STUDY OF IONIC CRYSTALS UNDER ELECTRON BOMBARDMENT

1951 ◽  
Vol 29 (2) ◽  
pp. 122-128 ◽  
Author(s):  
D. E. McLennan
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Electron Diffraction ◽  
Crystal Lattice ◽  
High Intensity ◽  
Alkali Halides ◽  
Electron Bombardment ◽  
High Electron ◽  
Ionic Crystals ◽  
Small Crystals

Electron bombardment experiments have been carried out on small crystals of the alkali halides within the electron microscope. Crystals of two size ranges were bombarded at high intensity, and evidence of a generalized photographic effect within the ionic group of solids is presented. The first group of crystal specimens ranged in size from 0.2 to 0.002 cm., the bombardment causing the formation of F-centers and entrapped metal colloids in the crystal lattice. Ionization pulses were observed to occur in the region of the specimen during bombardment. The second group ranged in size from 10 to 0.01 μ, observations on the effects of bombardment being carried out with electron diffraction techniques. A process has been suggested to explain the phenomenon of ionic crystals which appear to lose their centers under high electron beam intensity in the electron microscope.

Beam Sensitivity in the Electron Microscope: Strategies for Examination

1983 ◽  
Vol 41 ◽  
pp. 346-349
Author(s):  
Linn W. Hobbs
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Electron Bombardment ◽  
Reliable Information ◽  
Ionic Crystals ◽  
Heating Effect ◽  
Intense Electron

A large proportion of the specimens, both organic and inorganic, examined in the electron microscope undergo some form of alteration during examination in the electron beam. That deleterious consequences often result should not be surprising when one considers that, to be resolved, an atom requires interaction with > 104 electrons which deposit energy in the specimen at a rate > 104 W/mm3. It is indeed more surprising that reliable information can be extracted at all from so many materials under these conditions. The first evidence of beam sensitivity was reported in 1947 by Burton, Sennett and Ellis in NaCl crystallites. They concluded in commendably cautious language: We have recently observed changes in a number of substances, chiefly ionic crystals, when subjected to intense electron bombardment in the electron microscope. While the results are not readily interpretable, they do suggest that the effects may not be entirely due to the heating effect of the electron beam.

A New High Intensity Grid Cap for RCA-EMU-3 Electron Microscopes

1968 ◽  
Vol 26 ◽  
pp. 316-317
Author(s):  
George Christov ◽  
Bolivar J. Lloyd
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
High Voltage ◽  
High Intensity ◽  
Electron Gun ◽  
Tungsten Filament ◽  
Fluorescent Screen ◽  
Electron Microscopes ◽  
Pass Through ◽  
Ground Potential

A new high intensity grid cap has been designed for the RCA-EMU-3 electron microscope. Various parameters of the new grid cap were investigated to determine its characteristics. The increase in illumination produced provides ease of focusing on the fluorescent screen at magnifications from 1500 to 50,000 times using an accelerating voltage of 50 KV.The EMU-3 type electron gun assembly consists of a V-shaped tungsten filament for a cathode with a thin metal threaded cathode shield and an anode with a central aperture to permit the beam to course the length of the column. The cathode shield is negatively biased at a potential of several hundred volts with respect to the filament. The electron beam is formed by electrons emitted from the tip of the filament which pass through an aperture of 0.1 inch diameter in the cap and then it is accelerated by the negative high voltage through a 0.625 inch diameter aperture in the anode which is at ground potential.

scholarly journals The Effect of High-Intensity Electron Beam on the Crystal Structure, Phase Composition, and Properties of Al–Si Alloys with Different Silicon Content

2021 ◽  
Vol 22 (1) ◽  
pp. 129-157
Author(s):  
D. V. Zaguliaev ◽  
S. V. Konovalov ◽  
Yu. F. Ivanov ◽  
V. E. Gromov ◽  
V. V. Shlyarov ◽  
...  
Keyword(s):  
Solid Solution ◽  
Electron Beam ◽  
Phase Composition ◽  
Crystal Lattice ◽  
High Intensity ◽  
Materials Science ◽  
Lattice Parameter ◽  
Crystal Lattice Parameter ◽  
Material Surface ◽  
Modified Layer

