Rapid Synthesis of Uniformly Small Nickel Nanoparticles for the Surface Functionalization of Epitaxial Graphene

Nickel nanoparticles (Ni NPs) combined with carbon nanomaterials are of significant interest due to their wide range of applications, including catalysis, hydrogen storage, and sensor technologies. However, it is challenging to develop an efficient process to produce small and stable Ni NPs ideal for functionalizing graphene or substrates with complex geometries. For this purpose, a rapid, simple, and cost-effective method is presented for synthesizing uniformly small Ni NPs. The process involves cooling aqueous solutions of Ni(OAc)2 and cetyltrimethylammonium bromide (CTAB) to ≈1 °C, followed by the rapid addition of NaBH4. Crucial parameters, such as temperature and stirring rate, are precisely controlled to ensure uniform particle growth, with the reaction completing in just a few minutes. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) characterizations reveal spherical NPs with an average diameter of ≈11 nm and a narrow size distribution. Additionally, epitaxial graphene (EG) samples are functionalized with the synthesized NPs and their arrangement on the surface and their stability upon thermal annealing are investigated. X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) measurements demonstrate the degradation of CTAB, along with the recovery of Ni(0) under mild conditions (below 350 °C), with the NPs maintaining structural stability up to approximately 550 °C.