60 research outputs found
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 cmâ3 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 formĂ©e Ă©lectrochimiquement Ă la surface de l'Ă©metteur d'une jonction p-n+ peut jouer efficacement le rĂŽle d'une couche antireflet pour les cellules solaires au silicium. En ajustant la densitĂ© de courant et le temps de formation, des simple et double-couches antireflet aux propriĂ©tĂ©s optiques optimisĂ©es ont pu ĂȘtre rĂ©alisĂ©es, conduisant Ă des rĂ©flectivitĂ©s 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'Ă©nergie 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 edge have been compared with those recorded on reference specimens
(Si/SiO 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 SoufriĂšre 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 SoufriĂšre 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 ÎE 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 â t s suggest a constant ratio E s âÎE p â 10 â5. 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
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