Effective Extinction Distances in Zone Axis Silicon

2000 ◽  
Vol 6 (S2) ◽  
pp. 1028-1029
Author(s):  
Z. Yu ◽  
R. R. Vanfleet ◽  
J. Silcox
Keyword(s):  
Electron Microscopy ◽  
Plane Waves ◽  
Normal Incidence ◽  
Sample Surface ◽  
Bloch Wave ◽  
Zone Axis ◽  
Image Recording ◽  
Intensity Measurements ◽  
Digital Image Recording ◽  
Convergent Beam

Many scientific questions encountered in electron microscopy require quantitative deductions from the observations. Comparisons of experimental observations with simulations are however, still relatively rare since measurements of intensity are normally difficult. In this paper we discuss the use of experimental observations of the effective extinction distances for zone axis silicon using a convergent beam STEM mode for comparison with a number of simulations. On the experimental side, the measurements were made with a STEM that provides accurate intensity measurements directly with a digital image recording system. Two theoretical schemes widely used in electron microscopy simulations, multislice simulation and Bloch-wave calculation, were employed for the simulations. In each case, both a TEM case and a STEM case were calculated for comparison.The multislice simulations were carried out using codes available from Kirkland. For the TEM case with plane waves at normal incidence on the sample surface, the unscattered (0,0) exit beam gives the Bright Field (BF) intensity.

The symmetry of electron diffraction zone axis patterns

1976 ◽  
Vol 281 (1301) ◽  
pp. 171-194 ◽  
Keyword(s):  
Electron Microscopy ◽  
Group Theory ◽  
Graphical Representation ◽  
Zone Axis ◽  
Fast Electrons ◽  
Extinction Contour ◽  
Symmetry Properties ◽  
Point Groups ◽  
Diffraction Patterns ◽  
Convergent Beam

The convergent beam and bend extinction contour techniques of electron microscopy are capable of providing much more information than can be obtained from conventional diffraction patterns and it is the objective of this work to examine the symmetry properties of each of these patterns. The diffraction of fast electrons by a thin parallelsided slab has been studied by group theory and by a graphical construction. We find that the pattern symmetries may be described by thirty-one diffraction groups and that each of these diffraction groups is isomorphic to one of the point groups of diperiodic plane figures and to one of the thirty-one Shubnikov groups of coloured plane figures. A graphical representation of each diffraction group is given, together with tables showing how the diffraction groups are related to the specimen point groups and under certain assumptions to the crystal point groups. These tables assume the symmetric Laue condition and ignore the presence of irreducible lattice translations normal to the slab. By using the tables, crystal point groups can be obtained from convergent beam or bend contour patterns. The method is demonstrated by experiments on several materials, but particularly on germanium and gallium-arsenide specimens since the similarity of these materials exemplifies the sensitivity of the technique.

Application of convergent beam electron microscopy in materials science

1978 ◽  
Vol 36 (1) ◽  
pp. 620-621
Author(s):  
J.W. Steeds ◽  
K. K. Fung
Keyword(s):  
Electron Microscopy ◽  
Materials Science ◽  
Zone Axis ◽  
Simple Relationship ◽  
Beam Electron ◽  
Small Probe ◽  
Yield Information ◽  
Semiconductor Contacts ◽  
Chalcogenide Layer ◽  
Convergent Beam

IntroductionWe have used a Philips EM400 electron microscope with a STEM pole- piece to carry out convergent beam electron microscopy on a wide variety of materials, including precipitates in stainless steels, metal/semiconductor contacts, metal oxide catalysts, environmental fibres, metastable phases in evaporated films, and transition metal chalcogenide layer compounds. Two features of this microscope make it particularly suitable for convergent beam work. These are its low hydrocarbon partial pressure which greatly reduces the carbon contamination of the specimen when working with a small probe (̴ 300 Ådiameter) and the very wide angular field of view in the diffraction plane (̴ 16°).Two-dimensional diffraction may be used to yield information about the projected crystal potential. In certain cases a simple relationship has been established between the form of zone axis patterns and the nature of the projected potential, Oneway of using this information is by making measurements of zone axis critical voltages and we have recently extended our measurements to a number of zone axis patterns with 6 mm symmetry having different sorts of projected potential.

Electron microscopy of a Gd–Ba–Cu–O superconductor

1989 ◽  
Vol 4 (3) ◽  
pp. 515-520 ◽  
Author(s):  
R. Ramesh ◽  
G. Thomas ◽  
R. L. Meng ◽  
P. H. Hor ◽  
C. W. Chu
Keyword(s):  
Electron Microscopy ◽  
Microscopy Study ◽  
Annealed Sample ◽  
Electron Microscopy Study ◽  
Zone Axis ◽  
Matrix Phase ◽  
The Matrix ◽  
Tetragonal Form ◽  
Convergent Beam ◽  
Beam Patterns

An electron microscopy study has been carried out to characterize the microstructure of a sintered Gd–Ba–Cu–O superconductor alloy. The GdBa2Cu3O7−x phase in the oxygen annealed sample is orthorhombic while in the vacuum annealed sample it is tetragonal. It is shown that the details of the fine structure in the [001] zone axis convergent beam patterns can be used to distinguish between the orthorhombic form and the tetragonal form. In addition to this matrix phase, an amorphous phase is frequently observed at the triple grain junctions. Gd-rich inclusions have been observed inside the matrix phase.

