Piezo-response in two-dimensional α-Tellurene films

Abstract: Monoelemental two-dimensional (2D) materials have attracted significant attention due to their exciting electro-mechanical properties and extreme thinness. However, most of these materials have stable centro-symmetric structures due to same electronegativities of all atoms and lack interesting properties such as piezoelectricity and ferroelectricity. Here we report the existence of piezoelectricity in atomically thin monoelemental α-Tellurium films. DFT calculations reveal that monoelemental few layer α-Tellurene is electrostrictive. However, group theory analysis shows that α-Tellurene belongs to piezoelectric C2 group due to negligible asymmetry and has high anomalous Born effective charges, similar to the traditional perovskite piezoelectric structures. Experimental exploration demonstrates the existence of through thickness piezoelectricity. With single and dual AC resonance tracking piezoelectric force microscopy, piezoelectric coefficient (d33) up to 1?pm/V is observed for the Te ultrathin films. Moderate layer dependent piezoelectricity observed in α-Te films makes it a promising candidate for the realization of atomically thin piezoelectric devices.