Torsional Structures to Enable Large Angle Deflections

Parallel Detection of Electron Energy Loss Spectra in Direct Mode

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100134004 ◽

1990 ◽

Vol 48 (2) ◽

pp. 82-83

Author(s):

Eckhard Quandt ◽

Stephan laBarré ◽

Andreas Hartmann ◽

Heinz Niedrig

Keyword(s):

Energy Loss ◽

Electron Energy ◽

Energy Resolution ◽

Large Angle ◽

Maximum Energy ◽

Semiconductor Detectors ◽

Parallel Detection ◽

Photodiode Arrays ◽

Electron Energy Loss ◽

Electron Energy Loss Spectra

Due to the development of semiconductor detectors with high spatial resolution -- e.g. charge coupled devices (CCDs) or photodiode arrays (PDAs) -- the parallel detection of electron energy loss spectra (EELS) has become an important alternative to serial registration. Using parallel detection for recording of energy spectroscopic large angle convergent beam patterns (LACBPs) special selected scattering vectors and small detection apertures lead to very low intensities. Therefore the very sensitive direct irradiation of a cooled linear PDA instead of the common combination of scintillator, fibre optic, and semiconductor has been investigated. In order to obtain a sufficient energy resolution the spectra are optionally magnified by a quadrupole-lens system.The detector used is a Hamamatsu S2304-512Q linear PDA with 512 diodes and removed quartz-glas window. The sensor size is 13 μm ∗ 2.5 mm with an element spacing of 25 μm. Along with the dispersion of 3.5 μm/eV at 40 keV the maximum energy resolution is limited to about 7 eV, so that a magnification system should be attached for experiments requiring a better resolution.

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Strain measurement by means of bend contour microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100153026 ◽

1989 ◽

Vol 47 ◽

pp. 210-211

Author(s):

Philip D. Hren

Keyword(s):

Strain Measurement ◽

Large Angle ◽

Single Crystal Silicon ◽

Convergent Beam Electron Diffraction ◽

Zone Axis ◽

Silicon Membrane ◽

Crystal Silicon ◽

Contour Pattern ◽

Convergent Beam ◽

Low Symmetry

The pattern of bend contours which appear in the TEM image of a bent or curled sample indicates the shape into which the specimen is bent. Several authors have characterized the shape of their bent foils by this method, most recently I. Bolotov, as well as G. Möllenstedt and O. Rang in the early 1950’s. However, the samples they considered were viewed at orientations away from a zone axis, or at zone axes of low symmetry, so that dynamical interactions between the bend contours did not occur. Their calculations were thus based on purely geometric arguments. In this paper bend contours are used to measure deflections of a single-crystal silicon membrane at the (111) zone axis, where there are strong dynamical effects. Features in the bend contour pattern are identified and associated with a particular angle of bending of the membrane by reference to large-angle convergent-beam electron diffraction (LACBED) patterns.

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Large-angle convergent-beam electron-diffraction study of coherent precipitates and decorated dislocations

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100167470 ◽

1996 ◽

Vol 54 ◽

pp. 1002-1004

Author(s):

J.M.K. Wiezorek ◽

H.L. Fraser

Keyword(s):

Electron Diffraction ◽

Angular Resolution ◽

Large Angle ◽

Electron Diffraction Study ◽

Convergent Beam Electron Diffraction ◽

Crystal Defects ◽

High Angular Resolution ◽

Beam Electron ◽

Diffraction Plane ◽

Convergent Beam

Conventional methods of convergent beam electron diffraction (CBED) use a fully converged probe focused on the specimen in the object plane resulting in the formation of a CBED pattern in the diffraction plane. Large angle CBED (LACBED) uses a converged but defocused probe resulting in the formation of ‘shadow images’ of the illuminated sample area in the diffraction plane. Hence, low-spatial resolution image information and high-angular resolution diffraction information are superimposed in LACBED patterns which enables the simultaneous observation of crystal defects and their effect on the diffraction pattern. In recent years LACBED has been used successfully for the investigation of a variety of crystal defects, such as stacking faults, interfaces and dislocations. In this paper the contrast from coherent precipitates and decorated dislocations in LACBED patterns has been investigated. Computer simulated LACBED contrast from decorated dislocations and coherent precipitates is compared with experimental observations.