The study deals with the element–phase composition, microstructure evolution, crystal-lattice parameter, and microdistortions as well as the size of the coherent scattering region in the Al–10.65Si–2.11Cu and Al–5.39Si–1.33Cu alloys irradiated with the high-intensity electron beam. As revealed by the methods of x-ray phase analysis, the principal phases in untreated alloys are the aluminium-based solid solution, silicon, intermetallics, and Fe2Al9Si2 phase. In addition, the Cu9Al4 phase is detected in Al–10.65Si–2.11Cu alloy. Processing alloys with the pulsed electron beam induces the transformation of lattice parameters of Al–10.65Si–2.11Cu (aluminium-based solid solution) and Al–5.39Si–1.33Cu (Al1 and Al2 phases). The reason for the crystal-lattice parameter change in the Al–10.65Si–2.11Cu and Al–5.39Si–1.33Cu alloys is suggested to be the changing concentration of alloying elements in the solid solution of these phases. As established, if a density of electron beam is of 30 and 50 J/cm2, the silicon and intermetallic compounds dissolve in the modified layer. The state-of-the-art methods of the physical materials science made possible to establish the formation of a layer with a nanocrystalline structure of the cell-type crystallization because of the material surface irradiation. The thickness of a modified layer depends on the parameters of the electron-beam treatment and reaches maximum of 90 µm at the energy density of 50 J/cm2. According to the transmission (TEM) and scanning (SEM) electron microscopy data, the silicon particles occupy the cell boundaries. Such changes in the structural and phase states of the materials response on their mechanical characteristics. To characterize the surface properties, the microhardness, wear parameter, and friction coefficient values are determined directly on the irradiated surface for all modification variants. As shown, the irradiation of the material surface with an intensive electron beam increases wear resistance and microhardness of the Al–10.65Si–2.11Cu and Al–5.39Si–1.33Cu alloys.

The Features of Investigations and Observations of Nanoamorphous Metals and Nanocrystalline Oxides on Electron Microscope

2004 ◽  
Vol 839 ◽  
Author(s):  
R. Malkhasyan ◽  
R. Karakhanyan ◽  
M. Nazaryan ◽  
A. Khachatryan ◽  
A. Markosyan
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Local Heating ◽  
Fine Sand ◽  
Inorganic Particles ◽  
Self Assembling ◽  
Small Crystals ◽  
Precautionary Measures ◽  
The One ◽  
Nanocrystalline Oxides

ABSTRACTThe present paper discusses two different active influences of an electron beam on a nanosize sample.The first observed influence is the formation of nanoparticle agglomerates due to the beam charge. This can be likened to the formation of fine sand and it enables the determination of grain magnitude of the given nanomaterial. This also enables to get a clear picture of the sample, which is latent at first due to the coating of nanoparticles and their agglomerates. For example, removal of nanopowder coatings has enabled for the first time to find self - assembling systems in a shape of double chain spatial helixes from inorganic particles (as DNA).The second type of influence is related to transformations, which distort the sample. Transformation of amorphous particles of metal into a crystalline state by means of local heating is the one of most importance.Growth of thread-shaped hollow and solid nanowhiskers from nanoparticles and their further disintegration to a great number of small crystals under influence of electron beam in the chamber of electron microscope was observed. Therefore it can be confirmed that it is necessary to use an electron microscope with special precautionary measures, when working with nanoamorphous metals.

The decomposition of magnesium hydroxide in an electron microscope

1958 ◽  
Vol 247 (1250) ◽  
pp. 346-352 ◽  
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Electron Diffraction ◽  
Single Crystals ◽  
Magnesium Oxide ◽  
Magnesium Hydroxide ◽  
Basal Plane ◽  
Morphological Changes ◽  
Water Molecules ◽  
Two Stages

The beam of an electron microscope has been used to dehydrate single crystals of magnesium hydroxide to magnesium oxide. Electron diffraction photographs and electron micrographs were taken at various stages to follow the crystallographic and morphological changes which accompany decomposition. The decomposition may be considered to occur in two stages. First, there is a small shrinkage in the basal plane, and the resulting strain causes a maze of cracks in the crystal. This change is followed by a collapse of the planes down the original [0001] of magnesium hydroxide. The collapse is controlled by the migration of water molecules from between the planes to a surface where they can escape. The product is a highly oriented aggregate of micro-crystallites of magnesium oxide. More intense irradiation in the electron beam occasionally causes bulk movement of the solid.

On the oriented conversion of Ca(OH)2 to CaO

1966 ◽  
Vol 35 (274) ◽  
pp. 867-870 ◽  
Author(s):  
S. Chatterji ◽  
J. W. Jeffery
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Electron Diffraction ◽  
Initial Stage ◽  
Degree Of Orientation ◽  
High Degree ◽  
Orientational Relationship

SummaryIn order to study the orientational relationship between Ca(OH)2 and CaO, the transformation was carried out in stages inside an electron microscope by condensing the electron beam, and the process was monitored by electron diffraction. It has been found that at the initial stage all the hexagonal spots of Ca(OH)2 split into two ; on further heating one set of spots disappear. The remaining set of spots corresponds to the CaO structure, which has an orientational relationship to the hydroxide structure. To estimate the degree of orientation, a sample of brucite was treated in a similar way to the Ca(OH)2; a comparison shows that a high degree of orientation is preserved in the conversion of Ca(OH)2 to CaO. This observation is contrary to earlier reports.

