MoS2 (Molybdenum Disulfide): Structure, Properties and Uses

Molybdenum disulfide (MoS₂) is a layered compound of molybdenum and sulfur. In bulk it has been used for decades as a dry lubricant. Thinned down to a single layer, it becomes a two-dimensional semiconductor, which is why it is one of the most studied materials in electronics, catalysis and energy storage research.

Structure

Each MoS₂ layer is a sheet of molybdenum atoms sandwiched between two sheets of sulfur atoms, held together by strong covalent bonds. Neighboring layers are held to each other only by weak van der Waals forces. That weak bonding between layers is what lets them slide over each other, which explains the lubricating behavior, and it is also what makes it possible to peel or grow single layers.

MoS₂ belongs to a family called transition metal dichalcogenides (TMDs), along with materials such as WS₂, MoSe₂ and WSe₂. It occurs naturally as the mineral molybdenite.

Phases: 2H and 1T

The most common and stable form is the 2H phase, which is semiconducting. A metastable 1T phase, which is metallic, can be produced by chemical treatment such as lithium intercalation. The 1T phase is of interest for catalysis and electrodes because of its higher conductivity, but it slowly converts back to 2H.

Band gap: why monolayer MoS₂ is different

Bulk MoS₂ has an indirect band gap of roughly 1.2 eV. As the material is thinned, the band gap widens, and a single layer has a direct band gap of around 1.8 to 1.9 eV. A direct gap means the material absorbs and emits light efficiently, so monolayer MoS₂ shows strong photoluminescence that bulk crystals do not. Unlike graphene, which has no band gap, MoS₂ can switch a transistor fully off, which makes it a candidate for thin, low-power electronics.

Main uses

• Lubrication: bulk powder is added to greases and coatings, especially where oil-based lubricants fail, such as in vacuum or at high load.
• Electronics and optoelectronics: field-effect transistors, photodetectors and flexible devices built on monolayer or few-layer films.
• Catalysis: the exposed edges of MoS₂ layers are active for the hydrogen evolution reaction, making it a low-cost alternative to platinum in electrolysis research.
• Batteries: as an anode material in lithium-ion and sodium-ion research, where its layered structure can host ions between sheets.
• Sensors: its large surface area and sensitivity to adsorbed molecules suit gas and biosensing.

How MoS₂ is made into 2D material

• Mechanical exfoliation: peeling layers from a bulk crystal with tape. It gives high-quality flakes but small, randomly placed ones.
• Liquid-phase exfoliation: breaking bulk powder into thin flakes in a solvent with sonication or shear. It scales well and produces dispersions and powders.
• Chemical vapor deposition (CVD): growing continuous monolayer films on substrates such as sapphire or SiO₂/Si. This is the usual route for device work.
• Physical vapor deposition: sputtering from an MoS₂ target for coatings and thin films.

Choosing a form of MoS₂

The right form depends on what you are building:

• For inks, composites, catalysts and electrodes, start with powders such as monolayer MoS₂ micron-size flakes or MoS₂ nano flakes.
• For optical and quantum confinement studies, MoS₂ quantum dots offer a much smaller particle size.
• For transistors and photodetectors, use a ready-made CVD monolayer MoS₂ film on sapphire or SiO₂/Si, or a mechanically exfoliated monolayer film.
• For sputtered coatings, an MoS₂ sputtering target.

Handling and storage

MoS₂ is stable in air at room temperature but slowly oxidizes at elevated temperatures, and thin films degrade faster than bulk material. Store powders and films dry and sealed, and handle nanopowders with the usual precautions for fine particles: work in a fume hood or enclosure and avoid breathing dust.

Related materials, including graphene and other nanopowders, are in the nanomaterials collection.