Tungsten diselenide
{{Chembox
| Name =
| ImageFile = STM of WSe2 on HOPG.jpg
| ImageSize = 230px
| ImageCaption = WSe2 monolayer on graphene (yellow) and its atomic image (inset){{cite journal|doi=10.1038/ncomms8666|pmid=26179885|pmc=4518320|title=Determination of band alignment in the single-layer MoS2/WSe2 heterojunction|journal=Nature Communications|volume=6|pages=7666|year=2015|last1=Chiu|first1=Ming-Hui|last2=Zhang|first2=Chendong|last3=Shiu|first3=Hung-Wei|last4=Chuu|first4=Chih-Piao|last5=Chen|first5=Chang-Hsiao|last6=Chang|first6=Chih-Yuan S.|last7=Chen|first7=Chia-Hao|authorlink8=Mei-Yin Chou|last8=Chou|first8=Mei-Yin|last9=Shih|first9=Chih-Kang|last10=Li|first10=Lain-Jong|arxiv=1406.5137|bibcode=2015NatCo...6.7666C}}
| ImageFile2 = Molybdenite-3D-balls.png
| ImageSize2 =
| ImageAlt =
| IUPACName =
| OtherNames =
| SystematicName =
| Section1 = {{Chembox Identifiers
| CASNo = 12067-46-8
| PubChem = 82910
| EINECS = 235-078-7
| SMILES = [Se]=[W]=[Se]
| InChI = 1S/2Se.W
| InChIKey = ROUIDRHELGULJS-UHFFFAOYSA-N
}}
| Section2 = {{Chembox Properties
| Formula = WSe2
| MolarMass = 341.76 g/mol
| Appearance = grey to black solid
| Odor = odorless
| MeltingPt = > 1200 °C
| BoilingPt =
| Solubility = insoluble
| BandGap = ~1 eV (indirect, bulk){{Cite journal|last1=Prakash|first1=Abhijith|last2=Appenzeller|first2=Joerg|date=2017-02-28|title=Bandgap Extraction and Device Analysis of Ionic Liquid Gated WSe2 Schottky Barrier Transistors|journal=ACS Nano|volume=11|issue=2|pages=1626–1632|doi=10.1021/acsnano.6b07360|pmid=28191930|issn=1936-0851}}
~1.7 eV (direct, monolayer){{cite journal|doi=10.1103/PhysRevB.85.033305|title=Thickness and strain effects on electronic structures of transition metal dichalcogenides: 2H-MX2 semiconductors (M = Mo, W; X = S, Se, Te)|journal=Physical Review B|volume=85|issue=3|pages=033305|year=2012|last1=Yun|first1=Won Seok|last2=Han|first2=S. W.|last3=Hong|first3=Soon Cheol|last4=Kim|first4=In Gee|last5=Lee|first5=J. D.|bibcode=2012PhRvB..85c3305Y}}
}}
| Section3 = {{Chembox Structure
| CrystalStruct = hP6, space group {{chem|P6|3}}/mmc, No 194{{Cite journal | doi = 10.1016/0025-5408(79)90144-2| title = Growth conditions and crystal structure parameters of layer compounds in the series Mo1−xWxSe2| journal = Materials Research Bulletin| volume = 14| issue = 6| pages = 825–830| year = 1979| last1 = Agarwal | first1 = M. K. | last2 = Wani | first2 = P. A. }}
| LattConst_a = 0.3297 nm
| LattConst_c = 1.2982 nm
| Coordination = Trigonal prismatic (WIV)
Pyramidal (Se2−)
}}
| Section4 = {{Chembox Thermochemistry
| DeltaGf =
| DeltaHc =
| Entropy =
| HeatCapacity =
}}
| Section7 = {{Chembox Hazards
| MainHazards = [http://www.espimetals.com/index.php/msds/297-tungsten-selenide External MSDS]
| FlashPt =
| AutoignitionPt =
}}
| Section8 = {{Chembox Related
| OtherAnions = Tantalum diselenide
}}
}}
Tungsten diselenide is an inorganic compound with the formula WSe2.{{Holleman&Wiberg}} The compound adopts a hexagonal crystalline structure similar to molybdenum disulfide. The tungsten atoms are covalently bonded to six selenium ligands in a trigonal prismatic coordination sphere while each selenium is bonded to three tungsten atoms in a pyramidal geometry. The tungsten–selenium bond has a length of 0.2526 nm, and the distance between selenium atoms is 0.334 nm.{{cite journal | last1 = Schutte | first1 = W.J. | last2 = De Boer | first2 = J.L. | last3 = Jellinek | first3 = F. | title = Crystal Structures of Tungsten Disulfide and Diselenide | journal = Journal of Solid State Chemistry | year = 1986 | volume = 70 | issue = 2 | pages = 207–209 | doi = 10.1016/0022-4596(87)90057-0|bibcode = 1987JSSCh..70..207S }} It is a well studied example of a layered material. The layers stack together via van der Waals interactions. WSe2 is a very stable semiconductor in the 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.{{Cite journal|last=Eftekhari|first=Ali|date=2017|title=Tungsten dichalcogenides (WS 2 , WSe 2 , and WTe 2 ): materials chemistry and applications|url=http://xlink.rsc.org/?DOI=C7TA04268J|journal=Journal of Materials Chemistry A|language=en|volume=5|issue=35|pages=18299–18325|doi=10.1039/C7TA04268J|issn=2050-7488}}
