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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

Evolution of the temperature with time during growth of a critical nucleus under Nph simulations conditions.The crystallized volume is also shown as a function of time. Selected snapshots of the grain structure corresponding to three distinct instants (2, 5, and 8 ns) are shown.
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f7: Evolution of the temperature with time during growth of a critical nucleus under Nph simulations conditions.The crystallized volume is also shown as a function of time. Selected snapshots of the grain structure corresponding to three distinct instants (2, 5, and 8 ns) are shown.

Mentions: As discussed earlier, grain growth is controlled by the magnitude of the driving force and the interface mobility. Both of these quantities are temperature dependent. The exothermic nature of the a → c reaction (i.e. internal energy density difference Δua→c < 0) results in a local energy deposition that increases the global system temperature. Thus, the temperature of the system correlates directly with the volume of material transformed. Such correlation is clearly visible in Fig. 7, where both quantities are exactly proportional to each other with a proportionality constant of ≈8.01 × 10−27 m3 K−1. The temperature is seen to increase from T0 to a final value of approximately 1250 K. This effectively arrests the growth process, as dictated by the sharp decrease in mobility at such temperature (cf. Fig. 4). We remark that this arrest is partially an artifact of the simulations which limits unrestricted heat flow due to periodic boundary effects.


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

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

Evolution of the temperature with time during growth of a critical nucleus under Nph simulations conditions.The crystallized volume is also shown as a function of time. Selected snapshots of the grain structure corresponding to three distinct instants (2, 5, and 8 ns) are shown.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f7: Evolution of the temperature with time during growth of a critical nucleus under Nph simulations conditions.The crystallized volume is also shown as a function of time. Selected snapshots of the grain structure corresponding to three distinct instants (2, 5, and 8 ns) are shown.
Mentions: As discussed earlier, grain growth is controlled by the magnitude of the driving force and the interface mobility. Both of these quantities are temperature dependent. The exothermic nature of the a → c reaction (i.e. internal energy density difference Δua→c < 0) results in a local energy deposition that increases the global system temperature. Thus, the temperature of the system correlates directly with the volume of material transformed. Such correlation is clearly visible in Fig. 7, where both quantities are exactly proportional to each other with a proportionality constant of ≈8.01 × 10−27 m3 K−1. The temperature is seen to increase from T0 to a final value of approximately 1250 K. This effectively arrests the growth process, as dictated by the sharp decrease in mobility at such temperature (cf. Fig. 4). We remark that this arrest is partially an artifact of the simulations which limits unrestricted heat flow due to periodic boundary effects.

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