scholarly journals Probability of Seeing (001) Cross-Fringes in a Random Cubic Nanocrystal Image

2000 ◽  
Vol 6 (S2) ◽  
pp. 1038-1039
Author(s):  
W. Qin ◽  
P. Fraundorf
Keyword(s):  
Electron Beam ◽  
Crystal Orientation ◽  
Solid Angle ◽  
Zone Axis ◽  
Bragg Condition ◽  
Oriented Crystal ◽  
Cubic Lattice ◽  
Upper Limit ◽  
Half Angle ◽  
Semi Empirical

As a crystal gets smaller, diffraction spots stay visible for larger deviations from the Bragg condition. The upper limit of such deviations is connected to the threshold for getting lattice fringes in TEM images. This in turn allows one to quantify the probability of seeing cross lattice fringes along a certain zone axis. In this abstract we examine a simple semi-empirical model for the probability of detecting (001) zone cross-fringes of a spherical crystal of cubic lattice.The upper limit for the deviation of crystal orientation from the exact Bragg condition, without losing cross fringes down a given zone, is expressed as the maximum half-angle θ1 between the zone and the electron beam. The solid angle σ subtended by a cone with this half-angle is proportional to the probability px that a randomly-oriented crystal will show the cross-fringes associated with that zone. A schematic, illustrating the principle used to calculate the probability of seeing cross-fringes, is given in Figure 1.

Lattice Fringe Visibility after Tilt

2000 ◽  
Vol 6 (S2) ◽  
pp. 1040-1041
Author(s):  
W. Qin ◽  
P. Fraundorf
Keyword(s):  
Empirical Model ◽  
Crystal Orientation ◽  
Reciprocal Lattice ◽  
Lattice Parameters ◽  
Bragg Condition ◽  
Fringe Visibility ◽  
Lattice Fringe ◽  
Ewald Sphere ◽  
Instrument Response ◽  
Semi Empirical

Factors that affect the visibility of lattice fringes include crystal orientation and thickness, as well as instrument response. As a crystal gets smaller, lattice fringes stay visible for larger deviations from the Bragg condition. Hence the persistence of fringes under tilt affects the abundance and range of lattice spacings (and angles) that one sees in an image of randomly-oriented crystals. A subset of the fringes in an image are “still-visible” after large (e.g. 35°) single or double axis tilts. If one is looking for “new-fringes” from the same crystal (e.g. to analyze it's 3D lattice parameters), rules for recognizing redundant fringes might also help out.Here we examine a semi-empirical model for predicting the visibility of lattice fringes after tilt, by connecting the visibility to intersection of the corresponding crystal reciprocal-lattice spot with the illuminating Ewald sphere.

scholarly journals Supershort avalanche electron beam generation in gases

2008 ◽  
Vol 26 (4) ◽  
pp. 605-617 ◽  
Author(s):  
V.F. Tarasenko ◽  
E.H. Baksht ◽  
A.G. Burachenko ◽  
I.D. Kostyrya ◽  
M.I. Lomaev ◽  
...  
Keyword(s):  
High Pressure ◽  
Electron Beam ◽  
Atmospheric Pressure ◽  
Electron Beams ◽  
Solid Angle ◽  
Generation Mechanism ◽  
Full Width ◽  
Half Maximum ◽  
Electron Beam Pulse ◽  
Supershort Avalanche Electron Beam

AbstractThis paper reports on the properties of a supershort avalanche electron beam generated in the air or other gases under atmospheric pressure and gives the analysis of a generation mechanism of supershort avalanche electron beam, as well as methods of such electron beams registration. It is reported that in the air under the pressure of 1 atm, a supershort (<100 ps) avalanche electron beam is formed in the solid angle more than 2π steradian. The electron beam has been obtained behind a 45 µm thick Al-Be foil in SF6 and Xe under the pressure of 2 atm, and in He, under the pressure of about 15 atm. It is shown that in SF6 under the high pressure (>1 atm) duration (full width at half maximum) of supershort avalanche electron beam pulse is about 150 ps.

Low Beam Energy X-Ray Micro Analysis: How Useful Is It?

