The Panoramic Rheed Patterns

1990 ◽  
Vol 48 (1) ◽  
pp. 324-325
Author(s):  
Yootaek Kim ◽  
Tung Hsu
Keyword(s):  
Electron Microscopy ◽  
Electron Beam ◽  
Electron Diffraction ◽  
Incidence Angle ◽  
High Energy ◽  
Rheed Pattern ◽  
Crystal Surfaces ◽  
Transmission Electron ◽  
Kikuchi Lines ◽  
Reflection Electron Microscopy

When applying the reflection high energy electron diffraction (RHEED) and reflection electron microscopy (REM) methods[1] on the study of crystal surfaces it is necessary to index the RHEED spots and recognize the azimuth of the electron beam direction. This can be difficult because the RHEED pattern, unlike the transmission electron diffraction (TED) pattern, is distorted by the inner potential of the specimen and only one half of the pattern is shown. We found that it is useful, at the beginning of working on a certain surface of a certain crystal, to record a panoramic RHEED pattern by rotating the crystal through a large azimuth angle. This produces a map which is similar to the Kikuchi maps[2] used in transmission electron microscopy (TEM).Two examples of these panoramic RHEED patterns, one from the Pt(111) [3] and the other from α-Al203 (0001) [4,5,6), are shown in Figs. 1 and 2.The transmission Kikuchi maps are recorded using a specimen of suitable thickness such that the Kikuchi lines are strong and the diffraction spots are practically invisible. On the contrary, in making the panoramic RHEED patterns (or RHEED maps) we have no control over the thickness of the specimen. The electron beam enters and exits the same surface of the crystal; therefore, the relative intensities of the Bragg diffracted spots and the Kikuchi lines are not adjustable. The only adjustment lies in choosing the accelerating voltage and the incidence angle of the electrons such that the RHEED pattern has relatively low diffuse scattering.

Convergence of the incident beam in reflection Electron Microscopy

1989 ◽  
Vol 47 ◽  
pp. 532-533
Author(s):  
Nan Yao ◽  
J. M. Cowley
Keyword(s):  
Electron Microscopy ◽  
Electron Beam ◽  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Rheed Pattern ◽  
Convergence Angle ◽  
Incident Electron Beam ◽  
Transmission Electron ◽  
Kikuchi Lines ◽  
Reflection Electron Microscopy

The RHEED (Reflection High Energy Electron Diffraction) patterns as essential indications of the diffraction conditions in relation to REM (Reflection Electron Microscopy) imaging provide a wealth of information about the surfaces. They contain extensive patterns of Kikuchi lines, bands and envelopes resulting from diffuse inelastic scattering processes. They also contain arrays of diffuse spots forbidden by the boundary conditions for elastic scattering but generated by multiple diffuse scattering processes.However, a word of caution has to be sounded. Strictly speaking, the normal RHEED pattern does not exactly present the diffraction condition for REM imaging in a commercial transmission electron microscope. Practical and theoretical studies of the electron optics of the illuminating system on a Philip-400T transmission electron microscope, in which the specimen is immersed in the magnetic field of the twin objective lens, indicate that the convergent angle of the incident electron beam can be adjusted precisely, in a range from about 0.1 mrad to 5 mrad, with a selection of the second condenser aperture size, by adjusting the excitation current in the second condenser lens. For the best contrast and illumination, the RHEED pattern is generally obtained by focusing the electron beam on the surface with the maximum convergence angle, and the REM image is obtained with an almost parallel illumination with the minimum convergence angle. A typical example obtained from a fresh cleavage (110) surface of InP single crystal is demonstrated in figure 1, in which (a) and (b) are RHEED patterns with the (10,10,0) specular Bragg-reflection condition fulfilled and correspond to the incident electron beam with 2 mrad and 0.2 mrad convergence angles, respectively; (c) is a REM image obtained under exactly the same operation condition as (b) except for changing from diffraction mode to image mode, which indeed has nothing to do with the illumination condition above the specimen position; and (c) is taken from an area consisting of many steps of atomic height. Comparison of (a) and (b) shows that, for the parallel electron illumination, only those diffraction spots are dominant which represent the possible diffracted directions and mark the intersections of Ewald sphere with reciprocal lattice rods of the crystal surface. The extensive Kikuchi lines, bands and envelopes, and even the parabolas appearing in (a), are scarcely visible in (b). This suggests that the channeling effects characterized as the appearance of surface diffraction parabolas showing in RHEED pattern are mainly caused by the portion of electrons with incident direction slightly deviated from the rows of atoms; that is, the inelastically scattered electrons propagating in the directions of rows of atoms only occur when the initial incident electrons interact with the lattice in a direction slightly different from that of the rows of atoms. Following this argument, we may propose that the contrasts observed in REM image are mostly contributed from the diffraction and phase contrasts.

