Characterization of Surface Resonance Conditions for Surface Imaging

1990 ◽  
Vol 48 (1) ◽  
pp. 332-333
Author(s):  
Nan Yao ◽  
John M. Cowley
Keyword(s):  
Crystal Surface ◽  
Incident Angle ◽  
Bragg Reflection ◽  
Three Dimensional ◽  
High Energy ◽  
Kikuchi Line ◽  
Surface Resonance ◽  
Kikuchi Lines ◽  
Reflection Electron Microscopy ◽  
Diffraction Patterns

In order to increase intensity and contrast in the image of a surface, the surface resonance conditions have been widely used to enhance the Bragg reflection for image formation in REM (Reflection Electron Microscopy). However, detailed studies of how the resonance conditions relate to the imaging contrast have not been reported. This paper will concentrate on the general properties of the different resonance conditions, as well as the resulting image contrast.Figure 1 shows a series of RHEED (Reflection High Energy Electron Diffraction) patterns and REM images from the same region of a Pt(l11) surface with the incident electron beam in a direction close to the [112] zone axis at 200 KeV, with a glancing incident angle of about 24 mrad which corresponds to the (555) Bragg reflection condition inside the crystal. For the purpose of convenience in discussion, the four different diffraction conditions shown in figures l(al)-(dl) have been named as D1-D4. With Dl, the specular reflected spot falls in an intersection of a parallel Kikuchi line with a parabola; with D2, the specular reflected spot coincides with an intersection of the Kikuchi lines running parallel to and inclined to the crystal surface; with D3, the specular reflected spot crosses only the parallel Kikuchi line; and with D4, the specular reflected spot intersects only with a parabola. It was found that the diffraction conditions Dl and D2 can not be considered as identical, although the specular reflected spots for both cases are commonly regarded as (555) Bragg reflection in the RHEED pattern. Detailed inspection indicates that for Dl, both the Bragg reflection and the electron surface channelling wave are excited, and for D2, the excitement of simultaneous Bragg reflection occurs closely associated with the properties of three-dimensional dynamical diffraction for a bulk crystal.

Inelastic Electron Scattering and Total Reflectivity in RHEED

1990 ◽  
Vol 48 (2) ◽  
pp. 392-393
Author(s):  
Nan Yao ◽  
John M. Cowley
Keyword(s):  
Energy Loss ◽  
Electron Energy ◽  
Crystal Surface ◽  
Bragg Reflection ◽  
Inelastic Electron ◽  
Kikuchi Line ◽  
Transmission Electron ◽  
Platinum Single Crystal ◽  
Kikuchi Lines ◽  
Electron Energy Loss

The detailed studies of the electron energy distribution of the specular reflected beam and the total reflectivity for a platinum single crystal (111) surface under a variety of diffraction conditions were carried out on a JEM-2000FX transmission electron microscope equipped with a Gatan 666 paralleldetection electron energy loss spectrometer.Five different diffraction conditions are characterized as D1-D5. With D1, the specular reflected spot falls in an intersection of a parallel Kikuchi line with a parabola; with D2, the specular reflected spot coincides with an intersection of the Kikuchi lines running parallel to and inclined to the crystal surface; with D3, that is pure specular Bragg reflection (the specular reflected spot crosses only the parallel Kikuchi line); with D4, the specular reflected spot intersects only with a parabola; and with D5, the specular reflected spot falls only on the oblique K-lines. A series of specular reflected beam energy loss spectra collected from the first four different diffraction conditions is shown in figure 1, where the spectra 1-4 correspond to conditions D1-D4, respectively.

Effects of High-Energy Ions on Synthetic Quartz

1972 ◽  
Vol 30 ◽  
pp. 544-545
Author(s):  
Joseph J. Comer ◽  
Charles Bergeron ◽  
Lester F. Lowe
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Electron Beam ◽  
High Energy ◽  
Transmission Electron ◽  
Kikuchi Lines ◽  
High Energy Ions ◽  
Diffraction Patterns ◽  
Dauphiné Twinning ◽  
Beam Damage

Using a Van De Graaff Accelerator thinned specimens were subjected to bombardment by 3 MeV N+ ions to fluences ranging from 4x1013 to 2x1016 ions/cm2. They were then examined by transmission electron microscopy and reflection electron diffraction using a 100 KV electron beam.At the lowest fluence of 4x1013 ions/cm2 diffraction patterns of the specimens contained Kikuchi lines which appeared somewhat broader and more diffuse than those obtained on unirradiated material. No damage could be detected by transmission electron microscopy in unannealed specimens. However, Dauphiné twinning was particularly pronounced after heating to 665°C for one hour and cooling to room temperature. The twins, seen in Fig. 1, were often less than .25 μm in size, smaller than those formed in unirradiated material and present in greater number. The results are in agreement with earlier observations on the effect of electron beam damage on Dauphiné twinning.

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.

