Molybdenum diselenide MoSe2

spore: profile
id: molybdenum-diselenide
spore_version: 0.2
family: lubricant
name: Molybdenum diselenide
abbreviation: MoSe2
role: dry film lubricant and 2D semiconductor
category: tribology
type: dry-lubricants
summary: |
  Molybdenum diselenide (MoSe2) is a layered solid, like molybdenum disulfide. Its sheets slide over one another because they are held together only by weak van der Waals forces, so it can be used as a dry lubricant coating where oil or grease cannot be used. Its single layer is a semiconductor with a direct band gap, which is why it is studied for transistors and photodetectors. Tungsten diselenide (WSe2), the same layered family, is profiled alongside it and labelled in the properties. The MoSe2 lubricant data come from a sputtered pure coating that was stored for 40 months in ambient air; it still gave a steady friction coefficient of 0.081 in air, with the highest wear of its series. The WSe2 data come from sputtered WSe films, which kept a friction of 0.04 to 0.07 in both humid air and dry nitrogen. No vacuum, space or lunar data were found for either compound in the sources opened.
best_for: Dry sliding coatings where WSe films must keep friction near 0.04 to 0.07 in both humid air and dry nitrogen, or where MoSe2 friction near 0.08 in air is acceptable
weakest_at: Wear after long storage in air. The pure MoSe2 coating had the highest wear rate of its series (8.67 x 10-7 mm3/N m), and the MoSe2 supplier SDS calls the powder moisture sensitive
identity:
  formula: MoSe2
  cas: 12058-18-3
  crystal_system: hexagonal (2H), layered, molybdenite type
  space_group: P6_3/mmc (No. 194)
  source: wiki-mose2
  where: Infobox, Crystal structure hP6 and Space group P6 3/mmc No 194; CAS from the infobox and the Stanford and Angstrom SDS section 3. The WSe2 CAS 12067-46-8 is in the Wikipedia tungsten diselenide infobox.
tags:
  environments: []
  stresses: []
  applications:
    - mechanisms
    - electronics-and-chips
properties:
  - benchmark: density
    label: Density, MoSe2 (Wikipedia infobox)
    value: 6.9
    unit: g/cm3
    scope: material
    conditions:
      basis: MoSe2, crystalline solid, value as printed in the infobox
    method: Infobox value as printed
    status: ground
    source: wiki-mose2
    where: Infobox, Density row (6.90 g/cm3)
  - benchmark: density
    label: Density, MoSe2 (supplier SDS)
    value: 6
    unit: g/cm3
    scope: material
    conditions:
      basis: MoSe2 powder, dark grey, density at 20 degC as printed in the supplier SDS
    method: Density at 20 degC as printed (6 g/cm3). The SDS gives no decimal places, so the value is 6 as printed
    status: ground
    source: sds-sam-mose2
    where: Section 9, Density at 20 degC (68 degF), 6 g/cm3
  - benchmark: melting_point
    label: Melting point, MoSe2 (supplier SDS)
    value: 1200
    unit: degC
    scope: material
    conditions:
      basis: MoSe2 powder, supplier SDS
    method: Melting point/range as printed in Section 9 (1200 degC, 2192 degF)
    status: ground
    source: sds-sam-mose2
    where: Section 9, Melting point/Melting range (1200 degC)
  - benchmark: melting_point
    label: Melting point, MoSe2 (Wikipedia infobox, lower bound)
    value: 1200
    unit: degC
    scope: material
    conditions:
      basis: printed as more than 1200 degC, so 1200 is a lower bound and not a measured melting point
    method: Infobox value as printed (greater than 1200 degC)
    status: ground
    source: wiki-mose2
    where: Infobox, Melting point row (>1200 degC)
  - benchmark: molar_mass
    label: Molar mass, MoSe2
    value: 253.86
    unit: g/mol
    scope: material
    conditions:
      basis: MoSe2, molar mass as printed
    method: Infobox value as printed (253.86 g/mol)
    status: ground
    source: wiki-mose2
    where: Infobox, Molar mass row
  - benchmark: band_gap_optical_indirect
    label: Indirect band gap, MoSe2 bulk
    value: 0.85
    unit: eV
    scope: material
    conditions:
      basis: bulk MoSe2, approximate value (printed with a tilde)
    method: Infobox value as printed (about 0.85 eV)
    status: ground
    source: wiki-mose2
    where: Infobox, Band gap row (~0.85 eV indirect, bulk)
  - benchmark: band_gap_optical_direct
    label: Direct band gap, MoSe2 monolayer
    value: 1.5
    unit: eV
    scope: material
    conditions:
      basis: MoSe2 monolayer, approximate value (printed with a tilde)
    method: Infobox value as printed (about 1.5 eV)
    status: ground
    source: wiki-mose2
    where: Infobox, Band gap row (~1.5 eV direct, monolayer)
  - benchmark: coefficient_of_friction
