  Layered transition-metal dichalcogenides have emerged as exciting material
systems with atomically thin geometries and unique electronic properties.
Pressure is a powerful tool for continuously tuning their crystal and
electronic structures away from the pristine states. Here, we systematically
investigated the pressurized behavior of MoSe2 up to ~ 60 GPa using multiple
experimental techniques and ab -initio calculations. MoSe2 evolves from an
anisotropic two-dimensional layered network to a three-dimensional structure
without a structural transition, which is a complete contrast to MoS2. The role
of the chalcogenide anions in stabilizing different layered patterns is
underscored by our layer sliding calculations. MoSe2 possesses highly tunable
transport properties under pressure, determined by the gradual narrowing of its
band-gap followed by metallization. The continuous tuning of its electronic
structure and band-gap in the range of visible light to infrared suggest
possible energy-variable optoelectronics applications in pressurized
transition-metal dichalcogenides.
