Neutron Production Characteristics and Emission Properties of Spherically Convergent Beam Fusion

Wide-angle convergent beam shadow images(CBSI) exhibit several characteristic distortions resulting from spherical aberration. The most prominent is a circle of infinite magnification resulting from rays having equal values of a forming a cross-over on the optic axis at some distance before reaching the paraxial focal point. This distortion is called the tangential circle of infinite magnification; it can be used to align and stigmate a STEM and to determine Cs for the probe forming lens. A second distortion, the radial circle of infinite magnification, results from a cross-over on the lens caustic surface of rays with differing values of ∝a, also before the paraxial focal point of the lens.

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Disappearance Voltage Determinations Using a Convergent Beam

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100064979 ◽

1971 ◽

Vol 29 ◽

pp. 184-185

Author(s):

W. L. Bell

Keyword(s):

Second Order ◽

Objective Method ◽

Uniform Thickness ◽

Rocking Curve ◽

Crystal Perfection ◽

Kikuchi Line ◽

Central Maximum ◽

Diffraction Patterns ◽

Convergent Beam ◽

Beam Technique

Disappearance voltages for second order reflections can be determined experimentally in a variety of ways. The more subjective methods, such as Kikuchi line disappearance and bend contour imaging, involve comparing a series of diffraction patterns or micrographs taken at intervals throughout the disappearance range and selecting that voltage which gives the strongest disappearance effect. The estimated accuracies of these methods are both to within 10 kV, or about 2-4%, of the true disappearance voltage, which is quite sufficient for using these voltages in further calculations. However, it is the necessity of determining this information by comparisons of exposed plates rather than while operating the microscope that detracts from the immediate usefulness of these methods if there is reason to perform experiments at an unknown disappearance voltage.The convergent beam technique for determining the disappearance voltage has been found to be a highly objective method when it is applicable, i.e. when reasonable crystal perfection exists and an area of uniform thickness can be found. The criterion for determining this voltage is that the central maximum disappear from the rocking curve for the second order spot.

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Symmetries and Extinction Rules in CBED

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100055758 ◽

1982 ◽

Vol 40 ◽

pp. 684-685

Author(s):

K. Ishizuka

Keyword(s):

Electron Diffraction ◽

Incident Beam ◽

Convergent Beam Electron Diffraction ◽

Beam Direction ◽

Beam Electron ◽

Convergent Beam

The technique of convergent-beam electron diffraction (CBED) has been established. However there is a distinct discrepancy concerning the CBED pattern symmetries associated with translation symmetries parallel to the incident beam direction: Buxton et al. assumed no detectable effects of translation components, while Goodman predicted no associated symmetries. In this report a procedure used by Gjønnes & Moodie1 to obtain dynamical extinction rules will be extended in order to derive the CBED pattern symmetries as well as the dynamical extinction rules.

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Prospects for convergent beam electron diffraction with a 200kV cold field-emission transmission electron microscope

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100086635 ◽

1991 ◽

Vol 49 ◽

pp. 466-467

Author(s):

J W Steeds ◽

R Vincent

Keyword(s):

Field Emission ◽

High Performance ◽

Small Diameter ◽

Convergent Beam Electron Diffraction ◽

Zone Axis ◽

Medium Voltage ◽

Transmission Electron ◽

Good Crystallinity ◽

Special Modification ◽

Convergent Beam

We review the analytical powers which will become more widely available as medium voltage (200-300kV) TEMs with facilities for CBED on a nanometre scale come onto the market. Of course, high performance cold field emission STEMs have now been in operation for about twenty years, but it is only in relatively few laboratories that special modification has permitted the performance of CBED experiments. Most notable amongst these pioneering projects is the work in Arizona by Cowley and Spence and, more recently, that in Cambridge by Rodenburg and McMullan.There are a large number of potential advantages of a high intensity, small diameter, focussed probe. We discuss first the advantages for probes larger than the projected unit cell of the crystal under investigation. In this situation we are able to perform CBED on local regions of good crystallinity. Zone axis patterns often contain information which is very sensitive to thickness changes as small as 5nm. In conventional CBED, with a lOnm source, it is very likely that the information will be degraded by thickness averaging within the illuminated area.

