Non-Monotonic Change of the Composition of Surface Layers of the Melt Co57 Ni10Fe5Si11B17 During Isothermal Process

Comments on collision mechanics in ring systems

International Astronomical Union Colloquium ◽

10.1017/s0252921100101472 ◽

1984 ◽

Vol 75 ◽

pp. 407-422

Author(s):

William K. Hartmann

Keyword(s):

Asteroid Belt ◽

Surface Erosion ◽

Surface Layers ◽

Ring Systems ◽

Eclipse Observations ◽

Saturn’S Rings ◽

Saturn's Rings

ABSTRACTThe nature of collisions within ring systems is reviewed with emphasis on Saturn's rings. The particles may have coherent icy cores and less coherent granular or frosty surface layers, consistent with thermal eclipse observations. Present-day collisions of such ring particles do not cause catastrophic fragmentation of the particles, although some minor surface erosion and reaccretion is possible. Evolution by collisional fragmentation is thus not as important as in the asteroid belt.

Download Full-text

Applications of Photoelectron Microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100092499 ◽

1976 ◽

Vol 34 ◽

pp. 506-507

Author(s):

William J. Baxter

Keyword(s):

Electron Microscopy ◽

Thermal Decomposition ◽

Chemical Composition ◽

Ultraviolet Radiation ◽

Thin Layer ◽

Edge Effects ◽

Electron Optics ◽

Surface Layers ◽

Crystalline Orientation ◽

Fluorescent Screen

In this form of electron microscopy, photoelectrons emitted from a metal by ultraviolet radiation are accelerated and imaged onto a fluorescent screen by conventional electron optics. image contrast is determined by spatial variations in the intensity of the photoemission. The dominant source of contrast is due to changes in the photoelectric work function, between surfaces of different crystalline orientation, or different chemical composition. Topographical variations produce a relatively weak contrast due to shadowing and edge effects.Since the photoelectrons originate from the surface layers (e.g. ∼5-10 nm for metals), photoelectron microscopy is surface sensitive. Thus to see the microstructure of a metal the thin layer (∼3 nm) of surface oxide must be removed, either by ion bombardment or by thermal decomposition in the vacuum of the microscope.

Download Full-text

Etching of Polymers by Oxygen Plasma

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100101797 ◽

1968 ◽

Vol 26 ◽

pp. 408-409

Author(s):

Virgil Peck ◽

W. L. Carter

Keyword(s):

Molecular Weight ◽

Oxygen Plasma ◽

Flow Time ◽

Microscopical Study ◽

Surface Layers ◽

Organic Vapors ◽

Sample Position ◽

Accuracy Of Measurement ◽

Bulk Polymers ◽

Electron Microscopical

Any electron microscopical study of the morphology of bulk polymers has throughout the years been hampered by the lack of any real ability to produce meaningful surface variations for replication. True etching of polymers should show crystalline and amorphous regions in some form of relief. The use of solvents, acids, organic vapors, and inert ion bombardment to etch samples has proved to be useful only in limited applications. Certainly many interpretations of these results are subject to question.The recent use of a radiofrequency (R. F.) plasma of oxygen to degrade and remove organic material with only minor heating has opened a new possibility for etching polymers. However, rigid control of oxygen flow, time, current, and sample position are necessary in order to obtain reproducible results. The action is confined to surface layers; the molecular weight of the polymer residue after heavy etching is the same as the molecular weight of the polymer before attack, within the accuracy of measurement.

Download Full-text

Surface reconstructions of (001) cleaved GdBa2Cu3O7-δ

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010012093x ◽

1992 ◽

Vol 50 (1) ◽

pp. 106-107

Author(s):

H.W. Zandbergen ◽

M.R. McCartney

Keyword(s):

Electron Microscopy ◽

Copper Oxide ◽

Grain Boundaries ◽

Atomic Structure ◽

Oxygen Deficiency ◽

Surface Layers ◽

Layer Sequence ◽

Surface Reconstructions ◽

Good Agreement

Very few electron microscopy papers have been published on the atomic structure of the copper oxide based superconductor surfaces. Zandbergen et al. have reported that the surface of YBa2Cu3O7-δ was such that the terminating layer sequence is bulk-Y-CuO2-BaO-CuO-BaO, whereas the interruption at the grain boundaries is bulk-Y-CuO2-BaO-CuO. Bursill et al. reported that HREM images of the termination at the surface are in good agreement with calculated images with the same layer sequence as observed by Zandbergen et al. but with some oxygen deficiency in the two surface layers. In both studies only one or a few surfaces were studied.

