Electronic structure of nickel nanoparticles encapsulated in carbon was characterized by photoelectron, X-ray absorption, and X-ray emission spectroscopies. Experimental spectra are compared with the density of states calculated in the frame of the density functional theory.The carbon shell of Ni nanoparticles has been found to be multilayer graphene with significant (about 6%) amount of Stone-Wales defects. Results of the experiments evidence protection of the metallic nanoparticles from the environmental degradation by providing a barrier against oxidation at least for two years. Exposure in air for 2 years leads to oxidation only of the carbon shell of Ni@C nanoparticles with coverage of functional groups.

Nickel and iron nanoparticles encapsulated in carbon were synthesized by contactless levitation melting of metal drops and their evaporation in a flow of an inert gas containing a hydrocarbon. The products were characterized by means of transmission electron microscopy, photoelectron spectroscopy, and X-ray absorption spectroscopy. It was established that carbon coating protects the metallic nanoparticles from the environmental degradation by providing a barrier against oxidation and ensures stability of the ferromagnetic core metal inside that provides their extremely high catalytic activity, biocompatibility, and nontoxicity.

iThe changes in the electronic structure and nature of the chemical bonds due to the ordering of the intercalated atoms inside the van der Waals gap were observed for the first time.