Figure 1

(a) STM image ($180\times 180\AA {}^2$) of a full water monolayer adsorbed at room temperature on the $\mathrm{ZnO}(10\overline{1}0)$ surface. The water layer is comprised of long and narrow regions with three different structures: the half-dissociated monolayer with a clear ($2\times 1$) periodicity (labeled HD), areas that appear to have a ($1\times 1$) periodicity which are assigned as a molecular overlayer (labeled M), and patches with an intermediate structure with ($2\times 1$) periodicity, albeit a weaker corrugation (labeled IM). The three different structures are more clearly displayed in the insets at the top. To the left and right, the structural configurations of the HD and M regions, respectively, are shown together with the simulated STM images. (b) STM image ($42\times 42{\AA }^2$) of the three different structures and the corresponding line profiles, taken at the lines indicated in the image. (c) STM image ($120\times 70{\AA }^2$) showing domains with HD structure that are out of registry by one half of an (overlayer) unit cell in $[1\overline{2}10]$ direction. Domain boundaries (arrows) exhibit a ($2\times 1$)-IM periodicity.Reuse & Permissions

Figure 2

Three consecutive STM images ($210\times 140{\AA }^2$) of the water overlayer on the $\mathrm{ZnO}(10\overline{1}0)$ surface. Arrows mark the same position in the images. Note the change in the appearance of the different regions labeled HD, M, and IM.Reuse & Permissions

Figure 3

Calculated time-averaged STM images of the partially dissociated ($2\times 1$) water monolayer. The graph shows the time evolution of the height above the ZnO surface of the topmost H atom of the undissociated (red) and the dissociated (black) water molecule of a selected water pair during a cpmd simulation. The position of the two H atoms in the STM images are marked with red (left) and black (right) arrows, respectively. STM images were calculated along the trajectory in time steps of 100 fs. At $t=0$ (vertical line) the cleaved water molecule was deliberately recombined by shifting the dissociated H atom back to its OH group. The time-averaged STM images for $t<0$ and $t>0$, respectively, show a transition from a HD to a M appearance.Reuse & Permissions