Comment on ‘ ‘ Ag organisation on Ni ( 1 1 1 ) surface ” [ Surface Science 602 ( 2008 ) 2363 ]

In a recent paper [1], Chambon et al. have reported on the early growth stages of Ag on the Ni(1 1 1) surface by means of scanning tunneling microscopy (STM). The authors have concluded that Ag on Ni(1 1 1) (at 300–625 K) forms mostly bilayer islands, even for a low coverage of 0.1 monolayer (ML). The interpretation of Chambon et al. is based on the assumption that the first atomic layer of Ag on Ni(1 1 1) is imaged with a very low apparent height of 1 Å [1], compared to the separation of the Ag(1 1 1) planes in the bulk crystal structure which is 2.36 Å. In the present Comment we will demonstrate that this assumption is not consistent with the STM images of the authors reported in Ref. [1], nor with our own STM investigations of the early growth of Ag on Ni(1 1 1). We will show that 1 ML thick Ag islands form on Ni(1 1 1) in the submonolayer regime due to the high Ag mobility on the surface above room temperature. This Ag growth mode is well explained by Bauer’s criterion [2] and the difference in surface energy between Ag(1 1 1) and Ni(1 1 1). The experiments discussed in the following were performed in ultrahigh vacuum with a low-temperature STM system from Omicron [3] operated at 77 K. The STM images were recorded in the constant-current mode (with the stated voltage referring to the electric potential of the sample with respect to the tip), and they have been processed with the WSxM software [4]. The clean Ni(1 1 1) single crystal surface was prepared by several cycles of room temperature Ar-ion sputtering followed by annealing at 1000 K. Surface crystallographic order and absence of surface