open access

https://hdl.handle.net/2115/45419

Elementary steps at the surface of ice crystals visualized by advanced optical microscopy

英語

spiral growth

2010-11-16

National Academy of Sciences

Proceedings of the National Academy of Sciences of the United States of America

107(46)

19702-19707

Due to the abundance of ice on earth, the phase transition of ice plays crucially important roles in various phenomena in nature. Hence, the molecular-level understanding of ice crystal surfaces holds the key to unlocking the secrets of a number of fields. In this study we demonstrate, by laser confocal microscopy combined with differential interference contrast microscopy, that elementary steps (the growing ends of ubiquitous molecular layers with the minimum height) of ice crystals and their dynamic behavior can be visualized directly at air-ice interfaces. We observed the appearance and lateral growth of two-dimensional (2D) islands on ice crystal surfaces. When the steps of neighboring 2D islands coalesced, the contrast of the steps always disappeared completely. We were able to discount the occurrence of steps too small to detect directly because we never observed the associated phenomena that would indicate their presence. In addition, classical 2D nucleation theory does not support the appearance of multi-layered 2D islands. Hence, we concluded that 2D islands with elementary height (0.37 and 0.39 nm on basal and prism faces, respectively) were visualized by our optical microscopy. On basal and prism faces, we also observed the spiral growth steps generated by screw dislocations. The distance between adjacent spiral steps on a prism face was about 1/20 of that on a basal face. Hence, the step ledge energy of a prism face was 1/20 of that on a basal face, in accord with the known lower-temperature roughening transition of the prism face.

学術雑誌論文

Accepted Manuscript

0027-8424