Vertical Quantum Confinement in Bulk MoS2

We experimentally observe quantum confinement states in bulk MoS2 by using angle-resolved photoemission spectroscopy (ARPES). The band structure at the Gamma point reveals quantum well states (QWSs) linked to vertical quantum confinement of the electrons, confirmed by the absence of dispersion in k z and a strong intensity modulation with the photon energy. Notably, the binding energy dependence of the QWSs versus n does not follow the quadratic dependence of a two-dimensional electron gas. Instead, a linear behavior is observed that is consistent with a parabolic-like quantum well. This confinement arises from the mechanical exfoliation preparation method, which leads to the detachment of a multilayer stack from the underlying bulk. This is confirmed by density functional theory (DFT) calculations. The quantum confinement in bulk-like MoS2 not only offers the opportunity to explore intersubband transitions to exploit optical properties but also provides a means to study fundamental quantum phenomena in multilayer stacks of different thicknesses.