期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 110, 期 29, 页码 11757-11762出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1303001110
关键词
ice growth mechanisms; molecular surface steps; molecular-layer nucleation; scanning probe microscopy; spiral growth
资金
- Office of Basic Energy Sciences, Division of Materials Sciences, US Department of Energy (DOE) [DEAC04-94AL85000]
- Laboratory Directed Research and Development Program at Sandia National Laboratories
- US DOE's National Nuclear Security Administration [DE-AC04-94AL85000]
From our daily life we are familiar with hexagonal ice, but at very low temperature ice can exist in a different structure-that of cubic ice. Seeking to unravel the enigmatic relationship between these two low-pressure phases, we examined their formation on a Pt (111) substrate at low temperatures with scanning tunneling microscopy and atomic force microscopy. After completion of the one-molecule-thick wetting layer, 3D clusters of hexagonal ice grow via layer nucleation. The coalescence of these clusters creates a rich scenario of domain-boundary and screw-dislocation formation. We discovered that during subsequent growth, domain boundaries are replaced by growth spirals around screw dislocations, and that the nature of these spirals determines whether ice adopts the cubic or the hexagonal structure. Initially, most of these spirals are single, i.e., they host a screw dislocation with a Burgers vector connecting neighboring molecular planes, and produce cubic ice. Films thicker than similar to 20 nm, however, are dominated by double spirals. Their abundance is surprising because they require a Burgers vector spanning two molecular-layer spacings, distorting the crystal lattice to a larger extent. We propose that these double spirals grow at the expense of the initially more common single spirals for an energetic reason: they produce hexagonal ice.
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