Mechanochemical properties of one-dimensional ZnO structures

GERMÁN JOSÉ SOLDANO; MARCELO M. MARISCAL; FRANCO MARTÍN ZANOTTO

Punta de Tralca

Workshop; workshop of computational chemistry and molecular spectroscopy; 2016

Zinc oxide (ZnO) stands out as one of the most versatile nanomaterials. Among its well known application in solar cells,catalysis, chemical sensors and cosmetics, there is one particularly promising : piezoelectricity, the capacity of converting mechanical energy into electricity. The voltage induced by mechanical stress is proportional to the maximum achievable strain. This make ZnO nanowires ideal systems to use in piezoelectric nanodevices since they can stand five times more strain than the bulk material.Despite the abundant literature on these structures on the experimental side, little has been inquired from the theoretical field. The reason is mainly the lack of a reliable potential that can accurately describe the complex zinc-oxygen interaction. Previous theoretical works attempted to study these structures with simple pair potential which led to artifacts such as the formation of endless monoatomic chains. They also predict a stress-induced phase transition which has not been observed experimentally up to date. We tackled these issues using a reactive for field carefully validating results with density functional calculations. Our study is in agreement with experimental observations, and explains the artifacts of pair potentials. A detailed reaction mechanism for the phase transformation is proposed with the associated rate constant and its temperature dependence. Based on these results we propose an experimental procedure to finally observe the transformation. Further on, we make an insight on the formation of an unprecedented structure: atomic chains containing a O2 species (shown in the figure below). This species was found to be the most common one in ZnO atomic chains and drastically weakens the chain strength. Finally we show the behavior of ZnO nanowires in an aqueous media, such as the induced water structuration and the size effect on nanowire reactivity.In particular, this study gives answers to key questions on the behavior of ZnO structures at the nanoscale. From a broader perspective, it illustrates the importance of checking simulation outcomes with density functionals calculations in order to validate the use of potentials.