chemistry

Molybdenum diselenide

Molybdenum diselenide is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Molybdenum diselenide rather than just read about it. In short: Molybdenum diselenide (MoSe2) is an inorganic compound of molybdenum and selenium. Its structure is similar to that of MoS2.

Key takeaways

Molybdenum diselenide belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Molybdenum diselenide to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Molybdenum diselenide from memory before moving on to harder problems.

Reference excerpt

Molybdenum diselenide (MoSe2) is an inorganic compound of molybdenum and selenium. Its structure is similar to that of MoS2. Compounds of this category are known as transition metal dichalcogenides, abbreviated TMDCs. These compounds, as the name suggests, are made up of a transition metals and elements of group 16 on the periodic table of the elements. Compared to MoS2, MoSe2 exhibits higher electrical conductivity.

Structure Like many TMDCs, MoSe2 is a layered material with strong in-plane bonding and weak out-of-plane interactions. These interactions lead to exfoliation into two-dimensional layers of single unit cell thickness. The most common form of these TMDCs have trilayers of molybdenum sandwiched between selenium ions causing a trigonal prismatic metal bonding coordination, but it is octahedral when the compound is exfoliated. The metal ion in these compounds is surrounded by six Se2− ions. The coordination geometry of the Mo is sometimes found as octahedral and trigonal prismatic.

Synthesis Synthesis of MoSe2 involves direct reaction of molybdenum and selenium in a sealed tube at high temperature. Chemical vapor transport with a halogen (usually bromine or iodine) is used to purify the compound at very low pressure (less than 10-6 torr) and very high temperature (600–700 °C). It has to be heated very gradually to prevent explosion due to its strong exothermic reaction. Stoichiometric layers crystallize in a hexagonal structure as the sample cools. Excess selenium can be removed by sublimation under vacuum. The synthesis reaction of MoSe2 is:

Mo + 2 Se → MoSe2 Single-crystal-thick layers of MoSe2 are produced by scotch tape exfoliation from bulk crystals, by chemical vapor deposition (CVD) or molecular-beam epitaxy (MBE).

Properties The electron mobility of 2D-MoSe2 is significantly higher than that of 2D-MoS2. 2D MoSe2 adopts structures reminiscent of graphene, although the latter's electron mobility is thousands of times greater still. In contrast to graphene, monolayer MoSe2 has a direct band gap, suggesting applications in transistors and photodetectors. However, the band gap of multilayer MoSe2 is indirect.

Molybdenum diselenide exhibits anisotropy of the refractive index. The in-plane refractive index has exceptionally high values, extending 4 for wavelengths above 430 nm and reaching a maximum value of 5.117 for 825 nm, while the out-of-plane refractive index is near 3 in the visible and the infrared range of the spectrum. MoSe2 highly absorb the visible light but is transparent for the infrared.

Natural occurrence Molybdenum(IV) selenide occurs in the nature as the extremely rare mineral drysdallite.

References

Illustrations

Worked examples

Example 1 — a first encounter with Molybdenum diselenide

Start with the simplest possible case. Write down what Molybdenum diselenide claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Molybdenum diselenide before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Molybdenum diselenide ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Molybdenum diselenide

In research: Molybdenum diselenide appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Molybdenum diselenide in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Molybdenum diselenide is common in secondary-school and first-year university syllabi. It links to neighbouring topics Molybdenum(IV) compounds, Monolayers, Selenides, so understanding it makes those chapters shorter.
In everyday life: Look for Molybdenum diselenide outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Molybdenum diselenide in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Molybdenum diselenide means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Molybdenum diselenide out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Molybdenum diselenide in simple terms?

Molybdenum diselenide (MoSe2) is an inorganic compound of molybdenum and selenium. Its structure is similar to that of MoS2.

Why does Molybdenum diselenide matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Molybdenum diselenide?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Molybdenum diselenide.