Hydrolysis at $\mathrm{Mg}\mathrm{O}\left(100\right)∕\mathrm{Ag}\left(100\right)$ oxide-metal interfaces studied by $\mathrm{O}1s$ x-ray photoelectron and Mg $K{L}_{23}{L}_{23}$ Auger spectroscopy

Using $\mathrm{O}1s$ x-ray photoelectron and Mg $K{L}_{23}{L}_{23}$ Auger spectroscopy, we demonstrate that monolayer $\mathrm{Mg}\mathrm{O}\left(100\right)∕\mathrm{Ag}\left(100\right)$ exposed at $300\mathrm{K}$ to ${\mathrm{H}}_2\mathrm{O}$ vapor pressure of ${10}^{-8}\text{Torr}$ is strongly hydrated up to 0.8 ${\mathrm{H}}_2\mathrm{O}$ per MgO formula unit, half of the water molecules being dissociatively adsorbed at the fourfold coordinated surface oxide sites. These dramatic hydrolysis and molecular adsorption phenomena are strikingly different from those observed at perfect bulklike MgO(100) surfaces, and provide strong experimental support to the concept of unprecedented interactions and properties at oxide-metal interfaces.

Figure 1

(Color online) $\mathrm{O}1s$ from 0.8 ML $\mathrm{Mg}\mathrm{O}\left(100\right)∕\mathrm{Ag}\left(100\right)$ film: as grown (blue), $30\min$ (black) and $50\min$ (red) after growth. Time dependent effects are negligible on time scale of about $30\min$.

Figure 2

(Color online) (a) As measured $\mathrm{Ag}3d$ reference in $\mathrm{Ag}3d-\mathrm{O}1s-\mathrm{Ag}3d$ repeated sequences. [(b) and (c)] $\mathrm{O}1s$ of clean (dash) and ${\mathrm{H}}_2\mathrm{O}$ saturated (dots) 0.2 and 0.8 ML $\mathrm{Mg}\mathrm{O}\left(100\right)∕\mathrm{Ag}\left(100\right)$ at $\theta =67°$; data fit (yellow) by Gaussian deconvolution (red, blue, and green). (d) Experiment as in (c) repeated at $\theta =0°$.

Figure 3

(Color online) (a) $\mathrm{O}1s$ of 0.8 ML $\mathrm{Mg}\mathrm{O}\left(100\right)∕\mathrm{Ag}\left(100\right)$ at different ${\mathrm{H}}_2\mathrm{O}$ doses. (b) ${\mathrm{H}}_2\mathrm{O}$ dose dependence of $\Delta I_{TG}$ and $\delta I_{\mathrm{O}}$ (right scale), and $I_S∕I_{\mathrm{O}}$ (left scale), from several 0.8 ML samples.

Figure 4

(Color online) (a) and (b) Mg $K{L}_{23}{L}_{23}$ of 0.2 and 0.8 ML $\mathrm{Mg}\mathrm{O}\left(100\right)∕\mathrm{Ag}\left(100\right)$ at selected ${\mathrm{H}}_2\mathrm{O}$ doses. (c) and (d) Dose dependent Mg $K{L}_{23}{L}_{23}$ FWHM from several 0.2 and 0.8 ML samples (color markers, left); FWHM of $\mathrm{Ag}3d$ reference (black circles, right) recorded together with the Mg $K{L}_{23}{L}_{23}$ of 0.8 ML, showing the spectrometer energy stability.

Figure 5

(Color online) [(a) and (b)] $\mathrm{O}1s$ of ${\mathrm{H}}_2\mathrm{O}$ saturated 0.2 and 0.8 ML at $\theta =0°$ (red) and $\theta =77°$ (blue). (c) $I_S∕I_{\mathrm{O}}$ versus $\theta$ for saturated 0.2 ML (triangles) and 0.8 ML (circles); fit (violet, green) by Eq. (1). Brown: calculated values for $2.5–2.7\mathrm{eV}$ satellite arising from Ag subsurface.