Localized versus delocalized states: Photoluminescence from electrochemically synthesized ZnO nanowires

We analyze the near-band-edge photoluminescence of electrochemically deposited ZnO nanowires and directly correlate the photoluminescence properties with the carrier concentration in the nanowires as determined from electrochemical impedance spectroscopy. We find a donor density of 81019 cm−3 in the as-deposited nanowires and show that the near-band-edge emission results from band-to-band recombination processes delocalized states. A photoluminescence band centered at 3.328 eV scales with the diameter of the nanowires and is assigned to recombination processes involving surface states. We show that annealing at 500 °C in air reduces the donor density in the nanowires by more than one order of magnitude, leading to sharp excitonic transitions in the electrochemically deposited nanowire

Properties of Electrodeposited CuSCN 2D Layers and Nanowires Influenced by Their Mixed Domain Structure

International audienc

Propriétés optiques du silicium mésoporeux et ses applications potentielles

Une couche de silicium poreux formée électrochimiquement à la surface de l'émetteur d'une jonction p-n+ peut jouer efficacement le rôle d'une couche antireflet pour les cellules solaires au silicium. En ajustant la densité de courant et le temps de formation, des simple et double-couches antireflet aux propriétés optiques optimisées ont pu être réalisées, conduisant à des réflectivités effectives respectives de 7.3 et 2.7 % sur l'ensemble du spectre solaire utile pour les cellules (400-1000 nm). De hauts rendements de conversion de l'énergie solaire, de l'ordre de 13-13.4 %, sont ainsi actuellement obtenus pour des cellules au silicium multicristallin avec une couche antireflet de silicium poreux

Nanostructural and nanochemical investigation of luminescent photoelectrochemically etched porous n-type silicon

Porous silicon obtained on n-type silicon by photoelectrochemical etching in HF, is formed of a macroporous silicon layer beneath a nanoporous silicon layer. Microstructural investigations and chemical analysis at the atomic level of the nanoporous silicon film (obtained from a highly doped (111) oriented Si substrate) have been done by high resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) using a scanning transmission electron microscope (STEM). We have found chat the nanoporous Si consists of a regular Si macroarray with triangular geometry. Nanometer-size tangled wires are contained within and attached to the macroarray. HRTEM images clearly demonstrate the existence of quantum-sized Si wires made of a crystalline core covered with an amorphous layer. Electron energy loss spectra (EELS) have been recorded for different positions of the incident probe across the quantum-sized Si wires. The results obtained in the low-loss region and at the Si L$_{23}$ edge have been compared with those recorded on reference specimens (Si/SiO$_2$ interface and hydrogenated Si sample). Although they do not exclude the presence of one or a few monolayers of foreign species, of hydrogen in particular, on the outer surface, our results generally support the quantumconfinement model to interpret the observed photoluminescence in nanoporous Si

Friction weakening in granular flows deduced from seismic records at the Soufrière Hills Volcano, Montserrat

International audienceAccurate modeling of rockfalls and pyroclastic flows is still an open issue, partly due to a lack of measurements related to their dynamics. Using seismic data from the Soufrière Hills Volcano, Montserrat, and granular flow modeling, we show that the power laws relating the seismic energy E s to the seismic duration t s and relating the loss of potential energy ΔE p to the flow duration t f are very similar, like the power laws observed at Piton de la Fournaise, Reunion Island. Observations showing that t f ≃ t s suggest a constant ratio E s ∕ΔE p ≃ 10 −5. This similarity in these two power laws can be obtained only when the granular flow model uses a friction coefficient that decreases with the volume transported. Furthermore, with this volume-dependent friction coefficient, the simulated force applied by the flow to the ground correlates well with the seismic energy, highlighting the signature of this friction weakening effect in seismic data