THE LATTICE EXPANSION IN NANOMETER-SIZED NI POLYCRYSTALS

Solid Ni thin film samples with grain sizes of 6-15 nm were prepared by using a JG-PF high-frequency sputtering system. Quantitative x-ray diffraction measurements on the as-sputtered samples revealed that the peak positions of the x-ray diffraction lines of Ni nanocrystallites are lower than those of the corresponding perfect Ni crystal and that the deviation increases with a decrease in grain size. Further investigations showed that the lattice parameter of the Ni nanocrystallite is significantly increased by refining the grain size. The above results were qualitatively interpreted ia terms of the thermodynamic theory, which suggests that a supersaturation of vacancies in the lattice structure of a nm-grained system is obtained as the grain size is decreased down to a few nanometres.