Tatarkhanov M, Fomin E, Salmeron M, Andersson K, Ogasawara H, Pettersson L G M, Nilsson A, Cerdá J I
Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
J Chem Phys. 2008 Oct 21;129(15):154109. doi: 10.1063/1.2988903.
Scanning tunneling microscopy (STM) and x-ray absorption spectroscopy (XAS) have been used to study the structures produced by water on Ru(0001) at temperatures above 140 K. It was found that while undissociated water layers are metastable below 140 K, heating above this temperature produces drastic transformations, whereby a fraction of the water molecules partially dissociate and form mixed H(2)O-OH structures. X-ray photoelectron spectroscopy and XAS revealed the presence of hydroxyl groups with their O-H bond essentially parallel to the surface. STM images show that the mixed H(2)O-OH structures consist of long narrow stripes aligned with the three crystallographic directions perpendicular to the close-packed atomic rows of the Ru(0001) substrate. The internal structure of the stripes is a honeycomb network of H-bonded water and hydroxyl species. We found that the metastable low temperature molecular phase can also be converted to a mixed H(2)O-OH phase through excitation by the tunneling electrons when their energy is 0.5 eV or higher above the Fermi level. Structural models based on the STM images were used for density functional theory optimizations of the stripe geometry. The optimized geometry was then utilized to calculate STM images for comparison with the experiment.
扫描隧道显微镜（STM）和X射线吸收光谱（XAS）已被用于研究温度高于140K时水在Ru(0001)上形成的结构。研究发现，未解离的水层在140K以下是亚稳的，而加热到该温度以上会产生剧烈转变，部分水分子会发生部分解离并形成混合的H₂O-OH结构。X射线光电子能谱和XAS揭示了羟基的存在，其O-H键基本平行于表面。STM图像显示，混合的H₂O-OH结构由与垂直于Ru(0001)衬底密排原子列的三个晶体学方向对齐的狭长条纹组成。条纹的内部结构是由氢键连接的水和羟基物种构成的蜂窝状网络。我们发现，当隧穿电子的能量高于费米能级0.5eV或更高时，亚稳的低温分子相也可以通过隧穿电子的激发转化为混合的H₂O-OH相。基于STM图像的结构模型被用于对条纹几何结构进行密度泛函理论优化。然后利用优化后的几何结构计算STM图像，以便与实验进行比较。