Surface zone-axis patterns

1984 ◽  
Vol 42 ◽  
pp. 516-517
Author(s):  
J. A. Eades ◽  
M. D. Shannon ◽  
M. E. Meichle
Keyword(s):  
Crystal Structure ◽  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Incident Beam ◽  
Zone Axis ◽  
Surface Zone ◽  
Transmission Electron ◽  
Beam Orientation ◽  
Convergent Beam ◽  
Beam Diffraction

In electron diffraction from crystals, whether it be in reflection or transmission, the intensity of the emergent beams varies in a complex way with the angle that the incident beam makes with the crystal structure. The techniques for displaying this variation of intensity as a function of incident beam orientation have mostly been applied to zone-axis orientations, where the variation is particularly elaborate. The resulting patterns, known as zone-axis patterns or zaps, have become an important part of transmission electron microscopy.There are several techniques for obtaining zaps. The best known is convergent-beam diffraction but they can also be obtained in the form of bend-contour patterns and Tanaka patterns, and by rocking methods.

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

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.

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

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.

Convergent-beam electron diffraction at high spatial resolution

1992 ◽  
Vol 50 (2) ◽  
pp. 1152-1153 ◽  
Author(s):  
J W Steeds
Keyword(s):  
Electron Diffraction ◽  
High Temperature Superconductors ◽  
Bloch Wave ◽  
Convergent Beam Electron Diffraction ◽  
Beam Electron ◽  
Energy Filtering ◽  
Small Probe ◽  
Transmission Electron ◽  
Electron Microscopes ◽  
Convergent Beam

That the techniques of convergent beam electron diffraction (CBED) are now widely practised is evident, both from the way in which they feature in the sale of new transmission electron microscopes (TEMs) and from the frequency with which the results appear in the literature: new phases of high temperature superconductors is a case in point. The arrival of a new generation of TEMs operating with coherent sources at 200-300kV opens up a number of new possibilities.First, there is the possibility of quantitative work of very high accuracy. The small probe will essentially eliminate thickness or orientation averaging and this, together with efficient energy filtering by a doubly-dispersive electron energy loss spectrometer, will yield results of unsurpassed quality. The Bloch wave formulation of electron diffraction has proved itself an effective and efficient method of interpreting the data. The treatment of absorption in these calculations has recently been improved with the result that <100> HOLZ polarity determinations can now be performed on III-V and II-VI semiconductors.

Convergent Beam Electron Diffraction Zone Axis Pattern Map of Zirconium

1990 ◽  
Vol 48 (2) ◽  
pp. 496-497
Author(s):  
E. Silva ◽  
R. Scozia
Keyword(s):  
Electron Diffraction ◽  
Convergent Beam Electron Diffraction ◽  
Zone Axis ◽  
Pole Piece ◽  
Small Particles ◽  
Present Communication ◽  
Beam Electron ◽  
Zero Layer ◽  
Set Up ◽  
Convergent Beam

The purpose in obtaining zone axis pattern map (zap map) from a given material is to provide a quick and reliable tool to identify cristaline phases, and crystallographic directions, even in small particles. Bend contours patterns and Kossel lines patterns maps from Zr single crystal in the [0001] direction have been presented previously. In the present communication convergent beam electron diffraction (CBED) zap map of Zr will be shown. CBED patterns were obtained using a Philips microscope model EM300, which was set up to carry out this technique. Convergent objective upper pole piece for STEM and some electronic modifications in the lens circuits were required, furthermore the microscope was carefully cleaned and it was operated at a vacuum eminently good.CBED patterns in the Zr zap map consist of zero layer disks, showing fine details within them which correspond to intersecting set of higher order Laue zone (HOLZ) deficiency lines.

Parabolas from Reconstructed Surfaces Observed in Convergent-Beam RHEED Patterns

1990 ◽  
Vol 48 (2) ◽  
pp. 398-399
Author(s):  
M. Gajdardziska-Josifovska
Keyword(s):  
Electron Microscopy ◽  
High Energy ◽  
Two Dimensional ◽  
High Energy Electron ◽  
Reflection And Transmission ◽  
Experimental Diffraction Pattern ◽  
Surface Resonance ◽  
Reconstructed Surfaces ◽  
Reflection Electron Microscopy ◽  
Convergent Beam

Parabolas have been observed in the reflection high-energy electron diffraction (RHEED) patterns from surfaces of single crystals since the early thirties. In the last decade there has been a revival of attempts to elucidate the origin of these surface parabolas. The renewed interest stems from the need to understand the connection between the parabolas and the surface resonance (channeling) condition, the latter being routinely used to obtain higher intensity in reflection electron microscopy (REM) images of surfaces. Several rather diverging descriptions have been proposed to explain the parabolas in the reflection and transmission Kikuchi patterns. Recently we have developed an unifying general treatment in which the parabolas are shown to be K-lines of two-dimensional lattices. Here we want to review the main features of this description and present an experimental diffraction pattern from a 30° MgO (111) surface which displays parabolas that can be attributed to the surface reconstruction.

Strain measurement by means of bend contour microscopy

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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