  Nickel nanoparticles (Ni NPs), thanks to their peculiar properties, are
interesting materials for many applications including catalysis, hydrogen
storage, and sensors. In this work, Ni NPs are synthesized in aqueous solution
by a simple and rapid procedure with cetyltrimethylammonium bromide (CTAB) as a
capping agent, and are extensively characterized by dynamic light scattering
(DLS), scanning electron microscopy (SEM), and atomic force microscopy (AFM).
We investigated their shape, dimension, and their distribution on the surfaces
of SiO2 and epitaxial graphene (EG) samples. Ni NPs have an average diameter of
~11 nm, with a narrow size dispersion, and their arrangement on the surface is
strongly dependent on the substrate. EG samples functionalized with Ni NPs are
further characterized by X-ray photoelectron spectroscopy (XPS), as made and
after thermal annealing above 350{\deg}C to confirm the degradation of CTAB and
the presence of metallic Ni(0). Moreover, high resolution scanning tunneling
microscopy (STM) topographies reveal the structural stability of the NPs up to
550 {\deg}C.
