Ultrasmooth metal nanolayers for plasmonic applications: surface roughness and specific resistivity

Area of Science:

• Materials Science
• Nanotechnology
• Optoelectronics

Background:

• Plasmonic devices rely on surface plasmon-polariton waves at metal-dielectric interfaces.
• Energy losses in plasmonics stem from resistive heating and surface roughness.
• Achieving smooth noble metal nanolayers is crucial but challenging.

Purpose of the Study:

• To investigate the impact of different wetting layers (Ge, Ti, Ni) on the properties of silver (Ag) nanolayers.
• To evaluate the surface roughness and electrical resistivity of Ag films with varying thicknesses and interlayers.
• To identify optimal fabrication strategies for reducing losses in plasmonic devices.

Main Methods:

• Fabrication of Ag nanolayers (10, 30, 50 nm) on fused-silica substrates.
• Introduction of a 1 nm wetting layer of Germanium (Ge), Titanium (Ti), or Nickel (Ni).
• Characterization using atomic-force microscopy (AFM) for surface roughness and four-probe measurements for electrical resistivity.

Main Results:

• Specific resistivity of Ag films decreased with increasing thickness for all wetting layers.
• A 10 nm Ag film with a Ge interlayer exhibited the lowest root mean squared roughness (0.4 nm).
• Ge segregation in Ag/Ge/SiO₂ structures led to approximately double the specific resistivity compared to Ag/Ti/SiO₂ and Ag/Ni/SiO₂.

Conclusions:

• Wetting layer selection critically impacts both surface smoothness and electrical resistivity of Ag nanolayers.
• While Ge promotes surface smoothness, Ti and Ni interlayers are more effective in reducing electrical resistivity.
• Optimizing interlayers is key to mitigating energy losses and enhancing the performance of plasmonic devices.