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

摘要

Sintered targets of ZrO{sub}2 and Al{sub}2O{sub}3 are ablated by KrF excimer laser radiation. The processing gas atmosphere consists of O{sub}2 at pressures of 0.1-50 Pa. The films of 100 nm-10μm 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 2-10μm 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 PM MA, as antireflective coatings in the spectral rangeλ= 800-900 nm yielding a transmittance >99%.