  The properties of metal-semiconductor junctions are often unpredictable
because of non-ideal interfacial structures, such as interfacial defects or
chemical reactions introduced at junctions. Black phosphorus (BP), an elemental
two-dimensional (2D) semiconducting crystal, possesses the puckered atomic
structure with high chemical reactivity, and the establishment of a realistic
atomic-scale picture of BP's interface toward metallic contact has remained
elusive. Here we examine the interfacial structures and properties of
physically-deposited metals of various kinds on BP. We find that Au, Ag, and Bi
form single-crystalline films with (110) orientation through guided van der
Waals epitaxy. Transmission electron microscopy and X-ray photoelectron
spectroscopy confirm that atomically sharp van der Waals metal-BP interfaces
forms with exceptional rotational alignment. Under a weak metal-BP interaction
regime, the BP's puckered structure play an essential role in the adatom
assembly process and can lead to the formation of a single crystal, which is
supported by our theoretical analysis and calculations. The experimental survey
also demonstrates that the BP-metal junctions can exhibit various types of
interfacial structures depending on metals, such as the formation of
polycrystalline microstructure or metal phosphides. This study provides a
guideline for obtaining a realistic view on metal-2D semiconductor interfacial
structures, especially for atomically puckered 2D crystals.
