  The formation of an ideal van der Waals (vdW) contacts at
metal/transition-metal dichalcogenide (TMDC) interfaces is a critical step for
the development of high-performance and energy-efficient electronic and
optoelectronic applications based on the two-dimensional (2D) semiconductors.
In overcoming the key chal-lenges of the conventional metal deposition process
that leads to an uncontrol-lable Schottky barrier height and high contact
resistance, notable advances were recently made by transferring atomically flat
metal thin films or thermally evapo-rating indium/gold alloy. However, the
realization of an ideal vdW contact be-tween an elemental metal and TMDC
through the evaporation process is yet to be demonstrated, and particularly the
evidence of an Ohmic contact between three-dimensional metallic electrodes and
TMDCs is still unavailable. Herein, we report the fabrication of atomically
clean metal/TMDC contacts by evaporating metals at a relatively low thermal
energy and subsequently cooling the substrate holder down to 100 K by liquid
nitrogen, achieving for the indium (In)/molybdenum disulfide (MoS2) case an
accumulation-type Ohmic contact with a metal-induced electron doping density of
10$^{12}$/cm$^2$. We find that the transport at the In/MoS2 contact is
dominated by the field-emission mechanism over a wide temperature range from
2.4 to 300 K, and the contact resistance reaches 600 Ohm um and 1,000 Ohm um at
cryogenic temperatures for the few-layer and monolayer MoS2 cases,
respectively. Based on first-principles calculations, we find that the na-ture
of the ideal In/MoS2 vdW contact is characterized by the formation of in-gap
states within TMDC together with the abrupt and rigid shift of the TMDC band.
