Young's modulus and hardness of Pd thin films

Young's modulus Ef and hardness Hf of Pd thin films were measured by the nano-indentation technique. Pd films were made under various conditions with the film thickness tf varied from 20 to 280 nm and deposition temperature Ts from 25 to 360 °C in vacuum. As an independent check, the Young's modulus 〈Ef〉 of some selected Pd films was measured again by the X-ray diffraction plus stress measurement. The values of Ef and 〈Ef〉 in general agree with each other for the same Pd film. The surface morphology of each film was examined by an atomic force microscope, and the surface roughness parameters, such as Sq and Sa, were calculated. From X-ray diffraction studies we estimated the grain size D and the ratio I111 / I200, where I111 and I200 are the peak amplitudes of the (111) and (200) diffraction lines, of the Pd films. We also find that both Ef and Hf are dependent on tf. In short, Ef increases when 20 nm < tf < 196 nm, reaches a maximum at tf = 196 nm, and decreases afterwards, while Hf decreases monotonically with increasing tf. The Ef data are analyzed based on the structural properties, such as the ratio I111 / I200 and the density δ, of each Pd film. The Hf data are discussed based on the tf dependence of grain size D. Finally, the conditions required to make a good nano-indentation measurement on a thin-film sample are summarized.