Given the precise control enabled by using monodisperse PS nanospheres and ALD deposition of TiO2, we considered the combination as a generic, transferrable route to light trapping in ultra-thin film absorbers. We proposed a monolithic structure for transfer to thin film, light absorber as might be used for a PCA device for THz emission. A schematic is shown in Figure -a transparent quartz carrier substrate is coated with a planar base layer of TiO2, then a core-shell PS-TiO2 monolayer monolith. This structure can be placed directly onto a light absorber such as a thin layer of GaAs-on-Si substrate that is commonly used in PCA devices. Figure shows the in-plane unit cell structure of the hexagonally close-packed monolayer of nanospheres used to simulate the enhanced absorption in a 40 nm GaAs-on-Si thin film substrate due to the use of the proposed monolithic light concentrator. An example of the steady state electric field magnitude, |E(x,y,z)| 2 , from an FDTD simulation is shown in Figure . The integrated, in-plane absorption profile (Figure )