Tailoring the Anodic Hafnium Oxide Morphology Using Different Organic Solvent Electrolytes.

Arlete Apolinário,Armandina M L Lopes,Adélio Mendes,Gonçalo N P Oliveira,Célia T Sousa,João P Araújo,Luísa Andrade,João Ventura

doi:10.3390/nano10020382

Abstract

Highly ordered anodic hafnium oxide (AHO) nanoporous or nanotubes were synthesized by electrochemical anodization of Hf foils. The growth of self-ordered AHO was investigated by optimizing a key electrochemical anodization parameter, the solvent-based electrolyte using: Ethylene glycol, dimethyl sulfoxide, formamide and N-methylformamide organic solvents. The electrolyte solvent is here shown to highly affect the morphological properties of the AHO, namely the self-ordering, growth rate and length. As a result, AHO nanoporous and nanotubes arrays were obtained, as well as other different shapes and morphologies, such as nanoneedles, nanoflakes and nanowires-agglomerations. The intrinsic chemical-physical properties of the electrolyte solvents (solvent type, dielectric constant and viscosity) are at the base of the properties that mainly affect the AHO morphology shape, growth rate, final thickness and porosity, for the same anodization voltage and time. We found that the interplay between the dielectric and viscosity constants of the solvent electrolyte is able to tailor the anodic oxide growth from continuous-to-nanoporous-to-nanotubes.

Highlights

Advances in nanoscience and nanotechnology are interconnected with the development of new platforms where the physical properties of materials/structures, like size, porosity, geometry and surface functionalization can be controlled at the nanoscale
Hafnium oxide (HfO2) with its high thermal, chemical and mechanical stability, as well as its high refractive index and dielectric constant is remarkably appealing for new nanostructure architectures like nanoporous or nanotube (NT) arrays and a large range of applications [5,6,7,8,9,10,11,12]
We investigated the growth of self-ordered anodic hafnium oxide (AHO) nanoporous/nanotubes templates synthesized by the electrochemical anodization of Hf foils

Summary

Introduction

Advances in nanoscience and nanotechnology are interconnected with the development of new platforms where the physical properties of materials/structures, like size, porosity, geometry and surface functionalization can be controlled at the nanoscale. In this way, the potential of applications is created for a large number of areas [1,2,3,4], and are pushing fast the research on the topic. Metal-oxide nanostructures, such as nanotube arrays, have been instigating great interest, due to their demand for optoelectronics, microelectronics, energy storage, solar cells, catalysis or biomedical applications [1,2,3,4,5,6]. The truth is that the use of an HfO2 compact layer on dye-sensitized solar cells (DSCs) results in improved photovoltaic performance of 66%, compared to DSCs with a conventional sol-gel processed TiO2 layer [8]

Methods

Results

Conclusion