A Globally Conforming Lattice Structure for 2D Stress Tensor Visualization

It is well known that incident photons carrying momentum ℏkexert a positive photon pressure. But if light is impinging from a negative refractive medium in which ℏkis directed toward the source of radiation, should light exert a photon “tension” instead of a photon pressure? Using an ab initio method that takes the underlying microstructure of a material into account, we find that when an electromagnetic wave propagates from one material into another, the electromagnetic stress at the boundary is, in fact, indeterminate if only the macroscopic parameters are specified. Light can either pull or push the boundary, depending not only on the macroscopic parameters but also on the microscopic lattice structure of the polarizable units that constitute the medium. Within the context of an effective-medium approach, the lattice effect is attributed to electrostriction and magnetostriction, which can be accounted for by the Helmholtz stress tensor if we use the macroscopic fields to calculate the boundary optical stress.

Download Full-text

Structural analysis of the photosynthetic membrane from Ectothiorhodospira halochloris

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010007727x ◽

1983 ◽

Vol 41 ◽

pp. 740-741

Author(s):

H. Engelhardt ◽

R. Guckenberger ◽

W. Baumeister

Keyword(s):

Lattice Structure ◽

Bacterial Species ◽

Hexagonal Lattice ◽

Reaction Centre ◽

Photosynthetic Membrane ◽

Rhodopseudomonas Viridis ◽

Photosynthetic Membranes ◽

Ectothiorhodospira Halochloris ◽

Main Components

Bacterial photosynthetic membranes contain, apart from lipids and electron transport components, reaction centre (RC) and light harvesting (LH) polypeptides as the main components. The RC-LH complexes in Rhodopseudomonas viridis membranes are known since quite seme time to form a hexagonal lattice structure in vivo; hence this membrane attracted the particular attention of electron microscopists. Contrary to previous claims in the literature we found, however, that 2-D periodically organized photosynthetic membranes are not a unique feature of Rhodopseudomonas viridis. At least five bacterial species, all bacteriophyll b - containing, possess membranes with the RC-LH complexes regularly arrayed. All these membranes appear to have a similar lattice structure and fine-morphology. The lattice spacings of the Ectothiorhodospira haloohloris, Ectothiorhodospira abdelmalekii and Rhodopseudomonas viridis membranes are close to 13 nm, those of Thiocapsa pfennigii and Rhodopseudomonas sulfoviridis are slightly smaller (∼12.5 nm).

Download Full-text

Electron-Channelling Patterns: Principles and Techniques

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100091986 ◽

1976 ◽

Vol 34 ◽

pp. 400-401

Author(s):

David C. Joy

Keyword(s):

Crystal Structure ◽

Electron Flux ◽

Lattice Structure ◽

Incident Beam ◽

Bloch Wave ◽

Crystalline Solid ◽

Angle Of Incidence ◽

Electron Channelling ◽

Regular Arrangement ◽

Backscattered Signals

In a crystalline solid the regular arrangement of the lattice structure influences the interaction of the incident beam with the specimen, leading to changes in both the transmitted and backscattered signals when the angle of incidence of the beam to the specimen is changed. For the simplest case the electron flux inside the specimen can be visualized as the sum of two, standing wave distributions of electrons (Fig. 1). Bloch wave 1 is concentrated mainly between the atom rows and so only interacts weakly with them. It is therefore transmitted well and backscattered weakly. Bloch wave 2 is concentrated on the line of atom centers and is therefore transmitted poorly and backscattered strongly. The ratio of the excitation of wave 1 to wave 2 varies with the angle between the incident beam and the crystal structure.

Download Full-text

Microstructural Study of Diamond Deformed Under High Pressure and Temperature

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100118072 ◽

1985 ◽

Vol 43 ◽

pp. 230-231

Author(s):

E. F. Koch

Keyword(s):

High Pressure ◽

High Temperature ◽

Lattice Structure ◽

Diamond Particle ◽

Polycrystalline Diamond ◽

Sintering Process ◽

Ion Milling ◽

Sintered Compact ◽

Transmission Electron ◽

High Pressure Sintering

Because of the extremely rigid lattice structure of diamond, generating new dislocations or moving existing dislocations in diamond by applying mechanical stress at ambient temperature is very difficult. Analysis of portions of diamonds deformed under bending stress at elevated temperature has shown that diamond deforms plastically under suitable conditions and that its primary slip systems are on the ﹛111﹜ planes. Plastic deformation in diamond is more commonly observed during the high temperature - high pressure sintering process used to make diamond compacts. The pressure and temperature conditions in the sintering presses are sufficiently high that many diamond grains in the sintered compact show deformed microtructures.In this report commercially available polycrystalline diamond discs for rock cutting applications were analyzed to study the deformation substructures in the diamond grains using transmission electron microscopy. An individual diamond particle can be plastically deformed in a high pressure apparatus at high temperature, but it is nearly impossible to prepare such a particle for TEM observation, since any medium in which the diamond is mounted wears away faster than the diamond during ion milling and the diamond is lost.

Download Full-text

Structure of stacking faults in pyrite using TEM techniques

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100122198 ◽

1992 ◽

Vol 50 (1) ◽

pp. 358-359

Author(s):

Raja Subramanian ◽

Kenneth S. Vecchio

Keyword(s):

Lattice Structure ◽

Stacking Faults ◽

Covalent Bond ◽

Group Symmetry ◽

Iron Pyrite ◽

Dislocation Glide ◽

Partial Dislocations ◽

Transmission Electron ◽

Contrast Analysis ◽

Chlorine Ions

The structure of stacking faults and partial dislocations in iron pyrite (FeS2) have been studied using transmission electron microscopy. Pyrite has the NaCl structure in which the sodium ions are replaced by iron and chlorine ions by covalently-bonded pairs of sulfur ions. These sulfur pairs are oriented along the <111> direction. This covalent bond between sulfur atoms is the strongest bond in pyrite with Pa3 space group symmetry. These sulfur pairs are believed to move as a whole during dislocation glide. The lattice structure across these stacking faults is of interest as the presence of these stacking faults has been preliminarily linked to a higher sulfur reactivity in pyrite. Conventional TEM contrast analysis and high resolution lattice imaging of the faulted area in the TEM specimen has been carried out.

Download Full-text

Distortion in lattice-resolution scanned-probe microscope images

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100148447 ◽

1993 ◽

Vol 51 ◽

pp. 522-523

Author(s):

L. Fei

Keyword(s):

Film Studies ◽

Lattice Structure ◽

Substrate Material ◽

Repulsive Force ◽

Instrument Calibration ◽

Microscope Images ◽

Probe Microscope ◽

Electron Microscopes ◽

Diffraction Patterns ◽

Lattice Resolution

Scanned probe microscopes (SPM) have been widely used for studying the structure of a variety material surfaces and thin films. Interpretation of SPM images, however, remains a debatable subject at best. Unlike electron microscopes (EMs) where diffraction patterns and images regularly provide data on lattice spacings and angles within 1-2% and ∽1° accuracy, our experience indicates that lattice distances and angles in raw SPM images can be off by as much as 10% and ∽6°, respectively. Because SPM images can be affected by processes like the coupling between fast and slow scan direction, hysteresis of piezoelectric scanner, thermal drift, anisotropic tip and sample interaction, etc., the causes for such a large discrepancy maybe complex even though manufacturers suggest that the correction can be done through only instrument calibration.We show here that scanning repulsive force microscope (SFM or AFM) images of freshly cleaved mica, a substrate material used for thin film studies as well as for SFM instrument calibration, are distorted compared with the lattice structure expected for mica.

Download Full-text