Novel hexagonal polytypes of silver: growth, characterization and first-principles calculations

We report a study of the relative effects of dimensional and kinetic constraints on the stabilization of metastable, polytypic forms of metallic silver. We show that the hexagonal 4H polytype (hitherto observed only in size-constrained systems) can be produced in the form of bulk thin films by suita...

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Bibliographic Details
Published in:Journal of physics. Condensed matter 2011-08, Vol.23 (32), p.325401-12
Main Authors: CHAKRABORTY, Indrani, CARVALHO, Daniel, SHIRODKAR, Sharmila N, LAHIRI, Sandeep, BHATTACHARYYA, Somnath, BANERJEE, Rajarshi, WAGHMARE, Umesh, AYYUB, Pushan
Format: Article
Language:English
Subjects:
Condensed matter
Condensed matter: structure, mechanical and thermal properties
Cross-disciplinary physics: materials science
rheology
Density
Dispersions
Entropy
Exact sciences and technology
Inorganic compounds
Materials science
Mathematical analysis
Methods of deposition of films and coatings
film growth and epitaxy
Physics
Polytypes
Silver
Stability analysis
Structure and morphology
thickness
Structure of solids and liquids
crystallography
Structure of specific crystalline solids
Surfaces and interfaces
thin films and whiskers (structure and nonelectronic properties)
Theory and models of film growth
Thin film structure and morphology
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Summary:We report a study of the relative effects of dimensional and kinetic constraints on the stabilization of metastable, polytypic forms of metallic silver. We show that the hexagonal 4H polytype (hitherto observed only in size-constrained systems) can be produced in the form of bulk thin films by suitably slowing down the growth kinetics. Further, using extremely slow growth conditions, we have been successful in depositing a novel, two-dimensional, metastable polytype (2H) of silver, which is highly reactive (easily oxidized) and has a density 23% lower than normal silver. First-principles calculations based on density functional theory confirm that the 4H structure is relatively stable. However, local stability analysis via a determination of the phonon dispersion of the 2H structure reveals that it is only marginally stable with an energy surface that is rather flat or weakly varying with respect to many of the modes. This makes a large contribution to the configurational entropy and is probably the reason for the metastability of the observed 2H polytype with an unusually large lattice constant along the c-direction.
ISSN:0953-8984
1361-648X
DOI:10.1088/0953-8984/23/32/325401