Monolithic NPG nanoparticles with large surface area, tunable plasmonics, and high-density internal hot-spots

Area of Science:

• Nanotechnology
• Plasmonics
• Materials Science

Background:

• Plasmonic nanostructures enhance local electric fields via surface plasmons, enabling applications in sensing, photovoltaics, imaging, and biomedicine.
• Nanoporous gold (NPG) offers unique 3D bicontinuous nanostructures and high surface area, but thin films show weak plasmonic extinction and limited tunability.
• Limitations arise because NPG pore size is smaller than the wavelength of light, hindering plasmon resonance manipulation.

Purpose of the Study:

• To overcome the limitations of thin-film nanoporous gold.
• To engineer nanoporous gold disks with enhanced plasmonic properties and tunable resonance.
• To demonstrate the fabrication and stability of these novel nanostructures.

Main Methods:

• Fabrication of nanoporous gold in the form of sub-wavelength diameter disks with sub-100 nm thickness.
• Characterization of plasmonic properties, including extinction and resonance tuning.
• Assessment of stability for both surface-bound and colloidal forms.

Main Results:

• Nanoporous gold disks exhibit high specific surface area and internal plasmonic "hot-spots" with significant electric field enhancement.
• Plasmon-matter interactions are greatly promoted, evidenced by spectral shifts in surface plasmon resonance.
• Plasmon resonance is tunable from 900 to 1850 nm by varying disk diameter (300-700 nm).

Conclusions:

• Nanoporous gold disks overcome the limitations of thin films, offering enhanced plasmonic performance.
• These disks provide tunable plasmon resonance and high electric field enhancement, promoting plasmon-matter interactions.
• Stable, fabricable nanoporous gold disks can be produced in surface-bound or colloidal forms for diverse applications.