Bloch wave treatment of symmetry and multiple beam cases in reflection high energy electron diffraction and reflection electron microscopy

1992 ◽  
Vol 20 (4) ◽  
pp. 360-370 ◽  
Author(s):  
L.-M. Peng ◽  
K. Gjønnes ◽  
J. Gjønnes
Keyword(s):  
Electron Microscopy ◽  
Electron Diffraction ◽  
High Energy ◽  
Bloch Wave ◽  
Energy Electron ◽  
High Energy Electron ◽  
Wave Treatment ◽  
Multiple Beam ◽  
Reflection Electron Microscopy

Energy-filtered reflection electron microscopy and reflection high-energy electron diffraction on Zeiss 912 TEM

1993 ◽  
Vol 51 ◽  
pp. 580-581
Author(s):  
JINGYUE LIU
Keyword(s):  
Electron Microscopy ◽  
Electron Diffraction ◽  
Ccd Camera ◽  
Chromatic Aberration ◽  
High Energy ◽  
Energy Electron ◽  
Objective Lens ◽  
High Energy Electron ◽  
Resolution Limit ◽  
Reflection Electron Microscopy

In reflection electron microscopy (REM) and reflection high energy electron diffraction (RHEED) the average path length of the elastically scattered electrons in the crystal ranges from 10 -100 nm and a significant portion of the electrons in the RHEED pattern spots used for imaging is inelastically scattered. The excitations of surface plasmons, bulk plasmons and valence electrons involves energy losses of 10 ∽30 eV. Thus the image contrast and resolution in REM are degraded due to chromatic aberration of the objective lens. The use of energy filters in a TEM should offer significant improvement in resolution and contrast of REM images. We present here some new results on the investigation of resolution limit and contrast mechanisms in energy filtered REM images.The experiments were performed on a Zeiss 912 TEM fitted with an Omega magnetic imaging energy filter. Digital RHEED patterns and REM images were acquired into 1024 pixels by 1024 pixels via a Gatan 679 CCD camera fitted to the microscope.

Bloch-wave channeling and HOLZ effects in high-energy electron diffraction

1989 ◽  
Vol 45 (10) ◽  
pp. 699-703 ◽  
Author(s):  
L. M. Peng ◽  
J. K. Gjønnes
Keyword(s):  
Electron Diffraction ◽  
High Energy ◽  
Bloch Wave ◽  
Energy Electron ◽  
High Energy Electron

Computer studies on reflection high-energy electron diffraction from the growing surface of Ge(001)

2013 ◽  
Vol 46 (4) ◽  
pp. 1024-1030 ◽  
Author(s):  
Zbigniew Mitura
Keyword(s):  
Experimental Data ◽  
Electron Diffraction ◽  
High Energy ◽  
Bloch Wave ◽  
Energy Electron ◽  
High Energy Electron ◽  
Homoepitaxial Growth ◽  
Scattering Potential ◽  
Computer Studies ◽  
Quantitative Explanation

The results of calculations of reflection high-energy electron diffraction intensities, measured at different stages of the homoepitaxial growth of Ge(001), are described. A two-dimensional Bloch wave approach was used in calculations of the Schrödinger equation with a one-dimensional potential. The proportional model was used for partially filled layers,i.e.the scattering potential was taken to be proportional to the coverage and the potential of the fully filled layer. Using such an approach, it was shown that it is possible to obtain valuable information for the analysis of experimental data. The results of these calculations were compared with data for off-symmetry azimuths from the literature, and satisfactory agreement between the theoretical and experimental data was found. Also assessed was whether developing more advanced models (i.e.going beyond the proportional model), to make a more detailed account of the diffuse scattering, might be important in achieving a fully quantitative explanation of the experimental data.

Why the Bloch Wave Solution for Reflection Fails on the Au(110) Surface

1990 ◽  
Vol 48 (2) ◽  
pp. 372-373
Author(s):  
YIQUN MA
Keyword(s):  
Electron Diffraction ◽  
Wave Solution ◽  
Incident Angle ◽  
High Energy ◽  
Bloch Wave ◽  
Energy Electron ◽  
Wave Method ◽  
High Energy Electron ◽  
Real Potential ◽  
Electron Reflection

The Bloch wave method has been widely used for interpreting reflection high energy electron diffraction (RHEED) patterns and the consistency between the theory and high energy electron reflection (HEER) experiments has been claimed by different authors. The recent rigorous investigation on the consistency between the Bloch wave method and the multislice approach due to Cowley and Moodie in the reflection case for Au(001) surface has also provided a clear theoretical proof for the validity of the Bloch wave method in reflection case. However, a severe deviation of the Bloch wave solution for the Au(110) surface in the reflection case from the stabilized solution of its multislicing via the multislice iteration has recently revealed by the BMCR method (Bloch wave + Multislice Combined for Reflection).Fig.1 shows the results calculated for the Au(110) surface using the BMCR method. The incident angle is 30mRad and the absorption is included by taking the imaginary potential as 10% of the real potential in both the Bloch wave and multislice calculation.

