NiB shells with tunable thickness were deposited on citrate-and CTAC-Au nanoparticles (Figure ). In Figure , all particles have an approximately 8 nm thick coating. Thicker coatings of up to 30 nm, as shown in Figure , can be made by decreasing the initial Au nanoparticle concentration. For thicker coatings, some smaller NiB nanoparticles (<15 nm) nucleate in solution but can be removed using size selective centrifugal precipitation. Particles show a distinct boundary between the core and the shell, indicating that there is no diffusion. We have previously shown that Au nanocubes can also be coated in a similar manner .