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Green hydrogen production by water splitting holds great potential as a clean and renewable source of energy for sustainable energy solutions. However, the efficiency of this process is hampered by the sluggish oxygen evolution reaction (OER). Overcoming these kinetic hurdles requires the development of highly efficient electrocatalysts. This study explores the effect of transition metal doping on the electrocatalytic properties of Ni(OH)2 microflowers towards alkaline OER. Transition metal‐doped Ni(OH)2 microflowers, with highly porous structures due to interconnected nanosheets, are synthesized by a facile, cheap, and scalable chemical bath deposition (CBD), and combined with graphene paper (GP) substrates to fabricate electrodes. Through a systematic exploration of the relationship between the transition metal dopant element type (Mn, Fe, Co, Zn) or concentration and the consequent electrochemical properties, Co‐doping demonstrates improvement in the overpotential at a current density of 10 mA cm−2 (329 mV), Tafel slope (45 mV dec−1), and other key performance indicators of Ni(OH)2 microflowers for OER. These results are attributed to the high number of active sites and their enhanced electrocatalytic activity benefiting from the presence of the transition metal dopant. The proposed strategy paves the way for the development of cost‐effective and highly efficient electrocatalysts for water splitting technologies. [ABSTRACT FROM AUTHOR]

In this work, we report the growth of MoO3 nanowires (NWs) by thermal evaporation with the aim of evaluating their use as catalysts for oxygen evolution reaction (OER) in water splitting application. Growth was performed on two different kinds of substrates, Si(100) and Si(111), and at different growth temperatures between 200 and 400 °C. The effect of such experimental parameters on the morphological, structural, and compositional properties was investigated. The deposited materials were characterized by in situ reflection high-energy electron diffraction, scanning electron microscopy, transmission electron microscopy, Rutherford backscattering spectroscopy, and X-ray diffraction. For a growth temperature of 200 °C, a flat and amorphous oxide layer is obtained, while as the temperature is increased, one-dimensional (1D) growth prevails on 2D layer formation. In particular, at 400 °C, the deposited material consists of a high-density array of MoO3 crystalline NWs a few nm in diameter and up to about 0.5 μm in length. Only in the case of Si(111) substrates have small three-dimensional structures formed and coexisted with NWs since the beginning of the growth process. Finally, the OER activity of MoO3 NWs was evaluated. The nanostructures were deposited on graphene paper, and their electrochemical activity was investigated and compared to other nonprecious metal-based catalysts for alkaline OER. Our MoO3-based electrodes showed overpotentials of 330 and 340 mV at 10 mA/cm2 (η10) depending on the average length of NWs and a quite high mass activity associated with a low catalyst loading, thus fitting the best performing electrocatalysts. Our results demonstrate that MoO3 NWs are suitable candidates for the development of anode electrodes for water splitting application. [ABSTRACT FROM AUTHOR]

Abstract The usage of semiconductor nanostructures is highly promising for boosting the energy conversion efficiency in photovoltaics technology, but still some of the underlying mechanisms are not well understood at the nanoscale length. Ge quantum dots (QDs) should have a larger absorption and a more efficient quantum confinement effect than Si ones, thus they are good candidate for third-generation solar cells. In this work, Ge QDs embedded in silica matrix have been synthesized through magnetron sputtering deposition and annealing up to 800°C. The thermal evolution of the QD size (2 to 10 nm) has been followed by transmission electron microscopy and X-ray diffraction techniques, evidencing an Ostwald ripening mechanism with a concomitant amorphous-crystalline transition. The optical absorption of Ge nanoclusters has been measured by spectrophotometry analyses, evidencing an optical bandgap of 1.6 eV, unexpectedly independent of the QDs size or of the solid phase (amorphous or crystalline). A simple modeling, based on the Tauc law, shows that the photon absorption has a much larger extent in smaller Ge QDs, being related to the surface extent rather than to the volume. These data are presented and discussed also considering the outcomes for application of Ge nanostructures in photovoltaics. PACS: 81.07.Ta; 78.67.Hc; 68.65.-k

Germanium quantum dots (QDs) embedded in SiO2 or in Si3N4 have been studied for light harvesting purposes. SiGeO or SiGeN thin films, produced by plasma enhanced chemical vapor deposition, have been annealed up to 850 °C to induce Ge QD precipitation in Si based matrices. By varying the Ge content, the QD diameter can be tuned in the 3-9 nm range in the SiO2 matrix, or in the 1-2 nm range in the Si3N4 matrix, as measured by transmission electron microscopy. Thus, Si3N4 matrix hosts Ge QDs at higher density and more closely spaced than SiO2 matrix. Raman spectroscopy revealed a higher threshold for amorphous-to-crystalline transition for Ge QDs embedded in Si3N4 matrix in comparison with those in the SiO2 host. Light absorption by Ge QDs is shown to be more effective in Si3N4 matrix, due to the optical bandgap (0.9-1.6 eV) being lower than in SiO2 matrix (1.2-2.2 eV). Significant photoresponse with a large measured internal quantum efficiency has been observed for Ge QDs in Si3N4 matrix when they are used as a sensitive layer in a photodetector device. These data will be presented and discussed, opening new routes for application of Ge QDs in light harvesting devices. [ABSTRACT FROM AUTHOR]

The pile-up of arsenic at the Si/SiO2 interface after As implantation and annealing was investigated by high resolution Z-contrast imaging, electron energy-loss spectroscopy (EELS), grazing incidence x-ray fluorescence spectroscopy (GI-XRF), secondary ion mass spectrometry, x-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, as well as Hall mobility and four-point probe resistivity measurements. After properly taking into account their respective artifacts, the results of all methods are compatible with each other, with EELS and GI-XRF combined with etching providing similar spatial resolution on the nanometer scale for the dopant profile. The sheet concentration of the piled-up As at the interface was found to be ∼1×1015 cm-2 for an implanted dose of 1×1016 cm-2 with a maximum concentration of ∼10 at. %. The strain observed in the Z-contrast images also suggests a significant concentration of local distortions within 3 nm from the interface, which, however, do not seem to involve intrinsic point defects. [ABSTRACT FROM AUTHOR]

A detailed study was conducted to examine the pile-up of arsenic at the Si/Si[O.sub.2] interface after As implantation and annealing. The results obtained provide insight into the strain observed in the Z-contrast images due to significant concentration of local distortions within 3 nm from the interface which does not involve intrinsic point defects.