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Structural and phase changes in amorphous solid water films revealed by positron beam spectroscopy
Physical Review Letters
|September 28, 2010
Summary
Variable-energy positron annihilation spectroscopy revealed pore evolution and crystallization in vapor-deposited amorphous solid water films. Crystallization occurred below 140 K, with the top layer transitioning earlier.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Surface Science
Background:
- Amorphous solid water films are relevant in various scientific fields.
- Understanding pore evolution and crystallization is crucial for materials characterization.
Purpose of the Study:
- To investigate the annealing and evolution of pores in vapor-deposited amorphous solid water films.
- To study the crystallization process of these films using positron annihilation spectroscopy.
- To determine the temperature ranges for pore evolution and crystallization.
Main Methods:
- Variable-energy positron annihilation spectroscopy (VEPAS) was employed.
- Measurements were conducted on vapor-deposited amorphous solid water films.
- Temperatures ranged from 50 K to 150 K.
Main Results:
- Positron and positronium annihilation provided insights into grown-in pores and their temperature-dependent evolution.
- Crystallization of the amorphous solid water films was observed just below 140 K.
- The topmost 80 nm of the films showed a crystallization transition between 90 K and 100 K.
Conclusions:
- VEPAS is effective in characterizing pore structures and phase transitions in amorphous solid water.
- The study confirms crystallization temperatures for amorphous solid water films.
- Distinct crystallization behaviors were observed in different film regions.
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