1997 ◽  
Vol 3 (S2) ◽  
pp. 881-882 ◽  
Author(s):  
Dale E. Newbury
Keyword(s):  
Electron Beam ◽  
Beam Energy ◽  
Strong Dependence ◽  
Incident Beam ◽  
X Ray ◽  
Upper Limit ◽  
History Of ◽  
Incident Beam Energy ◽  
Micro Analysis ◽  
Electron Range

Throughout the history of electron-beam X-ray microanalysis, analysts have made good use of the strong dependence of electron range on incident energy (R ≈ E1,7) to optimize the analytical volume when attacking certain types of problems, such as inclusions in a matrix or layered specimens. The “conventional” energy range for quantitative electron beam X-ray microanalysis can be thought of as beginning at 10 keV and extending to the upper limit of the accelerating potential, typically 30 - 50 keV depending on the instrument. The lower limit of 10 keV is selected because this is the lowest incident beam energy for which there is a satisfactory analytical X-ray peak excited from the K-, L-, or M- shells (in a few cases, two shells are simultaneously excited, e.g., Fe-K and Fe-L) for every element in the Periodic Table that is accessible to X-ray spectrometry, beginning with Be (Ek =116 eV) and extending to the transuranic elements. This criterion is based upon establishing a minimum overvoltage U = E0/Ec > 1.25, which is the practical minimum for useful excitation.

scholarly journals Electron Beam as Origin of White-Light Solar Flares

1989 ◽  
Vol 104 (1) ◽  
pp. 19-30
Author(s):  
J. Aboudarham ◽  
J. C. Henoux
Keyword(s):  
Electron Beam ◽  
White Light ◽  
Solar Flares ◽  
Light Emission ◽  
Continuum Emission ◽  
Continuum Radiation ◽  
Photospheric Level ◽  
Hydrogen Ionization ◽  
Semi Empirical ◽  
Flare Model

AbstractWe study the effect of chromospheric bombardment by an electron beam during solar flares. Using a semi-empirical flare model, we investigate energy balance at temperature minimum level and in the upper photosphere. We show that non-thermal hydrogen ionization (i.e., due to the electrons of the beam) leads to an increase of chromospheric hydrogen continuum emission, H− population, and absorption of photo-spheric and chromospheric continuum radiation. So, the upper photosphere is radiatively heated by chromospheric continuum radiation produced by the beam. The effect of hydrogen ionization is an enhanced white-light emission both at chromospheric and photospheric level, due to Paschen and H− continua emission, respectively. We then obtain white-light contrasts compatible with observations, obviously showing the link between white-light flares and atmospheric bombardment by electron beams.

scholarly journals Upper limits for the effective temperature of Wolf-Rayet stars from the presence of He I

1987 ◽  
Vol 122 ◽  
pp. 461-462
Author(s):  
W. Schmutz ◽  
W.-R. Hamann ◽  
U. Wessolowski
Keyword(s):  
Effective Temperature ◽  
Empirical Models ◽  
Stellar Radius ◽  
Upper Limit ◽  
Upper Limits ◽  
Effective Temperatures ◽  
Semi Empirical

A recently developed non-LTE code for realistic semi-empirical models of Wolf-Rayet atmospheres is used to calculate synthetic helium lines. From the resulting line strenghts it can be concluded that if He I lines are present, the effective temperatures of these stars have to be less than an upper limit. This limit depends on the stellar radius and is approximately 40kK for R* = 20 R⊙ to 60kK for R* = 5 R⊙.

scholarly journals Hrem Of General And Twist Grain Boundaries

1999 ◽  
Vol 5 (S2) ◽  
pp. 108-109
Author(s):  
K. L. Merkle ◽  
L. J. Thompson
Keyword(s):  
Thin Film ◽  
Electron Beam ◽  
Phase Space ◽  
Grain Boundaries ◽  
Scale Structure ◽  
Zone Axis ◽  
Low Energy ◽  
Atomic Scale ◽  
Dimensional Phase Space ◽  
Scale Structures

The observation of atomic-scale structures of grain boundaries (GBs) via axial illumination HREM has been largely restricted to tilt GBs, due to the requirement that the electron beam be parallel to a low-index zone axis on both sides of the interface. This condition can be fulfilled for all tilt GBs with misorientation about a low-index direction. The information obtained through HREM studies in many materials has brought important insights concerning the atomic-scale structure of such boundaries. However, it is well known that tilt GBs occupy only an infinitesimally small fraction of the 5-dimensional phase space which describes the macroscopic geometry of all GBs. Therefore, although tilt GBs are very important due to their low energy, it would be usefulto also study twist GBs and general GBs that contain twist and tilt components.We have prepared thin-film Au samples by an epitaxy technique in which (01l) and (001) grains are grown side by side.

scholarly journals Issues in Cathode Performance Part 3-Cathode Emitter Material

1995 ◽  
Vol 3 (5) ◽  
pp. 10-11
Author(s):  
Damon Heer
Keyword(s):  
Electron Beam ◽  
High Resolution ◽  
Crystal Orientation ◽  
High Stability ◽  
High Brightness ◽  
High Beam ◽  
Industry Standard ◽  
Small Spot ◽  
Long Lifetime ◽  
Beam Currents

Part 1 of this article series (October 1994 issue) covered the performance features of various tip shapes and explained why the <100> crystal orientation is the industry standard. Part 2 (January/February 1995 issue) covered cathode mounting design and explained how the Mini Vogel Mount cathode design provides high-stability and long-lifetime performance.LaB6 and CeB6 cathodes are used as high-brightness, high-stability, longlifetime cathodes in a variety of electron beam applications. A high-brightness source provides small spot sizes for high resolution and improved analytical results from high beam currents.