    label: Steady-state friction, pure MoSe2 coating, ambient air after 40 months storage
    value: 0.081
    unit: dimensionless
    scope: material
    conditions:
      basis: DC magnetron sputtered MoSe2 coating with no nitrogen (N0 reference), stored 40 months in ambient air in plastic bags, then tested in ambient air; steady-state average
    method: Average steady-state friction coefficient as printed in the text (0.081)
    status: ground
    source: paper-mosen-storage-2025
    where: Results, paragraph on average COF after 40 months of storage (pure N0 coating, 0.081)
  - benchmark: density
    label: Density, WSe2 (Wikipedia infobox)
    value: 9.32
    unit: g/cm3
    scope: material
    conditions:
      basis: WSe2, solid, value as printed in the infobox
    method: Infobox value as printed
    status: ground
    source: wiki-wse2
    where: Infobox, Density row (9.32 g/cm3)
  - benchmark: molar_mass
    label: Molar mass, WSe2
    value: 341.76
    unit: g/mol
    scope: material
    conditions:
      basis: WSe2, molar mass as printed
    method: Infobox value as printed (341.76 g/mol)
    status: ground
    source: wiki-wse2
    where: Infobox, Molar mass row
  - benchmark: melting_point
    label: Melting point, WSe2 (Wikipedia infobox, lower bound)
    value: 1200
    unit: degC
    scope: material
    conditions:
      basis: printed as more than 1200 degC, so 1200 is a lower bound and not a measured melting point
    method: Infobox value as printed (more than 1200 degC)
    status: ground
    source: wiki-wse2
    where: Infobox, Melting point row (> 1200 degC)
  - benchmark: band_gap_optical_indirect
    label: Indirect band gap, WSe2 bulk
    value: 1
    unit: eV
    scope: material
    conditions:
      basis: bulk WSe2, approximate value (printed with a tilde)
    method: Infobox value as printed (about 1 eV)
    status: ground
    source: wiki-wse2
    where: Infobox, Band gap row (~1 eV indirect, bulk)
  - benchmark: band_gap_optical_direct
    label: Direct band gap, WSe2 monolayer
    value: 1.7
    unit: eV
    scope: material
    conditions:
      basis: WSe2 monolayer, approximate value (printed with a tilde)
    method: Infobox value as printed (about 1.7 eV)
    status: ground
    source: wiki-wse2
    where: Infobox, Band gap row (~1.7 eV direct, monolayer)
  - benchmark: coefficient_of_friction
    label: Friction, sputtered WSe film, ambient air and dry nitrogen
    value: 0.04
    value_high: 0.07
    unit: dimensionless
    scope: material
    conditions:
      basis: pure WSex film (Se/W below 2) by RF magnetron sputtering, reciprocating sliding; same friction in ambient air (30 to 40 percent RH) and dry nitrogen (below 7 percent RH), as printed in the text
    method: Range as printed in the text for the pure WSex coating (0.04 to 0.07)
    status: ground
    source: paper-wse-mos2-2017
    where: Results and discussion, paragraph beginning The tribological behavior remains almost unaltered
  - benchmark: coefficient_of_friction
    label: Steady-state friction, sputtered WSe film, dry nitrogen, 125,000 cycles
    value: 0.03
    value_high: 0.05
    unit: dimensionless
    scope: material
    conditions:
      basis: WSex film and MoS2 film in dry nitrogen (below 7 percent RH), rotating ball-on-disk, 125,000 cycles, steady state; the text gives one range for both coatings
    method: Range as printed in the text (0.03 to 0.05 in both cases)
    status: ground
    source: paper-wse-mos2-2017
    where: Results, paragraph beginning The two samples exhibiting the best behavior in the dry nitrogen atmosphere
  - benchmark: hardness
    label: Hardness, sputtered WSe film
    value: 5.1
    unit: GPa
    scope: material
    conditions:
      basis: WSex coating, Vickers microindentation at loads up to 10 mN, film about 0.9 um thick
    method: Table 1, Hardness (GPa) column, WSex row
    status: ground
    source: paper-wse-mos2-2017
    where: Table 1, WSex row, Hardness (GPa) column
  - benchmark: elastic_modulus
    label: Elastic modulus, sputtered WSe film
    value: 90
    unit: GPa
    scope: material
    conditions:
      basis: WSex coating, Vickers microindentation at loads up to 10 mN
    method: Table 1, Elastic modulus (GPa) column, WSex row
    status: ground
    source: paper-wse-mos2-2017
    where: Table 1, WSex row, Elastic modulus (GPa) column
corrosion:
  - environment: Ambient air storage of a sputtered MoSe2 coating for 40 months
    headline: Forty months of storage in ambient air raised the friction of the pure MoSe2 coating only slightly, but its wear rate was the highest of the series.
