# Quantum confinement of transition metal dichalcogenides (TMDs)

TMDs (transition metal dichalcogenides) are materials that can have a layered structure. When moving from bulk to monolayers, the bandgap changes from indirect to direct according to the image (DFT to MoSe$$_2$$). From what I understand, this may be due to the effect of quantum confinement, but I didn't understand what this phenomenon consists of for the specific case of TMDs. What is quantum confinement for TMDs?

(Kumar, A. e Ahluwalia, P., Electronic structure of transition metal dichalcogenides monolayers 1H-­MX$$_2$$ (M = Mo, W; X = S, Se, Te) from ab-­initio theory: New direct band gap semiconductors. European Physical Journal B, 85:1–7, 2012.)

• When the length of the square potential well decreases, the energy increases and is quantized because it depends on $n$: $E_n=\frac{n^2\pi^2\hbar^2}{2mL^2}$. Is that what you meant by quantum confinement in TMDs? Thanks for the answer. – Carmen González Jul 10 at 1:10