Deborah C. Koeck

Microscopic Studies of Friction and Wear at the Benzotriazole/Copper Interface

Interfacial friction and topographic changes at copper surfaces have been measured in situ with AFM in nitric acid and in acidic and neutral solutions of benzotriazole (BTA), a known corrosion inhibitor. In addition, changes in the thickness of the copper film have been measured ex situ using stylus profilometry as a function of solution treatment. These measurements demonstrate isotropic dissolution in 0.10 M HNO3 solutions and little change in neutral solutions of BTA. However in acidified solutions of BTA, the formation of a substantial reaction overlayer, the presence of higher interfacial friction, and the tip-mediated, localized dissolution of copper interface is observed. These measurements indicate that BTA plays a multifunctional role under acidic conditions. In the absence of mechanical action, BTA acts to passivate the surface from isotropic etching under acidic conditions. In regions of interfacial contact, the dissolution of a BTA-Cu reaction layer leads to the localized removal of copper through a tip-mediated process.

pH-mediated frictional forces at tungsten surfaces in aqueous environments

We have used atomic-force microscopy to measure the change in interfacial friction and adhesion between a tungsten surface and bare or alumina-coated Si3N4 tips. These measurements have been made in aqueous solutions ranging in pH from 2.2 to 8.2 in the absence of chemical or mechanical dissolution of the surface oxide. Friction is observed to vary with solution pH, and the specific manner in which interfacial friction depends on pH is influenced by the composition of the interface. The maximum friction force of the tungsten/silicon nitride system occurs at a pH of 4.7. The tungsten/alumina system has a maximum in the frictional force at a pH of 6.6. Frictional variations in these systems are related to pH-mediated changes in the electrostatic interaction between the probe tip and the sample. The pH dependence of the electrostatic interaction is determined by the relative isoelectric points of the contacting surfaces. These nanometer-scale measurements demonstrate a fundamental pathway by which variations...