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.

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.

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.

Zero-loss omega-filtered REM and RHEED on the new Zeiss 912

1991 ◽  
Vol 49 ◽  
pp. 616-617
Author(s):  
J.C.H. Spence ◽  
J. Mayer
Keyword(s):  
Electron Microscopy ◽  
Materials Science ◽  
Surface States ◽  
Ccd Camera ◽  
Dark Field ◽  
Ion Pump ◽  
Magnetic Imaging ◽  
Reflection Electron Microscopy ◽  
Diffraction Patterns ◽  
Large Background

The Zeiss 912 is a new fully digital, side-entry, 120 Kv TEM/STEM instrument for materials science, fitted with an omega magnetic imaging energy filter. Pumping is by turbopump and ion pump. The magnetic imaging filter allows energy-filtered images or diffraction patterns to be recorded without scanning using efficient parallel (area) detection. The energy loss intensity distribution may also be displayed on the screen, and recorded by scanning it over the PMT supplied. If a CCD camera is fitted and suitable new software developed, “parallel ELS” recording results. For large fields of view, filtered images can be recorded much more efficiently than by Scanning Reflection Electron Microscopy, and the large background of inelastic scattering removed. We have therefore evaluated the 912 for REM and RHEED applications. Causes of streaking and resonance in RHEED patterns are being studied, and a more quantitative analysis of CBRED patterns may be possible. Dark field band-gap REM imaging of surface states may also be possible.

Towards quantitative simulations of inelastic electron diffraction patterns and images

1992 ◽  
Vol 50 (2) ◽  
pp. 1170-1171
Author(s):  
Z. L. Wang
Keyword(s):  
Phonon Scattering ◽  
Incident Beam ◽  
Dynamical Theory ◽  
Inelastic Electron ◽  
Additional Advantage ◽  
Coupled Equations ◽  
Atomic Vibrations ◽  
Diffraction Patterns ◽  
Primary Advantage ◽  
The One

A new dynamical theory has been developed based on Yoshioka's coupled equations for describing inelastic electron scattering in thin crystals. Compared to existing theories, the primary advantage of this theory is that the incoherent summation of the diffracted intensities contributed by electrons after exciting vast numbers of different excited states has been evaluated before any numerical calculation. An additional advantage is that the phase correlations of atomic vibrations are considered, so that full lattice dynamics can be combined in the phonon scattering calculation. The new theory has been proven to be equivalent to the inelastic multislice theory, and has been applied to calculate energy-filtered diffraction patterns and images formed by phonon, single electron and valence scattered electrons.A calculated diffraction pattern of elastic and phonon scattered electrons for a parallel incident beam case is in agreement with the one observed (Fig. 1), showing thermal diffuse scattering (TDS) streaks and Kikuchi pattern.

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.

scholarly journals Observation of a comb-shaped filamentary plasma array under subcritical condition in 303-GHz millimetre-wave air discharge

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Masafumi Fukunari ◽  
Shunsuke Tanaka ◽  
Ryuji Shinbayashi ◽  
Yuusuke Yamaguchi ◽  
Yoshinori Tatematsu ◽  
...  
Keyword(s):  
Electric Field ◽  
Focal Point ◽  
Incident Beam ◽  
Wave Structure ◽  
Field Vector ◽  
Interesting Phenomenon ◽  
Millimetre Wave ◽  
Field Plane ◽  
Subcritical Condition ◽  
Air Discharge

AbstractGas breakdown in the millimetre-wave frequency band is an interesting phenomenon in nonlinear dynamics such as self-organized structure formation. We observed the transition between two types of filamentary plasma arrays in air discharge driven by a 303-GHz millimetre wave. Plasma is ignited at a parabolic mirror’s focal point in the overcritical condition. One array parallel to the electric field vector appears with a spacing of λ/4 at the focal point. Filaments then separate into plasma lumps ~10 μs after ignition. At 20 μs, a new comb-shaped array grows in the subcritical condition. Filaments are parallel to the incident beam with spacing of 0.96 λ and elongate towards the incident beam. This comb-shaped array appears only in the electric field plane; bulk plasma with a sharp vertex forms in the magnetic field plane. This array is created by a standing wave structure generated by waves diffracted from the plasma surface. Filamentary plasma array formations can influence the energy absorption by the plasma, which is important for engineering applications such as beamed energy propulsion.

