Investigation of surface segregation in Ni/Cu/Si(100) nanometer layer during deposition and heat treatment of ultra thin Ni deposit

Surface segregation, whereby one species tend to preferentially move to free surface, is a hindrance phenomenon in obtaining sharp interfaces in nanometer multilayer. In this work, we studied Cu surface segregation during Ni deposition onto Cu substrate by electron beam evaporation in ultra high vacuum (UHV) and also during heat treatment. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and Atomic Force Microscopy (AFM) were used to study the surface in nanometer scale. XPS analysis revealed that the accumulated Cu is uniform over the surface with thickness of one monolayer. By increasing the thickness of Ni deposit, surface segregation decreased and was prevented in thickness of higher than 4 nm. Linear increase of the accumulated Cu was observed by in-situ measurements during heat treatment which is different behavior from micrometer layers. However, when the first accumulated Cu monolayer was completed, the rate of segregation was reduced. In addition, surface energy and surface concentration were computed by measurement of contact angle. Surface energy measurements showed that as the thickness of Ni decreased, surface energy reduced down to the surface energy of Cu.