Experiments on REM and SREM using a Tem/Stem Microscope with a Configurable Angle-Resolving Detector

1990 ◽  
Vol 48 (1) ◽  
pp. 338-339
Author(s):  
H. Banzhof ◽  
I. Daberkow
Keyword(s):  
Electron Microscopy ◽  
Single Crystal ◽  
Crystal Surface ◽  
High Energy ◽  
Contrast Effects ◽  
Atomic Steps ◽  
Single Crystal Surfaces ◽  
Platinum Single Crystal ◽  
Reflection Electron Microscopy ◽  
Beam Reflection

A Philips EM 420 electron microscope equipped with a field emission gun and an external STEM unit was used to compare images of single crystal surfaces taken by conventional reflection electron microscopy (REM) and scanning reflection electron microscopy (SREM). In addition an angle-resolving detector system developed by Daberkow and Herrmann was used to record SREM images with the detector shape adjusted to different details of the convergent beam reflection high energy electron diffraction (CBRHEED) pattern.Platinum single crystal spheres with smooth facets, prepared by melting a thin Pt wire in an oxyhydrogen flame, served as objects. Fig. 1 gives a conventional REM image of a (111)Pt single crystal surface, while Fig. 2 shows a SREM record of the same area. Both images were taken with the (555) reflection near the azimuth. A comparison shows that the contrast effects of atomic steps are similar for both techniques, although the depth of focus of the SREM image is reduced as a result of the large illuminating aperture. But differences are observed at the lengthened images of small depressions and protrusions formed by atomic steps, which give a symmetrical contrast profile in the REM image, while an asymmetric black-white contrast is observed in the SREM micrograph. Furthermore the irregular structures which may be seen in the middle of Fig. 2 are not visible in the REM image, although it was taken after the SREM record.

RESONANCE SCATTERING OF HIGH ENERGY ELECTRONS BY A CRYSTAL SURFACE

1996 ◽  
Vol 10 (02) ◽  
pp. 133-168 ◽  
Author(s):  
S.L. DUDAREV ◽  
M.J. WHELAN
Keyword(s):  
Crystal Surface ◽  
Theoretical Models ◽  
Resonance Scattering ◽  
High Energy ◽  
Crystal Surfaces ◽  
Molecular Beam Epitaxial ◽  
Semiconductor Crystals ◽  
High Energy Electrons ◽  
Reflection Electron Microscopy ◽  
Molecular Beam Epitaxial Growth

In this review we summarize the results of recent experimental and theoretical studies of the phenomenon known as resonance scattering of high-energy electrons from crystal surfaces. Resonance scattering is responsible for the appearance of bright features observed in reflection high-energy electron diffraction (RHEED) patterns and has found numerous applications in reflection electron microscopy and in RHEED studies of dynamics of molecular beam epitaxial growth of semiconductor crystals. The origin of the effect remained obscure for more than sixty years following the discovery of resonance scattering by Kikuchi and Nakagawa in 1933. Below we review theoretical models of the phenomenon which have been developed recently and which have provided the basis for understanding of the mechanism of resonance scattering. We conclude the review with a list of presently unsolved problems which, as we hope, can stimulate future progress in the theory of RHEED.

Efficient Algorithms for Computer Diffraction Pattern Analysis

1981 ◽  
Vol 39 ◽  
pp. 244-245
Author(s):  
J. B. Warren
Keyword(s):  
Diffraction Pattern ◽  
Automated Analysis ◽  
Radiation Detectors ◽  
Line Pair ◽  
Kikuchi Line ◽  
Beam Sample ◽  
Consistent Manner ◽  
Kikuchi Lines ◽  
Position Sensitive ◽  
Diffraction Patterns

The increasing availability of position-sensitive radiation detectors has facilitated the automated analysis of electron diffraction patterns with computers. One problem that lends itself to solution by these methods is the computation of the electron beam-sample orientation from Kikuchi patterns. A precise orientation is required for a wide variety of problems including the determination of grain boundary misorientations, precipitate-matrix relationships and the computer simulation of crystal defect images. In all of these investigations the beam-sample relationship is required for several sample orientations and computational labor can be excessive unless some form of automated analysis is employed.If a position-sensitive detector composed of two arrays of elements is placed at the electron microscope phosphor screen position, the orientation can be determined directly from the diffraction pattern. As shown in Fig. 2, a rectangular detector array would detect many Kikuchi lines and the algorithm used to interpret data must be able to determine which Kikuchi line pairs are suitable for use in computation, choose the proper (hkl) lattice plane associated with the Kikuchi line pair, and finally index the chosen line pairs in a consistent manner.