Negative Ion Resonance Evidenced by Vibrationally Resolved Electron Diffraction On the H/Si(111) Surface

1998 ◽  
Vol 05 (01) ◽  
pp. 63-67
Author(s):  
Y. He ◽  
L.-M. Yu ◽  
P. A. Thiry ◽  
R. Caudano
Keyword(s):  
Electron Diffraction ◽  
Resonant Scattering ◽  
Negative Ion ◽  
Resonance Mechanism ◽  
Resolution Electron ◽  
Surface Resonance ◽  
Surface Vibrations ◽  
Diffraction Patterns ◽  
Angular Diffraction ◽  
Electron Energy Loss

The surface vibrations of H-terminated Si(111) are investigated by high resolution electron energy loss spectroscopy (HREELS). Clear evidence is obtained for reassigning the electron resonant scattering from a surface resonance to a negative ion resonance mechanism. Since the electrons emitted from the trapping states show characteristic angular diffraction patterns realated with the geometric and vibrational symmetries of the surface, we suggest the possibility of using this system to investigate vibrationally resolved electron diffraction processes.

Kinematical two-dimensional multiple-diffraction intensity profiles. Application to ω–ψ scans of silicon and diamond obtained with synchrotron radiation

2001 ◽  
Vol 34 (2) ◽  
pp. 157-165 ◽  
Author(s):  
E. Rossmanith ◽  
A Hupe ◽  
R. Kurtz ◽  
H. Schmidt ◽  
H.-G. Krane
Keyword(s):  
Synchrotron Radiation ◽  
Incident Beam ◽  
Mosaic Structure ◽  
Two Dimensional ◽  
Diffraction Intensity ◽  
Multiple Diffraction ◽  
Crystal Sample ◽  
Diffraction Patterns ◽  
Kinematical Theory

In a previous paper by Rossmanith [J. Appl. Cryst.(2000),33, 1405–1414], expressions for the calculation of multiple-diffraction patterns observed in ω–ψ scans of Bragg reflections were derived within the framework of the kinematical theory, taking into account the divergence and wavelength spread of the incident beam, as well as the mosaic structure of the crystal sample. Agreement with CuKα experiments was demonstrated. In this paper, it is shown that the theoretical expressions are also suitable for synchrotron radiation experiments.

DIFFRACTION OF 3.2 CM. ELECTROMAGNETIC WAVES BY CYLINDRICAL OBJECTS

1954 ◽  
Vol 32 (6) ◽  
pp. 372-380 ◽  
Author(s):  
A. B. McLay ◽  
S. T. Wiles
Keyword(s):  
Electromagnetic Waves ◽  
Incident Beam ◽  
Diffraction Theory ◽  
Central Peak ◽  
Beam Direction ◽  
Cylinder Axis ◽  
Scalar Diffraction ◽  
Conducting Cylinder ◽  
Scalar Diffraction Theory ◽  
Diffraction Patterns

Diffraction patterns of a brass tube and a hard rubber rod, each a cylinder of 1 in. diameter, in a nearly plane beam of square-wave modulated 3 cm. waves with electric vector parallel to the cylinder axis, have been measured in several planes transverse to the incident beam direction. Experimental results for the conducting cylinder agree closely with calculations based on scalar diffraction theory. Patterns of the dielectric rod show a pronounced central peak immediately behind the rod and other intensity effects differing from the conducting cylinder patterns, particularly in the vicinity of the shadow.

Electron Diffraction Study of Multilayer Structures with Partially Coherent Illumination

1985 ◽  
Vol 62 ◽  
Author(s):  
N. Otsuka ◽  
C. Choi ◽  
L. A. Kolodziejski ◽  
R. L. Gunshor
Keyword(s):  
Electron Diffraction ◽  
Incident Beam ◽  
Electron Diffraction Study ◽  
Diffraction Theory ◽  
Diffraction Spot ◽  
Multilayer Structures ◽  
Intensity Calculations ◽  
Diffraction Patterns ◽  
Monochromatic Source

ABSTRACTThe effect of partial coherency on electron diffraction patterns of Cd1−xMnxTe – Cd1−yMny Te superlattices has been investigated. Observed diffraction patterns are compared with intensity calculations performed using dynamical diffraction theory with a model of an extended incoherent monochromatic source. From this study, a new method of electron diffraction for characterization of multilayer structures can be developed. Under the condition that the lateral coherent distance of the incident beam covers two adjacent layers, diffraction beams arising from the two layers give rise to an interference fringe in a diffraction spot. With this type of diffraction pattern, one can determine the refractive index of a crystal in the multilayer structure.

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