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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.


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Temperature dependence of Δg0,a→c expressed on a per atom basis (referred to the left vertical axis).Also shown are the internal energies u of both amorphous and crystalline Ge as a function of temperature (right vertical axis). The heat capacity Cp is calculated from the slope of u(T), which for c-Ge results in a value of ≈2.69 × 10−4 eV · K−1 per atom (≈0.36 J · g−1 · K−1), in excellent agreement with experimental measurements47.
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f1: Temperature dependence of Δg0,a→c expressed on a per atom basis (referred to the left vertical axis).Also shown are the internal energies u of both amorphous and crystalline Ge as a function of temperature (right vertical axis). The heat capacity Cp is calculated from the slope of u(T), which for c-Ge results in a value of ≈2.69 × 10−4 eV · K−1 per atom (≈0.36 J · g−1 · K−1), in excellent agreement with experimental measurements47.

Mentions: In classical nucleation theory, the critical nucleus size r* is governed by the balance between the volumetric and interfacial driving forces expressed, respectively, as the derivative of the net free energy release ΔG0,a→c and a surface energy penalty ΔGs with respect to the radius of the nucleus. In principle, this balance must also account for the expansion of Ge upon crystallization, which is approximately 10% less dense than its amorphous counterpart (cf. Fig. 3b in ref. 22) at p = 0 and T0 = 1100 K. However, the procedure detailed in the previous section to seed an amorphous matrix with crystalline grains removes any differential strains by construction. This allows us to write:


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

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

Temperature dependence of Δg0,a→c expressed on a per atom basis (referred to the left vertical axis).Also shown are the internal energies u of both amorphous and crystalline Ge as a function of temperature (right vertical axis). The heat capacity Cp is calculated from the slope of u(T), which for c-Ge results in a value of ≈2.69 × 10−4 eV · K−1 per atom (≈0.36 J · g−1 · K−1), in excellent agreement with experimental measurements47.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Temperature dependence of Δg0,a→c expressed on a per atom basis (referred to the left vertical axis).Also shown are the internal energies u of both amorphous and crystalline Ge as a function of temperature (right vertical axis). The heat capacity Cp is calculated from the slope of u(T), which for c-Ge results in a value of ≈2.69 × 10−4 eV · K−1 per atom (≈0.36 J · g−1 · K−1), in excellent agreement with experimental measurements47.
Mentions: In classical nucleation theory, the critical nucleus size r* is governed by the balance between the volumetric and interfacial driving forces expressed, respectively, as the derivative of the net free energy release ΔG0,a→c and a surface energy penalty ΔGs with respect to the radius of the nucleus. In principle, this balance must also account for the expansion of Ge upon crystallization, which is approximately 10% less dense than its amorphous counterpart (cf. Fig. 3b in ref. 22) at p = 0 and T0 = 1100 K. However, the procedure detailed in the previous section to seed an amorphous matrix with crystalline grains removes any differential strains by construction. This allows us to write:

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