In addition to the typical semiconducting hexagonal structure, a second metallic polymorph of WSe2 exists. This phase, 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.{{Cite journal|last1=Ma|first1=Yuqiang|last2=Liu|first2=Bilu|last3=Zhang|first3=Anyi|last4=Chen|first4=Liang|last5=Fathi|first5=Mohammad|last6=Shen|first6=Chenfei|last7=Abbas|first7=Ahmad N.|last8=Ge|first8=Mingyuan|last9=Mecklenburg|first9=Matthew|last10=Zhou|first10=Chongwu|date=2015-07-28|title=Reversible Semiconducting-to-Metallic Phase Transition in Chemical Vapor Deposition Grown Monolayer WSe 2 and Applications for Devices|journal=ACS Nano|language=en|volume=9|issue=7|pages=7383–7391|doi=10.1021/acsnano.5b02399|pmid=26125321|issn=1936-0851}} WSe2 can form a fullerene-like structure.
The Young's modulus varies 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.{{cite journal |last1=Falin |first1=Alexey |last2=Holwill |first2=Matthew |last3=Lv |first3=Haifeng |last4=Gan |first4=Wei |last5=Cheng |first5=Jun |last6=Zhang |first6=Rui |last7=Qian |first7=Dong |last8=Barnett |first8=Matthew R. |last9=Santos |first9=Elton J. G. |last10=Novoselov |first10=Konstantin S. |last11=Tao |first11=Tao |last12=Wu |first12=Xiaojun |last13=Li |first13=Lu Hua |title=Mechanical Properties of Atomically Thin Tungsten Dichalcogenides: WS 2 , WSe 2 , and WTe 2 |journal=ACS Nano |date=23 February 2021 |volume=15 |issue=2 |pages=2600–2610 |doi=10.1021/acsnano.0c07430|pmid=33503379 |arxiv=2101.11869 |s2cid=231719536 }}
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.{{cite journal | last1 = Pouzet | first1 = J. | last2 = Bernede | first2 = J.C. | last3 = Khellil | first3 = A. | last4 = Essaidi | first4 = H. | last5 = Benhida | first5 = S. | title = Preparation and characterization of tungsten diselenide thin films | journal = Thin Solid Films | year = 1992 | volume = 208 | issue = 2 | pages = 252–259 | doi = 10.1016/0040-6090(92)90652-R|bibcode = 1992TSF...208..252P }}
:W + 2 Se → WSe2
Potential applications
The potential applications of transition metal dichalcogenides in solar cells and photonics are often discussed.{{cite journal|doi=10.1038/nphoton.2015.282|title=Photonics and optoelectronics of 2D semiconductor transition metal dichalcogenides|year=2016|last1=Mak|first1=Kin Fai|last2=Shan|first2=Jie|journal=Nature Photonics|volume=10|issue=4|pages=216–226|bibcode=2016NaPho..10..216M|s2cid=124091327 }} Bulk {{chem|WSe|2}} has an optical band gap of ~1.35 eV with a temperature dependence of −4.6{{e|-4}} eV/K.{{cite journal | last1 = Upadhyayula | first1 = L.C. | last2 = Loferski | first2 = J.J. | last3 = Wold | first3 = A. | last4 = Giriat | first4 = W. | last5 = Kershaw | first5 = R. | title = Semiconducting Properties of Single Crystals of n- and p-Type Tungsten Diselenide (WSe2) | journal = Journal of Applied Physics | year = 1968 | volume = 39 | issue = 10 | pages = 353–358 | doi = 10.1063/1.1655829|bibcode = 1968JAP....39.4736U }} {{chem|WSe|2}} photoelectrodes are stable in both acidic and basic conditions, making them potentially useful in electrochemical solar cells.