    effect: The pure N0 coating gave a steady-state friction of 0.081 and a specific wear rate of 8.67 x 10-7 mm3/N m after storage. The authors attribute the small rise in friction, compared with the result when new, to a thin oxidation layer on the surface. Wear was higher than in the nitrogen-alloyed coatings (5.36 x 10-7 to 4.76 x 10-7 mm3/N m), which the authors put down to the porous morphology and low load-bearing capacity of the pure coating.
    rating: moderate
    conditions:
      basis: DC magnetron sputtered MoSe2 coating, ambient air, 40 months in plastic bags without extra precautions
    source: paper-mosen-storage-2025
    where: Results (wear rates in Figure 2b and text; friction in Figure 2a and text)
  - environment: Ambient air at 30 to 40 percent relative humidity versus dry nitrogen below 7 percent relative humidity, sputtered WSe film
    headline: The sputtered WSex film kept the same friction and wear in humid air and dry nitrogen. The MoS2 film from the same study did not.
    effect: In the same tribometer tests, the pure WSex film gave friction of 0.04 to 0.07 and a wear rate of 1.5 to 3 x 10-7 mm3/N m in both environments. The pure MoS2 film wore at 2.4 x 10-6 mm3/N m in ambient air and 9 x 10-8 mm3/N m in dry nitrogen. The authors state that the moisture sensitivity of the selenides is lower than that of MoS2.
    rating: low
    conditions:
      basis: RF magnetron sputtered WSex film (Se/W below 2), reciprocating sliding, same tribometer for all coatings
    source: paper-wse-mos2-2017
    where: Results and discussion, paragraph beginning The tribological behavior remains almost unaltered
  - environment: Heating in air and combustion of the powder
    headline: No oxidation temperature for MoSe2 in air was found in the sources opened. A fire gives off selenium and molybdenum oxides.
    effect: The Stanford SDS lists selenium oxides and molybdenum oxides as the fire products and gives no oxidation onset temperature. The Angstrom SDS lists metal oxide fume as its decomposition product. No test of heated MoSe2 in air was opened.
    rating: unknown
    conditions:
      basis: no temperature or time given in the sources opened
    source: sds-sam-mose2
    where: Section 5, Special hazards arising from the substance (selenium oxides, molybdenum oxides)
risks:
  hazards:
    - text: The MoSe2 supplier SDS (Stanford Advanced Materials) classes it as acute toxic by swallowing (Category 3, H301) and by inhalation (Category 3, H331), with the Danger signal word. It also lists specific organ toxicity after repeated exposure (H373) and acute and chronic aquatic toxicity (H400, H410).
      ghs:
        - H301
        - H331
        - H373
        - H400
        - H410
      source: sds-sam-mose2
      where: Section 2, GHS classification and label elements
    - text: The Angstrom Sciences SDS gives the Danger signal word with H301 + H331 and H373. It gives no aquatic hazard statement, and it lists the HMIS health rating as 2.
      ghs:
        - H301
        - H331
        - H373
      source: sds-angstrom-mose2
      where: Section 2, Hazard statements, and HMIS health ratings
    - text: PubChem aggregates 215 company reports from 5 ECHA notifications for MoSe2. H301 with H331 appears in 19.1 percent of them, and H373, H400 and H410 are listed at 100 percent each with the Warning signal word, which differs from the SDS Danger word.
      ghs:
        - H301
        - H331
        - H373
        - H400
        - H410
      source: pubchem-mose2
      where: GHS Classification section, CID 82894
    - text: The Wikipedia infobox for WSe2 gives the GHS06, GHS08 and GHS09 pictograms with the Warning signal word, and the hazard statements H301, H331, H373 and H410. No WSe2 supplier SDS was opened.
      ghs:
        - H301
        - H331
        - H373
        - H410
      source: wiki-wse2
      where: Infobox, Occupational safety and health row
    - text: PubChem aggregates 7 company reports from 3 ECHA notifications for WSe2. H301 with H331 appears in 42.9 percent of them, and H373, H400 and H410 are listed at 100 percent each.
