We investigate the prospects of HgTe/HgCdTe quantum wells for long-wavelength interband lasers (λ = 15–30 μm). The properties of stimulated emission (SE) and magnetoabsorbtion data of QWs structures with wide-gap HgCdTe dielectric waveguide provide an insight on dominating non-radiative carrier recombination mechanism. It is shown that the carrier heating under intense optical pumping is the main factor limiting the SE wavelength and intensity, since the Auger recombination is greatly enhanced when carriers populate high energy states in the valence band.

The search for room temperature quantum spin Hall insulators (QSHIs) based on widely available materials and a controlled manufacturing process is one of the major challenges of today’s topological physics. We propose a new class of semiconductor systems based on multilayer broken-gap quantum wells, in which the QSHI gap reaches 60 meV and remains insensitive to temperature. Depending on their layer thicknesses and geometry, these novel structures also host a graphene-like phase and a bilayer graphene analog. Our theoretical results significantly extend the application potential of topological materials based on III–V semiconductors.

We propose a minimal effective two-dimensional Hamiltonian for HgTe/CdHgTe quantum wells (QWs) describing the side maxima of the first valence subband. By using the Hamiltonian, we explore the picture of helical edge states in tensile and compressively strained HgTe QWs. We show that both dispersion and probability density of the edge states can differ significantly from those predicted by the Bernevig-Hughes-Zhang (BHZ) model. Our results pave the way towards further theoretical investigations of HgTe-based quantum spin Hall insulators with direct and indirect band gaps beyond the BHZ model.

Les nanotubes de carbone monofeuilltes (SWCNT) sont fonctionnalisés avec des nanoparticules d'hexacyanoferrate de cuivre (CuHCF) pour préparer des substrats solides pour la sorption des ions de césium (Cs +) des écoulements de liquide. La haute résistance mécanique et la grande conductivité électrique des SWCNT sont associées à la capacité des nanoparticules de CuHCF à complexer sélectivement les ions Cs + afin de réaliser des buckypapers de type membrane présentant une capacité de charge élevée du césium. Les matériaux sont soigneusement caractérisés en utilisant la microscopie électronique, la diffusion Raman, la spectroscopie de photoélectrons X et les analyses thermogravimétriques. Les isothermes de sorption de Cs sont portées après avoir mesuré la concentration en Cs + par chromatographie ionique en phase liquide dans la solution avant et après l'exposition aux matériaux. On trouve que la capacité totale de sorption du matériau atteint 230 mg.g-1, et qu'environ un tiers du Cs sorbé (80 mg.g-1) est sélectivement complexé dans les nanoparticules de CuHCF greffées sur SWCNTs. Les valeurs ouvrent des perspectives intéressantes dans l'intégration de tels matériaux dans des dispositifs de sorption et de désorption contrôlée de ces ions.

Single-walled carbon nanotubes (SWCNTs) are functionalized with copper hexacyanoferrate (CuHCF) nanoparticles to prepare solid substrates for the sorption of cesium ions (Cs+) from liquid outflows. The high mechanical resistance and large electrical conductivity of SWCNTs are associated to the ability of CuHCF nanoparticles to selectively complex Cs+ ions in order to achieve membrane-like buckypapers presenting high loading capacity of cesium. The materials are thoroughly characterized using electron microscopy, Raman scattering, X-ray photoelectron spectroscopy and thermogravimetric analyses. Cs sorption isotherms are plotted after having measured the Cs+ concentration by liquid phase ionic chromatography in the solution before and after exposure to the materials. It is found that the total sorption capacity of the material reaches 230 mg.g-1, and that about one third of the sorbed Cs (80 mg.g-1) is selectively complexed in the CuHCF nanoparticles grafted on SWCNTs.1 These high values open interesting outlooks in the integration of such materials in devices for the controlled sorption and desorption of these ions.

The interactions between the layers of double-walled carbon nanotubes induce a measurable shift of the G bands relative to the isolated layers. While experimental data on this shift in freestanding double-walled carbon nanotubes has been reported in the past several years, a comprehensive theoretical description of the observed shift is still lacking. The prediction of this shift is important for supporting the assignment of the measureddouble-walled nanotubes to particular nanotube types. Here, we report a computational study of the G-band shift as a function of the semiconducting inner layer radius and interlayer separation. We find that with increasing interlayer separation, the G band shift decreases, passes through zero and becomes negative, and further increases in absolute value for the wide range of considered inner layer radii. The theoretical predictions are shown to agree with the available experimental data within the experimental uncertainty.

Excitons recombination dynamics in ZnMgO alloy have been studied by time-resolved photoluminescence according to temperature. At low temperature, localization effects of the exciton are found to play a significant role. The photoluminescence (PL) decays are bi-exponential. The short lifetime has a constant value, whereas the long lifetime shows a dependency with temperature. For temperature higher than 100 K the declines show an mono-exponential decay. The PL declines are dominated by non-radiative process at temperatures above 150 K. The PL lifetime dependancy with temperature is analysed using a model including localisation effects and non-radiative recombinations.