Free standing membranes to study the optical properties of anodic TiO2 nanotube layers

TL;DR

This study investigates the optical properties of free-standing anodic TiO2 nanotube membranes, revealing how their structure and carbon content influence light absorption and reflectance, aiding the design of photo-electrochemical devices.

Contribution

It introduces a method to analyze optical properties of free-standing TiO2 nanotube membranes in transmission mode, highlighting the impact of carbon contamination on their optical response.

Findings

Optical properties vary with nanotube thickness and crystallinity.

Carbon content causes a sub-bandgap optical response.

Data supports improved design of TiO2-based photo-electrochemical devices.

Abstract

In the present work we investigate various optical properties (such as light absorption and reflectance) of anodic TiO2 nanotubes layers directly transferred as self-standing membranes onto quartz substrates. This allows investigation in a transmission geometry which provides significantly more reliable data than measurements on the metallic Ti substrate. Light transmission and reflectance measurements were carried out for layers of thicknesses varying from 1.8 to 50 micrometer, and the layers were investigated in their amorphous and crystalline form. A series of wavelength-dependent light attenuation coefficients are extrapolated and found to match the photocurrent vs. irradiation wavelength behavior. However, a feature specific to anodic nanotubes is that their intrinsic carbon content causes a sub-bandgap response that is proportional to the carbon contamination content in the TiO2 nanotubes. Overall the extracted data provide valuable basis and understanding for the design of photo-electrochemical devices based on TiO2 nanotubes.