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Abstract Nanostructured dielectric overlayers can be used to increase light absorption in nanometer-thin films used for various optoelectronic applications. Here, the self-assembly of a close-packed monolayer of polystyrene nanospheres is used to template a core–shell polystyrene-TiO₂light-concentrating monolithic structure. This is enabled by the growth of TiO₂at temperatures below the polystyrene glass-transition temperature via atomic layer deposition. The result is a monolithic, tailorable nanostructured overlayer fabricated by simple chemical methods. The design of this monolith can be tailored to generate significant absorption increases in thin film light absorbers. Finite-difference, time domain simulations are used to explore the design polystyrene-TiO₂core–shell monoliths that maximize light absorption in a 40 nm GaAs-on-Si substrate as a model for a photoconductive antenna THz emitter. An optimized core–shell monolith structure generated a greater than 60-fold increase of light absorption at a single wavelength in the GaAs layer of the simulated model device. 

The size-distribution, coverage, electrochemical impedance, and mass-transport properties of H 2 gas-bubble films were measured for both planar and microwire-array platinized n + -Si cathodes performing the hydrogen-evolution reaction in 0.50 M H 2 SO 4 (aq). Inverted, planar n + -Si/Ti/Pt cathodes produced large, stationary bubbles which contributed to substantial increases in ohmic potential drops. In contrast, regardless of orientation, microwire array n + -Si/Ti/Pt cathodes exhibited a smaller layer of bubbles on the surface, and the formation of bubbles did not substantially increase the steady-state overpotential for H 2 (g) production. Experiments using an electroactive tracer species indicated that even when oriented against gravity, bubbles enhanced mass transport at the electrode surface. Microconvection due to growing and coalescing bubbles dominated effects due to macroconvection of gliding bubbles on Si microwire array cathodes. Electrodes that maintained a large number of small bubbles on the surface simultaneously exhibited low concentrations of dissolved hydrogen and small ohmic potential drops, thus exhibiting the lowest steady-state overpotentials. The results indicate that microstructured electrodes can operate acceptably for unassisted solar-driven water splitting in the absence of external convection and can function regardless of the orientation of the electrode with respect to the gravitational force vector.