Fig. 5
The c(2 × 6) and (1 × 3) OH overlayer. a STM image of 0.5 L water dosed at 110 K and subsequently annealed for 1 h at room temperature. The (OH)ads along [010] are not perfectly straight but slightly undulate (marked by lines to guide the eye). STM parameters: T sample = 78 K, V sample = −0.4 V, I tunnel = 0.2 nA; fast scan direction is 18° clockwise from horizontal. b Fourier transform of the STM image in panel a. The grid shows the primitive unit cell of the OH overlayer; the circles mark the substrate spots. The overlayer exhibits a c(2 × 6) periodicity corresponding to a coverage of 0.58 ML (7/6 H2O per unit cell). c STM image after exposing the c(2 × 6) OH overlayer to 0.15 L at 100 K and annealing at room temperature for 1 h. The surface is covered by domains of a (1 × 3) OH overlayer (solid box) as well as a mixture of bright-dark features (dashed box) and water monomers STM parameters: T sample = 78 K, V sample = −0.8 V, I tunnel = 0.1 nA; fast scan direction is 18.5° clockwise from horizontal. d DFT model and TH simulation of the (1 × 3) OH overlayer, corresponding to 0.67 ML. Along [010] pairs of dissociated water in the most favorable configurations are formed, i.e., B1O1 and B2O2 (shown here), or B2O2 and B1O1, with one unoccupied bridge site between them. The box marks the superstructure cell, which spans three substrate unit cells in [010] direction. All scale bars correspond to 3 nm
