Microscopic study of thin films of Ni-filled carbon nanocapsules

The work reports on Scanning Probe Microscopy (SPM) of electrical and magnetic properties of thin (∼30 nm in thickness) Ni-C nanocomposite films. The films were prepared on Si substrates by cosputtering Ni and graphite, and subsequent thermal annealing in vacuum at 400°C that led to a self-assembly of Ni-filled carbon nanocapsules (∼ 5 nm in size) uniformly dispersed in the film. The SPM measurements were carried out in a combined Scanning Tunneling Microscopy/Atomic Force Microscopy (STM/AFM) device Solver P47. Spreading resistance imaging with STM revealed a periodical structure in which the cell consisted of a low conducting central part and a periphery region 0.5-1 nm in size, with high conductivity inclusions. The cell was found to be about 5 nm in diameter that allowed us to associate this object with the carbon nanocapsule. In magnetic force microscopy (MFM) measurements, a phase shift of the Co-coated cantilever oscillations was registered during scanning. It was established that the phase image had a spotted structure with the spot size of 0.2-0.5 μm. The phase signal inside the spot was found to be irregular. Such results were obtained irrespectively of the magnetization history, i.e., whether the sample was magnetized normal or parallel to the surface, or was demagnetized. The influence of electrodynamic forces on the accuracy of MFM measurements was analyzed.