Materials Literature
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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…
New methods have been developed in recent years that are now being successfully applied in the preparation of pillared interlayered clays (PILCs). Variations in the procedures concern different parameters involved in the synthesis, such as the starting clay, the intercalating solution, the intercalation process, and t…
First principles density functional calculations of the electronic and magnetic properties of the layered oxide ${\mathrm{NaCo}}_{2}{\mathrm{O}}_{4}$ have been performed using the general potential linearized augmented plane wave method. The electronic transport properties are discussed in terms of the calculated para…
We probe the influence of grating effects on plasmon excitations in gold nanoparticles arranged in regular two-dimensional patterns. Samples produced by electron-beam lithography are investigated by femtosecond time-resolved and spectroscopic methods. We find a strong dependence of the plasmon lifetime and resonance w…
The infrared spectral performance of the N x O y species observed on oxide surfaces [N2O, NO−, NO, (NO)2, N2O3, NO+, NO2 − (different nitro and nitrito anions), NO2, N2O4, N2O5, NO2, and NO3 − (bridged, bidentate, and monodentate nitrates)] is considered. The spectra of related compounds (N2, H-, and C-containing nitr…