Two-dimensional system - black phosphorus: electronic, atomic structure and transport properties of bP(100) single crystals

Abstract

The electronic, atomic structure and transport properties of black phosphorus (bP) single crystals prepared by high-pressure methods and a gas-transport reaction were studied by X-ray photoelectron spectroscopy (XPS) and scanning probe microscopy (STM, AFM). After exposure of the clean surface under atmospheric conditions, the features in the XPS spectra corresponding to the oxidized form of phosphorus were observed. The appearance of oxidized areas on the surface was also detected using AFM. The atomic resolution of the surface of a single crystal was obtained by the STM method. As a result of low-temperature transport measurements, impurity activation energies were determined, and negative magnetoresistance along the Y direction was detected. 1. INTRODUCTION Recently, in condensed-matter physics, greater attention has been paid to systems with reduced dimensionality. Two-dimensional materials, quantum threads, quantum dots, as well as various hybrid structures based on them, attract the attention of scientists for the reason that their properties often differ from those of a bulk material. Among twodimensional materials, graphene, dichalcogenides of transition metals, hexagonal boron nitride, and monoatomic layers of Si, Ge, Sn have also been extensively studied. 2D materials are thin sheets of atomic thickness that exhibit exotic physical and mechanical properties with promising potential for technological applications and fundamental science. So far, most conventional 2D materials have been derived from a limited set of bulk solids consisting of stacked, weakly bound sheets (graphite, MoS2, hexagonal boron nitride, and black phosphorus). The simplest examples exist in elemental 2D materials, of which two are known to also occur in a bulk layered form: graphite (graphene) and 2D black phosphorus (phosphorene). Phosphorus demonstrates multiple bulk allotropes such as highly reactive white phosphorus, red phosphorus and purple phosphorus, and relatively inert black phosphorus. 2D phosphorus, or phosphorene, is among the few 2D materials isolated directly from a bulk solid, specifically from black phosphorus. Black phosphorus exhibits an orthorhombic crystal structure composed of stacked, weakly bound layers. However, these layers are buckled out of the plane to form corrugated rows, resulting in significant anisotropy in mechanical strength, electrical and thermal conductivity, and optical properties. As a promising two-dimensional material, black phosphorus was also proposed which is the allotropic modification of phosphorus most stable under normal conditions [1, 2, 3]. Black phosphorus is a layered material where atomic layers are held by weak van der Waals forces. Atomic layers of bP have a "corrugated" structure, and are not flat, as, for example, in graphene. The lattice belongs to orthorhombic syngony, pr. Cmca, a = 4.37, b = 3.31, c = 10.47 Å. The distance between the layers is 5.3 Å. In the black phosphorus