The growth of thin NiO films on Ag(001) studied by scanning tunneling microscopy and spectroscopy

Abstract

We have used scanning tunneling microscopy and spectroscopy to study the growth of NiO films on Ag(001) at a coverage of 1.5 monolayers. The films have been obtained by reactive deposition of Ni in O-2 atmosphere. Particular attention has been paid to the development of the growth morphology of the deposit as a function of substrate and annealing temperature. For room temperature deposition, the Ag(001) surface is completely covered with the (2 x 1) NiO precursor structure with a thickness of one monolayer and small double-layer NiO islands. The Ag(001) substrate surface is nearly unaffected. Subsequent annealing leads to drastic changes of the morphology of the film. The (2 x 1) precursor structure gradually disappears with annealing time and transforms to double-layer NiO islands. One part of these NiO islands is embedded in the initially flat Ag substrate, and additional Ag islands appear on the surface. Local I/U characteristics (1: tunneling current, U: tunneling bias) have been measured on each kind of island and we found characteristic differences for the various parts of the surface, e.g. for Ag, the (2 x 1) precursor, double-layer and trilayer NiO. These differences can be used to directly map the individual species on the surface

Metamorphosis of ultrathin Ni oxide nanostructures on Ag(100)

“…Well-defined rectangular island shapes with polar island boundaries (i.e., rows of either Ni or O atoms) have been reported for annealing at 450 K in the absence of O 2 . 6,8 In contrast, Caffio et al have observed more roundish island shapes upon annealing at 500 K in vacuum and have ascribed the occurrence of the geometric island shapes to oxygen-rich annealing conditions. 7 In either case, however, the stoichiometry of the film appears to remain the same.…”

“…[6][7][8] For submonolayer coverages, a NiO p(2 × 1) precursor phase forms upon deposition. The (2 × 1) phase is of monoatomic thickness and gradually covers the surface upon increasing the surface coverage.…”

Positron-electron pairs emitted from metallic and oxide surfaces

“…For the deposition of metal films e-beam evaporators were available. The preparation of NiO films on a Ag(100) substrate is well documented [22][23][24][25][26][27]. The Ni evaporation was performed in an O 2 atmosphere of 10 −7 mbar.…”

Initial stages of nickel oxide growth on Ag(001) by pulsed laser deposition

“…For both cases, the oxides islands could be imaged as protrusions only at high V sample , which indi- cates the insulating nature of those islands. Großer et al 46 observed that the STM of 3-ML-thick NiO islands undergoes contrast reversal between two images obtained at V sample = 2.5 and 1 V. They also observed that 2-ML-thick NiO islands show contrast reversal between two V sample 's, although the contrast change is much less than those shown from the 3-ML-thick NiO islands.…”

“…This indicates to the possibility of the some NiO layer͑s͒ embedded in Ag substrate, as also reported by many groups. 22,23,46 Therefore, we propose that the regions of 0.22 nm height in Fig. 3͑e͒ should be the NiO layers thicker than 2 ML.…”