Mixed layer formation on the copper-deposited Ni(110) surface

Abstract

We studied initial Cu overlayer formation on the Ni͑110͒ surface by scanning tunneling microscopy ͑STM͒ in an ultrahigh vacuum. Initially, deposited Cu displaces the top Ni layer, forming two-dimensional Cu-Ni alloy on the substrate. The Cu atom embedded into the top layer was depressed in the STM image. The depression due to the lack of Ni 3d-derived surface local density of states was confirmed by the first-principles calculation. Ni atoms squeezed out from the top substrate layer agglomerated in the anisotropic Ni island along the close-packed ͓110͔ direction. Further Cu deposition resulted in a Cu-Ni mixed island. Quantitative measurement of the Cu fraction on the substrate showed that 0.71Ϯ 0.04 of deposited Cu was embedded in the top Ni layer, whereas significant Cu enrichment was seen on the island.

First Principles Study of Cu-Embedded Ni(110) Surfaces

“…As clearly seen in the top panel of Fig. 5, the Cu LDOS at E F is smaller than that of Ni, which is consistent with scanning tunneling microscopy observations where clear depression was seen at the Cu sites in the topographic images and the calculated charge density maps [2]. The suppression indicates that adjacent Ni atoms do not significantly contribute to Cu LDOS at the Cu site.…”

“…To seek the stable atomic geometries of Cu-embedded Ni(110) surfaces and to study their electronic states in detail, we applied first principles ab initio calculation to these surfaces and found that the embedded Cu atoms occupy remarkably similar sites to those of Ni, but their corrugation is higher than the difference of the atomic radii. By embedding Cu, the local density of states near E F is considerably reduced in agreement with a previous STM study [2]. By augmentation of the hybridization between exchange-split Ni 3d bands and Cu/Ni sp conduction bands, the surface magnetic moments are found to be suppressed in accordance with the Cu coverages.…”

“…Therefore, Cu overlayers on Ni and Cu-Ni alloy surfaces are thought to be energetically stable. However, our recent scanning tunneling microscopy (STM) study [2] showed that, for such relatively open surface structures as the (110) face, deposited Cu displaces surface Ni, and Cu is embedded into the topmost layer rather than forming two-dimensional Cu islands on top of the Ni surface. As a result, even for one monolayer Cu deposition the surface is not fully covered by the Cu overlayer, but the Cu/Ni mixed layers are stabilized.…”