Goniometry for Interface Studies in Transmission Electron Microscopy

A method using a double-tilt goniometer stage for determining the orientation of crystalline specimens in transmission electron microscopy (TEM) is described. The procedure involves visual identification of two zone axes, and using the corresponding goniometer settings to plot these poles stereographically. Crystal orientations and misorientations can be established rapidly, and the method is intended for use as a practical complement to more precise but time-consuming techniques. The commutative operation of double-tilt stages and their goniometric capability are also discussed. Using Rodrigues-Frank space, it is shown that the set of attainable operations for such stages is represented by points on an hyperboloidal surface.     

Mapping the OH + CO-->HOCO reaction pathway through IR spectroscopy of the OH-CO reactant complex

A hydrogen-bonded complex composed of the OH and CO reactants has been identified along the OH + CO-->HOCO reaction pathway. IR action spectroscopy in the OH overtone region has been used to examine the vibrational modes of the linear OH-CO complex, including intermolecular bending modes that probe portions of the reaction path leading to HOCO. The spectroscopic measurements have accessed highly excited intermolecular levels, with energies up to 250 cm-1 above the zero-point level, which lie in close proximity to the transition state for reaction. The OH-CO binding energy, D0 < or = 430 cm-1, has also been established from the quantum state distribution of the OH fragments following vibrational predissociation of the OH-CO complex. Complementary electronic structure calculations have been performed to characterize the OH-CO and OH-OC complexes, the transition state for HOCO formation, and the direct reaction path that connects the experimentally observed OH-CO complex to the HOCO intermediate.     

Treibstoffe

Ohne Zusammenfassung     

Electrically and magnetically tunable microwave device using (Ba, Sr) TiO3/Y3Fe5O12 multilayer

Ferroelectric (Ba_0.6Sr_0.4)TiO₃ (BST) thin films have been deposited by pulsed laser deposition onto single-crystal Y₃Fe₅O₁₂ (YIG) substrates with/without a MgO buffer layer. The structure and microwave properties of the BST films have been investigated as a function of substrate orientation and O₂ deposition pressures (50-800 mTorr). The crystallographic orientation of BST film varies with the deposition conditions. The dielectric properties of the ferroelectric were measured using interdigitated capacitors deposited on top of the BST film. BST films exhibit high tunability (20-40%) and high dielectric Q=1/cos' (30-50) with a dc bias field of 67 kV/cm at 10 GHz. A coplanar waveguide transmission line was fabricated from a (001)-oriented BST film on (111)YIG which exhibited a 17° differential phase shift with an applied dc bias field of 21 kV/cm (10 GHz). An equivalent differential phase shift was achieved with a magnetic field of 160 Gauss.     

Zur Dampfdichtebestimmung

Ohne Zusammenfassung     

Impurities in Magnetic Insulators Studied by Low-Temperature Nuclear Orientation

Although the effects of impurities in metallic magnets have been extensively studied there have been far fewer experiments on impurities in insulating magnets, and, in an effort to understand this problem, we have investigated the effect of impurities in various systems. In MnCl₂⋅4H₂O samples doped with 1.6, 4.0 and 6.2% Co, the ⁵⁴Mn NMRON line is significantly broadened compared to the line in the pure crystal and shows structure on the low frequency side. The nuclear spin-lattice relaxation time is also lower by an order of magnitude. ⁵⁴Mn has also been doped into FeCl₂⋅4H₂O for which a 4-sublattice structure has been proposed and some details of this structure have been obtained. This revised version was published online in September 2006 with corrections to the Cover Date.     

Precipitate orientation relationships and interfacial structures in duplex stainless steel Zeron-100

Precipitation in a commercial duplex stainless steel, Zeron-100, has been investigated using conventional and high-resolution electron microscopy. Acicular fcc precipitates of Ni-rich nphase formed in the Cr-rich fmatrix by suitable heat treatment. The orientation relationships between a large number of particles and the matrix were studied and found to be distributed in a range between the Kurdjumov-Sachs and the Pitsch relationships. All particles were observed to be bounded by two types of longitudinal facets, designated I and C, representing 'incoherent' and 'coherent'. High-resolution microscopy showed that the I facet was based on the (112) alpha /(101) nincommensurate interface between Pitsch-related crystals. The C facet exhibited a coherent terrace structure with coherency strain parallel to accommodated by a disconnection array, causing the adjacent crystals to be slightly misoriented from the Kurdjumov-Sachs relationship. The orientational incompatibility between the I and C reference structures, 5.76° about , was found to be accommodated by networks of n-crystal dislocations superimposed on the facets. These acted as tilt walls of dislocations, but, although their combined angular tilt was always observed to equal about 5.7°, this was not partitioned between the I and C facets in a unique manner. Such differential partitioning of the incompatibility offers a natural explanation for the observed variation in particle orientation. Some issues, such as the growth mechanism, were not resolved and need further work.     

Communication: Generalizing Rosenfeld's excess-entropy scaling to predict long-time diffusivity in dense fluids of Brownian particles: from hard to ultrasoft interactions

Computer simulations are used to test whether a recently introduced generalization of Rosenfeld's excess-entropy scaling method for estimating transport coefficients in systems obeying molecular dynamics can be extended to predict long-time diffusivities in fluids of particles undergoing Brownian dynamics in the absence of interparticle hydrodynamic forces. Model fluids with inverse-power-law, Gaussian-core, and Hertzian pair interactions are considered. Within the generalized Rosenfeld scaling method, long-time diffusivities of ultrasoft Gaussian-core and Hertzian particle fluids, which display anomalous trends with increasing density, are predicted (to within 20%) based on knowledge of interparticle interactions, excess entropy, and scaling behavior of simpler inverse-power-law fluids.