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.

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.

Microprobe AES Combined With Scanning RHEED Microscope

1990 ◽  
Vol 48 (2) ◽  
pp. 368-369
Author(s):  
Y. Sakai ◽  
S. Kitamura ◽  
A. D. Buonaquisti
Keyword(s):  
Electron Microscopy ◽  
Electron Diffraction ◽  
High Energy ◽  
Low Energy ◽  
Energy Electron ◽  
Diffraction Spot ◽  
High Energy Electron ◽  
Micro Structure ◽  
Fluorescent Screen ◽  
Low Energy Electron

Surface micro-structure analysis is very important for surface study in material science. Observations of surface atomic steps and reconstructed structures have been made using several techniques: reflection high energy electron microscopy (RHEEM), low energy electron reflection microscopy (LEERM) and low energy electron diffraction microscopy (LEEDM).In the present experiment, observations of surface micro-structures have been made using a scanning type reflection high energy electron diffraction (RHEED) microscopy. This technique has certain advantages of easy combinations with multiple surface analyzing techniques such as scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and electron energy loss spectroscopy (ELS).A schematic diagram of the scanning RHEED microscope combined with the microprobe AES is shown in Fig. 1. RHEED patterns are observed on the fluorescent screen through a viewing port. To observe the micro-structure (scanning RHEED image or dark field image), a particular diffraction spot is selected by means of the other small fluorescent screen with an aperture.

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.

Kinematic Approximations in TED and RHEED Analysis of Reconstructed Surfaces

1990 ◽  
Vol 48 (2) ◽  
pp. 396-397
Author(s):  
L. -M. Peng ◽  
M. J. Whelan
Keyword(s):  
Electron Diffraction ◽  
Kinematic Analysis ◽  
Incident Beam ◽  
High Energy ◽  
Energy Electron ◽  
Great Success ◽  
High Energy Electron ◽  
Kinematic Approximation ◽  
Reconstructed Surfaces

In recent years there has been a trend in the structure determination of reconstructed surfaces to use high energy electron diffraction techniques, and to employ a kinematic approximation in analyzing the intensities of surface superlattice reflections. Experimentally this is motivated by the great success of the determination of the dimer adatom stacking fault (DAS) structure of the Si(111) 7 × 7 reconstructed surface.While in the case of transmission electron diffraction (TED) the validity of the kinematic approximation has been examined by using multislice calculations for Si and certain incident beam directions, far less has been done in the reflection high energy electron diffraction (RHEED) case. In this paper we aim to provide a thorough Bloch wave analysis of the various diffraction processes involved, and to set criteria on the validity for the kinematic analysis of the intensities of the surface superlattice reflections.The validity of the kinematic analysis, being common to both the TED and RHEED case, relies primarily on two underlying observations, namely (l)the surface superlattice scattering in the selvedge is kinematically dominating, and (2)the superlattice diffracted beams are uncoupled from the fundamental diffracted beams within the bulk.

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