusion coefficients don’t vary too much from each other. In general, smaller atomic islands diffuse more easily and have larger diffusion coefficients, however, diffusion coefficients don’t decrease monotonously as the atom number increases when the temperatures are relatively higher. For a specific atomic island, diffusion coefficients and variations of the mass center of the island increase as the temperature increases.It is also found that when temperatures are relatively low, evolved configurations of atomic islands containing more than three atoms would always be compact even though their initial configurations vary too much. However, evolved configurations would not be the same if temperatures increase and atomic island is likely to dissociate as temperatures are higher. The higher the temperatures are, the larger probability for the atomic island to dissociate is. When the atom number increases to a specific number, diffusion coefficient would be stable.Diffusion process of two-dimensional pulsed deposition of Cu thin films on a100×100Cu(100) substrate surface with different temperatures and intensities are simulated. Simulation of a single pulsed deposition of100Cu atoms illustrates that adatoms’ number would decrease sharply in a short time interval immediately after the deposition and Cu atoms would diffuse quickly to attach to each other to form an atomic island. An island could diffuse to other locations to coalesce with other atomic islands to form a larger one, which would result in reduction of the island number. However, larger islands diffuse slowly and take more time to diffuse to other locations. What’s more, larger island may evolve to other configurations or get smaller as atoms on the edge dissociate from the island.For simulations of multiple pulsed depositions, the diffusion process varies depending on different conditions. When deposition intensity increases, island size would increase and the island number decreases sharply immediately after deposition. The mean island size increases as the temperature increases. If the temperature is relatively lower, diffusibility for the atom would be very low and can form island only if the neighboring sits have atoms. As temperature increases, atoms could diffuse to further places and attach to other atoms to form an island. When the coverage increases, a few larger islands may form.By conducting calculations of the energy barriers, analysis of configuration evolution, simulation of atomic island diffusion and pulsed deposition of Cu thin films on Cu(100) surface, it is helpful to understand the kinetics in the initial deposition stage and predict the images of thin films and could also provide suggestions to optimize the deposition conditions.