{{cite journal | last1 = Gobrecht | first1 = J. | last2 = Gerischer | first2 = H. | last3 = Tributsch | first3 = H. | title = Electrochemical Solar Cell Based on the d-Band Semiconductor Tungsten-Diselenide | journal = Berichte der Bunsengesellschaft für physikalische Chemie | year = 1978 | volume = 82 | issue = 12 | pages = 1331–1335 | doi = 10.1002/bbpc.19780821212}}{{cite journal|doi=10.1038/nphoton.2014.271|arxiv=1410.3882|title=Two-dimensional material nanophotonics|journal=Nature Photonics|volume=8|issue=12|pages=899–907|year=2014|last1=Xia|first1=Fengnian|last2=Wang|first2=Han|last3=Xiao|first3=Di|last4=Dubey|first4=Madan|last5=Ramasubramaniam|first5=Ashwin|bibcode=2014NaPho...8..899X|s2cid=14682447 }}{{cite journal|doi=10.1039/C4CS00282B|pmid=25679474|title=Phonon and Raman scattering of two-dimensional transition metal dichalcogenides from monolayer, multilayer to bulk material|journal=Chem. Soc. Rev.|volume=44|issue=9|pages=2757–85|year=2015|last1=Zhang|first1=Xin|last2=Qiao|first2=Xiao-Fen|last3=Shi|first3=Wei|last4=Wu|first4=Jiang-Bin|last5=Jiang|first5=De-Sheng|last6=Tan|first6=Ping-Heng|arxiv=1502.00701|bibcode=2015arXiv150200701Z|s2cid=3215062 }}
The properties of {{chem|WSe|2}} monolayers differ from those of the bulk state, as is typical for semiconductors. Mechanically exfoliated monolayers of {{chem|WSe|2}} are transparent photovoltaic materials with LED properties.{{cite journal|doi=10.1021/ar4002312|title=Preparation and Applications of Mechanically Exfoliated Single-Layer and Multilayer MoS2 and WSe2 Nanosheets|year=2014|last1=Li|first1=Hai|last2=Wu|first2=Jumiati|last3=Yin|first3=Zongyou|last4=Zhang|first4=Hua|journal=Accounts of Chemical Research|volume=47|issue=4|pages=1067–1075|pmid=24697842}} The resulting solar cells pass 95 percent of the incident light, with one tenth of the remaining five percent converted into electrical power.{{cite web|url=http://www.gizmag.com/tungsten-diselenide-solar-cells/31161 |title=Tungsten diselenide shows potential for ultrathin, flexible, semi-transparent solar cells |publisher=Gizmag.com |date=11 March 2014 |accessdate=17 August 2014}}{{cite press release|author= Florian Aigenr |url=https://www.tuwien.ac.at/en/news/news_detail/article/8679/ |title=Atomically thin solar cells |publisher=Vienna University of Technology |date= 10 March 2014 |accessdate=18 August 2014}} 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.{{cite journal|doi=10.1038/s41928-020-00472-x|title=Programmable devices based on reversible solid-state doping of two-dimensional semiconductors with superionic silver iodide|year=2020|last1=Lee|first1=Sung-Joon|last2=Lin|first2=Zhaoyang|last3=Huang|first3=Jin|last4=Choi|first4=Christopher| last5=Chen|first5=Peng|last6=Liu|first6=Yuan|last7=Guo|first7=Jian|last8=Jia|first8=Chuancheng|last9=Wang|first9=Yiliu|last10=Liao|first10=Qingliang|last11=Shakir|first11=Imran|last12=Duan|first12=Xidong|last13=Dunn|first13=Bruce|last14=Zhang|first14=Yue|last15=Huang|first15=Yu|last16=Duan|first16=Xiangfeng|journal=Nature Electronics|volume=3|issue=10 |pages=630–637|s2cid=224896469 }}
Superconductivity has been reported in twisted bilayer {{chem|WSe|2}}, with a transition temperature of 200 mK.{{cite journal |last1=Xia |first1=Yiyu |last2=Han |first2=Zhongdong |last3=Watanabe |first3=Kenji |last4=Taniguchi |first4=Takashi |last5=Shan |first5=Jie |last6=Mak |first6=Kin Fai |title=Superconductivity in twisted bilayer WSe2 |journal=Nature |date=30 October 2024 |pages=1–6 |doi=10.1038/s41586-024-08116-2 |url=https://www.nature.com/articles/s41586-024-08116-2 |access-date=13 January 2025 |language=en |issn=1476-4687|arxiv=2406.03418 }}
See also
References
{{Commons category|Tungsten diselenide}}
{{reflist}}
{{Tungsten compounds}}
{{Selenides}}
Category:Tungsten(IV) compounds