Effects of ordered islands on surface resistivity: Ni on Au(111)

Abstract

The change in surface resistivity due to the formation of nickel islands on gold(111) was studied by measuring the resistance of a thin film of Au as a function of Ni coverage, θ. Previous studies showed that the Au(111) herringbone reconstruction provides a template for the periodic growth of ordered islands. Ni islands grow radially until θ ≈ 0.3 ML, after which subsequent Ni atoms contribute primarily to a second layer. Since Ni atoms on Au(111) grow in ordered nanoclusters, a nonlinear dependence of resistance on θ might be anticipated. Our results, however, show a linear dependence for Ni atoms in the first layer, as if they were independent point scatterers. Above θ ≈ 0.3 ML, there is little change in resistivity, which we attribute to Ni atoms in the second layer making no significant contribution to the resistivity. Although we did not directly image the islands, our results are consistent with the growth model and structures previously observed with scanning tunneling microscopy. Our results serve as an indirect probe of the growth kinetics of this system, as well as determining the contributions of Ni islands to the surface resistivity of the Au film.

CO adsorption on nanoislands: Ni on Au(111)

“…In our study of Ni islands, we found ρ s to increase linearly with the Ni coverage θ Ni , until a transition coverage, above which additional Ni atoms contributed very little to surface resistivity. 26 The transition point where ρ s plateaued corresponded closely with the transition point (approximately 0.3 ML) where second layer Ni begins forming, according to STM studies. We concluded that Ni atoms in the first layer contribute evenly to ρ s , while second layer Ni makes little to no contribution to ρ s .…”

“…The Ni island on Au(111) systems has been of interest in a variety of studies. 13,[21][22][23][24][25][26] When cleaned and annealed, the Au(111) surface configures into the herringbone reconstruction, [27][28][29] shown schematically in Fig. 1(a) and described in more detail in Ref.…”

“…1(a) and described in more detail in Ref. 26. Chambliss et al used scanning tunneling microscopy (STM) to study the behavior of Ni deposited onto herringbone-reconstructed Au(111) and found that for low Ni coverages, Ni grew in an ordered array of single-layer nanometer-scale Ni islands.…”

“…22 Cullen and First also observed structure within the islands deposited at room temperature (RT) and suggested that the structure is due to intermixing of Ni and Au atoms, with intermixing increasing as deposition and annealing temperatures rise above 400 K. 30 Previously, we studied changes in surface resistivity ρ s , of the Au(111) substrate due to the growth of the Ni islands. 26 Adsorbate-induced surface resistivity is known to be a firstlayer effect [31][32][33][34] and therefore can serve as an indirect probe of surface morphology. In our study of Ni islands, we found ρ s to increase linearly with the Ni coverage θ Ni , until a transition coverage, above which additional Ni atoms contributed very little to surface resistivity.…”

“…We concluded that Ni atoms in the first layer contribute evenly to ρ s , while second layer Ni makes little to no contribution to ρ s . 26 In the present experiment, we also monitored surface resistivity during Ni deposition and during CO exposure as a probe of adsorption behavior. Previous studies of CO on pure Ni measured an increase in ρ s .…”