A method for making a film of core-shell nanoparticles generally uniformly arranged on a substrate uses atomic layer deposition (ALD) to form the shells. The nanoparticle cores are placed in a solution containing a polymer having an end group for attachment to the cores. The solution is then applied to a substrate and allowed to dry, resulting in the nanoparticle cores being uniformly arranged by the attached polymer chains. ALD is then used to grow the shell material on the cores, using two precursors for the shell material that are non-reactive with the polymer. The polymer chains also form between the cores and the substrate surface, so the ALD forms shell material completely surrounding the cores. The uniformly arranged core-shell nanoparticles can be used as an etch mask to etch the substrate.