Preventing Corrosion of Aluminum Metal with Nanometer-Thick Films of Al₂O₃ Capped with TiO₂ for Ultraviolet Plasmonics

Abstract

Extending plasmonics into the ultraviolet range imposes the use of aluminum to achieve the best optical performance. However, water corrosion is a major limiting issue for UV aluminum plasmonics, as this phenomenon occurs significantly faster in presence of UV light, even at low laser powers of a few microwatts. Here we assess the performance of nanometer-thick layers of various metal oxides deposited by atomic layer deposition (ALD) and plasma-enhanced chemical vapor deposition (PECVD) on top of aluminum nanoapertures to protect the metal against UV photocorrosion. The combination of a 5 nm Al2O3 layer covered by a 5 nm TiO2 capping provides the best resistance performance, while a single 10 nm layer of SiO2 or HfO2 is a good alternative. We also report the influence of the laser wavelength, the laser operation mode and the pH of the solution. Properly choosing these conditions significantly extends the range of optical powers for which the aluminum nanostructures can be used.As application, we demonstrate the label-free detection of streptavidin proteins with improved signal to noise ratio. Our approach is also beneficial to promote the long-term stability of the aluminum nanostructures. Finding the appropriate nanoscale protection against aluminum corrosion is the key to enable the development of UV plasmonic applications in chemistry and biology.

Ultraviolet optical horn antennas for label-free detection of single proteins

“…Lastly, a 12 nm-thick SiO2 layer is deposited by plasma-enhanced chemical vapor protection (PECVD, PlasmaPro NGP80 from Oxford Instruments) to protect the aluminum surface against corrosion. 43,44 Protein samples and photostabilizing buffer β-galactosidase from Escherichia coli (156 tryptophan residues, PDB 1DP0), β-galactosidasestreptavidin conjugate (180 tryptophan residues) and streptavidin from Streptomyces avidinii (24 tryptophan residues) are purchased from Sigma-Aldrich. The proteins are dissolved in a Hepes buffer (25 mM Hepes, 300 mM NaCl, 0.1 v/v% Tween20, 1 mM DTT and 1 mM EDTA 1mM at pH 6.1) which was reported to stabilize β-galactosidase conformation and avoid aggregate formation.…”

Fluorescence Brightness, Photostability, and Energy Transfer Enhancement of Immobilized Single Molecules in Zero-Mode Waveguide Nanoapertures

“…39,73 To protect the aluminum surface against corrosion from the salt buffer, a 10 nm-thick SiO2 layer was deposited by plasma-enhanced chemical vapor protection (PECVD, PlasmaPro NGP80 from Oxford Instruments). 74,75 DNA samples. The sequence of the forward strand was 5'-Cy3B TG GCT GCG CAG GAC GAG CGC-3'biotin where the 5' end was labelled with a Cy3B dye using a NHS amino modifier C6 and the sample was incubated with a 300 pM solution of the biotin labelled DNA for 30 minutes, followed by three times rinsing with T50 buffer to remove the unadsorbed DNA.…”

“…We used the same conditions as in our previous studies. ,,,, A 100 nm-thick aluminum layer was deposited onto a microscope glass coverslip by electron-beam-assisted evaporation (Bühler Syrus Pro 710) with a 10 nm/s rate. , Arrays of nanoapertures with 110 nm diameter were then milled sequentially with an FIB system (FEI dual beam DB235 Strata) using 10 pA current and 30 kV voltage. The milling included a 80 nm-deep undercut into the borosilicate glass substrate to maximize the signal enhancement. , To protect the aluminum surface against corrosion from the salt buffer, a 10 nm-thick SiO 2 layer was deposited by plasma-enhanced chemical vapor protection (PlasmaPro NGP80 from Oxford Instruments). , …”

Al@TiO2 Core–Shell Nanoparticles for Plasmonic Photocatalysis

“…Many strategies, including sensitizing TiO 2 with dyes or quantum dots, , implanting metal or nonmetal dopants, and decorating TiO 2 with plasmonic nanostructures, − have been proposed to expand its photocatalytic reactivity into the visible region of the spectrum. There have been several demonstrations of Al–TiO 2 photocatalysts, such as Al nanovoid arrays and Al nanostructures on TiO 2 films. , The interaction between the Al and TiO 2 in these structures was solely limited to near-field enhancement; however, the structures include the native Al oxide layer, which impedes charge transfer between the two materials. Al–TiO 2 nanostructures in which Al is in direct contact with TiO 2 have not been previously reported.…”

“…There have been several demonstrations of Al−TiO 2 photocatalysts, such as Al nanovoid arrays and Al nanostruc-tures on TiO 2 films. 24,25 The interaction between the Al and TiO 2 in these structures was solely limited to near-field enhancement; however, the structures include the native Al oxide layer, which impedes charge transfer between the two materials. Al−TiO 2 nanostructures in which Al is in direct contact with TiO 2 have not been previously reported.…”