Abstract

A surface plasmon resonance (SPR) occurs when a thin metal film on the hypotenuse of a prism is illuminated with p-polarized light beyond the critical angle under conditions that permit the coupling into a surface plasmon, a progressive wave bound to the outer metal surface. The shape and angular position of the resonance are very sensitive functions of the conditions at the metal surface and have been used by many people to measure the properties of thin over-layers or contamination, and in the characterization of chemical and biological processes^1,2,3. Here we use it to probe environmentally induced changes in a silver layer that has been treated with a thin copper layer. In the probing of biomembranes by a surface plasmon resonance technique, the silver layers that support the plasmon are exposed to an aqueous phase. This exposure eventually leads to a deterioration of the silver, limiting its useful life. In the study of silver coatings for astronomical applications, Song discovered that an enhanced environmental resistance resulted from the incorporation of a copper underlayer⁴. Evidence supported the proposed mechanism of cathodic protection of the silver by copper that had migrated along the grain boundaries to the outer surface. This present contribution examines the effectiveness of a very thin copper layer deposited directly over the silver film in the SPR sensor.

© 1995 Optical Society of America