Analysis of Adhesion Strength between Silver Film and Substrate in Plain Silver Surface Plasmon Resonance Imaging Sensor

Recently, a plain silver surface plasmon resonance imaging (SPRi) sensor with a gold adhesion-enhancing layer has been studied extensively because of its desirable sensitivity and durability. To study the effect of the gold adhesion-enhancing layer on the durability of the sensor, we studied the adhesion strength between the silver film and the substrate. In a cross-sectional analysis, we observed the spatial elemental distribution of the sensor and found clear chromium-gold and gold-silver interfaces under transmission electron microscopy (TEM). By the indentation-inducing film method, we measured the critical load and depth of the silver film breaking. We also tested the working and shelf lives of the sensor with different thicknesses of the adhesion-enhancing layer. Testing results showed that the adhesion-enhancing layer thickness was related to the shelf life of the sensor. Results of the above studies showed that the gold adhesion-enhancing layer improved the adhesion strength of the silver film and the durability of the plain silver SPRi sensor.