Microdiffraction in Dedicated STEM

1981 ◽  
Vol 39 ◽  
pp. 356-357
Author(s):  
D.C. Houghton
Keyword(s):  
Diffraction Pattern ◽  
Crystal Orientation ◽  
Low Cost ◽  
Zone Axis ◽  
Phase Identification ◽  
Sequential Methods ◽  
Considerable Promise ◽  
Diffraction Patterns ◽  
Cu Foil

Microdiffraction in dedicated STEM instruments has shown considerable promise as a source of microanalytical information. A major problem has been the relatively inefficient sequential methods used to obtain the diffraction pattern. The apparatus shown schematically in Fig. 1 has facilitated parallel viewing and recording of diffraction patterns in the HB5 STEM. The equipment is robust, low cost and can be installed with no modifications to the microscope.A series of diffraction patterns were recorded under identical conditions at a (110) zone axis in an Al-4% Cu foil shown in Fig. 2(a) to allow direct comparison of sequential and parallel recording methods. The thickness in this part of the foil was ∼220 nm as measured from the projected widths of θ' plates. The selected area “rocking beam” images in Figs. 2(b) and (d) are clearly noisy, suffer from scan distortions and their usefulness for phase identification and crystal orientation is severely limited.

Control of Crystal Orientation of Hydroxyapatite by Imposing a High Magnetic Field

2005 ◽  
Vol 284-286 ◽  
pp. 75-78 ◽  
Author(s):  
Cun You Wu ◽  
Yuichiro Murakami ◽  
Kensuke Sassa ◽  
Kazuhiko Iwai ◽  
Shigeo Asai
Keyword(s):  
Magnetic Field ◽  
Crystal Structure ◽  
Mechanical Properties ◽  
Surface Properties ◽  
High Magnetic Field ◽  
Crystal Orientation ◽  
Hexagonal Crystal ◽  
Hard Tissue ◽  
Oriented Crystal ◽  
Mineral Constituent

The controlled development of texture microstructure in ceramics is one effective way to improve their properties, such as electrical, mechanical properties and biocompatibility. A bioceramics with oriented crystal structure has attracted great interest. In bone reparations, Hydroxyapatite (HAp)-based biomaterials were frequently used. And HAp is the main mineral constituent of the hard tissue of human bodies, which occurs with a hexagonal crystal. A HAp crystal turns out to have different surface properties in a- (or b-) plane and c-plane. In this regard, to get highly oriented HAp is very important before using HAp as a biomaterial. And the crystal orientated HAp is useful not only as biomaterials but also as protein absorbents. In this research, two different kinds of HAp-based biomaterial with oriented structure (HAp bioceramics and HAp-coated titanium composite) were studied.

Measurement and Mapping of Small Changes of Crystal Orientation by Electron Backscattering Diffraction

2005 ◽  
Vol 11 (4) ◽  
pp. 341-353 ◽  
Author(s):  
Xiaodong Tao ◽  
Alwyn Eades
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Hough Transform ◽  
Crystal Orientation ◽  
Zone Axis ◽  
Electron Backscattering ◽  
Electron Backscattering Diffraction ◽  
Orientation Maps ◽  
Ebsd Pattern ◽  
Scanning Electron

We have explored the possibility of measuring small changes of orientation within grains by electron backscattering diffraction (EBSD), in the scanning electron microscope. Conventional orientation maps (using EBSD) index the orientation of each position on the sample separately. This does not give accurate results for small differences of orientation. We have studied methods of measuring small changes in orientation by measuring the change from one EBSD pattern to the next directly, without indexing either. Previous workers have measured the change of position of a zone axis in the EBSD pattern. We have compared this with an alternative method, which we show to be superior, of measuring the shift of the peaks in the Hough transform from one diffraction pattern to the next. This means that we are measuring the change of orientation of sets of crystal planes within the grain, rather than measuring the change of orientation of zone axes. We show that it is possible, with a standard EBSD configuration, to measure the shift of the Kikuchi bands to a precision of about a 10th of a pixel, which corresponds to a change of orientation in the sample of about 0.1 mrad (0.006°).

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