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Topologic connection between 2-D layered structures and 3-D diamond structures for conventional semiconductors.

Wang J, Zhang Y - Sci Rep (2016)

Bottom Line: When coming to identify new 2D materials, our intuition would suggest us to look from layered instead of 3D materials.Each path is found to further split into two branches under tensile strain-low buckled and high buckled structures, which respectively lead to a low and high buckled monolayer structure.Most promising new layered or planar structures identified include BeO, GaN, and ZnO on the tensile strain side, Ge, Si, and GaP on the compressive strain side.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical and Computer Engineering, The University of North Carolina at Charlotte 9201 University City Boulevard, Charlotte, NC 28223, USA.

ABSTRACT
When coming to identify new 2D materials, our intuition would suggest us to look from layered instead of 3D materials. However, since graphite can be hypothetically derived from diamond by stretching it along its [111] axis, many 3D materials can also potentially be explored as new candidates for 2D materials. Using a density functional theory, we perform a systematic study over the common Group IV, III-V, and II-VI semiconductors along different deformation paths to reveal new structures that are topologically connected to but distinctly different from the 3D parent structure. Specifically, we explore two major phase transition paths, originating respectively from wurtzite and NiAs structure, by applying compressive and tensile strain along the symmetry axis, and calculating the total energy changes to search for potential metastable states, as well as phonon spectra to examine the structural stability. Each path is found to further split into two branches under tensile strain-low buckled and high buckled structures, which respectively lead to a low and high buckled monolayer structure. Most promising new layered or planar structures identified include BeO, GaN, and ZnO on the tensile strain side, Ge, Si, and GaP on the compressive strain side.

No MeSH data available.


Related in: MedlinePlus

Strain-stress relations and strain-buckling relations for nine semiconductors.
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f3: Strain-stress relations and strain-buckling relations for nine semiconductors.

Mentions: To get more insight about the mechanical and structural properties moving along the total energy curve shown in Fig. 2, the strain-dependent stress X(ɛzz) and buckling height Δ(ɛzz) are calculated and plotted in Fig. 3 for the 9 materials. Taking the WZ structure as a reference, the strain is defined as ɛzz = (c − c0wz)/c0wz, and the stress value is obtained directly from the output of the VASP calculation. As shown in Fig. 3, qualitatively, the X(ɛzz) profile is highly asymmetric with respect to ɛzz = 0. On the compressive strain side (X > 0 and ɛzz < 0), a large “stress barrier” exists between WZ and HP phase; and after passing the barrier XB, the buckling Δ reduces quickly to zero for all the materials, for the reason already given above. On the tensile strain side (ɛzz > 0), the magnitude of the negative “stress barrier” is usually somewhat smaller than the compressive side. With increasing the c value from c0wz, the buckling increases initially then quickly reduce to zero for C, BN, GaN, BeO, and ZnO, which all involve at least one first row element, but only to a finite value for Si, Ge, GaP, and ZnTe. For the latter group, as c → ∞, Δ will approach the low-buckled monolayer value reported previously6722. For C, BN, and BeO, after passing the negative “stress barrier”, there appears a zero stress point at finite c, corresponding to the secondary total energy minimum. For the rest materials, X → 0 only as c → ∞, which implies that upon unloading the tensile stress, the material will go back to WZ. For those materials involving the first row elements, one could think of that the buckling is maintained due to the bonding with the atoms in the adjacent bilayer. Thus, as soon as the bonding is weakened to certain extent with increasing the bilayer spacing, the bilayer will collapse spontaneously, because there is adequate lateral space in the lower sub-layer of the bilayer for the atoms in the upper sub-layer to drop down. For those materials involving larger atoms, even the bonding with the other bilayer is fully removed with increasing the bilayer spacing, because the atoms in either the lower or upper sublayer are too big for the atoms of the two sublayers to join each other in the same plane. Thus, compression along the c axis is required to expand the lateral size of the unit cell to make room for the atoms of the upper sub-layer to drop down, while weakening the vertical coupling. Interestingly, such compressed but non-buckled structure actually has a larger interlayer spacing along the c axis. However, the overall atomic density of HP phase is higher than that of WZ. Note that C, BN, and BeO may also reach such a planar structure under compressive strain, but it does not yield a total energy minimum (see Fig. 2).


