Out‐of‐Plane Polarization in Bent Graphene‐Like Zinc Oxide and Nanogenerator Applications

• Published in: Advanced functional materials Vol. 30; no. 5
• Main Authors: Tan, Dan, Willatzen, Morten, Wang, Zhong Lin
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.01.2020
• Subjects: Bending; Computer simulation; Electric power generation; Graphene; graphene‐like ZnO; Linear polarization; Materials science; Molecular dynamics; monolayers; Nanogenerators; out‐of‐plane polarization; piezoelectric effect; Piezoelectricity; Symmetry; Zinc oxide; Zinc oxides
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201907885

Highly efficient piezoelectric nanogenerator operation is demonstrated based on dynamic bending of graphene‐like ZnO nanosheets. Energy is harvested by an external resistor by virtue of a strong time‐varying piezoelectric polarization component perpendicular to the graphene‐like ZnO plane. It is shown analytically and verified numerically using molecular dynamics simulations that the 6¯m2 point group of flat graphene‐like ZnO is reduced to monoclinic m symmetry for bent graphene‐like ZnO. The latter symmetry allows for a nonzero and large piezoelectric polarization component perpendicular to the plane of the 2D structure. The numerical results confirm that flexoelectric effects are negligible subject to graphene‐like ZnO bending operation. Piezoelectric properties of bent graphene‐like ZnO are studied by molecular dynamics simulations. It is demonstrated that the 6¯m2 point group of flat graphene‐like ZnO is reduced to the monoclinic m subject to bending, which leads to a large out‐of‐plane polarization. Applications in nanogenerators are discussed and the results show that the bent graphene‐like ZnO can generate highly‐efficient piezoelectric power output.