  Multilayer MoS2 possesses highly anisotropic thermal conductivities along
in-plane and cross-plane directions that could hamper heat dissipation in
electronics. With about 9% cross-plane compressive strain created by
hydrostatic pressure in a diamond anvil cell, we observed about 12 times
increase in the cross-plane thermal conductivity of multilayer MoS2. Our
experimental and theoretical studies reveal that this drastic change arises
from the greatly strengthened interlayer interaction and heavily modified
phonon dispersions along cross-plane direction, with negligible contribution
from electronic thermal conductivity, despite its enhancement of 4 orders of
magnitude. The anisotropic thermal conductivity in the multilayer MoS2 at
ambient environment becomes almost isotropic under highly compressive strain,
effectively transitioning from 2D to 3D heat dissipation. This strain tuning
approach also makes possible parallel tuning of structural, thermal and
electrical properties, and can be extended to the whole family of 2D Van der
Waals solids, down to two layer systems.
