Core-shell hybrid nanoparticles are promising candidates for a wide range of applications such as waveguides, chemical and biological sensors and photonic crystals. A combination of an inorganic core comprising silica nanoparticles (SiNP) with a poly(methyl methacrylate) (PMMA) shell, obtained by reversible addition fragmentation chain transfer (RAFT) polymerization, was used to fabricate core shell nanoparticles. The surface functionalization of SiNP was successfully achieved by covalently binding the triethoxy groups of a chain transfer agent (EHT) onto the SiNP. The surface-modified SiNP were used to mediate RAFT polymerization of methyl methacrylate (MMA) by the 'grafting from' approach to form core-shell hybrid particles with high polymer grafting density. The use of RAFT allowed the design of two families of particles of different grafting densities, in order to establish the effect of grafting density on the particle self-organisation. We find that high grafting density enables these hybrid particles to form two-dimensional (2D) arrays in a colloidal crystal film as evidenced by TEM, SEM, EDX and AFM.