Metamorphosis of ultrathin Ni oxide nanostructures on Ag(100)

Abstract

The evolution of the morphology of Ni-oxide nanostructures on Ag(100) as a function of temperature has been followed experimentally by scanning tunneling microscopy (STM) and theoretically by density-functional theory (DFT) calculations. After reactive deposition at room temperature and annealing at 450 K, the NiO(2 × 1) phase embedded into the Ag substrate is formed due to kinetic stabilization during growth. The (2 × 1) structure is replaced by the thermodynamically more stable NiO (100)(1 × 1) phase, also embedded into the Ag substrate, for annealing at T > 500 K. As shown by DFT modeling and in agreement with experimental STM contrast, the formation of second-layer NiO patches below the NiO(1 × 1) monolayer is an effective means of strain relief in the NiO(1 × 1) monolayer islands. For T > 600 K, the increased possibilities of mass transport lead to an intriguing surface morphology called "labyrinth" phase, with narrow high-aspect ratio embedded NiO(1 × 1)-type islands. The latter are stabilized by the interaction of the NiO borders with the Ag(100) substrate via double-layer boundary lines, which according to the DFT calculations provide the essential elements of this thermodynamic ground state.

Surface structure of nickel oxide layers on a Rh(111) surface

“…close to that of the NiO(100) surface (2.95 Å). Since empty states have been probed, we attribute the protrusions in the image to the positions of the Ni ions [37]. The LEED image in Fig.…”

Atomistic and Electronic Structure Methods for Nanostructured Oxide Interfaces

“…Indeed, to compensate the polarity of these borders M atoms prefer to bury in subsurface positions thus rationalizing the experimental observation of dark features at the domain borders, see Fig. 2.8c [125].…”

“…2.8a, b [97,125]. This represents an example of embedded growth, in which the thermodynamically more stable phase is non-polar but presents polar border along certain directions, and this fact kinetically destabilizes its growth while favoring the formation of a higher-energy polar competitor which exhibits non-polar borders.…”

“…Unfortunately, the situation in the field of nanoscale oxide interfaces is such that information is available only in a very limited number of cases. Here we will discuss one of these cases: MnO and NiO mono-layer (ML) phases on Ag(100), which have been investigated via a combined experimental and theoretical investigation [97,125], thus deriving three main points concerning the description of kinetic phenomena (and their interplay with polarity effects).…”

High Resolution STM Imaging

“…Nevertheless, application of nonconventional modes [106] or measurements at elevated temperatures [107] allow atomically resolved imaging of single crystalline surfaces even on insulators. High-resolution STM imaging is also feasible on insulating thin films deposited on metallic substrates [75,[108][109][110][111][112][113]. Figure 15.11a demonstrates an example of high-resolution STM imaging achieved on the diamond surface in a resonant electron injection mode [106].…”