Phonon evidence of Kohn Anomalies in nanogenerator ZnO

Abstract

The origin of unique piezotronic properties within low dimensional nanomaterial systems will enable an in-depth understanding of nanogenerators for broad applications in the future. Notably, the low dimensional ZnO exhibits stronger temperature sensitivity than the bulk ZnO, which will be proved by the extreme phonon instability at room temperature 300 K. The temperature dependence shows a nearly Fermi-Dirac δ-function. We have proposed the selection criteria for the nanogenerator material screening based on the theoretical derivation of elastic perturbation entropy (EP-S). The resulted phonon conservation behaviors induced by the discontinuity in phonon dispersion dominates the highly sensitive response to the local electrical field change. The Kohn Anomalies (KA) has been identified in the wide bandgap semiconductor ZnO, in which discontinuous energy conversions induced by such KA or boundary discontinuity will not only minimize the degeneration effect but also induce the high piezotronic response. Moreover, we have carefully examined the ZnO surface on both structural and electronic structures, which identified the surface metallic properties. Thus, these theoretical results have supplied sound phonon evidence for the unique piezotronic properties in ZnO, which will facilitate the new insight in the future research of nanogenerators.