The correlation of structural with optical measurements on thin aluminium films evaporated in ultra high vacuum

The optical constants n and k are given for thin aluminium films which were deposited in vacuum at a pressure ∼ 1 × 10−9 torr on glass substrates held at 25°c or –196°c. The measurements were made in situ st light wavelengths 5490 Å and 5461 Å using an ellipsometer. All films showed some degree of preferred orientation. Several films were subjected to a detailed x-ray line profile analysis. The optical constants given for opaque films are higher than values previously reported in the literature. The effect of vacuum annealing at 230°c was also studied. The optical constants of opaque films showed little change in contrast to thinner films for which marked changes in n and k were observed on annealing. A decrease in k was observed for thin films irrespective of substrate deposition temperature. A film deposited at 25°c showed a decrease in n. A film deposited at – 196°c showed an increase in n. An increase in n is attributed to an increase of defect concentration. A combination of x-ray and optical results supports the view that the substrate has a significant effect on the early stages of growth of a film. A layer of material close to the substrate influences the optical constants of non-opaque films but because of the skin depth limitation, thick films do not show such variations.