In this study, we report the fabrication and characterization of a novel PEC tandem cell, consisting of p-Si/TiO2/Fe2O3 core/shell/hierarchical nanowire (csh-NW) array photocathode and TiO2/TiO2 core/shell nanotube (cs-NT) array photoanode, for overall solar water splitting in a neutral pH water. The p-Si/n-TiO2/n-Fe2O3 csh-NWs, made mainly by solution-processed methods, offer significantly improved performance in the neutral pH water with a low (positive) onset potential and photoactivity at zero bias, due to the increased reaction surface area, effective energy band alignment among p-Si, n-TiO2 and n-Fe2O3 enhancing the charge separation, improved optical absorption, and enhanced gas evolution. Nitrogen modification (annealing under N2) is used to further enhance the csh-NWs photocathodic performance. The PEC tandem cell is then able to handle overall solar water splitting in the neutral pH water with a solar-to-hydrogen (STH) efficiency of ~0.18%. The achieved results demonstrate initial steps toward the realization of full PEC devices using earth-abundant materials for solar hydrogen generation suggesting competitive performance when solar matched photoanode core material and co-catalysts are used.

Highly sensitive hydrogen detection at room temperature can be realized by employing solution-processed MoS₂ nanosheet-Pd nanoparticle composite. A MoS₂-Pd composite exhibits greater sensing performance than its graphene counterpart, indicating that solvent exfoliated MoS₂ holds great promise for inexpensive and scalable fabrication of highly sensitive chemical sensors.

Nanoscale size-effects drastically alter the fundamental properties of semiconductors. Here, we investigate the dominant role of quantum confinement in the field-effect device properties of free-standing InAs nanomembranes with varied thicknesses of 5-50 nm. First, optical absorption studies are performed by transferring InAs "quantum membranes" (QMs) onto transparent substrates, from which the quantized sub-bands are directly visualized. These sub-bands determine the contact resistance of the system with the experimental values consistent with the expected number of quantum transport modes available for a given thickness. Finally, the effective electron mobility of InAs QMs is shown to exhibit anomalous field- and thickness-dependences that are in distinct contrast to the conventional MOSFET models, arising from the strong quantum confinement of carriers. The results provide an important advance towards establishing the fundamental device physics of 2-D semiconductors.