Refurbishment of W/B₄C multilayers on Si substrate by etching a chromium buffer layer

Area of Science:

• Materials Science
• Optics
• Surface Engineering

Background:

• Multilayer coatings on optical substrates are crucial for synchrotron applications like beam monochromatization and focusing.
• Damage to these coatings from heat load, poor adhesion, stress, or vacuum necessitates substrate refurbishment.
• High-quality optical substrates are expensive and have long lead times, driving the need for reusable solutions.

Purpose of the Study:

• To develop a method for stripping W/B4C multilayer coatings from Si substrates.
• To assess the feasibility of reusing stripped substrates for recoating.
• To ensure the refurbished coating quality matches that of a new one.

Main Methods:

• Preparation of W/B4C multilayer coatings with a 2 nm Cr buffer layer on Si substrates.
• Stripping of the coating by selectively dissolving the Cr buffer layer using an etchant.
• Characterization of surface roughness and morphology using Grazing Incidence X-ray Reflectivity (GIXRR) and a 3D surface profiler.
• Recoating of the etched substrates with W/B4C multilayer coatings.

Main Results:

• A successful method for stripping W/B4C multilayer coatings by etching the Cr buffer layer was established.
• The etching time required for the multilayer structure differed significantly from that of a single Cr film.
• Post-etching surface roughness was comparable to that of a brand-new substrate, with a silicon dioxide layer identified during analysis.
• Recoated multilayer coatings on etched substrates maintained interface integrity, demonstrating the process's effectiveness.

Conclusions:

• The developed etching process enables the effective stripping of W/B4C multilayer coatings from Si substrates.
• Refurbished substrates exhibit surface roughness comparable to new ones, allowing for successful recoating.
• This technique offers a viable path to reusability for expensive optical components in synchrotron facilities.