PLD-grown Al/Zr multilayers: crystallinity, morphology, and thermal effects

In this study, Al/Zr multilayer thin films were synthesized using pulsed laser deposition (PLD) with a 248 nm KrF excimer laser to investigate their structural and surface properties for extreme ultraviolet (EUV) optical and protective coatings. Alternating Al and Zr layers were deposited on Si substrates under high vacuum, with nanometer-scale thickness control achieved via spectroscopic ellipsometry. X-ray diffraction revealed enhanced crystallinity at 400 °C, notably with strong Zr(002) orientation. SEM and AFM showed a morphological transition from smooth 2D to rough 3D growth at 500 °C, attributed to increased adatom mobility and interfacial strain. SEM images of Al at 400 °C exhibited a uniform nanocrystalline surface with compact grains and low porosity, suggesting stable 2D growth. Computational modeling based on free energy minimization supported the 2D–3D transition, predicting a critical film thickness of 1–2 nm, consistent with observations. These results demonstrate PLD’s capability to produce high-quality Al/Zr multilayers for EUV mirrors and advanced coatings.