Understanding the morphological evolution of anodic tantalum oxide nanostructures in acidic medium†
Abstract
Nanostructures of tantalum oxide (Ta2O5) have been recognised as important and versatile materials in nanotechnology and medicinal science. However, the synthesis of shape- and size-controlled Ta2O5 nanostructures faces enormous challenges due to multi-step and expensive procedures. Over the past two decades, anodic oxidation or anodization of Ta has emerged as a facile top-down method for fabricating Ta2O5 nanostructures. Nevertheless, controlling the fabrication geometry, such as the thickness of the Ta2O5 oxide layer, and the conditions for regulating nanodimple/nanoporous/nanotube/nanorod structures remains difficult, particularly in acidic media. In the present work, we aim to understand the formation and growth mechanism of anodic Ta2O5 (ATO) nanostructures, and the conditions necessary for achieving the desired nanopatterns by adjusting various anodization parameters (i.e., anodization potential, time and HF : H2O ratio in the electrolyte). By controlling the anodizing potential and HF : H2O ratio, we have successfully obtained ATO layers with thicknesses ranging from ∼1.25 to ∼10.7 μm. Self-organized Ta2O5 nanotubes with a diameter of ∼55 nm were fabricated under the applied potential of 30 V for 2 or 4 min. The concepts and conditions for formation of Ta2O5 nanorods and agglomeration of nanotubes are revealed in this study. Furthermore, we have elucidated the rate limiting steps of Ta2O5 growth by applying various growth models. The crystallization of amorphous ATO structures and formation of Ta4O and Ta2O5 phases were understood by temperature programmed X-ray diffraction (XRD) analyses. We anticipate that the results presented in this study will enhance the current understanding of the growth of other anodic oxide nanostructures as well.
- This article is part of the themed collection: Advances in nanoporous metal films: production methods and applications