Limits...
Formation of Nanotwin Networks during High-Temperature Crystallization of Amorphous Germanium.

Sandoval L, Reina C, Marian J - Sci Rep (2015)

Bottom Line: We find that crystallization occurs by the recurrent transfer of atoms via a diffusive process from the amorphous phase into suitably-oriented crystalline layers.We accompany our simulations with a comprehensive thermodynamic and kinetic analysis of the growth process, which explains the energy balance and the interfacial growth velocities governing grain growth.We calculate the equivalent X-ray diffraction pattern of the obtained nanotwin networks, providing grounds for experimental validation.

View Article: PubMed Central - PubMed

Affiliation: Los Alamos National Laboratory, Los Alamos, NM 87545, United States.

ABSTRACT
Germanium is an extremely important material used for numerous functional applications in many fields of nanotechnology. In this paper, we study the crystallization of amorphous Ge using atomistic simulations of critical nano-metric nuclei at high temperatures. We find that crystallization occurs by the recurrent transfer of atoms via a diffusive process from the amorphous phase into suitably-oriented crystalline layers. We accompany our simulations with a comprehensive thermodynamic and kinetic analysis of the growth process, which explains the energy balance and the interfacial growth velocities governing grain growth. For the 〈111〉 crystallographic orientation, we find a degenerate atomic rearrangement process, with two zero-energy modes corresponding to a perfect crystalline structure and the formation of a Σ3 twin boundary. Continued growth in this direction results in the development a twin network, in contrast with all other growth orientations, where the crystal grows defect-free. This particular mechanism of crystallization from amorphous phases is also observed during solid-phase epitaxial growth of 〈111〉 semiconductor crystals, where growth is restrained to one dimension. We calculate the equivalent X-ray diffraction pattern of the obtained nanotwin networks, providing grounds for experimental validation.

No MeSH data available.


Related in: MedlinePlus

Structure of the crystalline grain after 9.1 ns of growth in the NpH ensemble.(a) Atomistic structure: Only atoms possessing an ordered crystallographic structure are shown. Dark blue and orange spheres represent atoms with diamond cubic and twin plate structure, respectively. Light blue spheres represent atoms belonging to the amorphous/crystalline interface and dislocation cores. The circular region in the center of the image indicates the extent of the critical grain at the beginning of the simulation. (b) Through-thickness view of the nanotwin structure corresponding to (a).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4660462&req=5

f5: Structure of the crystalline grain after 9.1 ns of growth in the NpH ensemble.(a) Atomistic structure: Only atoms possessing an ordered crystallographic structure are shown. Dark blue and orange spheres represent atoms with diamond cubic and twin plate structure, respectively. Light blue spheres represent atoms belonging to the amorphous/crystalline interface and dislocation cores. The circular region in the center of the image indicates the extent of the critical grain at the beginning of the simulation. (b) Through-thickness view of the nanotwin structure corresponding to (a).

Mentions: In a 3D (spherical) nucleus, in principle all growth orientations are sampled, which means that in materials with sizable interface energy anisotropies and/or interface velocities, some growth directions will be preferred over others. A complete animation of the grain growth process starting from (super)critical nuclei is provided in the Supporting Information. A snapshot of the simulation at the point of maximum growth –which occurs 9.1 ns after the system is equilibrated at T0– is shown in Fig. 5. Atoms in the image are colored using structure analysis as implemented in the OVITO visualization package24, which assigns dark blue to atoms with diamond cubic structure and orange to atoms with hexagonal diamond crystal structure.


Formation of Nanotwin Networks during High-Temperature Crystallization of Amorphous Germanium.

Sandoval L, Reina C, Marian J - Sci Rep (2015)

Structure of the crystalline grain after 9.1 ns of growth in the NpH ensemble.(a) Atomistic structure: Only atoms possessing an ordered crystallographic structure are shown. Dark blue and orange spheres represent atoms with diamond cubic and twin plate structure, respectively. Light blue spheres represent atoms belonging to the amorphous/crystalline interface and dislocation cores. The circular region in the center of the image indicates the extent of the critical grain at the beginning of the simulation. (b) Through-thickness view of the nanotwin structure corresponding to (a).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4660462&req=5

f5: Structure of the crystalline grain after 9.1 ns of growth in the NpH ensemble.(a) Atomistic structure: Only atoms possessing an ordered crystallographic structure are shown. Dark blue and orange spheres represent atoms with diamond cubic and twin plate structure, respectively. Light blue spheres represent atoms belonging to the amorphous/crystalline interface and dislocation cores. The circular region in the center of the image indicates the extent of the critical grain at the beginning of the simulation. (b) Through-thickness view of the nanotwin structure corresponding to (a).
Mentions: In a 3D (spherical) nucleus, in principle all growth orientations are sampled, which means that in materials with sizable interface energy anisotropies and/or interface velocities, some growth directions will be preferred over others. A complete animation of the grain growth process starting from (super)critical nuclei is provided in the Supporting Information. A snapshot of the simulation at the point of maximum growth –which occurs 9.1 ns after the system is equilibrated at T0– is shown in Fig. 5. Atoms in the image are colored using structure analysis as implemented in the OVITO visualization package24, which assigns dark blue to atoms with diamond cubic structure and orange to atoms with hexagonal diamond crystal structure.

Bottom Line: We find that crystallization occurs by the recurrent transfer of atoms via a diffusive process from the amorphous phase into suitably-oriented crystalline layers.We accompany our simulations with a comprehensive thermodynamic and kinetic analysis of the growth process, which explains the energy balance and the interfacial growth velocities governing grain growth.We calculate the equivalent X-ray diffraction pattern of the obtained nanotwin networks, providing grounds for experimental validation.

View Article: PubMed Central - PubMed

Affiliation: Los Alamos National Laboratory, Los Alamos, NM 87545, United States.

ABSTRACT
Germanium is an extremely important material used for numerous functional applications in many fields of nanotechnology. In this paper, we study the crystallization of amorphous Ge using atomistic simulations of critical nano-metric nuclei at high temperatures. We find that crystallization occurs by the recurrent transfer of atoms via a diffusive process from the amorphous phase into suitably-oriented crystalline layers. We accompany our simulations with a comprehensive thermodynamic and kinetic analysis of the growth process, which explains the energy balance and the interfacial growth velocities governing grain growth. For the 〈111〉 crystallographic orientation, we find a degenerate atomic rearrangement process, with two zero-energy modes corresponding to a perfect crystalline structure and the formation of a Σ3 twin boundary. Continued growth in this direction results in the development a twin network, in contrast with all other growth orientations, where the crystal grows defect-free. This particular mechanism of crystallization from amorphous phases is also observed during solid-phase epitaxial growth of 〈111〉 semiconductor crystals, where growth is restrained to one dimension. We calculate the equivalent X-ray diffraction pattern of the obtained nanotwin networks, providing grounds for experimental validation.

No MeSH data available.


Related in: MedlinePlus