Pulsed laser deposition of alumina and zirconia thin films on polymers and glass as optical and protective coatings

Abstract

Sintered targets of ZrO2 and Al2O3 are ablated by KrF excimer laser radiation. The processing gas atmosphere consists of O2 at pressures of 0.1–50 Pa. The films of 100 nm–10 μm in thickness are deposited on polymethylmethacrylate (PMMA), polycarbonate (PC) and glass (fused silica) substrates. Analytical techniques used for the determination of structural characteristics of the films are optical and electron microscopy. The thickness and the complex refractive index are determined by ellipsometry. The optical film thickness, reflectivity and transmittivity of the films at different wavelengths are determined in situ and ex situ using optical spectroscopy. The hardness and elastic modulus of the films are investigated using nano-indentation.The investigations concentrate on the influence of the oxygen pressure, the target-to-substrate distance and the laser fluence on the refractive index of the films, which is correlated with the film density. The compaction of the films is achieved by particles impinging with kinetic energies above 30 eV on the growing surface.Dense (94% of the bulk density), transparent and hard (Vickers hardness 1200, elastic modulus 190 GPa) alumina films 2–10 μm in thickness have been deposited on glass substrates. Alumina films thicker than 500 nm deposited on PMMA or PC substrates delaminate due to large compressive stress in the films. Multilayer systems of alumina and zirconia are deposited on micro-optics of PMMA, as antireflective coatings in the spectral range λ=800–900 nm yielding a transmittance >99%.