Fabrication Of Micro-Nano-structural Ni Films And Research Of Ultrafast Electron Dynamics

The ultrafast electron dynamics of ferromagnetic Nickle film and the Nickel film with nano-structure means great for the information industry. That is because they offer the way to improve the reading and writing speed and the stability of the micro-nano-device. Besides the femtosecond laser is an effective tool to investigate the ultrafast dynamics. The femtosecond laser offers much shorter pulse than the fundamental relaxation time in nickel film. It means it can stimulate the film to a real nonequilibrium condition。And with the femtosecond pump-probe technique, the time resolution in the experiment have reached femtosecond domain. So we used femtosecond laser pump-probe technique to investigate the ultrafast dynamics in nickel film and the film with nano size structure.Ni films with different parameters(thickness,substrate) were prepared by magnetron sputter technique. Then the ammonia etching technique was used to form nano particles on film surface. After that the component,surface topography and crystallinity property of Ni thin films were investigated by scanning electronic microscope (SEM),X-ray diffraction (XRD) and atom force microscope (AFM) methods. And it was shown that there were micro-nano-structures on the surface of the film.The transient reflectivity changes of the samples were measured through femtosecond pump-probe technique. The signals on Ni film revealed that the substrate,the thickness of the film influence the reflectivity signal. Also the measurements revealed the electron thermalization time was between 18 and 47fs in Ni film. This value is some faster than reported before. The signals on the films with micro-nano -structure revealed that the electron thermalization time was longer than the nickel film. We deduced that it was caused by the discontinuity of the electron band which was close to the Fermi level.