Publications

We report on the profound effect of vibrations on the formation and ordering of aggregates of gold nanoparticles formed at the toluene–water interface using high-resolution atomic force microscopy. We obtain 2.3nm thick monolayer films composed of gold nanoparticles of 1.2nm diameter, with an organic capping of 1.1nm, at the early stages of the reaction carried out on an anti-vibration table. Reaction carried out on a table without anti-vibration fixtures produces thicker films composed of 1.2nm nanoparticles. The results demonstrate that the reduction reaction carried out at the toluene–water interface on an anti-vibration table provides a suitable means for large scale synthesis of Au-55 like nanoparticles.

Grain size has marked effects on charge-ordering and other properties of Nd0.5A0.5MnO3 (A=Ca or Sr). Thus, the antiferromagnetic (AFM) transition in Nd0.5Ca0.5MnO3 is observed distinctly only in samples sintered at 1273K or higher. The sample with a small grain size (sintered at 1173K) shows evidence for greater ferromagnetic (FM) interaction at low temperatures, probably due to phase segregation. The FM transition as well as the charge-ordering transition in Nd0.5Sr0.5MnO3 becomes sharper in samples sintered at 1273K or higher. The sample sintered at 1173K does not show the AFM–CO transition around 150K and is FM down to low temperatures; the apparent T c−T co gap decreases with the increase in the grain size. The samples sintered at lower temperatures (<1673K) show evidence for greater segregation of the AFM and FM domains.

A comparative study of the magnetic properties of a few members of the Ln 0.5Sr0.5CoO3 family with different radii of the A-site cations, 〈rA 〉, in the range 1.19–1.40Å has been carried out. The apparent T c (where the magnetization undergoes an abrupt increase) decreases markedly with 〈rA 〉 as well as the size-disorder arising from the mismatch in the size of the A-site cations. The value of the magnetization at low temperatures decreases markedly with decrease in 〈rA 〉 or increase in size-disorder, suggesting that the relative proportion of the ferromagnetic (FM) species decreases relative to that of the paramagnetic (PM) species. Such a variation of the FM/PM ratio with composition and temperature is evidenced from the Mössbauer spectra of La0.5Sr0.5CoO3 as well. The variation of the FM/PM ratio with 〈rA 〉 and size-disorder, as well as a local-probe study using 59Co Nuclear magnetic resonance spectroscopy suggest that electronic phase separation is an inherent feature of the Ln 0.5Sr0.5CoO3 type cobaltates, with the nature of the different magnetic species in the phase-separated system varying with 〈rA 〉 and size disorder.

Boron- and nitrogen-doped graphenes are are prepared by the arc discharge between carbon electrodes or by the transformation of nanodiamond under appropriate atmospheres. Using a combination of experiment and theories based on first principles, systematic changes in the carrier-concentration and electronic structure of the doped graphenes are demonstrated. Stiffening of the G-band mode and intensification of the defect-related D-band in the Raman spectra are also observed.

Temperature-dependent Raman spectroscopic studies have been carried out on KHSO4 single crystals in the temperature range 298−493 K. A structural phase transition driven by the lattice and molecular disorder is observed at 473 K. The spectral data enable an understanding of the nature of the lattice disorder across the phase transition leading to the superionic phase. The disorder in the HSO4− polymeric hydrogen-bonded chain leading to a higher symmetry in the high temperature phase is clearly captured from our Raman results. The internal S−OH and S−O stretching modes and, to a limited extent, the external modes throw light on the disorder mechanism and the enhancement of conductivity after transition.

Two kinds in a box: The electronic and optical properties of ZnO substituted with nitrogen and fluorine are studied both experimentally and theoretically. The presence of fluorine enhances the incorporation of nitrogen in the lattice. Co-substitution reduces the optical band gap of ZnO significantly and increases the dielectric constant. The long-wavelength visible absorption of N, F-ZnO is reflected in its bright orange color (see picture). As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

A novel supramolecular strategy based on host–guest chemistry has been proposed for the noncovalent functionalization of MoS2 nanosheets with organic chromophores. Stable ternary complexes are formed between benzyl imidazole functionalized MoS2 and chromophores in the presence of cucurbit[8]uril host, resulting in noncovalent anchoring of donor and acceptor chromophores on the surface. On the other hand, in the case of graphene, we observe π–π stacking resulting in the face-on organization of chromophore on the surface. The MoS2 and graphene hybrids have been characterized by various spectroscopic techniques. The present design opens up new possibilities for the noncovalent functionalization of transition metal dichalcogenides even in the absence of delocalized π-electrons which are essential to alter their optoelectronic properties. In addition, these novel supramolecular hybrid materials with strong electronic communication between noncovalently anchored chromophores and the 2D nanosheets may find applications in optoelectronics and related areas.