      ghs:
        - H301
        - H331
        - H373
        - H400
        - H410
      source: pubchem-wse2
      where: GHS Classification section, CID 82910
    - text: The MoSe2 SDS lists no carcinogen. Selenium compounds are limited at 0.2 mg/m3 as Se in the USA (OSHA PEL) and the ACGIH TLV, and at 0.1 mg/m3 in the UK and Germany.
      ghs: []
      source: sds-sam-mose2
      where: Section 8, Control parameters (selenium and selenium compounds as Se)
  failure_risks:
    - mode: Moisture and air storage of a coating
      trigger: Coating kept 40 months in plastic bags in ambient air without extra protection
      consequence: Friction stayed near 0.08, but wear was the highest of the series (8.67 x 10-7 mm3/N m), and the authors report a thin surface oxide and abrasive wear debris.
      severity: moderate
      source: paper-mosen-storage-2025
      where: Results, wear rates and discussion of the oxidation layer
    - mode: Surface oxidation during sliding in air
      trigger: Sliding in ambient air, where water and oxygen reach the contact
      consequence: The authors say that water and oxygen in the contact increase oxidation, debris and film wear, and that the nitrogen-alloyed coatings resist this better.
      severity: moderate
      source: paper-mosen-storage-2025
      where: Discussion of counterface micrographs (ambient air and dry nitrogen)
  side_effects:
    - text: In a fire, MoSe2 gives off selenium oxides and molybdenum oxides.
      affects: Responders and nearby materials in a fire
      source: sds-sam-mose2
      where: Section 5, Special hazards arising from the substance
  handling:
    - text: The MoSe2 SDS says to keep the container tightly closed in a dry and well-ventilated place. It calls the powder moisture sensitive and says to store it locked up.
      source: sds-sam-mose2
      where: Section 7, conditions for safe storage; Section 2, precautionary statement P405
    - text: Avoid dust and provide exhaust ventilation where dust forms. Further processing of the solid may produce combustible dust.
      source: sds-sam-mose2
      where: Section 7, precautions for safe handling
    - text: Keep MoSe2 away from hydrogen peroxide and strong oxidizing agents.
      source: sds-sam-mose2
      where: Section 10, incompatible materials
    - text: Wear respiratory protection, gloves and eye protection when handling the powder. The Angstrom SDS calls for a dust respirator, rubber gloves and safety glasses.
      source: sds-angstrom-mose2
      where: Section 8, Respiratory protection, Protective gloves and Eye protection
uses:
  - application: mechanisms
    device: Sputtered solid-lubricant coating on sliding steel parts, including parts of complex shape
    example: The authors deposit MoSe2 coatings by DC magnetron sputtering so that they can coat 3D complex parts. They describe the coating as a solid lubricant for the aerospace industry.
    source: paper-mosen-storage-2025
    where: Introduction and Keywords
  - application: mechanisms
    device: Sputtered WSe solid-lubricant film for vacuum and space contacts
    example: The 2017 paper concludes that the WSex nanocomposite is a good competitor for MoS2 as a solid lubricant for vacuum and space applications where components see variable surroundings.
    source: paper-wse-mos2-2017
    where: Conclusions, last paragraph
  - application: electronics-and-chips
    device: Monolayer MoSe2 channel in a transistor or photodetector
    example: The Wikipedia article says monolayer MoSe2 has a direct band gap, suggesting applications in transistors and photodetectors. It also says MoSe2 has higher electrical conductivity than MoS2, with no number given.
    source: wiki-mose2
    where: Uses section, Electronics
  - application: electronics-and-chips
    device: Layered WSe2 semiconductor with switchable p-type and n-type behaviour
    example: The Wikipedia article says WSe2 can be changed from p-type to n-type by changing the voltage of an adjacent metal electrode, and that mechanically exfoliated monolayers are described as transparent photovoltaic materials with LED properties.
    source: wiki-wse2
    where: Electronics use section
supply:
  - subject: Molybdenum (feedstock for MoSe2)
    producers:
      - country: China
        tonnes: 97000
        share_percent: 37.3
        year: 2025
      - country: United States
        tonnes: 40000
        share_percent: 15.4
        year: 2025
      - country: Chile
        tonnes: 42000
        share_percent: 16.2
        year: 2025
      - country: Peru
        tonnes: 39000
        share_percent: 15
        year: 2025
      - country: Mexico
        tonnes: 17000
        share_percent: 6.5
        year: 2025
    reserves: 'USGS 2026, reserves in thousand metric tons: China 7,800; Chile 2,600; United States 3,500; Peru 1,000; world total 17,000.'
    critical_lists: []
    recycling: 'USGS 2026: molybdenum is recycled as a component of catalysts, ferrous scrap and superalloy scrap. The USGS says the amount of recycled content in alloys is significant and reused.'
    export_controls: 'USGS 2026: the Government of China imposed export controls on molybdenum powders in February 2025, prompting the United States and other countries to seek alternative sources.'
    source: usgs-mcs2026-molybdenum
    where: World Mine Production and Reserves table (2025e column, world total 260,000 t); Events, Trends and Issues. Shares calculated by Space Mushroom as tonnes divided by the 260,000 t world total.
