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Molecular dynamics investigations of mechanical behaviours in monocrystalline silicon due to nanoindentation at cryogenic temperatures and room temperature.

Du X, Zhao H, Zhang L, Yang Y, Xu H, Fu H, Li L - Sci Rep (2015)

Bottom Line: Molecular dynamics simulations of nanoindentation tests on monocrystalline silicon (010) surface were conducted to investigate the mechanical properties and deformation mechanism from cryogenic temperature being 10 K to room temperature being 300 K.By searching for the presence of the unique non-bonded fifth neighbour atom, the metastable phases (Si-III and Si-XII) with fourfold coordination could be distinguished from Si-I phase during the loading stage of nanoindentation process.The Si-II, Si-XIII, and amorphous phase were also found in the region beneath the indenter.

View Article: PubMed Central - PubMed

Affiliation: School of Mechanical Science and Engineering, Jilin University, Renmin Street 5988, Changchun, Jilin 130025, China.

ABSTRACT
Molecular dynamics simulations of nanoindentation tests on monocrystalline silicon (010) surface were conducted to investigate the mechanical properties and deformation mechanism from cryogenic temperature being 10 K to room temperature being 300 K. Furthermore, the load-displacement curves were obtained and the phase transformation was investigated at different temperatures. The results show that the phase transformation occurs both at cryogenic temperatures and at room temperature. By searching for the presence of the unique non-bonded fifth neighbour atom, the metastable phases (Si-III and Si-XII) with fourfold coordination could be distinguished from Si-I phase during the loading stage of nanoindentation process. The Si-II, Si-XIII, and amorphous phase were also found in the region beneath the indenter. Moreover, through the degree of alignment of the metastable phases along specific crystal orientation at different temperatures, it was found that the temperature had effect on the anisotropy of the monocrystalline silicon, and the simulation results indicate that the anisotropy of monocrystalline silicon is strengthened at low temperatures.

No MeSH data available.


Related in: MedlinePlus

Lateral cross-sectional illustration of the hydrostatic stress at the maximum indentation depth at different temperatures.
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f4: Lateral cross-sectional illustration of the hydrostatic stress at the maximum indentation depth at different temperatures.

Mentions: where σx , σy , σz are the normal stresses in the X, Y, and Z direction, respectively, and are calculated using the virial theorem30. The hydrostatic stress was computed by dividing the simulation space into 5.43 × 5.43 × 5.43 Å3 cells31, where 5.43 is the lattice distance. The atomic volume of the silicon was assumed as the cell volume divided by the number of atoms in a given cell19. The per-atom volume computed this way may be slightly larger than the actual volume because the substrate surface is compressed by the indenter20. This means that the calculated stress (pressure) is slightly too low for some atoms. However, this will not affect the decision whether the pressure has exceeded the threshold for inducing the phase transformation. Figure 4 shows an illustration of the lateral cross-sectional distribution of the hydrostatic stress in the specimen at the maximum indentation depth at the different temperatures. As shown in Fig. 4, the hydrostatic stress beneath the indenter is larger than 12 GPa. Therefore, we can assume that a phase transformation from Si-I to Si-II has occurred at the four different temperatures.


Molecular dynamics investigations of mechanical behaviours in monocrystalline silicon due to nanoindentation at cryogenic temperatures and room temperature.

Du X, Zhao H, Zhang L, Yang Y, Xu H, Fu H, Li L - Sci Rep (2015)

Lateral cross-sectional illustration of the hydrostatic stress at the maximum indentation depth at different temperatures.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4633730&req=5

f4: Lateral cross-sectional illustration of the hydrostatic stress at the maximum indentation depth at different temperatures.
Mentions: where σx , σy , σz are the normal stresses in the X, Y, and Z direction, respectively, and are calculated using the virial theorem30. The hydrostatic stress was computed by dividing the simulation space into 5.43 × 5.43 × 5.43 Å3 cells31, where 5.43 is the lattice distance. The atomic volume of the silicon was assumed as the cell volume divided by the number of atoms in a given cell19. The per-atom volume computed this way may be slightly larger than the actual volume because the substrate surface is compressed by the indenter20. This means that the calculated stress (pressure) is slightly too low for some atoms. However, this will not affect the decision whether the pressure has exceeded the threshold for inducing the phase transformation. Figure 4 shows an illustration of the lateral cross-sectional distribution of the hydrostatic stress in the specimen at the maximum indentation depth at the different temperatures. As shown in Fig. 4, the hydrostatic stress beneath the indenter is larger than 12 GPa. Therefore, we can assume that a phase transformation from Si-I to Si-II has occurred at the four different temperatures.

Bottom Line: Molecular dynamics simulations of nanoindentation tests on monocrystalline silicon (010) surface were conducted to investigate the mechanical properties and deformation mechanism from cryogenic temperature being 10 K to room temperature being 300 K.By searching for the presence of the unique non-bonded fifth neighbour atom, the metastable phases (Si-III and Si-XII) with fourfold coordination could be distinguished from Si-I phase during the loading stage of nanoindentation process.The Si-II, Si-XIII, and amorphous phase were also found in the region beneath the indenter.

View Article: PubMed Central - PubMed

Affiliation: School of Mechanical Science and Engineering, Jilin University, Renmin Street 5988, Changchun, Jilin 130025, China.

ABSTRACT
Molecular dynamics simulations of nanoindentation tests on monocrystalline silicon (010) surface were conducted to investigate the mechanical properties and deformation mechanism from cryogenic temperature being 10 K to room temperature being 300 K. Furthermore, the load-displacement curves were obtained and the phase transformation was investigated at different temperatures. The results show that the phase transformation occurs both at cryogenic temperatures and at room temperature. By searching for the presence of the unique non-bonded fifth neighbour atom, the metastable phases (Si-III and Si-XII) with fourfold coordination could be distinguished from Si-I phase during the loading stage of nanoindentation process. The Si-II, Si-XIII, and amorphous phase were also found in the region beneath the indenter. Moreover, through the degree of alignment of the metastable phases along specific crystal orientation at different temperatures, it was found that the temperature had effect on the anisotropy of the monocrystalline silicon, and the simulation results indicate that the anisotropy of monocrystalline silicon is strengthened at low temperatures.

No MeSH data available.


Related in: MedlinePlus