Ref HAL: hal-02167326_v1
DOI: 10.1002/chem.201901221
WoS: 000469274700022
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6 Citations
Résumé:

As three‐dimensional folding is prerequisite to biopolymer activity, complex functions may also be achieved through foldamer science. Because of the diversity of sizes, shapes and folding available with synthetic monomers, foldamer frameworks enable a numerous opportunities for designing new generations of catalysts. We herein demonstrate that heterocyclic γ‐peptide scaffolds represent a versatile platform for enamine catalysis. One central feature was to determine how the catalytic activity and the transfer of chiral information might be under the control of the conformational behaviours of the oligomer.

Ref HAL: hal-02167377_v1
DOI: 10.15407/spqeo22.02.237
WoS: WOS:000485818200011
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3 Citations
Résumé:

We have presented the results of terahertz time-domain spectroscopy measurements and a rigorous electrodynamic modeling of the optical characteristics of grating-based AlGaN/GaN plasmonic structures with low-doped two-dimensional electrongas in the frequency range of 0.1...1.5 THz. Two samples with grating aspect ratios (strip width/period) of 2.4/3 and 1.2/1.5 μm have been investigated. The measured transmission spectra are reconstructed in the calculations with high accuracy. The transmission spectrafor p-polarized incident radiation exhibits Fabri–Pérot oscillation behavior due to theoptically-thick substrate. The specific values of amplitude and spectral position of thetransmission maxima are associated with the coupling of terahertz radiation with 2Delectron gas due to plasmon excitations. Both calculations and transmission/reflectionmeasurements demonstrate that plasmonic structures with micro-scaled metallic gratinghave three-fold increase of non-resonant absorption of terahertz radiation in comparisonwith the bare heterostructure. The polarization measurements of the transmission spectra ofthe plasmonic structures well agree with calculations and indicate a well-pronounced filtering effect of the grating for the s-component of the incident electromagnetic wave. The obtained values of the transmission for p- and s-polarized incident radiation demonstrate the high quality of deposited metallic grating with the extinction ratio higher than 80:1 for sub- and few THz frequency range.

Ref HAL: hal-02162002_v1
Ref Arxiv: 1902.08580
DOI: 10.1063/1.5093240
WoS: WOS:000473301400001
Ref. & Cit.: NASA ADS
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15 Citations
Résumé:

Despite the diversity of materials designated as active matter, virtually all active systems undergo a form of dynamic arrest when crowding and activity compete, reminiscent of the dynamic arrest observed in colloidal and molecular fluids undergoing a glass transition. We present a short perspective on recent and ongoing efforts to understand how activity competes with other physical interactions in dense systems. We first review recent experimental work on active materials that uncovered both classic signatures of glassy dynamics and intriguing novel phenomena at large density. We introduce a minimal model of self-propelled particles where the competition between interparticle interactions, crowding, and self-propulsion can be studied in great detail. We discuss more complex models that include some additional, material-specific ingredients. We end with some general perspectives on dense active materials, suggesting directions for future research, in particular for theoretical work.

Commentaires: 16 pages, 8 figures. Réf Journal: J. Chem. Phys. 150, 200901 (2019)

Ref HAL: hal-02160116_v1
DOI: 10.1103/PhysRevB.99.245414
WoS: 000471984200005
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10 Citations
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Light-matter interactions in conventional nanophotonic structures typically lack directionality. For example, differently from microwave antenna systems, most optical emitters (e.g., excited atoms/molecules and simple nanoantennas) exhibit quasi-isotropic dipolar radiation patterns with low directivity. Furthermore, surface waves supported by conventional material substrates do not usually have a preferential direction of propagation, and their wavefront tends to spread as it propagates along the surface, unless the surface or the excitation is properly engineered and structured. In this article, we theoretically demonstrate the possibility of realizing unidirectional and diffractionless surface plasmon polariton modes on a nonreciprocal platform, namely, a gyrotropic magnetized plasma. Based on a rigorous Green’s function approach, we provide a comprehensive and systematic analysis of all the available physical mechanisms that may bestow the system with directionality, both in the sense of one-way excitation of surface waves and in the sense of directive diffractionless propagation along the surface. The considered mechanisms include (i) the effect of strong and weak forms of nonreciprocity, (ii) the elliptic-like or hyperbolic-like topology of the modal dispersion surfaces, and (iii) the source polarization state, with the associated possibility of chiral surface-wave excitation governed by angular-momentum matching. We find that three-dimensional gyrotropic plasmonic platforms support a previously unnoticed wave-propagation regime that exhibit several of these physical mechanisms simultaneously, allowing us to theoretically demonstrate unidirectional surface plasmon polariton modes that propagate as a single ultranarrow diffractionless beam. We also assess the impact of dissipation and nonlocal effects. Our theoretical findings may enable a new generation of plasmonic structures and devices with highly directional response.

Ref HAL: hal-02157723_v1
DOI: 10.1134/S0021364019020085
WoS: WOS:000467096800005
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1 Citation
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The features of terahertz photoluminescence and magnetoabsorption in magnetic fields up to 16 T in threelayer InAs/GaSb/InAs quantum wells with a band structure corresponding to a “two-dimensional semimetal” are studied. The comparison of the positions and amplitudes of the photoluminescence lines with the theoretical calculations of oscillator strengths for interband and intraband transitions performed using the eight-band Kane Hamiltonian indicates the existence of a nonradiative recombination channel associated with the overlap of the conduction and valence bands. The energies of interband and intraband Landau level transitions observed in the magnetoabsorption spectra are in good agreement with theoretical calculations, which confirms the predicted band structure.

Ref HAL: hal-02157552_v1
DOI: 10.1021/acsami.9b04553
WoS: WOS:000468364500082
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4 Citations
Résumé:

The dynamic and static properties of the interfacial region between polymer and nanoparticles have wide-ranging consequences on performances of nanomaterials. The thickness and density of the static layer are particularly difficult to assess experimentally due to superimposing nanoparticle interactions. Here, we tune the dispersion of silica nanoparticles in nanocomposites by pre-adsorption of polymer layers in the precursor solutions, and by varying the molecular weight of the matrix chains. Nanocomposite structures ranging from ideal dispersion to repulsive order or various degrees of aggregation are generated and observed by small-angle scattering. Pre-adsorbed chains are found to promote ideal dispersion, before desorption in the late stages of nanocomposite formation. The microstructure of the interfacial polymer layer is characterized by detailed modeling of X-ray and neutron scattering. Only in ideally well-dispersed systems a static interfacial layer of reduced polymer density over a thickness of ca. 2 nm is evidenced based on the analysis with a form-free density profile optimized using numerical simulations. This interfacial gradient layer is found to be independent of the thickness of the initially adsorbed polymer, but appears to be generated by out-of-equilibrium packing and folding of the pre-adsorbed layer. The impact of annealing is investigated to study the approach of equilibrium, showing that initially ideally well-dispersed systems adopt a repulsive hard-sphere structure, while the static interfacial layer disappears. This study thus promotes the fundamental understanding of the interplay between effects which are decisive for macroscopic material properties: polymer-mediated interparticle interactions, and particle interfacial effects on surrounding polymer.

Ref HAL: hal-02154559_v1
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Résumé:

Tackling the question of specific interactions in a complex blend of Proteins. Edible Soft Matter – a SoftComp Topical Workshop