In-situ spectroscopic ellipsometry for deeply understanding the interface evolution dynamics of anodic ZrO2 nanotubes

The interface evolution dynamics within the initial anodization of Zr remains ambiguous while it occupies a pivotal role in understanding the growth kinetics and preparing desirable ZrO2 nanotubes. Herein, we conducted an in-situ study on the Zr electrode/electrolyte interface evolution with highly sensitive spectroscopic ellips-ometry. Based on the characteristic parameters of the interface layer derived from in-situ ellipsometric spectra, the dynamic evolution of the interface structure was visualized. In addition, the effects of temperature, voltage and F- concentration in the anodic solution on the interface evolution and growth kinetics of ZrO2 nanotubes were revealed. Without F-, ZrO2 grows with a self-limited mode and forms an ultrathin layer. In the presence of F-, the ZrO2 layer dissolves and forms nanotubes under the electric field-assisted dissolution (FAD) effect, and the interface evolution mainly includes three stages of ZrO2 layer formation, void initiation and nanotube generation. The interface parameters derived from in-situ ellipsometric spectra indicate that the preferred F -concentration, voltage and temperature are 0.15 M, 20 V and 293 K, respectively. Under the optimal condition, ZrO2 nanotubes grow linearly (25.4 nm s(-1)) with a porosity of similar to 50%. Moreover, the apparent activation energy of ZrO2 formation is approximately 13.5 kJ mol(-1) (fitted by the Arrhenius formula). This fundamental work on interface research provides practical guidance for the precise and controllable preparation of ZrO2 nanotubes via anodization.