Kelsey A. Folgner

Environmental durability of protected silver mirrors prepared by plasma beam sputtering

Various overcoat layers have been developed to protect silver mirrors from tarnish and corrosion. However, the mechanisms by which these protective layers improve mirror durability are not fully understood. Mixed flowing gas exposure was used to investigate the corrosion behavior of plasma beam sputtered silver mirrors with different adhesion layer materials. A small amount of nickel in the adhesion layer had a significant impact on the silver-dielectric interface. Additionally, lateral transport of silver was found to be an important factor in the corrosion process. Better stability at all layer interfaces is suggested to improve mirror durability.

Control of stress in protected silver mirrors prepared by plasma beam sputtering

Plasma beam sputtering was used to deposit dielectric-protected silver mirrors that exhibited excellent durability and controlled stress. The durability of the mirrors was strongly dependent upon the presence of a very thin chromium adhesion layer between the silver layer and the dielectric overcoat. The stress of the five-layer mirror was balanced by controlling the compressive stress in the top dielectric layer, offsetting the net tensile stress of the combination of layers below.

Digital Imaging of Particulate Contamination

The use of digital cameras and digital imaging software for the measurement of particle obscuration is discussed. Novel calibration standards are used to evaluate the sensitivity and accuracy of commercially available digital cameras for detecting microscopic dust particles and other contaminant features on surfaces. Lighting and illumination effects are also illustrated and discussed. The digital image histogram of particles on a surface is shown to give good results for the percent area coverage.

Effects of adhesion layer composition on the environmental durability of protected silver mirrors

While various layer schemes have been developed to protect thin film silver mirrors from tarnish and corrosion, the mechanisms by which these protective layers improve mirror durability are not fully understood. Mixed flowing gas exposure of plasma beam sputtered silver mirrors was used to investigate how the composition of the very thin adhesion layer changes the mechanism of corrosion feature growth. Two model mirror coatings were analyzed in which the composition of the base layer below the silver and the adhesion layer above were varied. Optical measurements and microscopy, SEM, TEM, and EDS were used to characterize the compositional and chemical effects at the layer interfaces. Large circular corrosion features formed along the silver-chromium interfaces; the addition of nickel to the layers on either side of the silver limited the growth of these features, but resulted in the corrosive attack of the silver itself.

Control of Stress in Protected Silver Mirrors Prepared by Plasma Beam Sputtering

Dielectric protected silver mirrors were prepared by plasma beam sputtering. Stress in the coatings was modified by adjusting deposition parameters. Reductions in stress were achieved without impacting coating durability.