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.

Reflection electron microscopy (REM) of NaCl crystals

1994 ◽  
Vol 52 ◽  
pp. 808-809
Author(s):  
Tung Hsu
Keyword(s):  
Electron Microscopy ◽  
Electron Beam ◽  
High Energy ◽  
Rheed Pattern ◽  
Considerable Effort ◽  
Cold Finger ◽  
Uncoated Surface ◽  
Diffuse Background ◽  
Reflection Electron Microscopy ◽  
Special Protection

NaCl and other alkaline halide crystals are unstable under the electron beam and therefore have seldom been examined with the various electron beam techniques. Surfaces of these crystals, however, are of fundamental and application interests. There has been a considerable effort in studying these surfaces using the replica methods.Reflection high energy electron diffraction (RHEED) and reflection electron microscopy (REM) have been successfully applied to the study of stable insulators. Since direct observation on an uncoated surface is always desirable, we tried RHEED and REM on cleaved NaCl(100) surfaces.The experiment was carried out on a JEOL JEM-200CX electron microscope with a high tilt side-entrystage. The accelerating voltage of lOOkV was used throughout the experiment. There is no special protection to the specimen except the standard anti-contamination cold finger. The initial effort of doing ordinary REM on NaCl was a failure: When the electron beam and the specimen were properly tilted toget a good RHEED pattern, the bright pattern remained for only a couple of seconds and then turned into a pattern of weak spots and high diffuse background. The bright REM image also lost its contrast in a few seconds.

In-Situ Transmission Electron Microscopy Studies of the Oxidation of Si (111) 7X7

1989 ◽  
Vol 159 ◽  
Author(s):  
J.M. Gibson
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Electron Beam ◽  
Electron Diffraction ◽  
High Energy ◽  
Energy Transmission ◽  
Transmission Electron Diffraction ◽  
Transmission Electron

ABSTRACTThe kinematical approximation is valid for High-Energy Transmission Electron Diffraction from monolayers in planview. We use this fact to study quantitatively the attack of Si (111) 7×7 by 02. Oxygen is found to bind in the bridging position of the adatom backbonds and render the structure very stable during subsequent 02 exposure. Electron-beam exposure during dosing additionally creates rapid disordering which is presumed to represent SiOx formation.

Transmission Electron Microscopy of Epitaxial silicides grown by ultra high vacuum deposition

1989 ◽  
Vol 47 ◽  
pp. 462-463
Author(s):  
D. Loretto ◽  
J. M. Gibson ◽  
S. M. Yalisove
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Electron Diffraction ◽  
High Vacuum ◽  
High Energy ◽  
Energy Electron ◽  
Ultra High Vacuum ◽  
Ex Situ ◽  
Transmission Electron

The silicides CoSi2 and NiSi2 are both metallic with the fee flourite structure and lattice constants which are close to silicon (1.2% and 0.6% smaller at room temperature respectively) Consequently epitaxial cobalt and nickel disilicide can be grown on silicon. If these layers are formed by ultra high vacuum (UHV) deposition (also known as molecular beam epitaxy or MBE) their thickness can be controlled to within a few monolayers. Such ultrathin metal/silicon systems have many potential applications: for example electronic devices based on ballistic transport. They also provide a model system to study the properties of heterointerfaces. In this work we will discuss results obtained using in situ and ex situ transmission electron microscopy (TEM).In situ TEM is suited to the study of MBE growth for several reasons. It offers high spatial resolution and the ability to penetrate many monolayers of material. This is in contrast to the techniques which are usually employed for in situ measurements in MBE, for example low energy electron diffraction (LEED) and reflection high energy electron diffraction (RHEED), which are both sensitive to only a few monolayers at the surface.

