  High quality electrical contact to semiconducting transition metal
dichalcogenides (TMDCs) such as $MoS_2$ is key to unlocking their unique
electronic and optoelectronic properties for fundamental research and device
applications. Despite extensive experimental and theoretical efforts reliable
ohmic contact to doped TMDCs remains elusive and would benefit from a better
understanding of the underlying physics of the metal-TMDC interface. Here we
present measurements of the atomic-scale energy band diagram of junctions
between various metals and heavily doped monolayer $MoS_2$ using ultra-high
vacuum scanning tunneling microscopy (UHV-STM). Our measurements reveal that
the electronic properties of these junctions are dominated by 2D metal induced
gap states (MIGS). These MIGS are characterized by a spatially growing measured
gap in the local density of states (L-DOS) of the $MoS_2$ within 2 nm of the
metal-semiconductor interface. Their decay lengths extend from a minimum of
~0.55 nm near mid gap to as long as 2 nm near the band edges and are nearly
identical for Au, Pd and graphite contacts, indicating that it is a universal
property of the monolayer semiconductor. Our findings indicate that even in
heavily doped semiconductors, the presence of MIGS sets the ultimate limit for
electrical contact.
