An electron diffraction investigation of the molecular structure of trichloroacetonitrile

The molecular structure of trichloroacetonitrile has been studied by electron diffraction by the visual interpretation of sectored photographs. These parameters were obtained: C-N = 1.165 ± 0.025, C-C = 1.465 ± 0.025, C-Cl = 1.765 ± 0.01 A., and < CCCl = 109.5 ± 1°.

Orientation Of Grain-Boundaries In Cadmium Recrystallized During Hot Deformation

The authors are grateful to Professor K. P. Abraham for the provision of facilities and encouragement. One of us (PRR) acknowledges the award of a National Associateship by the UGC which facilitated a short-time visit to the Indian Institute of Science.

Annealing response of the intermetallic alloy Ti-22Al-25Nb

A hot rolled two-phase Ti-22Al-25Nb (at.%) alloy containing the orthorhombic (O) and beta(B2) phases was subjected to thermal treatment under different conditions. The experiment was aimed to examine the recrystallization response of the beta(B2) phase (static and dynamic) to microstructure and crystallographic texture evolution using scanning electron microscopy coupled with electron backscattered diffraction (SEM-EBSD). Specimens rolled in the two-phase (O + beta(B2)) region consisted of highly deformed beta(B2) grains. The texture was close to that of the typical bcc deformation texture with a few additional texture components. A subsequent heat treatment of these rolled specimens in single beta(B2) phase region was characterized by static recrystallized beta(B2) grains with the final texture partly inherited from as-rolled material. In contrast, specimens rolled in the single beta(B2) region produced beta(B2) grains with the texture similar to that of completely dynamic recrystallized one. (C) 2010 Elsevier Ltd. All rights reserved.

Negative differential conductance and effective electron mass in highly asymmetric ballistic bilayer graphene nanoribbon

We present a simplified theory of the effective momentum mass (EMM) and ballistic current–voltage relationship in a degenerate two-folded highly asymmetric bilayer graphene nanoribbon. With an increase in the gap, the density-of-states in the lower set of subbands increases more than that of the upper set. This results in a phenomenological population inversion of carriers, which is reflected through a net negative differential conductance (NDC). It is found that with the increase of the ribbon width, the NDC also increases. The population inversion also signatures negative values of EMM above a certain ribbon-width for the lower set of subbands, which increases in a step-like manner with the applied longitudinal static bias. The well-known result for symmetric conditions has been obtained as a special case.

Advanced transmission electron microscope triboprobe with automated closed-loop nanopositioning

Here the design and operation of a novel transmission electron microscope (TEM) triboprobe instrument with real-time vision control for advanced in situ electron microscopy is demonstrated. The NanoLAB triboprobe incorporates a new high stiffness coarse slider design for increased stability and positioning performance. This is linked with an advanced software control system which introduces both new and flexible in situ experimental functional testing modes, plus an automated vision control feedback system. This advancement in instrumentation design unlocks new possibilities of performing a range of new dynamical nanoscale materials tests, including novel friction and fatigue experiments inside the electron microscope.

Intrinsic Electron localization in manganites

We mention here an unusual disorder effect in manganites, namely the ubiquitous hopping behavior for electron transport observed in them over a wide range of doping. We argue that the implied Anderson localization is intrinsic to manganites, because of the existence of polarons in them which are spatially localized, generally at random sites (unless there is polaron ordering). We have developed a microscopic two fluid lb model for manganites, where l denotes lattice site localized l polarons, and b denotes band electrons. Using this, and the self-consistent theory of localization, we show that the occupied b states are Anderson localized in a large range of doping due to the scattering of b electrons from l polarons. Numerical simulations which further include the effect of long range Coulomb interactions support this, as well the existence of a novel polaronic Coulomb glass. A consequence is the inevitable hopping behaviour for electron transport observed in doped insulating manganites.

Synthesis and Densification of Monolithic Zirconium Carbide by Reactive Hot Pressing

Synthesis and densification of monolithic zirconium carbide (ZrC) has been carried out by reactive hot pressing of zirconium (Zr) and graphite (C) powders in the molar ratios 1:1, 1.25:1, 1.5:1, and 2:1 at 40 MPa, 1200 degrees-1600 degrees C. Monolithic ZrC could be synthesized with a C/Zr ratio similar to 0.5-1.0 and the post heat-treated samples have the lattice parameter in the range 4.665 to 4.698 A. Densification improves with an increasing deviation from the stoichiometry. Fine-grained (similar to 1 mu m) and nearly fully dense material (99% RD) could be obtained at a temperature as low as 1200 degrees C with C/Zr similar to 0.67. Microstructural and XRD observations suggest that densification occurred at low temperatures with nonstoichiometric Zr-C powder mixtures.

Vibrational force constant and electron relaxation in H2 and Li2

The force constants of H2 and Li2 are evaluated employing their extended Hartree-Fock wavefunctions by a polynomial fit of their force curves. It is suggested that, based on incomplete multiconfiguration Hartree-Fock wavefunctions, force constants calculated from the energy derivatives are numerically more accurate than those obtained from the derivatives of the Hellmann-Feynman forces. It is observed that electrons relax during the nuclear vibrations in such a fashion as to facilitate the nuclear motions.

A semi-classical model of the electron containing tachyonic matter

It is shown that the mass of the electron could be conceived as the energy associated with its spinning motion and the angular velocity is such that the linear velocities at the surface exceed the velocity of light; this in fact accounts for its stability against the centrifugal forces in the core region.

Undamped Cooper pairs in a non-degenerate electron system

Following the reaction matrix technique and the Kanamori approximation. a condition is obtained for the occurence of undamped Cooper pairs in a non-degenerate electron system. Its relevance to induced superconductivity in systems with artificially populated (optically pumped) bands is pointed out.

Structure and electron transport anomalies in InSe-In6Se 7 composite

Rapid solidification of an equiatomic In-Se alloy resulted in the formation of an equilibrium InSe-In6Se7 phase mixture. The InSe phase was found to be polytypic and exhibited the structural variants 2H, 3H, and 4H. The 4H polytype was found to be in considerably higher proportion compared to 2H and 3H types. The In6Se7 phase was found to be hexagonal with a=0.8919 nm and c=1.4273 nm. Both In6Se 7 and the polytypes of InSe could be identified with the space group P61. The conductivity σ variation with temperature was found to be similar to that observed in disordered semiconducting materials. For temperatures >200 K, ln σ decreased linearly with T-1, phonon-assisted carrier excitation. For temperatures <200 K, ln σ decrease followed T-1/3 behavior, representative of variable-range hopping conduction of electrons.

Electron diffraction patterns from the Al-Mn decagonal phase

The variety of electron diffraction patterns arising from the decagonal phase has been explored using a stereographic analysis for generating the important zone axes as intersection points corresponding to important relvectors. An indexing scheme employing a set of five vectors and an orthogonal vector has been followed. A systematic tilting from the decagonal axis to one of the twofold axes has been adopted to generate a set of experimental diffraction patterns corresponding to the expected patterns from the stereographic analysis with excellent agreement.

Electronic structures of electron donor-acceptor complexes: results from ultraviolet photoelectron spectroscopy and molecular orbital calculations

HeI photoelectron spectra of 1:1 electron donor-acceptor complexes are discussed in the light of molecular orbital calculations. The complexes discussed include those formed by BH3, BF3 and SO2. Some systematics have been found in the ionization energy shifts of the complexes compared to the free components and these are related to the strength of the donor-acceptor bond. Hel spectra of hydrogen bonded complexes are discussed in comparison with results from MO calculations. Limitations of such studies as well as scope for further investigations are indicated.