Thermodynamic, Structural, and Piezoelectric Properties of Adatom-Doped Phosphorene and Its Applications in Smart Surfaces

Engineering the surface morphology is an effective way to obtain specific functionalities in applications of smart surfaces. Developing two-dimensional (2D) smart materials, which can undergo morphology changes under appropriate external stimuli, is a promising route to pursue for smart-surface design. In the work presented here, using density-functional-theory calculations, we systematically study the thermodynamic stability, crystal structure, and piezoelectric properties of black phosphorene (black P) doped with metallic atoms on one side with different concentrations. Particularly, Li-doped black P (P4Li2) has a d31 value of 6.28 pm/V, which is at least 4 times larger than that of any other 2D piezoelectric material. Via finite-element-method simulations, we show a P4Li2-based prototype design for obtaining a surface-morphology change under a vertical electric field. The surface swelling pattern can be detected by human fingers with an appropriate design of the geometry. This demonstrates the promise of 2D piezoelectric materials for use in smart-surface applications.