  - subject: Selenium (byproduct of copper refining, feedstock for MoSe2 and WSe2)
    producers:
      - country: China
        tonnes: 2000
        share_percent: 53
        year: 2025
      - country: Japan
        tonnes: 640
        share_percent: 16.8
        year: 2025
      - country: Russia
        tonnes: 320
        share_percent: 8.4
        year: 2025
      - country: Belgium
        tonnes: 200
        share_percent: 5.3
        year: 2025
      - country: Canada
        tonnes: 130
        share_percent: 3.4
        year: 2025
    reserves: 'USGS 2026: reserves and resources of selenium are generally not reported at the mine or country level and cannot be reliably quantified.'
    critical_lists: []
    recycling: 'USGS 2026: selenium recycling is insignificant. Most scrap from electronic materials was exported for recovery of contained selenium.'
    export_controls: No export control was found in the USGS selenium text opened.
    source: usgs-mcs2026-selenium
    where: World Refinery Production table (2025 column, world total 3,800 t); Events text (China 53 percent of estimated global production in 2025). Shares for countries other than China calculated by Space Mushroom as tonnes divided by the 3,800 t world total. Selenium is recovered principally as a byproduct of electrolytic copper refining.
media: []
documents:
  - title: Molybdenum(IV) selenide, powder, safety data sheet (Stanford Advanced Materials)
    type: sds
    url: https://samaterials.com/tds/1697120344-2595-molybdenum-selenide-powder-sds.pdf
    year: 2022
  - title: Molybdenum selenide, safety data sheet (Angstrom Sciences)
    type: sds
    url: https://angstromsciences.com/wp-content/uploads/files/SDS/Molybdenum%20Selenide.pdf
    year: 2015
  - title: Solid lubricant behavior of MoS2 and WSe2-based nanocomposite coatings (Science and Technology of Advanced Materials, 2017)
    type: paper
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC5402748/
    year: 2017
  - title: Investigating the Effects of Long-Term Ambient Air Storage on the Sliding Properties of N-Alloyed MoSe2 Coatings (Nanomaterials, 2025)
    type: paper
    url: https://doi.org/10.3390/nano15060414
    year: 2025
  - title: 'USGS Mineral Commodity Summaries 2026: Molybdenum'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-molybdenum.pdf
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Selenium'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-selenium.pdf
    year: 2026
  - title: 'PubChem: Molybdenum diselenide (CID 82894), GHS classification'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/82894
    year: 2026
  - title: 'PubChem: Tungsten selenide, WSe2 (CID 82910), GHS classification'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/82910
    year: 2026
gaps:
  - No vacuum, space, low Earth orbit or atomic oxygen data for MoSe2 or WSe2 was found in the sources opened. The NASA search returned only MoS2 reports, so no NASA MoSe2 or WSe2 document was read.
  - The 2025 storage paper tests only ambient air for the pure MoSe2 coating. Its Methods section (load, speed and counterface details) was not extracted in this run, so the friction value carries only the conditions given in its Results.
  - The dry-nitrogen friction of 0.03 to 0.05 and the 125,000-cycle test belong to the MoS2 and WSex films of the 2017 paper, not to MoSe2. No MoSe2 dry-nitrogen friction was found.
  - The 2017 paper's WSe film has a selenium to tungsten ratio below 2 (its Table 1 and text), so its data are for a substoichiometric WSex film, not stoichiometric WSe2. No stoichiometric WSe2 film friction was found.
  - 'Wear rates are written in the text and not as properties, because this file does not use E-notation. Values: pure MoSe2 coating 8.67 x 10-7 mm3/N m (after storage); WSex 1.5 to 3 x 10-7 mm3/N m (both environments) and 2 x 10-8 mm3/N m (dry nitrogen, 125,000 cycles).'
  - The hardness and elastic modulus values for WSex come from Table 1 of the 2017 paper, read from the table text. No hardness value for MoSe2 was found.
