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Structural, electronic and vibrational properties of few-layer 2H- and 1T-TaSe2.

Yan JA, Cruz MA, Cook B, Varga K - Sci Rep (2015)

Bottom Line: We present first- principles calculations of structural phase energetics, band dispersion near the Fermi level, phonon properties and vibrational modes at the Brillouin zone center for different layer numbers, crystal phases and stacking geometries.Evolution of the Fermi surfaces as well as the phonon dispersions as a function of layer number reveals dramatic dimensionality effects in this CDW material.Our results indicate strong electronic interlayer coupling, detail energetically possible stacking geometries, and provide a basis for interpretation of Raman spectra.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Astronomy, and Geosciences, Towson University, 8000 York Road, Towson, Md 21252, USA.

ABSTRACT
Two-dimensional metallic transition metal dichalcogenides (TMDs) are of interest for studying phenomena such as charge-density wave (CDW) and superconductivity. Few-layer tantalum diselenides (TaSe2) are typical metallic TMDs exhibiting rich CDW phase transitions. However, a description of the structural, electronic and vibrational properties for different crystal phases and stacking configurations, essential for interpretation of experiments, is lacking. We present first- principles calculations of structural phase energetics, band dispersion near the Fermi level, phonon properties and vibrational modes at the Brillouin zone center for different layer numbers, crystal phases and stacking geometries. Evolution of the Fermi surfaces as well as the phonon dispersions as a function of layer number reveals dramatic dimensionality effects in this CDW material. Our results indicate strong electronic interlayer coupling, detail energetically possible stacking geometries, and provide a basis for interpretation of Raman spectra.

No MeSH data available.


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Phonon frequencies for the high-energy optical modes at Γ in few-layer TaSe2.Symmetries for typical modes are labeled explicitly. The , E′, A1g and Eg are Raman active.
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f8: Phonon frequencies for the high-energy optical modes at Γ in few-layer TaSe2.Symmetries for typical modes are labeled explicitly. The , E′, A1g and Eg are Raman active.

Mentions: Figure 8 shows the evolution of the high-frequency vibrational mode frequencies as a function of layer number for both 2H and 1T phases. The vibrational modes for the bulk are also shown. In Fig. 8, the symmetries for the modes in monolayer and bulk are explicitly indicated. The monolayer 2H-TaSe2 belongs to point group of D3h. The Γ phonon modes can be represented by + A1″ + A2″ + E″. The mode at about 241 cm−1, the E′ mode at 214 cm−1, and the E″ mode at 140 cm−1 are all Raman-active. These modes correspond to the characteristic A1g, E2g and E1g modes in bulk 2H-TaSe2 (with D6h symmetry)15. In few-layer 2H-TaSe2, recent experiments already confirmed the Raman peaks at around 235 cm−1, 208 cm−1, and 150 cm−126. Our results are also in good agreement with the Raman observation by Yan et al.3. They found that the E2g mode falls into the range of 207–210 cm−1, while the A1g mode is in the range of 233–235 cm−1.


Structural, electronic and vibrational properties of few-layer 2H- and 1T-TaSe2.

Yan JA, Cruz MA, Cook B, Varga K - Sci Rep (2015)

Phonon frequencies for the high-energy optical modes at Γ in few-layer TaSe2.Symmetries for typical modes are labeled explicitly. The , E′, A1g and Eg are Raman active.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4644971&req=5

f8: Phonon frequencies for the high-energy optical modes at Γ in few-layer TaSe2.Symmetries for typical modes are labeled explicitly. The , E′, A1g and Eg are Raman active.
Mentions: Figure 8 shows the evolution of the high-frequency vibrational mode frequencies as a function of layer number for both 2H and 1T phases. The vibrational modes for the bulk are also shown. In Fig. 8, the symmetries for the modes in monolayer and bulk are explicitly indicated. The monolayer 2H-TaSe2 belongs to point group of D3h. The Γ phonon modes can be represented by + A1″ + A2″ + E″. The mode at about 241 cm−1, the E′ mode at 214 cm−1, and the E″ mode at 140 cm−1 are all Raman-active. These modes correspond to the characteristic A1g, E2g and E1g modes in bulk 2H-TaSe2 (with D6h symmetry)15. In few-layer 2H-TaSe2, recent experiments already confirmed the Raman peaks at around 235 cm−1, 208 cm−1, and 150 cm−126. Our results are also in good agreement with the Raman observation by Yan et al.3. They found that the E2g mode falls into the range of 207–210 cm−1, while the A1g mode is in the range of 233–235 cm−1.

Bottom Line: We present first- principles calculations of structural phase energetics, band dispersion near the Fermi level, phonon properties and vibrational modes at the Brillouin zone center for different layer numbers, crystal phases and stacking geometries.Evolution of the Fermi surfaces as well as the phonon dispersions as a function of layer number reveals dramatic dimensionality effects in this CDW material.Our results indicate strong electronic interlayer coupling, detail energetically possible stacking geometries, and provide a basis for interpretation of Raman spectra.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Astronomy, and Geosciences, Towson University, 8000 York Road, Towson, Md 21252, USA.

ABSTRACT
Two-dimensional metallic transition metal dichalcogenides (TMDs) are of interest for studying phenomena such as charge-density wave (CDW) and superconductivity. Few-layer tantalum diselenides (TaSe2) are typical metallic TMDs exhibiting rich CDW phase transitions. However, a description of the structural, electronic and vibrational properties for different crystal phases and stacking configurations, essential for interpretation of experiments, is lacking. We present first- principles calculations of structural phase energetics, band dispersion near the Fermi level, phonon properties and vibrational modes at the Brillouin zone center for different layer numbers, crystal phases and stacking geometries. Evolution of the Fermi surfaces as well as the phonon dispersions as a function of layer number reveals dramatic dimensionality effects in this CDW material. Our results indicate strong electronic interlayer coupling, detail energetically possible stacking geometries, and provide a basis for interpretation of Raman spectra.

No MeSH data available.


Related in: MedlinePlus