Hydrogen sensing via anomalous optical absorption of palladium-based metamaterials

Abstract

A palladium (Pd)-based optical metamaterial has been designed, fabricated and characterized for its application in hydrogen sensing. The metamaterial can replace Pd thin films in optical transmission schemes for sensing with performances far superior to those of conventional sensors. This artificial material consists of a palladium-alumina metamaterial fabricated using inexpensive and industrial-friendly bottom-up techniques. During the exposure to hydrogen, the system exhibits anomalous optical absorption when compared to the well-known response of Pd thin films, this phenomenon being the key factor for the sensor sensitivity. The exposure to hydrogen produces a large variation in the light transmission through the metamembrane (more than 30% with 4% in volume hydrogen-nitrogen gas mixture at room temperature and atmospheric pressure), thus avoiding the need for sophisticated optical detection systems. An optical homogenization model is proposed to explain the metamaterial response. These results contribute to the development of reliable and low-cost hydrogen sensors with potential applications in the hydrogen economy and industrial processes to name a few, and also open the door to optically study the hydrogen diffusion processes in Pd nanostructures.

New Trends in the Simulation of Nanosplasmonic Optical D-Type Fiber Sensors

“…Truly, the relevant feature of metamaterials is the capacity of exhibiting unusual optical characteristics that are not encountered in natural materials. For instance, metamaterials may present refractive indexes that stimulate the required boundary conditions to create surface plasmons at determined wavelengths or having optical properties that depend on the presence of certain environmental chemical species [16].…”

“…However, when considering optical structures with sizes of the order or even below the wavelength, and with complex geometries, these methods fail short. Optical devices and nanostructured materials such as photonic crystal fibers (PCF) [12], metamaterials [13], metallic nanowires [14,15,16], etc. require a distinct approach that considers the strongly localized optical modes supported and their mutual influence, that can adequately calculate the spatial distribution of optical power and the phase effects [17], using typically meshing methods.…”

Hydrogen Optical Metamaterial Sensor Based on Pd Dendritic Nanostructures

“…The Pd dendritic based sensors exhibit shorter response times than the H 2 sensor proposed in a previous work, where micrometer long Pd nanowires, within a AAO template, were used as the H 2 sensing structures . In the present case, the advantage of using Pd dendritic nanostructures is focused not only on the simplification of the fabrication process but also in achieving a faster H 2 detection within the explosive concentration range.…”

“…From these experimental data we observe that the sensor response time is of the order of minutes or even tens of minutes in the stationary regime sensing mode. The AAO template structure, although providing the mechanical stability and the alumina/Pd optical interface for which the sensitivity of the metamaterial sensor relies on, it has the disadvantage of reducing the effective exposed surface of the Pd structures. A higher Pd exposed surface, obtained e. g. through a higher alumina barrier etching time, should decrease the response time of the sensors (see section 3.3 for further details).…”

“…Either due to the increase of the surface to volume ratio or even due to the lowering of the activation energies, here related with a reduction of the enthalpy of the Pd‐hydride formation . Furthermore, working with well‐organized, nanometer sized structures also allow us to explore metamaterial phenomena at the visible range, where with a rigorous control of design and chosen materials we are capable of tuning the way light interacts with matter …”