  - 'The MoSe2 density disagrees across sources: Wikipedia 6.90 g/cm3, Stanford SDS 6 g/cm3, Angstrom SDS 6.0 g/cc. The values are recorded with their sources and not reconciled.'
  - The melting points for both compounds are given as more than 1200 degC in Wikipedia. The MoSe2 SDS gives 1200 degC. PubChem experimental melting point and density were not read; the PubChem property call returned no data.
  - The band gaps from Wikipedia are approximate (printed with a tilde) and have not been checked against a primary paper.
  - 'The MoSe2 hazard classes differ: the Stanford SDS gives the Danger word with H400 and H410; the Angstrom SDS gives H301 with H331 and H373 only; PubChem lists H400 and H410 with the Warning word. The aquatic classes are not reconciled.'
  - No WSe2 supplier SDS was opened. The WSe2 hazard data come from the Wikipedia infobox and PubChem only, and no WSe2 H315 or H319 statement was found.
  - The oxidation onset temperature of MoSe2 and WSe2 in air was not found in any source opened.
  - Molybdenum and selenium critical-mineral status was not found in the USGS extracts opened. The selenium and molybdenum USGS texts do not mention a critical list.
  - Tungsten feedstock supply for WSe2 was not re-read in this run; see the tungsten-disulphide profile for the USGS 2026 tungsten figures.
  - 'Benchmark names not in spores/property-canon.yaml and used here: molar_mass, coefficient_of_friction, band_gap_optical_direct, band_gap_optical_indirect, hardness. Check them against the canon before import.'
  - The Angstrom SDS repeats the 1200 degC and 6.0 g/cc values, and its section 3 text mentions molybdenum sulfide, so the Angstrom sheet is treated as a weaker source.
  - Atomic weights are the NIST standard values, printed with uncertainty in parentheses (95.95(1), 78.971(8), 183.84(1)); the value used is the printed central value without the uncertainty.
sources:
  wiki-mose2:
    title: Molybdenum diselenide
    id: Wikipedia, English edition
    url: https://en.wikipedia.org/wiki/Molybdenum_diselenide
    kind: web
    license: CC BY-SA 4.0
  wiki-wse2:
    title: Tungsten diselenide
    id: Wikipedia, English edition
    url: https://en.wikipedia.org/wiki/Tungsten_diselenide
    kind: web
    license: CC BY-SA 4.0
  pubchem-mose2:
    title: Molybdenum diselenide (CID 82894)
    id: PubChem, NIH National Library of Medicine
    url: https://pubchem.ncbi.nlm.nih.gov/compound/82894
    year: 2026
    kind: database
    license: public domain (NLM)
  pubchem-wse2:
    title: Tungsten selenide, WSe2 (CID 82910)
    id: PubChem, NIH National Library of Medicine
    url: https://pubchem.ncbi.nlm.nih.gov/compound/82910
    year: 2026
    kind: database
    license: public domain (NLM)
  sds-sam-mose2:
    title: Molybdenum(IV) selenide safety data sheet (Stanford Advanced Materials)
    id: SAM product MoSe2 powder, revised 05/11/2022
    url: https://samaterials.com/tds/1697120344-2595-molybdenum-selenide-powder-sds.pdf
    year: 2022
    kind: datasheet
    license: supplier SDS (cited, not reproduced)
  sds-angstrom-mose2:
    title: Molybdenum selenide safety data sheet (Angstrom Sciences)
    id: Angstrom Sciences SDS, revised 06/30/15
    url: https://angstromsciences.com/wp-content/uploads/files/SDS/Molybdenum%20Selenide.pdf
    year: 2015
    kind: datasheet
    license: supplier SDS (cited, not reproduced)
  paper-wse-mos2-2017:
    title: Solid lubricant behavior of MoS2 and WSe2-based nanocomposite coatings
    id: Dominguez-Meister et al., Science and Technology of Advanced Materials, 2017, DOI 10.1080/14686996.2016.1275784 (PubMed Central PMC5402748)
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC5402748/
    year: 2017
    kind: paper
    license: open access (PMC)
  paper-mosen-storage-2025:
    title: Investigating the Effects of Long-Term Ambient Air Storage on the Sliding Properties of N-Alloyed MoSe2 Coatings
    id: Nanomaterials, 2025, DOI 10.3390/nano15060414
    url: https://doi.org/10.3390/nano15060414
    year: 2025
    kind: paper
    license: open access (MDPI, CC BY)
  usgs-mcs2026-molybdenum:
    title: 'Mineral Commodity Summaries 2026: Molybdenum'
    id: USGS, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-molybdenum.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-mcs2026-selenium:
    title: 'Mineral Commodity Summaries 2026: Selenium'
    id: USGS, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-selenium.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  nist-atomic-weights-mo:
    title: Atomic weight of molybdenum (NIST)
    id: NIST Physical Measurement Laboratory, Atomic Weights and Isotopic Compositions
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Mo&all=all
    kind: database
