Abstract

Ion beam processes have been employed in different deposition techniques for the purpose of improving the optical and mechanical properties of thin films. One technique is ion-assisted deposition (IAD) which involves the bombardment of the growing film with low energy ions. In this investigation we examined the benefits of employing the IAD process on the optical properties of thorium fluoride (ThF₄) films. Films of ThF₄ were deposited using a resistively heated boat on fused silica and sapphire substrates. The substrates were not heated, and the deposition rate was 1 nm/s. A Kaufman ion source was used to bombard the film with 300-eV Ar ions. Conventionally deposited films adsorb moisture from the environment. This causes an increase in absorption at the water absorption band near 3 μm. Examination of IR transmission spectra at 3 μm indicated that films deposited using IAD had less absorption than those deposited with no bombardment. Samples were subjected to severe conditions of temperature and humidity for 72 h. Samples prepared using IAD showed only a slight increase in absorption, while the unbombarded sample cracked and delaminated. Spectrophotometric examination of samples showed that IAD films had a higher index of refraction than the unbombarded sample.

© 1987 Optical Society of America