scholarly journals The analysis of surface layers by electron diffraction

1930 ◽  
Vol 128 (808) ◽  
pp. 649-661 ◽  
Keyword(s):  
Electron Diffraction ◽  
High Vacuum ◽  
Point Of View ◽  
Thin Layers ◽  
Surface Layers ◽  
Considerable Uncertainty ◽  
Solid Films ◽  
Unknown Composition ◽  
Diffraction Patterns ◽  
Slow Electrons

The very close correspondence which has been shown to exist between the diffraction patterns formed by cathode rays passing through thin solid films,* and the crystal structure of these films, suggests the possibility of using electron diffraction to investigate surface layers of unknown composition. This possibility was indeed indicated in Davisson and Germer’s original paper and has since been further applied. These experiments have all been made with slow electrons, of energies of the order of 300 volts. With such electrons the experiments do not agree well with theory even in the case of known structures, so their application to the investigation of unknown structures involves considerable uncertainty. Further, slow electrons can only be detected photographically with very long exposures, while the electric method of detection is very cumbrous if it is desired to survey the complete diffraction pattern. For these reasons I decided to use the apparatus described in the previous paper to investigate the diffraction patterns obtained by the reflection of cathode rays from the surfaces of various solids. The discharge was generally produced by an induction coil and the energy of the rays was of the order of 30,000 volts. In a few cases, an Evershed and Vignolles direct-current generator was used giving about 6,000 volts. In the course of the investigations, it appeared that these fast rays are uninfluenced by the thin layers of gas which are normally present on surfaces in a vacuum, or, possibly, that they temporally remove the layers by bombardment. From one point of view this is an advantage, as it is therefore unnecessary to take special precautions to degas the surfaces used, or to keep a very high vacuum. On the other hand, it limits the range of the method to the investigation of solid layers.

Reduction of Charging in Biological Electron Cryomicroscopy

1997 ◽  
Vol 3 (S2) ◽  
pp. 365-366
Author(s):  
M.B. Sherman ◽  
J. Brink ◽  
W. Chiu
Keyword(s):  
Electron Diffraction ◽  
Ion Beam ◽  
High Energy ◽  
Carbon Layer ◽  
Thin Layers ◽  
Biological Macromolecules ◽  
Electron Cryomicroscopy ◽  
Obvious Effect ◽  
Diffraction Patterns ◽  
The Stability

High resolution imaging in electron cryomicroscopy of biological macromolecules is strongly affected by beam-induced charging1. Charging is often expressed in frozen or glucose-embedded specimens as an increase in apparent mass-thickness of the irradiated area. Another obvious effect of charging is blurring of both the unscattered beam and reflections in electron diffraction patterns recorded from crystalline specimens. Coating of ice-embedded specimens with a carbon layer helps to improve the stability of the ice and probably reduce charging of the specimen. Coating in a Gatan ion-beam coater (model 681) of glucose-embedded specimens with thin layers of various conductive materials did reduce charging but the specimens were damaged by the high energy ions used for the coating. In general, coating resulted in much weaker reflections in electron diffraction patterns obtained from coated crystals and faster resolution fall-off.We modified the Gatan coater by outfitting it with a new chamber that replaced the ion-beam deposition capability for thermal evaporation of carbon rods (Fig. 1).

scholarly journals Электронно-дифракционное изучение структуры эпитаксиального графена, выращенного методом термодеструкции 6H- и 4H-SiC (0001) в вакууме

2018 ◽  
Vol 60 (7) ◽  
pp. 1403
Author(s):  
И.С. Котоусова ◽  
С.П. Лебедев ◽  
А.А. Лебедев ◽  
П.В. Булат
Keyword(s):  
Electron Diffraction ◽  
Crystal Lattice ◽  
Thermal Desorption ◽  
Substrate Surface ◽  
High Vacuum ◽  
High Energy ◽  
High Energy Electron ◽  
Graphene Layers ◽  
Diffraction Patterns ◽  
Surface Diffraction

