Fig. 3.

The semiconducting gap of planar black and blue phosphorene monolayer disks increases as the number of atoms decreases. Even though the number of atoms must be reduced to create a conical shape from a planar structure, the gap decreases on conical structures with such decrease of the number of atoms, as indicated by open ticks and the tilted arrows: This reduction of the gap on a conical structure thus has a purely geometrical origin. (Dash and dash-dot lines indicate these gaps when the number of atoms is infinite.)