    license: public domain (NIST)
  nist-atomic-weights-se:
    title: Atomic weight of selenium (NIST)
    id: NIST Physical Measurement Laboratory, Atomic Weights and Isotopic Compositions
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Se&all=all
    kind: database
    license: public domain (NIST)
  nist-atomic-weights-w:
    title: Atomic weight of tungsten (NIST)
    id: NIST Physical Measurement Laboratory, Atomic Weights and Isotopic Compositions
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=W&all=all
    kind: database
    license: public domain (NIST)
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 17
  unreachable: 1
  caveats: 4
  note: Written 2026-10-26 from the Wikipedia infobox pages for MoSe2 and WSe2, two supplier SDSs for MoSe2, PubChem GHS data for CIDs 82894 and 82910, the Nanomaterials 2025 MoSe2 storage paper, the Science and Technology of Advanced Materials 2017 MoS2 and WSex paper (full text read from the Europe PMC copy because the PMC page showed a browser check), the USGS 2026 molybdenum and selenium chapters and NIST atomic weights. No NASA MoSe2 or WSe2 document was found. Density, hazard and band-gap disagreements are listed in gaps.
story:
  recipe:
    line: MoSe2 is a layered compound. Each formula unit combines one molybdenum atom with two selenium atoms, in trigonal prismatic coordination, with molybdenum layers between two selenium layers. Wikipedia gives the direct reaction Mo + 2 Se giving MoSe2 at high temperature, and purification by chemical vapour transport with a halogen. The coatings in the 2025 paper were made by DC magnetron sputtering of a MoSe2 target in argon, with nitrogen added in some coatings. WSe2 has the same hexagonal layered structure; Wikipedia gives W + 2 Se giving WSe2 by sputter deposition of tungsten under selenium vapour at more than 800 K.
    parts:
      - name: Molybdenum
        symbol: Mo
        atoms: 1
        atomic_weight: 95.95
        role: The metal centre in MoSe2. Each molybdenum sits between two selenium layers, and the selenium sheets are the sliding planes. NIST prints 95.95(1).
      - name: Selenium
        symbol: Se
        atoms: 2
        atomic_weight: 78.971
        role: Forms the top and bottom layers of each sheet in MoSe2 and WSe2. Weak van der Waals bonds link the sheets, which is why they slide. NIST prints 78.971(8).
  risk_groups:
    - title: For people
      level: 0
      verdict: Toxic if swallowed or inhaled, per the SDS
      lead: The MoSe2 SDS classes the powder as toxic by swallowing and by inhalation, with repeated-exposure organ damage. The WSe2 Wikipedia infobox and PubChem give the same toxic codes, with the Warning word in some sources.
      points:
        - label: Toxicity
          line: H301 and H331 (toxic if swallowed or inhaled) appear in the Stanford SDS and in both PubChem entries. The Danger word is in the SDS, and the Wikipedia WSe2 infobox uses Warning.
        - label: Organs
          line: H373 (damage to organs through prolonged or repeated exposure) appears in the MoSe2 SDSs and in the WSe2 infobox.
        - label: Dust
          line: Dust should be avoided, with exhaust ventilation where dust forms. Further processing may make combustible dust.
        - label: Limits
          line: Selenium compounds have a 0.2 mg/m3 limit as Se in the USA (PEL) and ACGIH TLV in the Stanford SDS.
    - title: Handling the coating
      points:
        - label: Storage
          line: Store in a dry, well-ventilated place in a closed container. The MoSe2 SDS calls the powder moisture sensitive.
        - label: Ageing
          line: Ambient air storage for 40 months gave a pure MoSe2 coating with a friction of 0.081 and the highest wear rate of its series. The authors also report a thin oxide film on the surface.
  why: Molybdenum diselenide is a layered lubricant that works like molybdenum disulfide. Its layers slide with little resistance, so it lubricates where oil or grease cannot. The MoSe2 coating tested in the 2025 paper gave a steady friction of 0.081 in ambient air after 40 months of storage. The WSe2 family (sputtered WSex films in the 2017 paper) kept a friction of 0.04 to 0.07 in both humid air and dry nitrogen. Both compounds have a single-layer form that is a semiconductor, so both are studied for transistors and photodetectors. The lubricant evidence is thinner than for MoS2, and no vacuum or space data were found in the sources opened.
  uses:
    - where: Solid lubricant coatings
      line: The 2025 paper tests sputtered MoSe2 coatings for sliding parts. The authors say the coatings suit 3D complex parts and cite the aerospace industry. The 2017 paper calls WSex a good competitor for MoS2 in vacuum and space.
