Time-of-flight secondary ion mass spectroscopy analysis of Na adatoms interacting with water-ice film.
The origins of a slow reaction rate between the sodium adatoms and the water-ice film have been investigated by analyzing the surface composition using time-of-flight secondary ion mass spectroscopy in the temperature range of 13-230 K. An unhydrated NaOH layer is formed at the water-Na interface at 13 K which is followed by the growth of the metallic Na layer, whereas domains of both NaOH and unreacted Na are created only in the multilayer regime at 100 K. The NaOH layer plays a role as a separator between the water and Na layers, and its poor solubility in water is responsible for the small reaction rate of Na on glassy water. The solubility of NaOH in the deeply supercooled liquid water is low as well, but the mobile water molecules diffusing to the surface react with the Na adatoms, thereby quenching the growth of the metallic Na overlayer.
Souda
Ryutaro
R
Nanoscale Materials Center, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan. souda.ryutaro@nims.go.jp