Materials Literature
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In this letter evidence for the formation of a valence-fluctuation state of iron, formally denoted as Fe2.5+, is presented. The system under study is the Sr2FeMoO6−w double perovskite, known for exhibiting a very large magnetoresistance. Samples of Sr2FeMoO6−w were synthesized by means of an encapsulation technique ut…
A right-handed helical motif is shown by the spiral silica shown in the picture. It is formed by sol–gel polycondensation of tetraethoxysilane in the gel phase supported by an azacrown-appended cholesterol gelator. This is rare example of “chirality” being created in the inorganic material by the template method.
We report atomic resolution Z-contrast scanning transmission electron microscopy images that reveal the incorporation of I atoms in the form of helical chains inside single-walled carbon nanotubes. Density functional calculations and topological considerations provide a consistent interpretation of the experimental da…
Bridging methylene groups are transformed into terminal methyl groups when periodic mesoporous methylenesilicas, prepared for the first time by surfactant-templated synthesis, are subjected to controlled thermal treatment at 350–600°C. The methylene groups integrated “inside the channel walls” transform smoothly to me…
Molecular simulations predict that a first-order amorphous-amorphous transformation occurs in SiO2 under pressure, analogous to the first-order amorphous-amorphous transformation known to occur in H2O. At low temperatures the first-order transformation is kinetically hindered, and an amorphous-amorphous transformation…
Plasma-sprayed mullite 3Al2O3s˙2SiO2 and mullite/yttria-stabilized-zirconia (YSZ) dual layer coatings have been developed to protect silicon-based ceramics from environmental attack. Mullite-based coating systems show excellent durability in air. However, in combustion environments, corrosive species such as molten sa…
The modeling of carbon nanotube-metal contacts is important from both basic and applied viewpoints. For many applications, it is important to design contacts such that the transmission is dictated by intrinsic properties of the nanotube rather than by details of the contact. In this paper, we calculate the electron tr…
The bonding in a series of unhydrogenated amorphous carbon films has been analyzed quantitatively using Raman spectroscopy excited by laser light in both the visible and ultraviolet regions of the spectrum. The asymmetry of the peak near 1550 cm−1 in the visible Raman spectra is correlated with the percentage of sp3 b…
The esterification of a representative redox-active polyoxometalate (POM), [H4P2V3W15O62]5−, with methanol and two simple dendrimers each having four tris(hydroxymethyl) termini has been investigated. The tetra(polyoxometalate) dendrimers are hydrolytically stable, and 1 has been shown to catalyze the oxidation of tet…
Electron-vibrational spectra of impurity-related optical centers of diamond are analyzed in terms of interaction with quasilocal and local vibrations connected with impurity atoms as well as with the short-wavelength lattice phonons. It is shown that the theoretical expressions for the energy and resonance width of qu…
Chitin and chitosan are known to possess multiple functional properties. Chitin is insoluble in any common solvent containing organic or mineral acid as well as water. Chitosan is water-insoluble and highly viscous in dilute acidic solutions. These solubility problems may restrict their use in physiological functional…
To evaluate the role of nonphonon energy relaxation mechanisms in quantum dots and in particular the role of electron-hole (e-h) interactions, we have studied femtosecond carrier dynamics in CdSe colloidal nanoparticles in which the e-h separation (coupling) is controlled using different types of surface ligands. In d…
An elastic model is presented to study infinitesimal buckling of a double-walled carbon nanotube under axial compression. A simple formula is derived for the critical axial strain, which clearly indicates the role of the van der Waals forces between the inner and outer tubes characterized by two parameters. In particu…
Grain-boundary and surface scattering are known to increase the electrical resistivity of thin metallic films and wires. The length scale at which these produce appreciable effects is of the order of the electronic mean free path. For the well-studied case of thin films, both mechanisms can, in principle, be used to e…
High-resolution core- and valence-level photoemission spectra of Nb-doped ${\mathrm{TiO}}_{2}$ ceramics $({\mathrm{Ti}}_{1\ensuremath{-}x}{\mathrm{Nb}}_{x}{\mathrm{O}}_{2}$ with $0.01<x<0.8)$ have been measured using monochromatic x-ray excitation. Nb doping produces a well-defined photoemission peak in the bulk…
Controlled growth of molecular magnets, in terms of their size, shape, and organization, is demonstrated with a model cyanometallate, Prussian blue crystals. The TEM image shows the hydrophobic cubic nanoparticles (scale bar 100 nm), prepared in a microemulsion and encapsulated in a shell of surfactant, which readily…
At semiconductor-metal junctions, the Schottky barrier height is generally fixed by "Fermi-level pinning." We find that when a semiconducting carbon nanotube is end contacted to a metal (the optimal geometry for nanodevices), the behavior is radically different. Even when the Fermi level is fully "pinned" at the inter…
We perform density-functional calculations to search for hydrogen adsorption sites and predict maximum storage capacity in single-walled carbon nanotubes. We find two chemisorption sites at top sites of the exterior and the interior of the tube wall. We further find that a form of H2 molecule can exist in an empty spa…
A temperature-dependent, single crystal x-ray diffraction study of the giant magnetocaloric material, ${\mathrm{Gd}}_{5}({\mathrm{Si}}_{2}{\mathrm{Ge}}_{2})$, across its Curie temperature (276 K) reveals that the simultaneous orthorhombic to monoclinic transition occurs by a shear mechanism in which the $(\mathrm{Si},…
We report the preparation of highly monodisperse ZnO nanoparticles using poly(vinyl pyrrolidone) (PVP) as the capping molecules. The surface-modified ZnO nanoparticles were found to be remarkably stable. The optical absorption shows distinct excitonic features. Markedly enhanced near-band-edge ultraviolet photolumines…