Silver Film Surface Modification by Ion Bombardment Decreases Surface Plasmon Resonance Absorption

Area of Science:

• Materials Science
• Optical Engineering
• Thin Film Technology

Background:

• Durable protective coatings for silver thin films are crucial for telescope mirrors.
• Existing dielectric coatings for protected silver mirrors lack long-term durability.
• Developing advanced coatings is essential for enhancing the performance and lifespan of astronomical optics.

Purpose of the Study:

• To investigate the effects of in-situ argon ion bombardment on silver thin films used in protected mirrors.
• To assess the impact of ion bombardment on the surface morphology and optical properties of silver films.
• To optimize the fabrication process for durable protected silver mirrors for astronomical applications.

Main Methods:

• Silver thin films were deposited using electron beam evaporation.
• Dielectric layers (silicon nitride and titanium dioxide) were applied via ion-assisted electron beam evaporation.
• In-situ argon ion bombardment was performed on silver films before dielectric layer deposition.

Main Results:

• Ion bombardment altered the surface morphology and reflectivity of the silver films.
• Overall reflectivity in the 350-800 nm range improved significantly after ion bombardment.
• Improved reflectivity was attributed to decreased surface plasmon resonance coupling.

Conclusions:

• Argon ion bombardment is an effective method for enhancing the reflectivity and durability of protected silver mirrors.
• Ion bombardment appears to pin silver grain boundaries, suppressing diffusion and creating smoother interfaces.
• This technique offers a promising approach for fabricating long-lived protected silver mirrors for telescopes.