A nanoindentation approach for unveiling the photoplastic effects by a “light switch”: A case study on ZnO

Abstract The nanoindentation method is a widely utilized approach for characterizing the mechanical properties of materials at the nanoscale. In typical nanoindentation tests, the mechanical responses of materials are monitored while maintaining constant environmental factors, such as lighting and temperature, in order to ensure the reliability of the results. Here, we propose a testing method that switches the light conditions during a single nanoindentation creep test to detect slight changes in the mechanical response due to weak light illumination. To achieve this, a reference sample of fused silica was employed, which is insensitive to light, in order to compensate for the thermal expansion/contraction of approximately 1 nm due to the light environment. The calibrated results revealed the instantaneous suppressive influence of light illumination on the indentation creep behavior of ZnO. It was found that upon initiating illumination, the indentation creep rate decreased by 45%, whereas terminating illumination led to a dramatic 19.4‐fold increase in the creep rate. The effective testing pattern involving a “light switch” enables quantitatively visualizing the light illumination effects through the instant “jump” in the creep strain rate within a single test, facilitating the detection of minor and instantaneous effects of light environments on indentation creep behavior.