  Inducing chirality in optically and electronically active materials is
interesting for applications in sensing and quantum information transmission.
Two-dimensional (2D) transition metal chalcogenides (TMDs) possess excellent
electronic and optical properties but are achiral. Here we demonstrate
chirality induction in atomically thin layers of 2D MoS2 by functionalization
with chiral thiol molecules. Analysis of X-ray absorption near-edge structure
and Raman optical activity with circularly polarized excitation suggest
chemical and electronic interactions that leads chirality transfer from the
molecules to the MoS2. We confirm chirality induction in 2D MoS2 with circular
dichroism measurements that show absorption bands at wavelengths of 380-520 nm
and 520-600 nm with giant molar ellipticity of 10^8 deg cm2/dmol 2-3 orders of
magnitude higher than 3D chiral materials. Phototransistors fabricated from
atomically thin chiral MoS2 for detection of circularly polarized light exhibit
responsivity of >10^2 A/W and maximum anisotropy g-factor of 1.98 close to the
theoretical maximum of 2.0, which indicates that the chiral states of photons
are fully distinguishable by the photodetectors. Our results demonstrate that
it is possible achieve chirality induction in monolayer MoS2 by molecular
functionalization and realise ultra-sensitive detectors for circularly
polarized photons.
