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In this article we present a study on the influence of the size of mesoscopic gold nanostructures on silicon (Si) with well-defined geometry on their reactivity towards hydrogen evolution and carbon dioxide reduction. The onset potential for these two reactions decreases by 170 mV with structure size decreasing from 1400 nm to 75 nm, whereby hydrogen evolution is accelerated somewhat more than carbon dioxide reduction. This effect is independent of the doping type and level of the substrate, i.e. it occurred for moderately doped p-type Si (p-Si) under illumination, as well as on n-type (n-Si) and degenerately doped p-type Si (p++-Si) in the dark. Therefore, the increase in reactivity is not influenced by the metal/semiconductor contact which changes from Schottky-type for p-Si to ohmic for p++-Si. Due to the relatively large structure size, quantum confinement and a change in surface defect density do not play a role. We argue that the role of the metal structure edges, which increases with decreasing structure size, is decisive. At the edges, the electrostatic charge and potential distribution as well as the chemical environment are different compared to the conditions at the interior surface. At present it remains unclear whether the reactivity enhancement is predominantly due to an electrostatic effect or a chemical, bifunctional mechanism.

Iron oxide nanoparticles represent a promising low-cost environmentally-friendly material for multiple applications. Especially hematite (α-Fe2O3) nanoparticles demonstrate great possibilities in energy storage and photoelectrochemistry. A hydrothermal one-pot synthesis can be used to synthesise hematite nanoparticles. Here, the particle formation, nucleation and growth of iron oxide nanoparticles using a FeCl3 precursor over time is monitored. The formation of 6-line ferrihydrite seeds of 2–8 nm which grow with reaction time and form clusters followed by a phase transition to ~15 nm hematite particles can be observed with ex situ X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman and UV/Vis spectroscopy. These particles grow with reaction time leading to 40 nm particles after 6 hours. The changes in plasmon and electron transition patterns, observed upon particle transition and growth lead to the possibility of tuning the photoelectrochemical properties. Catalytic activity of the hematite nanoparticles can be proven with visible light irradiation and the use of silver nitrate as scavenger material. The generation of elementary silver is dependent on the particle size of iron oxide nanoparticles while only slight changes can be observed in the oxygen generation. Low-cost nanoscale hematite, offers a range of future applications for artificial photosynthesis.

In this article, we present a refined nanostructuring method, lift-off nanoimprint lithography (LO-NIL), which allows the deposition of high-quality metal nanostructures due to a bilayer resist process and compare it to nano-transfer printing (nTP), a purely additive metal printing technique. LO-NIL and nTP are used as accurate methods for the fabrication of ordered plasmonic metal nanostructure arrays on semiconducting substrates over large areas using the example of gold nanodisks on silicon. The possibility of feature size adjustment in LO-NIL during the fabrication process is especially useful for tuning plasmonic resonance peaks between the visible and the mid-infrared range as well as fine-tuning of these resonances. In UV-VIS-NIR spectroscopic measurements, a significant blueshift in the plasmonic resonance was found for nTP samples compared to the ones fabricated with the lift-off technique. It was concluded that this shift originates from a metal/substrate interface roughness resulting in a chang...