The effect of nonuniform chemistry on interfacial fracture toughness

The adhesion of metallic-ceramic interfaces is generally ascribed to the mixture of several mechanisms, including chemical bonding, texture, strain transfer, and plasticity. This study examines the impact of alterations in chemical bonding along an interface on the nanometer scale on the interfacial fracture energy. Using a well-characterized system of W/SiO2, small areas of the interface were masked with polymer tubes to prohibit the area from adhering well to the W film. This showed that the interfacial fracture energy was proportional to the area of higher adhesion. This finding was then used to study the growth of a Ti interlayer used for adhesion promotion in a Pt/SiO2 system. Because the adhesion energy slowly grew from values near the Pt/SiO2 to values typical of Ti/SiO2, the growth mechanism for DC magnetron sputtering of thin film Ti on SiO2 was inferred to be island growth instead of layer-by-layer growth.