Bloch-wave solution in the Bragg case

1989 ◽  
Vol 45 (2) ◽  
pp. 174-182 ◽  
Author(s):  
Y. Ma ◽  
L. D. Marks
Keyword(s):  
Electron Diffraction ◽  
Current Flow ◽  
High Energy ◽  
Bloch Wave ◽  
Zone Axis ◽  
Wave Method ◽  
High Energy Electron ◽  
Stepped Surfaces ◽  
Reflection Electron Microscopy ◽  
Wave Phenomena

The Bloch-wave method for reflection diffraction problems, primarily electron diffraction as in reflection high-energy electron diffraction (RHEED) and reflection electron microscopy (REM), is developed. The basic Bloch-wave approach for surfaces is reviewed, introducing the current flow concept which plays a major role both in understanding reflection diffraction and determining the allowed Bloch waves. This is followed by a brief description of the numerical methods for obtaining the results including specific results for GaAs near to the [010] zone axis. A number of other Bloch-wave phenomena are also discussed, namely resonance diffraction and its relationship to internal and external reflection and variations in the boundary conditions and Bloch-wave character, splitting of diffraction spots due to stepped surfaces, which can be completely explained, and the reflection equivalent of thickness fringes.

REM observations of oxygen-annealed rutile (001) surfaces

1991 ◽  
Vol 49 ◽  
pp. 646-647
Author(s):  
J. Liu ◽  
L. Wang ◽  
J. M. Cowley
Keyword(s):  
Electron Microscopy ◽  
Electron Diffraction ◽  
High Energy ◽  
Annealing Process ◽  
Pure Oxygen ◽  
High Energy Electron ◽  
Catalytic Behavior ◽  
Catalytic Material ◽  
Reflection Electron Microscopy ◽  
Photocatalytic Reactions

Rutile (single crystal TiO2) is widely used in electrochemistry, photochemical energy conversion and photocatalytic reactions of gases as a catalytic material. It is important to characterize the surface properties of rutile in order to understand its catalytic behavior. The rutile (001) surface is extremely unstable, forming facets on annealing as revealed by the LEED results. In this paper we report some preliminary results on the investigation of oxygen annealed rutile (001) surface, obtained by reflection high energy electron diffraction (RHEED) and reflection electron microscopy (REM) techniques.The crystal was cut into strips, finely polished, cleaned and chemically etched in NaOH and H2SO4 before annealing. The samples were annealed in pure oxygen at 1473 K for 36 h. The purposes of annealing the samples in pure oxygen are to preserve surface stoichiometry and to prevent surface reactions with elements other than oxygen during the annealing process. The RHEED and REM observations were performed in a Philips 400T microscope operated at 120 kV.

The Surface of α-Al2O3(0001) Studied with the REM Method

1990 ◽  
Vol 48 (1) ◽  
pp. 326-327
Author(s):  
Yootaek Kim ◽  
Tung Hsu
Keyword(s):  
Electron Microscopy ◽  
Electron Diffraction ◽  
Atomic Layer ◽  
High Energy ◽  
High Energy Electron ◽  
Definite Evidence ◽  
Surface Steps ◽  
Wide Range ◽  
Reflection Electron Microscopy ◽  
Α Al2o3

Reflection electron microscopy (REM) and reflection high energy electron diffraction (RHEED) techniques[1] are applied to the study of single crystal α-Al203 surfaces [2,3,4,5] .Specimens were prepared by polishing and 1400°C annealing in air and microscopy was done on a JEOL JEM-200CX and a Philips 400T microscopes operated at 100KV. Most of the REM images were recorded in the mutually perpendicular azimuths.We found that the surface smoothness over a 1 mm2 specimen is not uniform. In some areas the surface steps follow the directions (Fig. 1a. The scale in this figure also applies to all other figures.) while in other areas the steps are continuously curved (Fig. lb). The steps have a rather wide range of heights, probably from one atomic layer to several nm. There is no definite evidence on the smallest steps being one atom high, we have observed steps terminating at a dislocation (Fig. 2) and the weak contrast indicates that the step is only one or two atoms high. But we cannot determine the projection of the Burger's vector in the surface normal [6]. Consequently, we cannot determine the exact height of the step.

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