Defect Mediated Thin Film Growth

Arizona State University, Scottsdale AZ

Investigators

Abstract

0090079 Sieradzki New approaches are employed to electrodeposit atomically flat heteroepitaxial overlayers of quality similar to that obtained by ultra high vacuum techniques at elevated temperature. An important issue covered in this grant is the generality of these new electrodeposition techniques. A number of heteroepitaxial metal/metal and metal/semiconductor systems are examined to address issues related to substrate orientation and electrolyte composition. A sensitive in situ stress monitoring technique is employed to study stress relaxation during growth. Using data from in situ measurements of stress evolution, important thermodynamic parameters are determined such as interface stresses that characterize overlayer/substrate systems. A special high speed (25 images per second with image sizes of at 300 x 300 pixels) scanning tunneling microscope (STM) is used to investigate details of the atomic scale kinetic processes that allow defect and surfactant mediate growth to operate. Theoretical work uses Kinetic Monte Carlo (KMC) techniques that incorporate elastic interactions to model growth and the defect-surfactant mediated growth. The results obtained from harmonic and atomic models and experimental kinetic results (high speed STM) are integrated into the KMC modeling. The role of elastic interactions in determining the evolution of superstructures during metal/metal adsorption processes is examined. The lateral interaction energies of adatoms in superstructures are accurately extracted from experimental adsorption isotherms using Monte Carlo techniques. These results are compared to elastic models of superstructures in order to determine whether the experimentally determined magnitudes of lateral interaction energies are consistent with elastic interactions. %%% This work could lead to new approaches of electrodeposition that produce atomically flat heteroepitaxial overlayers of quality similar to that obtained by ultra high vacuum techniques at elevated temperature. In one approach the metal of interest is co-deposited with a reversibly deposited mediator metal. The mediator is periodically deposited and stripped from the surface and each cycle creates new nuclei leading to layer-by layer growth. In another approach, a prescribed fraction of a monolayer of surfactant is used that floats on the surface of the depositing metal. The surfactant promotes an interlayer terrace exchange of the depositing metal that minimizes intralayer adatom diffusion. This serves to significantly increase the nucleation density of the adlayer, leading to flat two-dimensional growth. ***