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Structural analysis of a Σ5 grain boundary in YBa2Cu3O7δ

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010015054x ◽

1993 ◽

Vol 51 ◽

pp. 942-943

Author(s):

J.-Y. Wang ◽

Y. Zhu ◽

A.H. King ◽

M. Suenaga

Keyword(s):

Grain Boundary ◽

Lattice Mismatch ◽

Weak Link ◽

Coincidence Site Lattice ◽

Large Angle ◽

Dislocation Core ◽

Superconducting Order Parameter ◽

Outstanding Problem ◽

Transmission Electron

One outstanding problem in YBa2Cu3O7−δ superconductors is the weak link behavior of grain boundaries, especially boundaries with a large-angle misorientation. Increasing evidence shows that lattice mismatch at the boundaries contributes to variations in oxygen and cation concentrations at the boundaries, while the strain field surrounding a dislocation core at the boundary suppresses the superconducting order parameter. Thus, understanding the structure of the grain boundary and the grain boundary dislocations (which describe the topology of the boundary) is essential in elucidating the superconducting characteristics of boundaries. Here, we discuss our study of the structure of a Σ5 grain boundary by transmission electron microscopy. The characterization of the structure of the boundary was based on the coincidence site lattice (CSL) model.Fig.l shows two-beam images of the grain boundary near the projection. An array of grain boundary dislocations, with spacings of about 30nm, is clearly visible in Fig. 1(a), but invisible in Fig. 1(b).

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A study of twinning in YBa2Cu3O7−x by large-angle convergent-beam electron diffraction

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100173236 ◽

1990 ◽

Vol 48 (4) ◽

pp. 20-21

Author(s):

P.A. Midgley ◽

R. Vincent ◽

D. Cherns

Keyword(s):

Electron Diffraction ◽

Oxygen Atom ◽

Strain Field ◽

Large Angle ◽

Convergent Beam Electron Diffraction ◽

Orthorhombic Distortion ◽

Beam Electron ◽

Resultant Powder ◽

Convergent Beam ◽

Mesh Grid

The oxygenation of YBa2Cu3O7−x (YBCO) leads to an orthorhombic distortion of the unit cell to accommodate the extra oxygen atom. This makes the formation of twins energetically favourable with CuO4 planar unit chains running alternately along the a and b axes of the parent tetragonal structure. The geometry of this twinning is such that four possible twin variants may co-exist with the twin boundaries lying in the (110) or (110) planes of the deformed structure. The traces of these planes are not mutually perpendicular and thus the crystal is strained to allow for the mismatch. It is to the nature of this strain field that this work has been addressed.Sintered samples were prepared by crushing and dispersing the resultant powder onto a very fine Cu mesh grid. Single crystals were chemically thinned to perforation. No discernible artefacts were seen and similar results were obtained with either method.

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Atomic Imaging of Crystals using Large-Angle Electron Scattering in STEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100179129 ◽

1990 ◽

Vol 48 (1) ◽

pp. 74-75

Author(s):

D.E. Jesson ◽

S. J. Pennycook

Keyword(s):

Wave Function ◽

Electron Scattering ◽

Numerical Solutions ◽

Large Angle ◽

Real Space ◽

High Angle ◽

Analytical Treatment ◽

Order Zero ◽

Experimental Conditions ◽

Ewald Sphere

It is well known that conventional atomic resolution electron microscopy is a coherent imaging process best interpreted in reciprocal space using contrast transfer function theory. This is because the equivalent real space interpretation involving a convolution between the exit face wave function and the instrumental response is difficult to visualize. Furthermore, the crystal wave function is not simply related to the projected crystal potential, except under a very restrictive set of experimental conditions, making image simulation an essential part of image interpretation. In this paper we present a different conceptual approach to the atomic imaging of crystals based on incoherent imaging theory. Using a real-space analysis of electron scattering to a high-angle annular detector, it is shown how the STEM imaging process can be partitioned into components parallel and perpendicular to the relevant low index zone-axis.It has become customary to describe STEM imaging using the analytical treatment developed by Cowley. However, the convenient assumption of a phase object (which neglects the curvature of the Ewald sphere) fails rapidly for large scattering angles, even in very thin crystals. Thus, to avoid unpredictive numerical solutions, it would seem more appropriate to apply pseudo-kinematic theory to the treatment of the weak high angle signal. Diffraction to medium order zero-layer reflections is most important compared with thermal diffuse scattering in very thin crystals (<5nm). The electron wave function ψ(R,z) at a depth z and transverse coordinate R due to a phase aberrated surface probe function P(R-RO) located at RO is then well described by the channeling approximation;

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