Surface resonance channelling in scanning reflection electron microscopy

1988 ◽  
Vol 46 ◽  
pp. 692-693
Author(s):  
J.M. Cowley ◽  
P.A. Crozier
Keyword(s):  
Electron Microscopy ◽  
Crystal Surface ◽  
Scanning Transmission Electron Microscope ◽  
Diffraction Effect ◽  
Transmission Electron ◽  
Surface Resonance ◽  
Scanning Transmission ◽  
Reflection Electron Microscopy ◽  
Resolution Imaging ◽  
Electron Energy Loss

The phenomena of the channelling of electrons along planes or rows of atoms in the surface layers of crystals has been investigated recently in relation to microdiffraction and RHEED, REM, (reflection electron microscopy) and REELS (reflection electron energy loss spectroscopy) by using a conventional TEM in the reflection mode.The renewed interest in this phenomenon, known for many years, is the evidence from calculations of dynamical diffraction effect at surfaces that the electrons may be channelled along the topmost layers of atoms on a crystal surface and that the RHEED, REM and REELS signals may thus be sensitive to the structure and composition of the surface layer. These techniques may therefore provide a powerful new approach to the study of surfaces in which surface microanalysis and diffraction studies may be combined with nanometer-resolution imaging.An investigation has now been made of the analogous techniques which may be applied to the study of surfaces by use of a scanning transmission electron microscope.

EELS characterization of bulk crystal surfaces in Rem: Surface micro analysis and surface channelling effect

1987 ◽  
Vol 45 ◽  
pp. 398-399
Author(s):  
Z.L. Wang ◽  
J.M. Cowley
Keyword(s):  
Resonance Condition ◽  
Incident Angle ◽  
Chemical Characterization ◽  
Bulk Crystal ◽  
Surface Chemical ◽  
Crystal Surfaces ◽  
Surface Resonance ◽  
Reflection Electron Microscopy ◽  
Channeling Effect ◽  
Micro Analysis

Electron energy-loss spectroscopy (EELS) is used in parallel with reflection electron microscopy (REM) for studying surface chemical characterization. The successful observation of Pt and Au M4,5 edge modifications in the REM case has shown that it is possible to do surface chemical analysis for those heavy elements [1]. The reflection of electrons from the surface is critically affected by the surface resonance condition; it has been shown that the electrons will propagate parallel to the surface for some distance if the incident angle satisfies the surface resonance (SR) condition[2-3], then surface channeling is likely to be observed in this SR case. There is less propagation along the surface under the surface non-resonance (SNR) condition.The GaAs bulk crystal (011) surface was chosen for observing the surface channeling effect in REM case, using a Philips 400T TEM. The surface absorbed oxygen is identified with the O-K edge (fig.l(A)).

Characterization of rutile (110) surface structure by REM

1992 ◽  
Vol 50 (2) ◽  
pp. 1462-1463
Author(s):  
L. Wang ◽  
J. Liu ◽  
J. M. Cowley
Keyword(s):  
Resonance Condition ◽  
Specular Reflection ◽  
Azimuthal Angle ◽  
Incident Beam ◽  
High Energy ◽  
Surface Cleaning ◽  
Pure Oxygen ◽  
Surface Resonance ◽  
Cleaning Procedures ◽  
Reflection Electron Microscopy

Single crystal TiO2 (rutile) (110) surface has been characterized by several experimental techniques. In this paper, we report the investigations of “optically polished” as well as high temperature oxygen annealed rutile (110) surfaces by using reflection electron microscopy (REM) and reflection high energy electron diffraction (RHEED) techniques.The crystal was purchased, “optically polished” as-received, from Commercial Crystal Laboratories, Inc.. The details in specimen cutting and surface cleaning procedures have been reported previously. The samples were annealed in pure oxygen at 1425°C for 36 h. The experimental observations were carried out in a Philips 400T microscope operated at 120 kV. The REM images were obtained by selecting the specular reflection spots satisfying surface resonance conditions.Figure 1 is a REM image of as-received rutile (110) surface. The corresponding RHEED pattern is shown in the inset. The azimuthal angle of the incident beam was at 3.9° away from [001] zone axis and the image was formed by choosing (440) specular reflection spot under surface resonance condition.

Geometrical explanation of parabolas and resonance in electron diffraction

1989 ◽  
Vol 47 ◽  
pp. 498-499
Author(s):  
M. Gajdardziska-Josifovska ◽  
J. M. Cowley
Keyword(s):  
Focal Point ◽  
Specular Reflection ◽  
Incident Beam ◽  
Simple Geometry ◽  
Line Parallel ◽  
Surface Resonance ◽  
Reflection Electron Microscopy ◽  
Diffraction Patterns ◽  
Geometrical Explanation ◽  
Transmission And Reflection

Reflection electron microscopy (REM) relies on the surface resonance (channeling) conditions for enhancement of the intensity of the specular reflection from a flat surface of a single crystal. The two most frequently cited geometries for attaining surface resonance conditions are: i) tilting the incident beam such that the specular beam in the RHEED pattern falls on an intersection of a K-line parallel to the surface with some oblique K-line; ii) positioning the specular beam on an intersection of a K-Iine parallel to the surface with some of the surface resonance regions bound by parabolas. Parabolas are also observed in the transmission diffraction patterns and have been explained as Kikuchi envelopes. Recent studies indicated a similarity between the CBED transmission and reflection patterns. We will describe a simple geometry which can be used to interpret the above observations.A parabola is by definition a curve of equal distance from a point (called focus) and a line (called directrix; see Fig.1 ).Simple previously unnoticed facs are that the zone axis is a focal point of all the parabolas belonging to a given zone, and that the directrix of each parabola corresponds to a K-line.

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