AbstractThe method of reflection high-energy electron diffraction (RHEED) is used for studying the structure of graphene layers formed on the surface of the Si-face of conductive and semi-insulating 6 H - and 4 H -SiC(0001) substrates by thermal desorption of Si atoms in high vacuum, depending on the temperature and time of sublimating Si atoms as well as depending on the method of preprocessing the substrate surface. Diffraction patterns are recorded in the $$[\bar 12\bar 10]$$ [ 1 ¯ 2 1 ¯ 0 ] and $$[1\bar 100]$$ [ 1 1 ¯ 00 ] crystallographic directions of the substrates. It is found that in all experiments the formation of graphene layers occurs with a rotation of the graphene crystal lattice by 30° relative to the SiC lattice.

scholarly journals An Analysis of Kikuchi Lines Observed with a RHEED Apparatus for a TiO2-Terminated SrTiO3 (001) Crystal

Materials ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7077
Author(s):  
Jakub Pawlak ◽  
Marek Przybylski ◽  
Zbigniew Mitura
Keyword(s):  
Surface Wave ◽  
Electron Diffraction ◽  
High Vacuum ◽  
Analytical Models ◽  
Resonance Effects ◽  
Wave Resonance ◽  
Kikuchi Lines ◽  
Diffraction Patterns

In this study, electron diffraction patterns observed under high vacuum conditions for an SrTiO3 surface were interpreted in detail while paying special attention to the features of inelastic effects. The surface of the SrTiO2 was carefully prepared to enforce its termination with single domains of TiO2 layers at the top. The inelastic patterns were interpreted using analytical models. Two types of Kikuchi lines are recognized in this paper: those which can be described with the Bragg law and those which appear due to surface wave resonance effects. However, we also discuss that there exists a formal connection between the two types of the Kikuchi lines observed.

scholarly journals On the photographic action of slow electrons

1932 ◽  
Vol 136 (830) ◽  
pp. 651-662 ◽  
Keyword(s):  
Electron Diffraction ◽  
Fast Moving ◽  
Photographic Emulsion ◽  
X Ray ◽  
Electron Spectra ◽  
Diffraction Patterns ◽  
Slow Electrons ◽  
The Way

The fact that fast moving electrons have a blackening effect on photographic emulsion has been known for a quarter of a century and many investigators have utilised this important property in their researches. In the important fields of β-ray and X-ray electron investigation, for example, electron spectra have been recorded photographically, Innes leading the way in 1907, followed amongst others, by Robinson and Rawlinson, de Broglie and Whiddington. Within the last year or two, G. P. Thomson and Reid have also used this method for the recording of electron diffraction patterns.

Computer Indexing of Electron Diffraction Patterns Including the Effects of Lattice Symmetry

1977 ◽  
Vol 35 ◽  
pp. 22-23
Author(s):  
J. S. Lally ◽  
R. J. Lee
Keyword(s):  
Electron Diffraction ◽  
Zone Axis ◽  
Crystal Thickness ◽  
Double Diffraction ◽  
Automated Method ◽  
Lattice Symmetry ◽  
Intensity Calculations ◽  
Unknown Structure ◽  
Diffraction Patterns ◽  
Orientation Parameters

In the 50 year period since the discovery of electron diffraction from crystals there has been much theoretical effort devoted to the calculation of diffracted intensities as a function of crystal thickness, orientation, and structure. However, in many applications of electron diffraction what is required is a simple identification of an unknown structure when some of the shape and orientation parameters required for intensity calculations are not known. In these circumstances an automated method is needed to solve diffraction patterns obtained near crystal zone axis directions that includes the effects of systematic absences of reflections due to lattice symmetry effects and additional reflections due to double diffraction processes.Two programs have been developed to enable relatively inexperienced microscopists to identify unknown crystals from diffraction patterns. Before indexing any given electron diffraction pattern, a set of possible crystal structures must be selected for comparison against the unknown.

