Towards dark current suppression in metallic photocathodes by selected-area oxidation

Area of Science:

• Materials Science
• Surface Science
• Photocathode Technology

Background:

• Achieving oxide-free polycrystalline copper (Cu) surfaces is crucial for advanced applications.
• Surface properties like work function significantly influence photocathode performance.
• Minimizing dark current is essential for high-performance accelerator photocathodes.

Purpose of the Study:

• To investigate the effect of UV ozone treatment on the work function of cleaned copper surfaces.
• To evaluate the impact of this surface modification on quantum efficiency.
• To explore the feasibility of selective area oxidation for photocathode fabrication.

Main Methods:

• Preparation of oxide-free polycrystalline Cu surfaces via acetic acid etching and chemical-mechanical polishing.
• Application of UV ozone treatment to modify the Cu surface.
• Characterization of surface properties, including work function and quantum efficiency.
• Testing of masking techniques using Silicon (Si) and glass for selective oxidation.

Main Results:

• UV ozone treatment increased the work function of cleaned Cu by up to 0.5 eV.
• A significant reduction in quantum efficiency was observed at 265 nm.
• Selected-area oxidation was demonstrated using Si or glass masking.
• No increase in surface roughness was detected after oxidation.

Conclusions:

• UV ozone treatment effectively increases the work function of copper surfaces.
• This surface modification offers a potential method to reduce dark current in accelerator photocathodes.
• The process does not negatively affect the desired photoemission region, making it suitable for photocathode applications.