Enhanced Reactivity at Metal−Oxide Interface:  Water Interaction with MgO Ultrathin Films

Abstract

The interest in thin and ultrathin oxide films is increasing rapidly due to the new properties and the many possible technological applications of such materials. In this frame the interaction with water, a major constituent of our atmosphere, is an essential issue for a better characterization of oxide film-based devices. We report here a detailed high-resolution electron energy loss spectroscopy and X-ray photoelectron spectroscopy study of the reactivity of ultrathin MgO films grown on Ag(100) toward H 2 O. We find that only OH groups are detected at 310 K, while at low temperature molecular adsorption prevails. In the former case we observe a strongly enhanced dissociation probability for monolayer and submonolayer MgO films, indicative of an active role of the Ag substrate in the dissociation process. The active sites are suggested to be low-coordinated ions at the border of monolayer MgO islands. Aging phenomena, previously observed on MgO ultrathin films, 1 have been confirmed. Although their origin could not be definitively determined, our data strongly suggest water adsorption not to be the major cause of this process.

Controlling water dissociation on an ultrathin MgO film by tuning film thickness

“…[3][4][5][6] Compared with the MgO bulk surface, the chemical activity of water dissociation is remarkably enhanced on a single monolayer ͑ML͒ MgO film deposited on a Ag͑100͒ surface. [7][8][9][10] In studies using highresolution electron energy loss spectroscopy combined with x-ray photoemission spectroscopy, Savio et al reported that the dissociation probability of water at room temperature on the 1-ML MgO film surface increases by a factor of 6 compared with a multilayer film. 7,8 They suggest that this remarkable enhancement in chemical reactivity originates in the border sites of the 1-ML oxide film in contact with a metal substrate.…”

“…12,13 Although experimental studies so far have definitely demonstrated the superiority of ultrathin MgO film over bulk MgO for water dissociation, such details as the phenomenon's dependence on film thickness and the contribution of defect-free terrace sites as venues for chemical activity have not been clarified and demand systematic study. [7][8][9][10] In particular, Shin et al have demonstrated that the tunneling electron-induced dissociation of isolated water molecules on MgO film surfaces can be controlled depending on the film thickness.…”

“…12,13 Although experimental studies so far have definitely demonstrated the superiority of ultrathin MgO film over bulk MgO for water dissociation, such details as the phenomenon's dependence on film thickness and the contribution of defect-free terrace sites as venues for chemical activity have not been clarified and demand systematic study. [7][8][9][10] In particular, Shin et al have demonstrated that the tunneling electron-induced dissociation of isolated water molecules on MgO film surfaces can be controlled depending on the film thickness.14 This indicates that film thickness, as a controllable factor, can play an important role in determining various features of oxide films, such as catalytic and dielectric properties. 15,16 In this study, using first-principles calculations, we examine how chemical activity on an ultrathin MgO film on the Ag͑100͒ surface can be tuned by controlling film thickness.…”

Surface reactivity enhancement by O2 dissociation on a single-layer MgO film deposited on metal substrate

“…MgO(100) is one of the typical insulating surfaces, and it is usually inactive in surface reactions. For the past few years, metal-supported ultrathin MgO films have been extensively studied [7][8][9][10][11][12][13][14] due to their promising applications in surface chemistry and photocatalysis. The interaction between insulating oxide films with metal substrates may result in the enhancement of chemical reactivity.…”

Tailoring oxide properties: An impact on adsorption characteristics of molecules and metals

“…Among the calculated barriers, the rate determining step is the dissociation of the molecular oxygen, which is suggested to correspond to the [155][156][157] , where the active site was proposed to be at the metal-oxide interface. This was further supported by the DFT study of the system 158 .…”