Nanoporous structure of a GdF(3) thin film evaluated by variable angle spectroscopic ellipsometry

Area of Science:

• Materials Science
• Optics
• Laser Technology

Background:

• Deep-ultraviolet (DUV) and vacuum-ultraviolet (VUV) excimer lasers require advanced optical coatings.
• Environmental contamination, scattering loss, and laser irradiation durability are key challenges for optical coatings at these wavelengths.
• Wide bandgap metal fluorides are emerging as preferred materials for DUV/VUV laser optics.

Purpose of the Study:

• To investigate the optical properties and nanostructure of gadolinium fluoride (GdF3) thin films.
• To understand the relationship between film structure, porosity, and surface roughness.
• To assess the susceptibility of nanostructured fluoride films to environmental contamination.

Main Methods:

• Variable angle spectroscopic ellipsometry (VASE) was employed to analyze thin GdF3 films on CaF2 (111) substrates.
• An effective medium approximation (EMA) model was utilized to extract film porosity and surface roughness parameters.
• Atomic force microscopy (AFM) was used to corroborate the nanostructure and surface topography.

Main Results:

• Ellipsometric modeling revealed a multilayer film structure with a dense bottom layer and progressively porous middle layers.
• Significant surface roughness was quantified and confirmed by AFM.
• The nanostructure of the GdF3 films was shown to attract environmental contaminants.

Conclusions:

• Nanostructured GdF3 films exhibit complex structural evolution.
• Film porosity and surface roughness are critical factors influencing optical performance and contamination.
• Understanding these nanostructural characteristics is essential for developing durable DUV/VUV laser optics.