Download Full-text

TEM study of Cosi2 formation via annealing of Co-Ti bilayers on Si

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100138695 ◽

1995 ◽

Vol 53 ◽

pp. 464-465

Author(s):

N. David Theodore ◽

Andre Vantomme ◽

Peter Crazier

Keyword(s):

Thermal Instability ◽

Lattice Mismatch ◽

Field Effect Transistors ◽

Contact Layer ◽

Interface Roughness ◽

Oxide Semiconductor ◽

Surface Layers ◽

Silicide Layer ◽

Small Lattice ◽

Buried Layers

Contact is typically made to source/drain regions of metal-oxide-semiconductor field-effect transistors (MOSFETs) by use of TiSi2 or CoSi2 layers followed by AI(Cu) metal lines. A silicide layer is used to reduce contact resistance. TiSi2 or CoSi2 are chosen for the contact layer because these silicides have low resistivities (~12-15 μΩ-cm for TiSi2 in the C54 phase, and ~10-15 μΩ-cm for CoSi2). CoSi2 has other desirable properties, such as being thermally stable up to >1000°C for surface layers and >1100°C for buried layers, and having a small lattice mismatch with silicon, -1.2% at room temperature. During CoSi2 growth, Co is the diffusing species. Electrode shorts and voids which can arise if Si is the diffusing species are therefore avoided. However, problems can arise due to silicide-Si interface roughness (leading to nonuniformity in film resistance) and thermal instability of the resistance upon further high temperature annealing. These problems can be avoided if the CoSi2 can be grown epitaxially on silicon.

Download Full-text

Quantitative energy-filtered electron diffraction

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100172693 ◽

1994 ◽

Vol 52 ◽

pp. 992-993

Author(s):

R. Vincent

Keyword(s):

Electron Diffraction ◽

Inelastic Scattering ◽

Dynamic Range ◽

Electron Optics ◽

Surface Layers ◽

High Brightness ◽

Inclined Surfaces ◽

Perfect Symmetry ◽

Amorphous Surface ◽

The Ideal

Microanalysis and diffraction on a sub-nanometre scale have become practical in modern TEMs due to the high brightness of field emission sources combined with the short mean free paths associated with both elastic and inelastic scattering of incident electrons by the specimen. However, development of electron diffraction as a quantitative discipline has been limited by the absence of any generalised theory for dynamical inelastic scattering. These problems have been simplified by recent innovations, principally the introduction of spectrometers such as the Gatan imaging filter (GIF) and the Zeiss omega filter, which remove the inelastic electrons, combined with annual improvements in the speed of computer workstations and the availability of solid-state detectors with high resolution, sensitivity and dynamic range.Comparison of experimental data with dynamical calculations imposes stringent requirements on the specimen and the electron optics, even when the inelastic component has been removed. For example, no experimental CBED pattern ever has perfect symmetry, departures from the ideal being attributable to residual strain, thickness averaging, inclined surfaces, incomplete cells and amorphous surface layers.

Download Full-text

In vitro assembly of 2-D crystals from partially purified EA1 protein secreted by Bacillus anthracis strain Delta Sterne-1

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100169110 ◽

1994 ◽

Vol 52 ◽

pp. 276-277

Author(s):

Mary Beth Downs ◽

Wilson Ribot ◽

Joseph W. Farchaus

Keyword(s):

Cell Wall ◽

Molecular Sieves ◽

Cell Envelope ◽

Single Species ◽

Supporting Cell ◽

Surface Layers ◽

Rabbit Igg ◽

In Vitro Assembly ◽

Covalently Linked

Many bacteria possess surface layers (S-layers) that consist of a two-dimensional protein lattice external to the cell envelope. These S-layer arrays are usually composed of a single species of protein or glycoprotein and are not covalently linked to the underlying cell wall. When removed from the cell, S-layer proteins often reassemble into a lattice identical to that found on the cell, even without supporting cell wall fragments. S-layers exist at the interface between the cell and its environment and probably serve as molecular sieves that exclude destructive macromolecules while allowing passage of small nutrients and secreted proteins. Some S-layers are refractory to ingestion by macrophages and, generally, bacteria are more virulent when S-layers are present.When grown in rich medium under aerobic conditions, B. anthracis strain Delta Sterne-1 secretes large amounts of a proteinaceous extractable antigen 1 (EA1) into the growth medium. Immunocytochemistry with rabbit polyclonal anti-EAl antibody made against the secreted protein and gold-conjugated goat anti-rabbit IgG showed that EAI was localized at the cell surface (fig 1), which suggests its role as an S-layer protein.

Download Full-text