Tailoring the photoelectrochemistry of catalytic metal-insulator-semiconductor (MIS) photoanodes by a dissolution method.

Apart from being key structures of modern microelectronics, metal-insulator-semiconductor (MIS) junctions are highly promising electrodes for artificial leaves, i.e. photoelectrochemical cells that can convert sunlight into energy-rich fuels. Here, we demonstrate that homogeneous Si/SiOx/Ni MIS junctions, employed as photoanodes, can be functionalized with a redox-active species and simultaneously converted into high-photovoltage inhomogeneous MIS junctions by electrochemical dissolution. We also report on the considerable enhancement of performance towards urea oxidation, induced by this process. Finally, we demonstrate that both phenomena can be employed synergistically to design highly-efficient Si-based photoanodes. These findings open doors for the manufacturing of artificial leaves that can generate H2 under solar illumination using contaminated water.

Spontaneous decoration of silicon surfaces with MoOx nanoparticles for the sunlight-assisted hydrogen evolution reaction.

The immersion of oxide-free Si surfaces in MoS42- aqueous solutions induces their spontaneous decoration with isolated MoOx nanoparticles (NPs). The process is versatile and was used on planar Si (100) as well as on antireflective Si (111) micro-pyramid (SimPy) arrays. The NP decoration does not affect the optical properties of the surface in the visible range and improves the performance of the hydrogen evolution reaction (HER) under simulated sunlight. The simplicity and the scalability of the technique make it highly promising for the fabrication of catalytically active photoelectrodes. More specifically, the MoOx-decorated SimPy produced H2 at a rate of 11 µmol cm-2 min-1 with a faradaic efficiency higher than 90% at -0.35 V vs. RHE. Furthermore, this process can be of great interest for other applications in high-performance electronic devices.

Phase-matched frequency doubling at photonic band edges: efficiency scaling as the fifth power of the length.

By exploiting the unique properties of periodic stratified media we demonstrate simultaneously phase matching and enhancement of the optical field under second order nonlinear interaction. This leads to a second harmonic efficiency growth faster than the fifth power of the structure length, far better than the usual quadratic behavior associated with second order nonlinear effects.