Morphology, chemical composition, and electrical characteristics of hybrid (Ni–C) nanocomposite structures grown on the van der Waals GaSe(0001) surface

The morphology and chemical composition of metal (Ni), carbon, and composite (Ni–C) nanostructures grown on oxidized and unoxidized (0001) surfaces of a layered GaSe crystal by electron beam vacuum evaporation of the material from a liquid ion source in an electric field have been investigated using atomic force microscopy and X-ray photoelectron spectroscopy. It has been demonstrated that this technology makes it possible to grow nanostructures with different morphologies depending on the growth mode and substrate surface state. Dense homogeneous arrays of nickel nanoparticles (Ni@C) (with geometrical sizes of $\sim$1–15 nm and a lateral density of higher than 10$^{10}$ сm$^{-2}$) encapsulated into carbon shells, as well as carbon layers (with a thickness of the order of several nanometers), are grown on the unoxidized van der Waals GaSe(0001) surface, whereas Ni–C composite nanostructures are grown on the oxidized surface. The formation of oxide nanostructures on the van der Waals surface and their chemical composition have been examined. Vertical hybrid Au/Ni/(Ni–C)/$n$-Ga$_2$O$_3$(Ni@C)/$p$-GaSe structures grown on the GaSe(0001) surface contain Ni@C nanoparticles embedded in the wide-band-gap $n$-Ga$_2$O$_3$ oxide. The current-voltage characteristics of these structures at temperatures close to $T$ = 300 K exhibit specific features of the Coulomb blockade effect.