Single-Crystalline Metallic Films Induced by van der Waals Epitaxy on Black Phosphorus

Abstract

The properties of metal-semiconductor junctions are often unpredictable\nbecause of non-ideal interfacial structures, such as interfacial defects or\nchemical reactions introduced at junctions. Black phosphorus (BP), an elemental\ntwo-dimensional (2D) semiconducting crystal, possesses the puckered atomic\nstructure with high chemical reactivity, and the establishment of a realistic\natomic-scale picture of BP's interface toward metallic contact has remained\nelusive. Here we examine the interfacial structures and properties of\nphysically-deposited metals of various kinds on BP. We find that Au, Ag, and Bi\nform single-crystalline films with (110) orientation through guided van der\nWaals epitaxy. Transmission electron microscopy and X-ray photoelectron\nspectroscopy confirm that atomically sharp van der Waals metal-BP interfaces\nforms with exceptional rotational alignment. Under a weak metal-BP interaction\nregime, the BP's puckered structure play an essential role in the adatom\nassembly process and can lead to the formation of a single crystal, which is\nsupported by our theoretical analysis and calculations. The experimental survey\nalso demonstrates that the BP-metal junctions can exhibit various types of\ninterfacial structures depending on metals, such as the formation of\npolycrystalline microstructure or metal phosphides. This study provides a\nguideline for obtaining a realistic view on metal-2D semiconductor interfacial\nstructures, especially for atomically puckered 2D crystals.\n