ROOM-TEMPERATURE REACTION OF THIN NI FILMS WITH AL(110) SURFACES

We report the results of high-energy ion backscattering and channeling (HEIS) experiments together with x-ray photoemission spectroscopy (XPS) to determine the interface structure for thin Ni films deposited on Al(110) single crystal surfaces at room temperature. Measurements of the Al and Ni surface peak areas (SPA) show that the Ni atoms do not form a simple overlayer on the Al substrate, but react with and displace Al substrate atoms. The reaction continues with two different rates for a range of Ni coverage from 0 to 8 monolayers (ML) before Ni begins to cover the surface, which differs significantly from the thermally reacted Ni/Al systems. For the first 2.3 monolayers of deposited Ni, the NiAl phase is formed with additional displaced Al atoms at the interface, while for Ni depositions between 2.3 and 8.1 ML, a Ni3Al phase is formed. These phase identifications were made using XPS measurements of the Ni-2p3/2 peak chemical shifts and the shape and separation of the energy loss peak. The reaction at the interface is simulated using the embedded atom method to calculate the interaction between Al and Ni atoms. One ML of Ni atoms was initially distributed in small clusters on the Al surface, and a Monte Carlo approach was used to generate snapshots of the evolving interface. Computer simulations of the HEIS yield from these snapshots show an increase in the SPA of Al in good agreement with our experimental measurements.