Tungsten diselenide

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Tungsten diselenide

WSe2 monolayer on graphene (yellow) and its atomic image (inset)[1]
Identifiers
3D model (
JSmol
)
ECHA InfoCard
 100.031.877 Edit this at Wikidata
EC Number
  • 235-078-7
  • InChI=1S/2Se.W
    Key: ROUIDRHELGULJS-UHFFFAOYSA-N
  • [Se]=[W]=[Se]
Properties
WSe2
Molar mass 341.76 g/mol
Appearance grey to black solid
Odor odorless
Density 9.32 g/cm3[2]
Melting point > 1200 °C
insoluble
Band gap ~1 eV (indirect, bulk)[3]
~1.7 eV (direct, monolayer)[4]
Structure
hP6, space group P6
3/mmc, No 194[2]
a = 0.3297 nm, c = 1.2982 nm
Trigonal prismatic
(WIV)
Pyramidal (Se2−)
Thermochemistry
Std enthalpy of
formation
(ΔfH⦵298)
 -185.3 kJ mol−1[5]
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 External MSDS
Related compounds
Other anions
 Tantalum diselenide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Tungsten diselenide is an

group-VI transition metal
dichalcogenides.

Structure and properties

The hexagonal (P63/mmc) polymorph 2H-WSe2 is isotypic with hexagonal MoS2. The two-dimensional lattice structure has W and Se arranged periodically in layers with hexagonal symmetry. Similar to graphite, van der Waals interactions hold the layers together; however, the 2D-layers in WSe2 are not atomically thin. The large size of the W cation renders the lattice structure of WSe2 more sensitive to changes than MoS2.[8]

In addition to the typical semiconducting hexagonal structure, a second metallic polymorph of WSe2 exists. This phasem 1T-WSe2, is based on a tetragonal symmetry with one WSe2 layer per repeating unit. The 1T-WSe2 phase is less stable and transitions to the 2H-WSe2 phase.[8][9] WSe2 can form a fullerene-like structure.

The

Young’s modulus vary greatly as a function of the number of layers in a flake. For a single monolayer, the reported Young’s modulus is 258.6 ± 38.3 GPa.[10]

Synthesis

Heating thin films of tungsten under pressure from gaseous selenium and high temperatures (>800 K) using the sputter deposition technique leads to the films crystallizing in hexagonal structures with the correct stoichiometric ratio.[11]

W + 2 Se → WSe2

Potential applications

Atomic image of a WSe2 monolayer showing hexagonal symmetry and three-fold defects. Scale bar: 2 nm (0.5 nm in the inset).[12]

The potential applications of

optical band gap of ~1.35 eV with a temperature dependence of −4.6×10−4 eV/K.[14] WSe
2 photoelectrodes are stable in both acidic and basic conditions, making them potentially useful in electrochemical solar cells.[15][16][17]

The properties of WSe
2 monolayers differ from those of the bulk state, as is typical for semiconductors. Mechanically exfoliated monolayers of WSe
2 are transparent photovoltaic materials with LED properties.[18] The resulting solar cells pass 95 percent of the incident light, with one tenth of the remaining five percent converted into electrical power.[19][20] The material can be changed from p-type to n-type by changing the voltage of an adjacent metal electrode from positive to negative, allowing devices made from it to have tunable bandgaps.[21]

See also

References

Wikimedia Commons has media related to Tungsten diselenide.
  1. PMID 26179885
    .
  2. ^
    doi:10.1016/0025-5408(79)90144-2
    .
  3. PMID 28191930
    .
  4. doi:10.1103/PhysRevB.85.033305
    .
  5. doi:10.1016/0021-9614(88)90019-5
    .
  6. ISBN 0-12-352651-5
  7. doi:10.1016/0022-4596(87)90057-0
    .
  8. ^
    ISSN 2050-7488
    .
  9. PMID 26125321
    .
  10. S2CID 231719536
    .
  11. doi:10.1016/0040-6090(92)90652-R
    .
  12. PMID 25832503
    .
  13. S2CID 124091327
    .
  14. doi:10.1063/1.1655829
    .
  15. doi:10.1002/bbpc.19780821212
    .
  16. S2CID 14682447
    .
  17. S2CID 3215062
    .
  18. PMID 24697842
    .
  19. ^ "Tungsten diselenide shows potential for ultrathin, flexible, semi-transparent solar cells". Gizmag.com. 11 March 2014. Retrieved 17 August 2014.
  20. ^ Florian Aigenr (10 March 2014). "Atomically thin solar cells" (Press release). Vienna University of Technology. Retrieved 18 August 2014.
  21. S2CID 224896469
    .
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