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Relative Intensities in ED Patterns From Thin Gold Films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100096436 ◽

1972 ◽

Vol 30 ◽

pp. 636-637

Author(s):

R. H. Morriss ◽

J. D. C. Peng ◽

C. D. Melvin

Keyword(s):

Theoretical Calculations ◽

Diffraction Theory ◽

Gold Films ◽

Reasonable Accuracy ◽

Experimental Conditions ◽

Crystal Perfection ◽

Heavy Atoms ◽

Fine Focus ◽

Convergent Beam ◽

Beam Diffraction

Although dynamical diffraction theory was modified for electrons by Bethe in 1928, relatively few calculations have been carried out because of computational difficulties. Even fewer attempts have been made to correlate experimental data with theoretical calculations. The experimental conditions are indeed stringent - not only is a knowledge of crystal perfection, morphology, and orientation necessary, but other factors such as specimen contamination are important and must be carefully controlled. The experimental method of fine-focus convergent-beam electron diffraction has been successfully applied by Goodman and Lehmpfuhl to single crystals of MgO containing light atoms and more recently by Lynch to single crystalline (111) gold films which contain heavy atoms. In both experiments intensity distributions were calculated using the multislice method of n-beam diffraction theory. In order to obtain reasonable accuracy Lynch found it necessary to include 139 beams in the calculations for gold with all but 43 corresponding to beams out of the [111] zone.

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Transmission Scanning Electron Microscopy and Energy Analysis with the Siemens ELMISKOP 101

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100095509 ◽

1972 ◽

Vol 30 ◽

pp. 450-451

Author(s):

H. M. Thieringer

Keyword(s):

Objective Lens ◽

Transmission Microscopy ◽

Image Recording ◽

Mode Of Operation ◽

Scanning Transmission ◽

Electron Microscopes ◽

And Performance ◽

Convergent Beam ◽

Ray Path ◽

Beam Diffraction

It has repeatedly been show that with conventional electron microscopes very fine electron probes can be produced, therefore allowing various micro-techniques such as micro recording, X-ray microanalysis and convergent beam diffraction. In this paper the function and performance of an SIEMENS ELMISKOP 101 used as a scanning transmission microscope (STEM) is described. This mode of operation has some advantages over the conventional transmission microscopy (CTEM) especially for the observation of thick specimen, in spite of somewhat longer image recording times.Fig.1 shows schematically the ray path and the additional electronics of an ELMISKOP 101 working as a STEM. With a point-cathode, and using condensor I and the objective lens as a demagnifying system, an electron probe with a half-width ob about 25 Å and a typical current of 5.10-11 amp at 100 kV can be obtained in the back focal plane of the objective lens.

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Crystal Structure Analysis of Cu-Zr Alloys by Convergent Beam Diffraction

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100098277 ◽

1981 ◽

Vol 39 ◽

pp. 354-355

Author(s):

A. F. Marshall ◽

J. W. Steeds ◽

D. Bouchet ◽

S. L. Shinde ◽

R. G. Walmsley

Keyword(s):

Crystal Structure ◽

Point Group ◽

Intermetallic Phase ◽

Three Dimensional ◽

Crystal Structure Analysis ◽

Ion Milling ◽

Composition And Structure ◽

Unit Cells ◽

Sputter Deposited ◽

Convergent Beam

Convergent beam electron diffraction is a powerful technique for determining the crystal structure of a material in TEM. In this paper we have applied it to the study of the intermetallic phases in the Cu-rich end of the Cu-Zr system. These phases are highly ordered. Their composition and structure has been previously studied by microprobe and x-ray diffraction with sometimes conflicting results.The crystalline phases were obtained by annealing amorphous sputter-deposited Cu-Zr. Specimens were thinned for TEM by ion milling and observed in a Philips EM 400. Due to the large unit cells involved, a small convergence angle of diffraction was used; however, the three-dimensional lattice and symmetry information of convergent beam microdiffraction patterns is still present. The results are as follows:1) 21 at% Zr in Cu: annealed at 500°C for 5 hours. An intermetallic phase, Cu3.6Zr (21.7% Zr), space group P6/m has been proposed near this composition (2). The major phase of our annealed material was hexagonal with a point group determined as 6/m.

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