Here, we show that a self-assembled, 2D colloidal crystal of monodisperse polystyrene nanospheres can be used as a template for further functionalization via atomic layer deposition (ALD). ALD-deposited TiO2 can penetrate the nanospheres to add a higher refractive index material while preserving the structure of the selfassembled, monodisperse layer. A key reason for this is that we showed that the TiO2 deposition in the ALD reactor was possible at temperatures low enough to avoid disrupting the periodicity of the polystyrene templating layer. This process is related to other chemical infiltration techniques described elsewhere. Further, we use finite difference time domain (FDTD) simulations to study the optical properties of these coreshell surfaces. We use these simulations to design favorable optical resonances in a monolithic, light-concentrating structure that shows enhanced absorption in a simulated ultra-thin, GaAs-based PCA device. Finally, we discuss the implications and potential advantages of a device architecture based on this monolithic structure.