Synthetic control over the binding configuration of luminescent sp3-defects in single-walled carbon nanotubes

The controlled functionalization of single-walled carbon nanotubes with luminescent sp3-defects has created the potential to employ them as quantum-light sources in the near-infrared. For that, it is crucial to control their spectral diversity. The emission wavelength is determined by the binding configuration of the defects rather than the molecular structure of the attached groups. However, current functionalization methods produce a variety of binding configurations and thus emission wavelengths. We introduce a simple reaction protocol for the creation of only one type of luminescent defect in polymer-sorted (6,5) nanotubes, which is more red-shifted and exhibits longer photoluminescence lifetimes than the commonly obtained binding configurations. We demonstrate single-photon emission at room temperature and expand this functionalization to other polymer-wrapped nanotubes with emission further in the near-infrared. As the selectivity of the reaction with various aniline derivatives depends on the presence of an organic base we propose nucleophilic addition as the reaction mechanism.

Tailoring surface-supported water–melamine complexes by cooperative H-bonding interactions

A surface science approach provides synthetic and characterization tools for an accurate assessment of the H-binding configuration in water/organocatalyst interfaces.

Structural and Optical Properties of Thermally Oxidized Zirconium Dioxide Films

Zirconium oxide (ZrO2) thin films were grown by thermal oxidation of metallic zirconium films deposited by sputtering of zirconium target by DC magnetron sputtering technique. The metallic zirconium films were thermally oxidized in oxygen atmosphere at different temperatures in the range from 300°C to 500°C. The as-deposited and oxidized films were characterized for their chemical composition by energy dispersive X-ray analysis, structure by X-ray diffraction, chemical binding configuration with Fourier transform infrared spectroscopy and optical absorption using UV-Vis NIR spectrophotometer. Metallic zirconium film was polycrystalline in nature with hexagonal structured Zr. The zirconium films were transformed into monoclinic ZrO2 with polycrystalline in nature at oxidation temperature of 400°C. Crystallite size of the ZrO2 films increased from 78 nm to 108 nm with increase in the oxidation temperature form 400°C to 500°C. The optical band gap increased from 5.42 eV to 5.46 eV and refractive index decreased from 2.05 to 2.02 with increase of oxidation temperature from 400°C to 500°C.

Prediction of mechanical properties of 2D solids with related bonding configuration

A chemical reference model is introduced to estimate unknown mechanical properties of 2D solids for groups with related binding configuration using a minimal data base.

Molecular degradation of D35 and K77 sensitizers when exposed to temperatures exceeding 100 °C investigated by photoelectron spectroscopy

PES measurements on heat-treated D35 electrodes show that the binding configuration changes and K77 dissociates and desorbs from the surface.

The Electron-Hole Interactions in Si Hydrogenate Nanocrystals: Tight-Binding Theory

Theory of electronic and optical properties of excitonic states confining in Si nanocrystals is presented. The electron and hole states are numerically computed using the atomistic empirical tight-binding Hamiltonian including the spin-orbit coupling together with the first nearest-neighboring interaction. We theoretically study the electron-hole interactions in spherical silicon hydrogenated nanocrystals by incorporating coulomb and exchange interaction into the empirical tight-binding model. The comparisons of coulomb and exchange energies with empirical pseudopotential method (EPM), tight-binding method (TB), effective-mass approximation (EMA) and ab initio calculations are quantitatively realized. Finally the energies of the excitonic ground states obtained from diagonalizing the tight-binding configuration-interaction scheme are in a good agreement with other theoretical and experimental data.

Drosophila Ncd reveals an evolutionarily conserved powerstroke mechanism for homodimeric and heterodimeric kinesin-14s

Drosophila melanogaster kinesin-14 Ncd cross-links parallel microtubules at the spindle poles and antiparallel microtubules within the spindle midzone to play roles in bipolar spindle assembly and proper chromosome distribution. As observed for Saccharomyces cerevisiae kinesin-14 Kar3Vik1 and Kar3Cik1, Ncd binds adjacent microtubule protofilaments in a novel microtubule binding configuration and uses an ATP-promoted powerstroke mechanism. The hypothesis tested here is that Kar3Vik1 and Kar3Cik1, as well as Ncd, use a common ATPase mechanism for force generation even though the microtubule interactions for both Ncd heads are modulated by nucleotide state. The presteady-state kinetics and computational modeling establish an ATPase mechanism for a powerstroke model of Ncd that is very similar to those determined for Kar3Vik1 and Kar3Cik1, although these heterodimers have one Kar3 catalytic motor domain and a Vik1/Cik1 partner motor homology domain whose interactions with microtubules are not modulated by nucleotide state but by strain. The results indicate that both Ncd motor heads bind the microtubule lattice; two ATP binding and hydrolysis events are required for each powerstroke; and a slow step occurs after microtubule collision and before the ATP-promoted powerstroke. Note that unlike conventional myosin-II or other processive molecular motors, Ncd requires two ATP turnovers rather than one for a single powerstroke-driven displacement or step. These results are significant because all metazoan kinesin-14s are homodimers, and the results presented show that despite their structural and functional differences, the heterodimeric and homodimeric kinesin-14s share a common evolutionary structural and mechanochemical mechanism for force generation.