Topologic connection between 2-D layered structures and 3-D diamond structures for conventional semiconductors.

Wang J, Zhang Y - Sci Rep (2016)

Strain-stress relations and strain-buckling relations for nine semiconductors.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4835777&req=5

f3: Strain-stress relations and strain-buckling relations for nine semiconductors.
Mentions: To get more insight about the mechanical and structural properties moving along the total energy curve shown in Fig. 2, the strain-dependent stress X(ɛzz) and buckling height Δ(ɛzz) are calculated and plotted in Fig. 3 for the 9 materials. Taking the WZ structure as a reference, the strain is defined as ɛzz = (c − c0wz)/c0wz, and the stress value is obtained directly from the output of the VASP calculation. As shown in Fig. 3, qualitatively, the X(ɛzz) profile is highly asymmetric with respect to ɛzz = 0. On the compressive strain side (X > 0 and ɛzz < 0), a large “stress barrier” exists between WZ and HP phase; and after passing the barrier XB, the buckling Δ reduces quickly to zero for all the materials, for the reason already given above. On the tensile strain side (ɛzz > 0), the magnitude of the negative “stress barrier” is usually somewhat smaller than the compressive side. With increasing the c value from c0wz, the buckling increases initially then quickly reduce to zero for C, BN, GaN, BeO, and ZnO, which all involve at least one first row element, but only to a finite value for Si, Ge, GaP, and ZnTe. For the latter group, as c → ∞, Δ will approach the low-buckled monolayer value reported previously6722. For C, BN, and BeO, after passing the negative “stress barrier”, there appears a zero stress point at finite c, corresponding to the secondary total energy minimum. For the rest materials, X → 0 only as c → ∞, which implies that upon unloading the tensile stress, the material will go back to WZ. For those materials involving the first row elements, one could think of that the buckling is maintained due to the bonding with the atoms in the adjacent bilayer. Thus, as soon as the bonding is weakened to certain extent with increasing the bilayer spacing, the bilayer will collapse spontaneously, because there is adequate lateral space in the lower sub-layer of the bilayer for the atoms in the upper sub-layer to drop down. For those materials involving larger atoms, even the bonding with the other bilayer is fully removed with increasing the bilayer spacing, because the atoms in either the lower or upper sublayer are too big for the atoms of the two sublayers to join each other in the same plane. Thus, compression along the c axis is required to expand the lateral size of the unit cell to make room for the atoms of the upper sub-layer to drop down, while weakening the vertical coupling. Interestingly, such compressed but non-buckled structure actually has a larger interlayer spacing along the c axis. However, the overall atomic density of HP phase is higher than that of WZ. Note that C, BN, and BeO may also reach such a planar structure under compressive strain, but it does not yield a total energy minimum (see Fig. 2).

Bottom Line: When coming to identify new 2D materials, our intuition would suggest us to look from layered instead of 3D materials.Each path is found to further split into two branches under tensile strain-low buckled and high buckled structures, which respectively lead to a low and high buckled monolayer structure.Most promising new layered or planar structures identified include BeO, GaN, and ZnO on the tensile strain side, Ge, Si, and GaP on the compressive strain side.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical and Computer Engineering, The University of North Carolina at Charlotte 9201 University City Boulevard, Charlotte, NC 28223, USA.

ABSTRACT
When coming to identify new 2D materials, our intuition would suggest us to look from layered instead of 3D materials. However, since graphite can be hypothetically derived from diamond by stretching it along its [111] axis, many 3D materials can also potentially be explored as new candidates for 2D materials. Using a density functional theory, we perform a systematic study over the common Group IV, III-V, and II-VI semiconductors along different deformation paths to reveal new structures that are topologically connected to but distinctly different from the 3D parent structure. Specifically, we explore two major phase transition paths, originating respectively from wurtzite and NiAs structure, by applying compressive and tensile strain along the symmetry axis, and calculating the total energy changes to search for potential metastable states, as well as phonon spectra to examine the structural stability. Each path is found to further split into two branches under tensile strain-low buckled and high buckled structures, which respectively lead to a low and high buckled monolayer structure. Most promising new layered or planar structures identified include BeO, GaN, and ZnO on the tensile strain side, Ge, Si, and GaP on the compressive strain side.

No MeSH data available.


Related in: MedlinePlus