Ideal Spin Filters: Theoretical Study of Electron Transmission Through Ordered and Disordered Interfaces Between Ferromagnetic Metals and Semiconductors

It is predicted that certain atomically ordered interfaces between some ferromagnetic metals (F) and semiconductors (S) should act as ideal spin filters that transmit electrons only from the majority spin bands or only from the minority spin bands of the F to the S at the Fermi energy, even for F with both majority and minority bands at the Fermi level. Criteria for determining which combinations of F, S and interface should be ideal spin filters are formulated. The criteria depend only on the bulk band structures of the S and F and on the translational symmetries of the S, F and interface. Several examples of systems that meet these criteria to a high degree of precision are identified. Disordered interfaces between F and S are also studied and it is found that intermixing between the S and F can result in interfaces with spin anti-filtering properties, the transmitted electrons being much less spin polarized than those in the ferromagnetic metal at the Fermi energy. A patent application based on this work has been commenced by Simon Fraser University.Comment: RevTeX, 12 pages, 5 figure

A transmission electron microscope study of hydrothermally synthesized yttrium disilicate powders

The crystallization of three hydrothermally synthesized Y2Si2O7 precursor powders at temperatures between 991 and 1038°C has been studied using transmission electron microscopy. Powders prepared in acidic or near-neutral conditions were found to be highly inhomogeneous both chemically and microstructurally, with a wide range of crystalline phases formed. In contrast to this, a powder prepared in alkaline conditions was found to be very homogeneous. Small crystalline nuclei were formed in this powder on heating to 1006°C which grew rapidly at 1038°C to form large single crystal particles. The majority of these had the α-Y2Si2O7 phase but some were of the y-Y2Si2O7 phase. The reasons for the formation of this y-phase are unclear, although it would be expected to transform to α-Y2Si2O7 on further heat treatment at 1200°C. Weaknesses in the current crystal structure data for yttrium disilicate phases are identified and suggestions made for rectifying them

Silica glass segregation in 3 wt.% LiF doped hot-pressed Y₂Si₂O₇

Hot-pressed yttrium disilicate ceramics have been characterized using analytical transmission electron microscopy (TEM). The microstructure consists of large grains of the γ phase of stoichiometric γ-Y2Si2O7 containing rounded glassy Y-doped SiO2 inclusions; excess glassy SiO2-rich material is also found at the grain boundaries. Two main reasons are found for the inhomogeneity: a slight SiO2 excess is inferred from the composition measurements, and the LiF flux used in hot pressing would also promote glass formation. Improved high-temperature mechanical properties would only be possible if residual glass formation was minimized, strategies for doing so are discussed, and the importance of analytical TEM for studying such submicron scale inhomogeneity is underlined

Snapshot: deep-sea wonders

From the whimsical to the downright scary, images featuring creatures from the deep are showcased in the BP Kongsberg Underwater Image Competition being held this week at the 11th International Deep-Sea Biology Symposium, UK. Narelle Towie takes a look at some of the most striking entries.<br/

Experiments at The Virtual National Laboratory for Heavy Ion Fusion

An overview of experiments is presented, in which the physical dimensions, emittance and perveance are scaled to explore driver-relevant beam dynamics. Among these are beam merging, focusing to a small spot, and bending and recirculating beams. The Virtual National Laboratory for Heavy Ion Fusion (VNL) is also developing two driver-scale beam experiments involving heavy-ion beams with I(sub beam) ~; 1 Ampere to provide guidance for the design of an Integrated Research Experiment (IRE) for driver system studies within the next 5 years. Multiple-beam sources and injectors are being designed and a one-beam module will be built and tested. Another experimental effort will be the transport of such a beam through ~;100 magnetic quadrupoles. The experiment will determine transport limits at high aperture fill factors, beam halo formation, and the influence on beam properties of secondary electron Research into driver technology will be briefly presented, including the development of ferromagnetic core materials, induction core pulsers, multiple-beam quadrupole arrays and plasma channel formation experiments for pinched transport in reactor chambers

Experiments at The Virtual National Laboratory for Heavy Ion Fusion

An overview of experiments is presented, in which the physical dimensions, emittance and perveance are scaled to explore driver-relevant beam dynamics. Among these are beam merging, focusing to a small spot, and bending and recirculating beams. The Virtual National Laboratory for Heavy Ion Fusion (VNL) is also developing two driver-scale beam experiments involving heavy-ion beams with I(sub beam) ~; 1 Ampere to provide guidance for the design of an Integrated Research Experiment (IRE) for driver system studies within the next 5 years. Multiple-beam sources and injectors are being designed and a one-beam module will be built and tested. Another experimental effort will be the transport of such a beam through ~;100 magnetic quadrupoles. The experiment will determine transport limits at high aperture fill factors, beam halo formation, and the influence on beam properties of secondary electron Research into driver technology will be briefly presented, including the development of ferromagnetic core materials, induction core pulsers, multiple-beam quadrupole arrays and plasma channel formation experiments for pinched transport in reactor chambers