Inorganically functionalized PbS-CdS colloidal nanocrystals: integration into amorphous chalcogenide glass and luminescent properties

Inorganic semiconductor nanocrystals (NCs) with bright, stable, and wavelength-tunable luminescence are very promising emitters for various photonic and optoelectronic applications. Recently developed strategies for inorganic surface capping of colloidal NCs using metal chalcogenide complexes have opened new perspectives for their applications. Here we report an all-inorganic surface functionalization of highly luminescent IR-emitting PbS-CdS NCs and studies of their luminescence properties. We show that inorganic capping allows simple low-temperature encapsulation of inorganic NCs into a solution-cast IR-transparent amorphous As(2)S(3) matrix. The resulting all-inorganic thin films feature stable IR luminescence in the telecommunication wavelength region. The high optical dielectric constant of As(2)S(3) also helps reduce the dielectric screening of the radiating field inside the quantum dot, enabling fast radiative recombination in PbS-CdS NCs.     

Moduli spaces of hyperelliptic curves with A and D singularities

We introduce moduli spaces of quasi-admissible hyperelliptic covers with at worst A and D singularities. The stability conditions for these moduli spaces depend on two rational parameters describing allowable singularities. For the extreme values of the parameters, we obtain the stacks of stable limits of $A_n$ and $D_n$ singularities, and the quotients of the miniversal deformation spaces of these singularities by natural $\mathbb G _m$ -actions. We interpret the intermediate spaces as log canonical models of the stacks of stable limits of $A_n$ and $D_n$ singularities.     

Towards quantum optics and entanglement with electron spin ensembles in semiconductors

We discuss a technique and a material system that enable the controlled realization of quantum entanglement between spin-wave modes of electron ensembles in two spatially separated pieces of semiconductor material. The approach uses electron ensembles in GaAs quantum wells that are located inside optical waveguides. Bringing the electron ensembles in a quantum Hall state gives selection rules for optical transitions across the gap that can selectively address the two electron spin states. Long-lived superpositions of these electron spin states can then be controlled with a pair of optical fields that form a resonant Raman system. Entangled states of spin-wave modes are prepared by applying quantum-optical measurement techniques to optical signal pulses that result from Raman transitions in the electron ensembles.     

On the role of longitudinal momenta in high energy hadron-hadron scattering

We demonstrate a new method to calculate inelastic scattering cross-sections, which in contrary to the Regge-based methods takes into account the energy momentum conservation law. It is shown that the main contribution to integral expressing inelastic scattering cross-sections does not come from the multi-Regge domain. In particular, accounting for the longitudinal momenta contribution to virtualities is sufficient and results in the new mechanism of cross-section growth. The reasons for taking into account the sufficiently high number of interference contributions are shown and the approximate method for this purpose is developed. By fitting single free parameter of the model achieved a qualitative agreement of the total and inelastic cross sections with experimental data.     

Metalla-Assembled Electron-Rich Tweezers: Redox-Controlled Guest Release Through Supramolecular Dimerization

Developing methodologies for on-demand control of the release of a molecular guest requires the rational design of stimuli-responsive hosts with functional cavities. While a substantial number of responsive metallacages have already been described, the case of coordination-tweezers has been less explored. Herein, we report the first example of a redox-triggered guest release from a metalla-assembled tweezer. This tweezer incorporates two redox-active panels constructed from the electron-rich 9-(1,3-dithiol-2-ylidene)fluorene unit that are facing each other. It dimerizes spontaneously in solution and the resulting interpenetrated supramolecular structure can dissociate in the presence of an electron-poor planar unit, forming a 1:1 host–guest complex. This complex dissociates upon tweezer oxidation/dimerization, offering an original redox-triggered molecular delivery pathway.     

Multiple scattering calculations of step contrast in REM images of the Si(001) surface

Simulations of reflection electron microscopy (REM) images of both monolayer and bilayer steps on the bulk-terminated Si(001) surface, for the case when the primary electron beam azimuth is directed parallel to the line of the step, are presented. The simulations employ our previously reported theory of REM image formation which uses a 2D Bloch wave formulation of dynamical (multiple scattering) elastic RHEED theory to calculate diffracted amplitudes propagating from the surface. The only step contrast mechanism considered here is phase contrast and this is sufficient to produce the characteristic “black-white” appearance observed experimentally. Defocusing of the simulated images is also discussed.     

AFM investigation of Pseudomonas aeruginosa lectin LecA (PA-IL) filaments induced by multivalent glycoclusters

Atomic force microscopy reveals that Pseudomonas aeruginosa LecA (PA-IL) and a tetra-galactosylated 1,3-alternate calix[4]arene-based glycocluster self-assemble according to an aggregative chelate binding mode to create monodimensional filaments. Lectin oligomers are identified along the filaments and defects in chelate binding generate branches and bifurcations. A molecular model with alternate 90° orientation of LecA tetramers is proposed to describe the organisation of lectins and glycoclusters in the filaments.     

Tetrafluoroborate Selective Electrodes on the Basis of Cations with Delocalized Charge

Screening of active substances based on styryl and trimethine cyanine dyes was carried out to prepare tetrafluoroborate ion‐selective electrodes. Correlations between the nature of the organic cation (pK_a) and working pH ranges of the sensors were studied. New tetrafluoroborate‐selective PVC membrane electrodes based on an active substance formed by the ion pair of 2‐(n‐ethylcarbazol‐3)‐ethenyl‐1,3,3‐trimethyl‐3H‐indolium and 2‐[3‐(5,6‐dimethyl‐3‐nonyl‐1,3‐benzothiazol‐2(3H)‐ylidene)propenyl]‐5,6‐dimethyl‐3‐nonyl‐1,3‐benzothiazolium with tetrafluoroborate ion were developed. The electrodes are non‐sensitive to pH in the range of 2–8 and can be used for boron determination in acidic media of 6–7 mol L^?1 H₂SO₄. The developed sensor was successfully applied for the determination of B₂O₃ in CdS(Se) nanocrystal‐doped glasses.     

Inverted electron-hole alignment in InAs-GaAs self-assembled quantum dots

New information on the electron-hole wave functions in InAs-GaAs self-assembled quantum dots is deduced from Stark effect spectroscopy. Most unexpectedly it is shown that the hole is localized towards the top of the dot, above the electron, an alignment that is inverted relative to the predictions of all recent calculations. We are able to obtain new information on the structure and composition of buried quantum dots from modeling of the data. We also demonstrate that the excited state transitions arise from lateral quantization and that tuning through the inhomogeneous distribution of dot energies can be achieved by variation of electric field.