528 research outputs found
Caractérisation électrique de films amorphes de As50Te 50 irradiés par des ions lourds
Des films amorphes de composition As50Te50 sont irradiés avec des ions azote et néon d'énergie comprise entre 0,5 et 2 MeV. L'évolution de leur résistance électrique est suivie pendant et après l'irradiation. La diminution de résistivité est corrélée à l'état initial de la couche ; en particulier, le recuit initial-prérecuit module l'amplitude de cette décroissance. L'accroissement de conductivité est attribué à une augmentation du nombre des défauts structuraux, lesquels provoquent une modification de la densité des états localisés dans la bande interdite
Multipole expansion of Bessel and Gaussian beams for Mie scattering calculations
Multipole expansions of Bessel and Gaussian beams, suitable for use in Mie scattering calculations, are derived. These results allow Mie scattering calculations to be carried out considerably faster than existing methods, something that is of particular interest for time evolution simulations where large numbers of scattering calculations must be performed. An analytic result is derived for the Bessel beam that improves on a previously published expression requiring the evaluation of an integral. An analogous expression containing a single integral, similar to existing results quoted, but not derived, in literature, is derived for a Gaussian beam,valid from the paraxial limit all the way to arbitrarily high numerical apertures
Tuning the properties of magnetic CdMnTe quantum dots
We show that CdMnTe self-assembled quantum dots can be formed by depositing a
submonolayer of Mn ions over a ZnTe surface prior to deposition of the CdTe dot
layer. Single dot emission lines and strongly polarized quantum dot
photoluminescence in an applied magnetic field confirm the presence of Mn in
individual quantum dots. The width of PL lines of the single CdMnTe dots is 3
meV due to magnetic moment fluctuations of the Mn ions. After rapid thermal
annealing, the emission lines of individual magnetic quantum dots narrow
significantly to 0.25 meV showing that effect of magnetic fluctuations is
strongly reduced most probably due to an increase in the average quantum dot
size. These results suggest a way to tune the spin properties of magnetic
quantum dots.Comment: 13 pages, 4 figure
Polarization control of metal-enhanced fluorescence in hybrid assemblies of photosynthetic complexes and gold nanorods
Fluorescence imaging of hybrid nanostructures composed of a bacterial light-harvesting complex LH2 and Au nanorods with controlled coupling strength is employed to study the spectral dependence of the plasmon-induced fluorescence enhancement. Perfect matching of the plasmon resonances in the nanorods with the absorption bands of the LH2 complexes facilitates a direct comparison of the enhancement factors for longitudinal and transverse plasmon frequencies of the nanorods. We find that the fluorescence enhancement due to excitation of longitudinal resonance can be up to five-fold stronger than for the transverse one. We attribute this result, which is important for designing plasmonic functional systems, to a very different distribution of the enhancement of the electric field due to the excitation of the two characteristic plasmon modes in nanorods
Laser annealing of silicon on sapphire
Silicon-implanted silicon-on-sapphire wafers have been annealed by 50-ns pulses from a Q-switched Nd : YAG laser. The samples have been analyzed by channeling and by omega-scan x-ray double diffraction. After irradiation with pulses of a fluence of about 5 J cm^–2 the crystalline quality of the silicon layer is found to be better than in the as-grown state
Optical Studies of Zero-Field Magnetization of CdMnTe Quantum Dots: Influence of Average Size and Composition of Quantum Dots
We show that through the resonant optical excitation of spin-polarized
excitons into CdMnTe magnetic quantum dots, we can induce a macroscopic
magnetization of the Mn impurities. We observe very broad (4 meV linewidth)
emission lines of single dots, which are consistent with the formation of
strongly confined exciton magnetic polarons. Therefore we attribute the
optically induced magnetization of the magnetic dots results to the formation
of spin-polarized exciton magnetic polarons. We find that the photo-induced
magnetization of magnetic polarons is weaker for larger dots which emit at
lower energies within the QD distribution. We also show that the photo-induced
magnetization is stronger for quantum dots with lower Mn concentration, which
we ascribe to weaker Mn-Mn interaction between the nearest neighbors within the
dots. Due to particular stability of the exciton magnetic polarons in QDs,
where the localization of the electrons and holes is comparable to the magnetic
exchange interaction, this optically induced spin alignment persists to
temperatures as high as 160 K.Comment: 26 pages, 7 figs - submitted for publicatio
Optical binding mechanisms: a conceptual model for Gaussian beam traps
Optical binding interactions between laser-trapped spherical microparticles
are familiar in a wide range of trapping configurations. Recently it has been
demonstrated that these experiments can be accurately modeled using Mie
scattering or coupled dipole models. This can help confirm the physical
phenomena underlying the inter-particle interactions, but does not necessarily
develop a conceptual understanding of the effects that can lead to future
predictions. Here we interpret results from a Mie scattering model to obtain a
physical description which predict the behavior and trends for chains of
trapped particles in Gaussian beam traps. In particular, it describes the
non-uniform particle spacing and how it changes with the number of particles.
We go further than simply \emph{demonstrating} agreement, by showing that the
mechanisms ``hidden'' within a mathematically and computationally demanding Mie
scattering description can be explained in easily-understood terms.Comment: Preprint of manuscript submitted to Optics Expres
Probing the inter-layer exciton physics in a MoS/MoSe/MoS van der Waals heterostructure
Stacking atomic monolayers of semiconducting transition metal dichalcogenides
(TMDs) has emerged as an effective way to engineer their properties. In
principle, the staggered band alignment of TMD heterostructures should result
in the formation of inter-layer excitons with long lifetimes and robust valley
polarization. However, these features have been observed simultaneously only in
MoSe/WSe heterostructures. Here we report on the observation of long
lived inter-layer exciton emission in a MoS/MoSe/MoS trilayer van
der Waals heterostructure. The inter-layer nature of the observed transition is
confirmed by photoluminescence spectroscopy, as well as by analyzing the
temporal, excitation power and temperature dependence of the inter-layer
emission peak. The observed complex photoluminescence dynamics suggests the
presence of quasi-degenerate momentum-direct and momentum-indirect bandgaps. We
show that circularly polarized optical pumping results in long lived valley
polarization of inter-layer exciton. Intriguingly, the inter-layer exciton
photoluminescence has helicity opposite to the excitation. Our results show
that through a careful choice of the TMDs forming the van der Waals
heterostructure it is possible to control the circular polarization of the
inter-layer exciton emission.Comment: 19 pages, 3 figures. Just accepted for publication in Nano Letters
(http://pubs.acs.org/doi/10.1021/acs.nanolett.7b03184
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