Density Functional Theory Study of Inducing Piezoelectric Response via Functionalization of a Sc ₂ C Nanosheet: Implications for Energy Conversion and Storage

Piezoelectricity is pivotal for applications in micro/nanoelectromechanical (MEMS/NEMS) systems. Inducing such a property into the two-dimensional Sc 2 CTT′ MXenes (where T and T′ are the functionalization atoms) via homogeneous and heterogeneous surface functionalization is explored. The functionalization atoms T and T′ located at the upper and lower surfaces, respectively, are identical in the case of homogeneous functionalization, while they differ in the case of heterogeneous functionalization. Upon T and T′ exchange, an additional reverse heterogeneous configuration is generated. The heterogeneous functionalization of Sc 2 CT 2 induces extraordinary in-plane and out-of-plane piezoelectric effects owing to symmetry breaking. Interestingly, both heterogeneous and its reverse configurations show approximately identical geometrical, energetic, and even elastic properties, but rather different piezoelectric coefficients. The obtained piezoelectric effect is more than ten times larger than the experimentally measured piezoelectricity of a MoS 2 -monolayer. Our study suggests a way toward more efficient nanoscale piezoelectric devices based on the Sc 2 C MXenes for energy conversion and storage.