    - where: Transistors and photodetectors
      line: Wikipedia says the direct band gap of monolayer MoSe2 suggests applications in transistors and photodetectors. For WSe2, Wikipedia says the type can be switched between p and n by an adjacent electrode. No device number was found in the sources opened.
  can_do:
    - label: Friction in ambient air, MoSe2
      value: '0.081'
      line: The pure sputtered MoSe2 coating gave a steady friction of 0.081 in ambient air after 40 months of storage (Nanomaterials 2025).
    - label: Wear in ambient air, MoSe2
      value: Highest of the series
      line: The same pure coating had the highest wear rate of the nitrogen-alloyed series (8.67 x 10-7 mm3/N m against 4.76 x 10-7 to 5.36 x 10-7 for the alloyed coatings).
    - label: Friction, WSe film
      value: 0.04 to 0.07
      line: The sputtered WSex film gave the same friction in ambient air and dry nitrogen (2017 paper). Its steady state in dry nitrogen was 0.03 to 0.05 over 125,000 cycles.
    - label: Melting point
      value: More than 1200 degC
      line: The MoSe2 SDS gives 1200 degC (2192 degF). Wikipedia prints more than 1200 degC for both MoSe2 and WSe2.
    - label: Temperature in air
      value: Not found
      line: No oxidation onset temperature for MoSe2 or WSe2 in air was found in the sources opened.
  compare: MoSe2, WSe2 and MoS2 are all layered dry lubricants with the same sliding mechanism. The 2017 paper tested pure MoS2 and WSex films on the same tribometer. It found the MoS2 film wore at 2.4 x 10-6 mm3/N m in ambient air and 9 x 10-8 mm3/N m in dry nitrogen. The WSex film wore at 1.5 to 3 x 10-7 mm3/N m in both environments, so it was far more humidity-tolerant than MoS2. The tungsten-disulphide profile (WS2) covers the sulfide of the same tungsten family; its numbers were not re-read in this run. The MoSe2 numbers here come from a pure coating after storage in air, so they are not directly comparable with the NASA vacuum tests in the MoS2 profile. WSe films are the better choice where humidity cannot be controlled.
  compare_rows:
    - scope: material
      label: Friction in ambient air (pure coating)
      benchmark: coefficient_of_friction
    - scope: material
      label: Density
      benchmark: density
    - scope: material
      label: Melting point
      benchmark: melting_point
  handling:
    - Read the supplier safety data sheet first. The MoSe2 Stanford SDS gives H301, H331 and H373, with the Danger signal word.
    - Store the powder closed, dry and well ventilated, away from hydrogen peroxide and strong oxidizers. The SDS calls it moisture sensitive.
    - Avoid dust. Use exhaust ventilation where dust forms, and wear respiratory and eye protection.
    - Keep coated parts out of long humid storage. The 2025 paper saw a thin oxide layer after 40 months in plastic bags.
  good_for:
    - Dry sliding coatings where a friction coefficient near 0.08 in ambient air is acceptable (MoSe2), or near 0.04 to 0.07 in humid air and dry nitrogen (WSe films).
    - Two-dimensional semiconductor research on transistors and photodetectors, where the direct band gap of the monolayer is the main reason for interest.
  watch_out:
    - Toxicity. The MoSe2 SDS classes the powder as toxic by swallowing and by inhalation (H301, H331). Handle it as a toxic powder.
    - Wear in air. The pure MoSe2 coating had the highest wear of its series after storage in air.
    - Limited data. No vacuum, space or lunar data and no oxidation temperature in air were found in the sources opened.
    - Conflicting data. Density, melting point and hazard classes differ between sources, and the values are kept separately.
  verdict: 'MoSe2 is a layered dry lubricant with the same sliding mechanism as MoS2, and its semiconductor form is of interest for electronics. Its lubricant data are thin: one ambient-air coating test gives a friction of 0.081 after storage, and its hazard data are a toxic classification with conflicting detail. WSe2 films are the better lubricant choice in this profile, keeping a friction of 0.04 to 0.07 in both humid air and dry nitrogen, but those films are substoichiometric and the sources hold no space data for either compound.'