The growth mechanism of the coating is dependent on the timing of adding oleic acid to the solution. If the methanol/oleic acid solution is added before NaBH4 reduction, then homogenous nucleation occurs and NiB nanoparticles will form without coating the core nanoparticles in solution. The lack of oleic acid in solution during NaBH4 reduction appears to increase the energy of homogenous nucleation, thereby promoting heterogenous nucleation on crystalline nanoparticles. By adding oleic acid one minute after NaBH4 reduction, nucleation on the core nanoparticles first occurs, after which the oleic acid binds to the surface to enhance stability. Longer wait times before adding Figure . CTAC-Au@NiB with a) 8 nm coating and b) 30 nm coating. Citrate-Au@NiB with c) 3 nm, d) 6 nm, and e) 10 nm coating. f) Selective area electron diffraction pattern of e). Scale bar is 50 nm for a, c-e), 100 nm for b), and 4 nm -1 for f). oleic acid (>5 minutes) led to dissolution of the shell as the MG shell is not stable in solution without oleic acid. The capping ligand on the core of the nanoparticle also plays a role in the nucleation of the MG shell on the surface of the core. Long polymeric ligands like polyvinyl pyrrolidone, commonly used in Ag nanoparticle synthesis, do not allow for the MG shell to nucleate on the core surface. Ionic and easily removable ligands like citrate and CTAC coated nanoparticles are ideal for MG shell nucleation.