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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

Stacking geometries and the corresponding band structures for various bilayer TaSe2.(a) Two H layers stacked together, with upper layer rotated 60° with respect to bottom layer. (b) Two H layers stacked together, with the upper layer translated along the Ta-Se bond direction. (c) One H layer stacked with a T layer. (d) One H layer stacked with a rotated T layer. The relative total energy per unit cell has been indicated for each configuration. (e–h) are the corresponding band structures without SOC. The Fermi level has been shifted to zero. (i–l) are the corresponding 2D Fermi surfaces.
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f4: Stacking geometries and the corresponding band structures for various bilayer TaSe2.(a) Two H layers stacked together, with upper layer rotated 60° with respect to bottom layer. (b) Two H layers stacked together, with the upper layer translated along the Ta-Se bond direction. (c) One H layer stacked with a T layer. (d) One H layer stacked with a rotated T layer. The relative total energy per unit cell has been indicated for each configuration. (e–h) are the corresponding band structures without SOC. The Fermi level has been shifted to zero. (i–l) are the corresponding 2D Fermi surfaces.

Mentions: Few-layer TaSe2 belongs to an intermediate design between bulk TaSe2 and monolayer sheet, so their band structures will be reminiscent of both. The van der Waals interlayer interaction, which gives rise to the band dispersions out of the 2D atomic plane in bulk, is now responsible for the band splitting/mixing between isolated monolayer bands occurring in few-layer TaSe2. One can expect that both of the hole and electron charge carriers may be present since different bands are present in the same energy range near the Fermi level (see Fig. 4 for example). The number of layers and the geometry dependence of the interlayer interaction are therefore key parameters influencing the transport properties of few-layer TaSe2, which may be important for their interconnect applications.


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

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

Stacking geometries and the corresponding band structures for various bilayer TaSe2.(a) Two H layers stacked together, with upper layer rotated 60° with respect to bottom layer. (b) Two H layers stacked together, with the upper layer translated along the Ta-Se bond direction. (c) One H layer stacked with a T layer. (d) One H layer stacked with a rotated T layer. The relative total energy per unit cell has been indicated for each configuration. (e–h) are the corresponding band structures without SOC. The Fermi level has been shifted to zero. (i–l) are the corresponding 2D Fermi surfaces.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Stacking geometries and the corresponding band structures for various bilayer TaSe2.(a) Two H layers stacked together, with upper layer rotated 60° with respect to bottom layer. (b) Two H layers stacked together, with the upper layer translated along the Ta-Se bond direction. (c) One H layer stacked with a T layer. (d) One H layer stacked with a rotated T layer. The relative total energy per unit cell has been indicated for each configuration. (e–h) are the corresponding band structures without SOC. The Fermi level has been shifted to zero. (i–l) are the corresponding 2D Fermi surfaces.
Mentions: Few-layer TaSe2 belongs to an intermediate design between bulk TaSe2 and monolayer sheet, so their band structures will be reminiscent of both. The van der Waals interlayer interaction, which gives rise to the band dispersions out of the 2D atomic plane in bulk, is now responsible for the band splitting/mixing between isolated monolayer bands occurring in few-layer TaSe2. One can expect that both of the hole and electron charge carriers may be present since different bands are present in the same energy range near the Fermi level (see Fig. 4 for example). The number of layers and the geometry dependence of the interlayer interaction are therefore key parameters influencing the transport properties of few-layer TaSe2, which may be important for their interconnect applications.

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