Optical Assets of In situ Electro-assembled Platinum Black Nanolayers

Abstract

Optoelectronic technology has been increasingly driven towards miniaturization. In this regard, maintaining the optical properties of the bulk materials while reducing their size is a critical need. How thin must the film be to preserve the bulk material´s optical absorbance and reflectance characteristics? This is the central question for our study of the in situ electro-assembly broad band optical absorber films of platinum in non-aqueous solution of PtCl4. By reducing the in situ constructed film to sub-visible-wavelength thicknesses, the measured reflectance in the region from the ultraviolet to the infrared remained close to that exhibited by the micrometre-width films. These platinum black films broadly absorb electromagnetic waves at a sub-incident-wavelength thickness owing to their plasmonically increased absorbance cross-section. Simulation of various incident energy electron trajectories gives insights into the electron depth through the porous platinum black of ρ = 1.6 g/cm3 and previews the optical behaviour close to the atomic thickness.

Electrochemical growth mechanism of nanoporous platinum layers

“…Fourier Transform Infra-red spectra have been recorded for the cathode (Fig. 3c ), before (green line) and after platinum deposition (blue line) show low reflectance of the porous platinum layer in the wavenumber region 500 cm −1 ÷ 7500 cm −1 , in agreement with our previous reported data 7 .…”

“…To create a nanoporous electrode, the co-generation of hydrogen along with metal deposition, represented a scientific interest for a long time 1 – 3 . This co-generation of hydrogen during the platinum ion reduction takes place at the electrochemical generation of platinum black at the cathode in aqueous media 1 – 3 or in non-aqueous media 7 . The role of hydrogen abundance at the cathode during the metal deposition is directly connected with the porosity of the metal foam formation.…”

“…The deposition starts in certain regions on the surface, where a cauliflower-like structure with a height of approximately 20 nm appears, which subsequently extends to cover the entire surface 7 . The initiation of platinum black can occur at the cathode defects; however, one cannot exclude that this effect results from unusual electric field interferences.…”

“…The infra-red absorbance has been shown to be best for nanoporous platinum layers on copper and silver electrodes 7 . In this work, we studied the mechanism of the formation of nanoporous platinum layers and excluded the influence of electrode material on the process.…”

“…Feltham and Spiro 3 mainly contributed to the understanding of the nucleation and growth mechanism of the platinum layer in aqueous media in 1972. Recently, we demonstrated the electrochemical growth of porous platinum layers from a non-aqueous solution of PtCl 4 7 . For example in microtechnology, electrochemistry from non-aqueous solutions is preferred over electrochemistry from aqueous solutions.…”