Cutting of 20 Å holes and lines in metal-β-aluminas

1983 ◽  
Vol 41 ◽  
pp. 100-101 ◽  
Author(s):  
M.E. Mochel ◽  
C. J. Humphreys ◽  
J. M. Mochel ◽  
J. A. Eades
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Carbon Film ◽  
Scanning Transmission Electron Microscope ◽  
High Electron ◽  
Transmission Electron ◽  
Solid Substrates ◽  
Scanning Transmission ◽  
Very High

Holes 20 Å in diameter and fine lines 20 Å wide can be cut in the metal-β-aluminas using the 10 Å electron beam of the Vacuum Generators, HB5 scanning transmission electron microscope. The minimum current density required for cutting was 103 amp/cm2. Electron energies of 40,60,80,100 keV were used.This technique has higher resolution than current lithography methods and is direct, requiring no chemical development. The width of isolated lines made on solid substrates is currently about .1μm (Ahmed and McMahon, 1981) and .03μm (Jackel et al., 1980). M. Isaacson and A. Murry have carried out electron beam writing on NaCl crystals supported on a carbon film on the scale we report here.In our case uniform 20Å holes and lines can be cut through self-supporting 1000A thick slabs of sodium-β-alumina to provide very high electron contrast. Once cut, the β-aluminas are stable and will tolerate exposure to air without degradation of the electron cut patterns. They may be used directly as masks (eg. for ion implantation). We believe they could be cut on the substrate with no damage to the underlying material.

The Structure and Texture of Y2O3:Tb Nanocrystals

1996 ◽  
Vol 452 ◽  
Author(s):  
J. Taylor ◽  
M. Libera ◽  
E. Goldburt ◽  
R. Bhargava
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Electron Diffraction ◽  
Selected Area Electron Diffraction ◽  
Incident Electron Beam ◽  
Transmission Electron ◽  
Cubic Structure ◽  
Diffraction Patterns ◽  
Electron Energy Loss ◽  
Microstructural Studies

AbstractThis paper presents the results of microstructural studies of terbium-doped yttria quantum nanocrystals by imaging and diffraction in a transmission electron microscope. The nanocrystals are typically found in clusters of varying size. Electron energy-loss spectroscopy confirms that the particles consist of yttrium and oxygen. Analysis of selected-area electron diffraction patterns shows that the nanocrystals largely have the cubic structure found in bulk yttria. These patterns furthermore suggest that within each cluster the nanocrystals align themselves with a preferred orientation relative to the incident electron beam as well as to each other.

Diffraction contrast of electron microscope images of crystal lattice defects - II. The development of a dynamical theory

1961 ◽  
Vol 263 (1313) ◽  
pp. 217-237 ◽  
Keyword(s):  
Electron Microscope ◽  
Electron Diffraction ◽  
Crystal Lattice ◽  
Formal Solution ◽  
Dynamical Theory ◽  
Perfect Crystal ◽  
Lattice Defects ◽  
Microscope Images ◽  
Crystal Lattice Defects ◽  
Kinematical Theory

The dynamical theory of electron diffraction is developed in a form suitable for the computation of images of crystal lattice defects such as dislocations observed by transmission electron microscopy. As shown in a previous kinematical theory, the contrast arises because the waves diffracted by atoms near the defect are changed in phase as a result of the displacements of these atoms from the perfect crystal positions. The two-beam dynamical theory of diffraction in the symmetrical Laue case is derived from simple kinematical principles by methods similar to those used by Darwin in the Bragg case. Simultaneous differential equations describing the changes of incident and diffracted wave amplitudes with depth in a crystal are obtained. In a perfect crystal these equations lead to the well-known Laue solutions of the dynamical equations of electron diffraction and in a deformed crystal they reduce to the kinematical theory when the deviation from the reflecting position is large. The effects of absorption can be included phenomenologically by use of a complex atomic scattering factor (complex lattice potential). Finally it is shown that an equivalent theory may be derived directly from wave mechanics in a way which allows the effects of absorption and several diffracted beams to be included. From the formal solution of this general theory some important symmetry relations for electron microscope images of defects can be deduced.

Simple Identification of Electron Diffraction Ring Patterns

1969 ◽  
Vol 27 ◽  
pp. 160-161
Author(s):  
Carolyn Nohr ◽  
Ann Ayres
Keyword(s):  
Electron Microscope ◽  
Electron Diffraction ◽  
Diffraction Ring ◽  
Image Position

Texts on electron diffraction recommend that the camera constant of the electron microscope be determine d by calibration with a standard crystalline specimen, using the equation

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