Electron-diffraction studies in synthetic polymer materials

1983 ◽  
Vol 41 ◽  
pp. 362-365
Author(s):  
D.T. Grubb
Keyword(s):  
Electron Diffraction ◽  
Synthetic Polymer ◽  
Polymer Materials ◽  
Crystallographic Structure ◽  
High Dose ◽  
Electron Dose ◽  
Dose Rates ◽  
First Case ◽  
Diffraction Patterns ◽  
The Many

Diffraction studies in polymeric and other beam sensitive materials may bring to mind the many experiments where diffracted intensity has been used as a measure of the electron dose required to destroy fine structure in the TEM. But this paper is concerned with a range of cases where the diffraction pattern itself contains the important information.In the first case, electron diffraction from paraffins, degraded polyethylene and polyethylene single crystals, all the samples are highly ordered, and their crystallographic structure is well known. The diffraction patterns fade on irradiation and may also change considerably in a-spacing, increasing the unit cell volume on irradiation. The effect is large and continuous far C94H190 paraffin and for PE, while for shorter chains to C 28H58 the change is less, levelling off at high dose, Fig.l. It is also found that the change in a-spacing increases at higher dose rates and at higher irradiation temperatures.

An Interactive Minicomputer Program for the Indexing and Simulation of Electron Diffraction Patterns

1976 ◽  
Vol 34 ◽  
pp. 542-543
Author(s):  
R.P. Goehner ◽  
W.T. Hatfield ◽  
Prakash Rao
Keyword(s):  
Electron Diffraction ◽  
Real Time ◽  
Pattern Analysis ◽  
Flow Diagram ◽  
Hard Copy ◽  
Time Analysis ◽  
Real Time Analysis ◽  
Transmission Electron ◽  
One Step ◽  
Diffraction Patterns

Computer programs are now available in various laboratories for the indexing and simulation of transmission electron diffraction patterns. Although these programs address themselves to the solution of various aspects of the indexing and simulation process, the ultimate goal is to perform real time diffraction pattern analysis directly off of the imaging screen of the transmission electron microscope. The program to be described in this paper represents one step prior to real time analysis. It involves the combination of two programs, described in an earlier paper(l), into a single program for use on an interactive basis with a minicomputer. In our case, the minicomputer is an INTERDATA 70 equipped with a Tektronix 4010-1 graphical display terminal and hard copy unit.A simplified flow diagram of the combined program, written in Fortran IV, is shown in Figure 1. It consists of two programs INDEX and TEDP which index and simulate electron diffraction patterns respectively. The user has the option of choosing either the indexing or simulating aspects of the combined program.

Formation Mechanisms for Multiply Twinned Particles During Nucleation in the Au/MICA System

1975 ◽  
Vol 33 ◽  
pp. 84-85
Author(s):  
Eal H. Lee ◽  
Helmut Poppa
Keyword(s):  
Deposition Time ◽  
High Vacuum ◽  
Dark Field ◽  
Ultra High Vacuum ◽  
Formation Mechanisms ◽  
Heat Treated ◽  
Cluster Density ◽  
Diffraction Patterns ◽  
Crystal Particle ◽  
Multiply Twinned Particles

The formation of thin films of gold on mica has been studied in ultra-high vacuum (5xl0-10 torr) . The mica substrates were heat-treated for 24 hours at 375°C, cleaved, and annealed for 15 minutes at the deposition temperature of 300°C prior to deposition. An impingement flux of 3x1013 atoms cm-2 sec-1 was used. These conditions were found to give high number densities of multiple twin particles and are based on a systematic series of nucleation experiments described elsewhere. Individual deposits of varying deposition time were made and examined by bright and dark field TEM after "cleavage preparation" of highly transparent specimens. In the early stages of growth, the films generally consist of small particles which are either single crystals or multiply twinned; a strong preference for multiply twinned particles was found whenever the particle number densities were high. Fig. 1 shows the stable cluster density ns and the variation with deposition time of multiple twin particle and single crystal particle densities, respectively. Corresponding micrographs and diffraction patterns are shown in Fig. 2.

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