Measurement of mechanical properties of nanoscaled ferrites using atomic force microscopy at ultrasonic frequencies

To measure local elasticity by Atomic Force Acoustic Microscopy (AFAM), the sample placed in a commerical AFM is insonified by ultrasonic waves or the cantilever is oscillated at ultrasonic frequencies. In contact with the specimen, the cantilever-tip system vibrates out-of-plane and its resonances are measured. A quantitative model based on linear tip-sample force shows that the stiffness of the specimen can be derived from the shift of the contact resonance frequencies relative to resonance frequencies of the free cantilever. We report AFAM results with a well-known material, silicon single-crystal oriented in <100> direction, to prove the consistence of the local measurement of elasticiy. Then, in thin films of magnetite Fe3O4 and maghemite gamma Fe2O3 with spinel structure, the influence of the deviation fi om the stoichiometry on the elasticity for a given grain size is determined. (C)1999 Acta Metallurgica Inc.