how to create nanoparticle from crystal lattice?

Hi,

I want to adsorb iron oxide nanoparticles inside silica matrix. For that,  I need to have structure of iron oxide nanoparticle.

In  material studio ->Import->structure->metal oxide->  , I  could find lattice of iron oxide. Now I want to make particle using that  lattice.

Could you suggest me how do I generate particle (spherical in shape) if lattice is known.