Evaporated coatings need generally high substrate temperature to obtain a more dense structure of the layers avoiding the humidity adsorption when the coating itself is exposed to the atmosphere. Moreover, the employment of fluorides as low refractive index layers can increase the stress level of the coating because of their frequent hygroscopicity. Under severe operational conditions, the adsorbed water causes an expansion of the layer with a consequent destruction of the coating if the adhesion strengths is not strong enough to counter balance the increased stress. The ion beam assistance can be a useful method to increase the density of the coating produced by the evaporation technique. In fact, the ion bombardment during the thin film growth improves the packing density and enhances thin film resistance to moisture penetration. Magnesium fluoride (MgF₂) and barium fluoride (BaF₂) are two low refractive index materials employed in the optical coatings production whereas yttria material (Y₂O₃) can be used as high refractive index layer. In this work the effect of the ion beam assistance on the optical coating capability to offer resistance to atmosphere humidity penetration was investigated. Since the presence of an absorption band at a wavelength of 3 micrometers reveals the presence of the water in the layers, some of the investigated coatings were deposited on silicon substrates to measure the transmittance in the infrared region.

Date Published: 4 November 1994
PDF: 10 pages
Proc. SPIE 2253, Optical Interference Coatings, (4 November 1994); doi: 10.1117/12.192066

Published in SPIE Proceedings Vol. 2253:
Optical Interference Coatings
Florin Abeles, Editor(s)