Crystallographic Characterization of Black Phosphorene and its Application in Nanostructures

Abstract

The central question in the field of two-dimensional (2D) materials is how a material behaves when it is patterned at nanometer scale with different edge geometries. Due to the anisotropy inherent in the puckered structure, black phosphorene nanostructures may have more varieties of edge geometries. Here, we present a comprehensive 2D planar crystallographic characterization of phosphorene uniformly by a chiral vector (angle), from which a new type of edge atomic configuration, the slope edge geometry is discovered. The phosphorene nanoribbons (PNRs) with slope edges, like previously noticed zigzag and skewed-armchair PNRs, also own interesting twofold-degenerate edge states. These three marginal directions, together with the skewed-zigzag and armchair directions without edge states, divide a phosphorene into four regions among which the electronic property is different from each other. Further, for a PNR cutting along any possible direction, by taking into account the z-direction in structure, whether or not it owns edge states depends on the existence of periodic zigzag-like morphology along the edges. For application, moreover, we propose a PNR-based z-shaped homogenous junction with scale ∼100 nm, where the central scattering region between two PNR electrodes is a phosphorene quantum dot (PQD) of PNR segment with various edge morphologies. Interestingly, the calculated conductance by Kwant code based on tight-binding combing with scattering-matrix for the junction relies sensitively on the central PQD edge states. In specification, for the junctions of PQD with edge states the conductance exhibit a terrace with resonant oscillations near Fermi energy, otherwise the electron transport is blocked due to the absence of edge states. Remarkably, the number of oscillating peaks exactly matches to the number of sawtooth along an edge of PQD, since the discrete energy levels of the zigzag-like edge provide the transporting channels for electrons. The results here may be extended to the group-VA 2D materials for observing the electronic property of nanostructures in experiments, and provide a reference for the preparation of better nano-devices. *

Edge and sublayer degrees of freedom for phosphorene nanoribbons with twofold-degenerate edge bands via electric field

“…The edge and layer, for instance, have been regarded as tunable equivalents of the spin-one-half DOF in bilayer phosphorene nanoribbons (PNRs) with zigzag-edge [5]. However, here we treat the edge and sublayer as two DOFs in a recently revealed monolayer slope-edged PNR (sPNR) with twofold-degenerate edge bands [6].…”

“…And the properties of these important edge states have been recognized [5,28,[31][32][33][34]. Moreover, we may cut a phosphorene sheet so that the zigzag (armchair) direction intersects the puckered ridges under an chiral angle other than 0º (90º), resulting in PNRs with other possible edge geometries [6]. These ribbons can be classified into two types, one type with edge states including zPNR and the other without edge states including aPNR.…”

“…These ribbons can be classified into two types, one type with edge states including zPNR and the other without edge states including aPNR. In specification, from our previous definition of the chiral vector T =ma 1 /2+na 2 /2 for the crystallographic characterizations on planar phosphorene with chiral numbers (m, n), the cases of m+n=even integer have defined the all possible planar crystal directions [6]. Hence a ribbon can be generally denoted as (m, n)PNR.…”

“…Furthermore, according to the edge atomic arrangement (morphology), PNRs with edge states can be further divided into two categories. When both m and n are odd, the outermost edge atoms of a PNR are alternately located at the two sublayers, resulting in the shuttle-shaped twofold-degenerate edge bands near E F , such as (1,3)PNR and (3,1)PNR [6,27,35,36]. While for both even m and n, the outermost atoms are located at the same sublayer and the ribbon only has a near-flat degenerate edge band, such as (2,4)PNR and (4,2)PNR [6].…”

“…When both m and n are odd, the outermost edge atoms of a PNR are alternately located at the two sublayers, resulting in the shuttle-shaped twofold-degenerate edge bands near E F , such as (1,3)PNR and (3,1)PNR [6,27,35,36]. While for both even m and n, the outermost atoms are located at the same sublayer and the ribbon only has a near-flat degenerate edge band, such as (2,4)PNR and (4,2)PNR [6]. And some of the typical ribbons with these two categories of edge states have already been observed in experiments [37,38].…”