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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.


Related in: MedlinePlus

The low-frequency layer-shearing modes (LSMs) and layer-breathing modes (LBMs) in bilayer and trilayer TaSe2.Arrows indicate the relative displacements of each layer.
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f10: The low-frequency layer-shearing modes (LSMs) and layer-breathing modes (LBMs) in bilayer and trilayer TaSe2.Arrows indicate the relative displacements of each layer.

Mentions: We have also analyzed the low-frequency modes in bilayer and trilayer 2H-TaSe2 and 1T-TaSe2. As shown in Fig. 10, the LSM in 2H-2L is 24 cm−1, slightly smaller than the LSM mode (26 cm−1) in bulk 2H-TaSe2 (not shown). On the other hand, the LBM of 2H-2L is at 30 cm−1, much smaller than the LBM of 43 cm−1 in bulk. The frequencies of these modes are in the same range of the reported low-frequency modes in Bernal 2L-MoS2 and 2L-WSe2, in which the interlayer shearing modes fall into 17–22 cm−1 while LBMs fall in 30–40 cm−150. All the LBM and LSM modes in 2H-2L and 1T-2L are Raman active, and therefore could provide a useful fingerprint to identify these two phases.


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

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

The low-frequency layer-shearing modes (LSMs) and layer-breathing modes (LBMs) in bilayer and trilayer TaSe2.Arrows indicate the relative displacements of each layer.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f10: The low-frequency layer-shearing modes (LSMs) and layer-breathing modes (LBMs) in bilayer and trilayer TaSe2.Arrows indicate the relative displacements of each layer.
Mentions: We have also analyzed the low-frequency modes in bilayer and trilayer 2H-TaSe2 and 1T-TaSe2. As shown in Fig. 10, the LSM in 2H-2L is 24 cm−1, slightly smaller than the LSM mode (26 cm−1) in bulk 2H-TaSe2 (not shown). On the other hand, the LBM of 2H-2L is at 30 cm−1, much smaller than the LBM of 43 cm−1 in bulk. The frequencies of these modes are in the same range of the reported low-frequency modes in Bernal 2L-MoS2 and 2L-WSe2, in which the interlayer shearing modes fall into 17–22 cm−1 while LBMs fall in 30–40 cm−150. All the LBM and LSM modes in 2H-2L and 1T-2L are Raman active, and therefore could provide a useful fingerprint to identify these two phases.

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