Models of Magnesium Oxide (111) Surface Reconstructions Obtained from Direct Phasing of Transmission Electron Diffraction Data

1997 ◽  
Vol 3 (S2) ◽  
pp. 1039-1040
Author(s):  
R. Plass ◽  
K. Egan ◽  
C. Collazo-Davila ◽  
D. Grozea ◽  
E. Landree ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Electron Diffraction ◽  
Electron Diffraction Data ◽  
Vacuum Furnace ◽  
Transmission Electron Diffraction ◽  
Transmission Electron ◽  
Surface Reconstructions ◽  
Reflection Electron Microscopy ◽  
Plane Disk ◽  
Flowing Oxygen

It has long been thought that (111) surfaces of rock salt oxides microfacet to neutral surfaces upon annealing because of the very large energies involved in bulk terminating a layer of like ions. However in a recent reflection electron microscopy (REM) study Gajdardziska-Josifovska et al. found that MgO(lll) surfaces annealed in flowing oxygen furnaces at 1500°C not only did not microfacet, but displayed a √3×√3R30° surface periodicity that was stable in air. To determine the structure of this unusually stable surface MgO (111) transmission electron microscopy (TEM) samples were annealed in a vacuum furnace in the present study and their transmission electron diffraction (TED) patterns were analyzed with direct phasing methods.The TEM samples were prepared by orienting a MgO single crystal and sawing lmm wafers along a (111) plane. Disk samples were then ultrasonically drilled, dimpled, mechanically polished and/or hot nitric acid etched, and milled with 5 KeV Ar+ ions.

Reflection Electron Microscopy and Diffraction from Crystal Surfaces

1983 ◽  
Vol 31 ◽  
Author(s):  
J.M. Cowley
Keyword(s):  
Electron Microscopy ◽  
Surface Structure ◽  
Crystal Surfaces ◽  
Local Composition ◽  
Surface Steps ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Reflection Electron Microscopy ◽  
Electron Microscopes ◽  
Geometric Effects

ABSTRACTThe recent revival of techniques for the imaging of crystal surfaces, using electrons forward-scattered in the RHEED mode and employing modern electron microscopes, has lead to the introduction of valuable new methods for the study of surface structure. Either fixed beam or scanning transmission electron microscopy (STEM) instruments may be used and in each case a lateral resolution of 10Å or better is possible. Simple theoretical treatments suggest that the contrast from surface steps may be attributed to a combination of phase-contrast, diffraction contrast and geometric effects. With a STEM instrument the image information can be combined with information on the local composition and crystal structure by use of microanalysis and microdiffraction techniques. Examples of applications include studies of the surface structure of metals, semiconductors and oxides, and the surface reactions.

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.

Growth and Structure of Al/MgO Interfaces

1994 ◽  
Vol 357 ◽  
Author(s):  
T. Wagner ◽  
M. Ruhle
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Electron Diffraction ◽  
High Vacuum ◽  
High Energy ◽  
Ultra High Vacuum ◽  
Structural Defects ◽  
Cross Sectional ◽  
Aluminum Films ◽  
Transmission Electron

AbstractThe A1/MgO system has been used as a model system to study growth processes and structure at metal/ceramic interfaces. Aluminum films were grown on air-cleaved MgO (100) substrates in ultra high vacuum (UHV) by molecular beam epitaxy (MBE). The substrates and films were characterized by reflection high energy electron diffraction (RHEED), x-ray diffraction (XRD), conventional transmission electron microscopy (CTEM), and high resolution transmission electron microscopy (HREM). XRD measurements exhibited a pronounced {100} texture. Employing electron diffraction in the TEM on cross sectional samples, we observed the following orientation relationship between Al and MgO: (100)A1 II (100)MgO; [010]A1 II [010]MgO. The atomistic structure of the interface was investigated by HREM. Regions of structural defects can be identified clearly at the interface.

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