  Three-dimensional confinement allows semiconductor quantum dots (QDs) to
exhibit size-tunable electronic and optical properties that enable a wide range
of opto-electronic applications from displays, solar cells and bio-medical
imaging to single-electron devices. Additional modalities such as spin and
valley properties can provide further degrees of freedom requisite for quantum
information and spintronics. When seeking to combine these material features
into QD structures, however, confinement can cause hybridization that inhibits
the robustness of these emergent properties for insertion into quantum devices.
Here, we show that a new class of laterally-confined materials, monolayer
MoS$_2$ QDs, can be created through top-down nanopatterning of an
atomically-thin two-dimensional semiconductor so that they exhibit the same
valley polarization as in a continuous monolayer sheet.
Semiconductor-compatible nanofabrication process allows for these
low-dimensional materials to be integrated into complex systems, an important
feature for advancing quantum information applications. The inherited bulk spin
and valley properties, the size dependence of excitonic energies, and the
ability to fabricate MoS$_2$ QDs using semiconductor-compatible processing
suggest that monolayer semiconductor QDs have the potential to be multimodal
building blocks of integrated quantum information and spintronics systems.
