Abstract
We report a novel patterning technique to direct-write microscale nanoporous gold (NPG) features by projecting laser patterns using a spatial light modulator (SLM) onto an Au/Ag alloy film immersed in diluted nitric acid solutions. Heat accumulation induced by the photothermal effect enables localized dealloying in such solutions, which is otherwise impotent at room temperature. Consequently, NPG micropatterns are formed at the irradiated spots while the surrounding alloy remains intact. We have studied the size of the patterned NPG microstructures with respect to laser power and irradiation time. The NPG microstructures become significantly more transparent compared to the original alloy film. The NPG microstructures also exhibit strong localized surface plasmon resonance (LSPR) which is otherwise weak in the original alloy film. Both the light transmission intensity and LSPR peak wavelength have been demonstrated to be sensitive to the local environmental refractive index as quantified by microscopy and spectroscopy.
Highlights
Porous materials are of great importance in many fundamental studies as well as technological applications
We reported an in situ nanoporous gold (NPG) micropatterning method by geometrical constraints to form hierarchical NPG structures during dealloying [15]. We present another in situ NPG micropatterning method by localized laser heating, during which dealloying occurs at the laser focal spots due to elevated temperature
The experimental setup consists of a 532 nm continuous wave (CW) laser (Spectra Physics Millennia Xs) with its beam expanded to ~7 mm in diameter
Summary
Porous materials are of great importance in many fundamental studies as well as technological applications. Nanoporous gold (NPG) has attracted significant interest due to its unique properties such as high surface area to volume ratio, bi-continuous nanostructure, high electrical conductivity and thiol-gold surface chemistry. NPG can be produced by dealloying of a gold alloy under open or applied electrochemical potential. Dealloying is a simple method where the less noble constituent of an alloy is selectively removed in a strong corrosive solution, e.g., concentrated nitric acid, while the more noble constituent forms an open porous network with bi-continuous pore and ligament structures. The desire to utilize NPG in various applications as well as fundamental studies motivates the development of novel fabrication and synthesis techniques since NPG properties are modified by morphological controls of the porous structures [5, 6]
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