173 research outputs found
Quantum vacuum photon-modes and superhydrophobicity
Nanostructures are commonly used for developing superhydrophobic surfaces.
However, available wetting theoretical models ignore the effect of vacuum
photon-modes alteration on van der Waals forces and thus on hydrophobicity.
Using first-principle calculations, we show that superhydrophibicity of
nanostructured surfaces is dramatically enhanced by vacuum photon-modes tuning.
As a case study, wetting contact angles of a water droplet above a polyethylene
nanostructured surface are obtained from the interaction potential energy
calculated as function of the droplet-surface separation distance. This new
approach could pave the way for the design of novel superhydrophobic coatings.Comment: 5 pages, 4 figures, final version published in Physical Review
Letter
First-principle calculation of solar cell efficiency under incoherent illumination
Because of the temporal incoherence of sunlight, solar cells efficiency
should depend on the degree of coherence of the incident light. However,
numerical computation methods, which are used to optimize these devices,
fundamentally consider fully coherent light. Hereafter, we show that the
incoherent efficiency of solar cells can be easily analytically calculated. The
incoherent efficiency is simply derived from the coherent one thanks to a
convolution product with a function characterizing the incoherent light. Our
approach is neither heuristic nor empiric but is deduced from first-principle,
i.e. Maxwell's equations. Usually, in order to reproduce the incoherent
behavior, statistical methods requiring a high number of numerical simulations
are used. With our method, such approaches are not required. Our results are
compared with those from previous works and good agreement is found.Comment: 13 pages, 3 figures, published in Optics Expres
Alternative expression of the Bloch wave group velocity in loss-less periodic media using the electromagnetic field energy
Growth dynamics and light scattering of gold nanoparticles in situ synthesized at high concentration in thin polymer films
Layer Homogenization Method for Modeling Additive Color Effect in Natural Photonic Polycrystals --- The Case of Entimus imperialis Weevil
Plasmon hybridization in pyramidal metamaterials: a route towards ultra-broadband absorption
Pyramidal metamaterials are currently developed for ultra-broadband
absorbers. They consist of periodic arrays of alternating metal/dielectric
layers forming truncated square-based pyramids. The metallic layers of
increasing lengths play the role of vertically and, to a less extent, laterally
coupled plasmonic resonators. Based on detailed numerical simulations, we
demonstrate that plasmon hybridization between such resonators helps in
achieving ultra-broadband absorption. The dipolar modes of individual
resonators are shown to be prominent in the electromagnetic coupling mechanism.
Lateral coupling between adjacent pyramids and vertical coupling between
alternating layers are proven to be key parameters for tuning of plasmon
hybridization. Following optimization, the operational bandwidth of Au/Ge
pyramids, i.e. the bandwidth within which absorption is higher than 90%,
extends over a 0.2-5.8 micrometers wavelength range, i.e. from UV-visible to
mid-infrared, and total absorption (integrated over the operational bandwidth)
amounts to 98.0%. The omni-directional and polarization-independent
high-absorption properties of the device are verified. Moreover, we show that
the choice of the dielectric layer material (Si versus Ge) is not critical for
achieving ultra-broadband characteristics, which confers versatility for both
design and fabrication. Realistic fabrication scenarios are briefly discussed.
This plasmon hybridization route could be useful in developing photothermal
devices, thermal emitters or shielding devices that dissimulate objects from
near infrared detectors.Comment: 13 pages, 9 figures, accepted for publication in Optics Expres
Bleaching of sol-gel glass film with embedded gold nanoparticles by thermal poling
Gold clusters embedded in glass are expected to be hard to dissolve in the form of ions since gold is essentially a nonreactive metal. In spite of that, bleaching of Au-doped nanocomposite sol-gel glass film on a soda-lime glass substrate is demonstrated in which electric-field thermal poling is employed to effectively dissolve randomly distributed gold nanoparticles (15 nm in diameter) embedded in a low conductivity sol-gel glass film with a volume filling factor as small as 2.3%. The surface plasmon absorption band at 520 nm is suppressed in the region covered by the anodic electrode. The phenomenon is explained by the ionization of the gold nanoparticles and the redistribution of gold ions in the glass matrix due to the action of the extremely high electrostatic field locally developed during poling
Influence of the pattern shape on the photonic efficiency of front-side periodically patterned ultrathin crystalline silicon solar cells
Patterning the front side of an ultra-thin crystalline silicon (c Si) solar
cell helps keeping the energy conversion efficiency high by compensating for
the light absorption losses. A super-Gaussian mathematical expression was used
in order to encompass a large variety of nanopattern shapes and to study their
influence on the photonic performance. We prove that the enhancement in the
maximum achievable photo-current is due to both impedance matching condition at
short wavelengths and to the wave nature of light at longer wavelengths. We
show that the optimal mathematical shape and parameters of the pattern depend
on the c Si thickness. An optimal shape comes with a broad optimal parameter
zone where fabricating errors would have much less influence on the efficiency.
We prove that cylinders are not the best suited shape. To compare our model
with a real slab, we fabricated a nanopatterned c Si slab via Nano Imprint
Lithography.Comment: 21 pages, 7 figure
- …