Epitaxial growth of magnetic nickel nanodots by pulsed laser deposition

Epitaxial nickel magnetic nanodots were obtained by pulsed laser deposition (PLD) technique on Si (100) substrate using epitaxial TiN film as the template. Characterization methods include: high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM) Z-contrast imaging, selected area electron diffraction (SAD), and X-ray diffraction (XRD) techniques. The results showed that as long as no coalescence between neighboring dots occurred, the dots are all single crystal. The predominant orientation relationship observed is Ni (100) // TiN (100) // Si (100), the so-called "cube-on-cube" orientation relationship. Other rotational orientation relationships, where the nickel crystal rotates an angle with respect to TiN (011) directions, were also observed. The dots are in faceted island shapes, bounded by (111) and (001) facets. The actual size of dots varies from a few nanometers to tens of nanometers, depending on the deposition time and temperature. The shape of a certain dot was found to be closely related to its epitaxial orientation. Effects of deposition temperature and template crystalline quality were studied. It was found that deposition temperature in a certain range does not have much influence on the epitaxial orientation of dots, while the crystalline quality of titanium nitride (the underlying template) is primarily responsible for the orientation variation. At the optimum condition, samples with a large fraction of cube-on-cube orientated nickel dots could be obtained in a rather wide temperature range (up to 250 SC), as evidenced by the strong reflections from both SAD and XRD. Samples containing more than one layer of nickel and titanium nitride matrix were also studied. The results showed that the degree of orientation perfection could be greatly improved by decreasing the size of dots.