Current Topics in Materials Science
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Ultrahigh-Vacuum Studies of Enhanced Raman Scattering from Pyridine on Ag Surfaces
Studies of surface-enhanced Raman scattering from pyridine adsorbed on Ag surfaces in ultrahigh vacuum show a strong dependence on both surface roughness and pyridine coverage. The observation of enhancement (${10}^{4}$) for physisorbed pyridine multilayers in addition to the first molecular layer implies that the enh…
Electron spin polarisation resulting from elastic scattering of electrons by mercury atoms between 8 and 18 eV collision energy
The spin polarisation of electrons scattered elastically by mercury atoms has been measured for collision energies between 8 and 18 eV. The results are discussed in comparison with ab initio calculations by Walker (1971) which show only fair agreement. The scattering at 14 eV incident energy and angles between 90 degr…
Quantum Magnetic Hamiltonians with Remarkable Spectral Properties
The Hamiltonian, $H$, of a spinless particle moving in two dimensions in an axially symmetric magnetic field $B(\ensuremath{\rho})$ is considered. If $B(\ensuremath{\rho})\ensuremath{\sim}{\ensuremath{\rho}}^{\ensuremath{-}\ensuremath{\alpha}}$ for $\ensuremath{\rho}$, large with $0<\ensuremath{\alpha}<1$, then…
Anionic Constitution of 1-Atmosphere Silicate Melts: Implications for the Structure of Igneous Melts
A structural model is proposed for the polymeric units in silicate melts quenched at 1 atmosphere. The anionic units that have been identified by the use of Raman spectroscopy are SiO(4)(4-) monomers, Si(2)O(7)(6-) dimers, SiO(3)(2-) chains or rings, Si(2)O(5)(2-) sheets, and SiO(2) three-dimensional units. The coexis…
Studies on the solid state properties of the solid solution system MgAl2−xFexO4
The solid solutions between the spinels MgAl2O4 and MgFe2O4 with the general formula MgAl2 − xFexO4 are synthesised and characterised by X-ray diffraction and application of Vegard's law. The cation distribution in this spinel system is determined from X-ray and magnetic susceptibility measurements. The electrical and…
Single crystal V2O5 and lower oxides. A survey of their electronic, optical, structural, and surface properties
A survey is given of experimental and theoretical studies related to the fundamental properties of single crystal vanadium oxides. Emphasis is put on the relationship which exists between V2O5 and the lower oxides, mainly V4O9 and V6O13. Special attention is paid to the role played by the vanadyl—oxygen vacancy, both…
Incommensurate Coexistent Density Fluctuations in Liquid-Crystal Phases of Cyano Compounds
X-ray diffraction investigations of both nematic and smectic phases of a number of compounds containing cyano end groups have revealed several of them to have a novel structure. This consists of two coexisting mass density fluctuations (heavily damped for the nematics) with incommensurate wavelengths corresponding, re…
Jahn-Teller-Distorted Nitrogen Donor in Laser-Annealed Silicon
Substitutional nitrogen donors in single-crystal silicon have been produced by pulsed ruby-laser annealing of amorphous silicon created by 4\ifmmode\times\else\texttimes\fi{}${10}^{15}$ 160-keV (0.995 $^{28}\mathrm{Si}^{+}$ + 0.005 $^{14}\mathrm{N}_{2}^{+}$)/${\mathrm{cm}}^{2}$. EPR measurements indicate that these is…
Ductile-brittle transition in refractory metal alloys containing a dispersed second phase
Mechanical properties and peculiarities of fracture surfaces of four dispersion strengthened alloys (Mo1, Nb1, Mo2, and Vl) are investigated in tension in the temperature range from −196 to 1600 °C with a strain rate of 10−3 s−1. At the choice of alloys for investigation two main parameters are taken into account: mat…
Trapping and emission centres in X-irradiated zircon. II. Contribution of the SiO44− groups
The 365 nm emission band observed at 100, 165, 205, 260, and 325 K in the thermoluminescence of undoped zircons, synthesized with the hydrothermal method, and which are X-irradiated at 77 K, is attributed to the SiO lattice groups. It is established that a paramagnetic trap centre is associated to most TL peaks. These…
New Class of Layered Materials
A new class of layered materials has been prepared by alternate deposition of two dissimilar metals. Strong experimental evidence is shown that coherent structures with layer thicknesses approaching interatomic spacing can be prepared in this fashion. The experimental x-ray measurements are found to be in good qualita…
Precise Determination of the Valence-Band Edge in X-Ray Photoemission Spectra: Application to Measurement of Semiconductor Interface Potentials
A highly precise method for locating the valence-band edge in x-ray photoemission spectra is reported. The application to measuring semiconductor interface potentials is discussed. X-ray photoemission-spectroscopy experiments on Ge and GaAs(110) crystals have given Ge $3d$, Ga $3d$, and As $3d$ core level to valence-b…
A method to reduce the number of two electron integral transformations in a second order multiconfigurational Hartree–Fock procedure
In standard multiconfigurational Hartree–Fock (MCSCF) theory, a two electron integral transformation is performed before application of the equation defining the MCSCF approach in each iterative cycle. It is shown how the two electron integral transformation may be replaced by an approximate orbital transformation int…
Molecular structure ofAs2Se3glassglass
Molecular models are constructed for large structural units appropriate to ${\mathrm{As}}_{x}{\mathrm{S}}_{1\ensuremath{-}x}({\mathrm{Se}}_{1\ensuremath{-}x})$ glasses near $x=0.4$. The models are similar to those previously constructed for ${\mathrm{Ge}}_{y}{\mathrm{S}}_{1\ensuremath{-}y}({\mathrm{Se}}_{1\ensuremath{…
Neutron study of magnetic-moment distribution in Ni-Pt alloys
The average moments and the moment disturbances of ferromagnetic Ni-Pt alloys with concentrations of 20, 30, 40, 50, 55, and 57 at.% Pt have been measured by the magnetic diffuse scattering of neutrons. The data have been analyzed with the linear superposition model of Marshall including short-range order. The data ha…
Semiconducting properties of amorphous V2O5 layers deposited from gels
Colloidal solutions of amorphous V2O5 are used for preparing semiconducting layers. Reasons for the high measured conductivity (σ≃0.8–1.0 Ω−1 cm−1) are discussed. The temperature dependence of σ is analyzed in terms of a temperature-dependent activation-energy model based upon the assumption of a random distribution o…
Luminescence and nonradiative energy transfer to surfaces
Luminescent molecules near metal surfaces can have dramatically decreased quantum efficiencies and lifetimes. For example, decreases of \ensuremath{\sim}${10}^{3}$ in quantum efficiency and in lifetime occur for nitrogen atoms within 3 nm of potassium surfaces. This paper presents experimental decay curves for light e…
Stress intensity factors at V-notched elastic, symmetrically loaded, plates by the method of caustics
The problem of experimental evaluation of the complex stress intensity factors K at the apices of sharp V-notches in homogeneous, isotropic and elastic plates, symmetrically loaded in their planes, is treated by applying the experimental method of reflected caustics. The symmetry in loading and in position of the notc…
Aragonite Twinning in the Molluscan Bivalve Hinge Ligament
Molluscan bivalve hinge ligaments are composed of long needle-shaped aragonite crystals embedded in a protein matrix. These crystals are twinned and, in general, the twin forms a thin lamella through the center of the crystal.