| AVS 56th International Symposium & Exhibition | |
| Surface Science | Wednesday Sessions |
| Session SS1-WeM |
| Session: | Water/Surface Interactions & Environmental Chemistry I |
| Presenter: | K. Thürmer, Sandia National Laboratories |
| Authors: | K. Thürmer, Sandia National Laboratories S. Nie, Sandia National Laboratories N.C. Bartelt, Sandia National Laboratories |
| Correspondent: | Click to Email |
Although extensive research has been aimed at the structure of ice films [1], important details of the morphology evolution, especially for films in the nm-thickness range, have remained elusive. Our capability to image up to 30 molecular layers of ice with STM [2], enables us to track the film evolution during growth and annealing. In particular, we investigate the role of new-layer nucleation and surface self-diffusion.
As reported before by others, we observe that water deposited onto Pt(111) below 120K forms amorphous films, whereas metastable cubic ice appears between 120K and ~150K. At 140K and a mean film thickness of ~1nm the film consists of 2-3 nm high crystallites, embedded in a one bilayer high wetting layer. Analyzing the annealing behavior of these crystallites we find [3] that the rate at which new layers nucleate, and not surface diffusion, determines how fast individual crystallites equilibrate. The resistance to nucleate new layers even during deposition has a surprising effect on thicker films: The deposited water attaches preferentially to growth spirals around screw dislocations, promoting the formation of metastable cubic ice [2].
Finally, we report the first measurements of surface self-diffusion on ice. Using uniform 5-nm-thick ice films (grown at 145K) as templates, we deposited a fraction of a monolayer of water at 115K to create metastable arrays of 2D-islands. By quantifying the Ostwald ripening of these arrays upon annealing between 115 and 135 K, we extract temperature-dependent diffusion rates and determine the activation energy for surface self-diffusion to be (0.4+-0.1) eV [4].
[1] A. Verdaguer, G. M. Sacha, H. Bluhm, and M. Salmeron, Chem. Rev. 106, 1478 (2006).
[2] K. Thürmer and N. C. Bartelt, Phys. Rev. B 77, 195425 (2008).
[3] K. Thürmer and N. C. Bartelt, Phys. Rev. Lett. 100, 186101 (2008).
[4] S. Nie, N. C. Bartelt, and K. Thürmer, Phys. Rev. Lett. 102, 136101 (2009).