Authors: A.R. Vaz, M.C. Salvadori, and M. Cattani
Affilation: Institute of Physics of the University of Sao Paulo, Brazil
Pages: 177 - 180
Keywords: Young modulus, nanostructured films, metallic films
Young moduli (E2) of nanostructured metallic thin films are determined by measuring the resonance frequencies of AFM cantilevers. The cantilevers have been uniformly coated with metallic films. The E2 is determined using the vibrating beam theory and taking into account the resonance frequencies of the coated and uncoated cantilevers. The E2 values were found to be smaller than the corresponding bulk elastic moduli. As well known, the elastic constants of a material are directly related to its atomic bonds strength. Theoretical models show that the elastic moduli of nanocrystalline materials are essentially due to the grain sizes and the grain boundaries structures. The interfacial adhesive energy between grains and, consequently, the interfacial strain, depends critically of the interfacial structure. It is expected that the interfacial structure, which is disordered, highly defected, produces an elastic softening. According to computer simulations, interfacial effects between grains are responsible by an elastic moduli softening in ns-materials. This softening effect is observed in our experimental results. It is also predicted, that the elastic constants decrease as the grain sizes decrease. This is also observed in our films, which have grain sizes between 30 and 50 nm.