Aluminum corrosion protection by ALD and PECVD for UV plasmonics
What happens when you shine a UV laser onto a single aluminum nanohole filled with water? See the video below of the experiment, accelerated 5x. Holes get brighter once exposed to the laser: this is laser-induced corrosion of the aluminum film by water molecules. It is not direct laser damage (we use a power of 60 µW, 3x below the direct photodamage threshold). This photocorrosion is very general once aluminum, water and UV laser are present, which correspond to 99% of the biosensing applications of UV plasmonics.
In a recent publication in ACS Applied Nano Materials, we use various metal oxides layers deposited by atomic layer deposition (ALD) or plasma-enhanced chemical vapor deposition (PECVD) on top of the aluminum to protect against UV photocorrosion. We discuss the best material choice, and report the influence of different experimental conditions. Choosing the optimum protection and conditions significantly extends the corrosion resistance by more than 20x.
This approach is the key to extend plasmonics into the UV range in water-based environments. We apply it to demonstrate the label-free UV detection of streptavidin proteins. Alternatively, the ALD/PECVD approach also improves the long-term corrosion resistance of Al structures in corrosive chloride solutions.
Preprint freely available on arXiv 2106.09392.