AbstractThis work reports the self-limiting synthesis of an atomically thin, two dimensional transition metal dichalcogenides (2D TMDCs) in the form of MoS₂. The layer controllability and large area uniformity essential for electronic and optical device applications is achieved through atomic layer deposition in what is named self-limiting layer synthesis (SLS); a process in which the number of layers is determined by temperature rather than process cycles due to the chemically inactive nature of 2D MoS₂. Through spectroscopic and microscopic investigation it is demonstrated that SLS is capable of producing MoS₂ with a wafer-scale (~10 cm) layer-number uniformity of more than 90%, which when used as the active layer in a top-gated field-effect transistor, produces an on/off ratio as high as 10⁸. This process is also shown to be applicable to WSe₂, with a PN diode fabricated from a MoS₂/WSe₂ heterostructure exhibiting gate-tunable rectifying characteristics.