The study of crystal growth with the electron microscope IV. The nucleation and growth of n -propyl n -pentacontanoate

1955 ◽  
Vol 228 (1175) ◽  
pp. 539-548 ◽  
Keyword(s):  
Electron Microscope ◽  
Crystal Growth ◽  
Nucleation And Growth ◽  
Twist Boundary ◽  
Crystal Face ◽  
Screw Dislocations ◽  
Perfect Lattice ◽  
Lattice Disorder ◽  
Monomolecular Films ◽  
Rotational Slip

The study of long-chain paraffin derivatives in the electron microscope has been extended to include the fatty acid ester n -propyl n -pentacontanoate, n -C 53 H 106 o 2 . Examination of crystals prepared by previously described methods has given information on two further aspects of crystal growth. In the first place micrographs have been obtained at a much earlier stage in the growth of the crystals, before recognizable growth-steps have developed. It would appear that growth arises from sheet nuclei consisting of small condensed monomolecular films of 0.25 to 20μ 2 area. Screw dislocations arise at the edge of these sheets through the condensation of molecules in positions of incomplete lattice register. Growth thereafter continues around these dislocation centres, and the resultant spiral is built in towards the centre of the crystal face. This information modifies the Frank (1951) concept of a buckling mechanism for the formation of screw dislocations in crystals, since it places the emphasis on the importance of edge condensation in the formation of lattice disorder and minimizes the importance of strain in the growing perfect lattice. The second finding has been that these crystals frequently occur with a twist boundary parallel to {001}. This effect cannot properly be described as rotational slip of the type discussed by Wilman (1951), since it does not arise through deformation of an already formed crystal but occurs during growth itself. This twist boundary is penetrated by a screw dislocation or by a group of screw dislocations.

The observation of spiral growth-steps in n -paraffin single crystals in the electron microscope

1951 ◽  
Vol 206 (1087) ◽  
pp. 555-562 ◽  
Keyword(s):  
Electron Microscope ◽  
Crystal Growth ◽  
Single Crystals ◽  
Long Range ◽  
Electron Micrographs ◽  
Spiral Growth ◽  
Crystal Face ◽  
Screw Dislocations ◽  
Range Migration ◽  
Visual Confirmation

Electron micrographs of single crystals of the n -paraffin, n -hexatriacontane, C 36 H 74 , show clearly the successive monomolecular steps on the growing face of the crystal. Examination of the edge of these molecular steps shows, in many crystals, not a succession of closed terraces, but a continuous spiral on the crystal face. The results thus afford direct visual confirmation of the theory of crystal growth by spiral growth-steps ending on screw dislocations. There is no evidence of the long-range migration of molecules over the growing face of the crystals. The molecules appear to condense only on the developing edge.

scholarly journals On the role of surface energy in the flattening of a crystal face

2005 ◽  
Vol 3 (1) ◽  
pp. 188-197
Author(s):  
Christo Nanev
Keyword(s):  
Free Energy ◽  
Crystal Growth ◽  
Surface Energy ◽  
Atomic Scale ◽  
Crystal Face ◽  
Screw Dislocations ◽  
The Face ◽  
Kinetic Effects ◽  
Face Morphology

AbstractThe question addressed in this paper is the flattening of the valley separating two growth hillocks emanating from screw dislocations during crystal growth. It is argued that both thermodynamic and kinetic effects contribute to this result, at least on a quasi-atomic scale. If performed under low enough supersaturation the growth leads to the formation of the face morphology corresponding to the minimum of the surface free energy. Accelerated step annihilation in the valley floor is a universal factor, which favors face flatting under any supersaturation.

Index to Volume

1955 ◽  
Vol 228 (1175) ◽  
Keyword(s):  
Crystal Structure ◽  
Electron Microscope ◽  
Crystal Growth ◽  
Nucleation And Growth ◽  
Flow Through

Aerofoils, flow through a cascade of (Woods), 50. Anderson, N. G. & Dawson, I. M. The study of crystal growth with the electron microscope. IV. The nucleation and growth of n-propyl n-pentacontanoate, 539. Andrews, J. N. & Ubbelohde, A. R. Melting and crystal structure: the melting parameters of some polyphenyls, 435.

Structure and migration of planar defects in crystals observed in atomic scale

1978 ◽  
Vol 36 (1) ◽  
pp. 284-285 ◽  
Author(s):  
H. Hashimoto ◽  
Y. Sugimoto ◽  
Y. Takai ◽  
H. Endoh
Keyword(s):  
Electron Microscope ◽  
Rotation Angle ◽  
Crystal Surface ◽  
Electron Gun ◽  
Atomic Scale ◽  
Present Observation ◽  
Twist Boundary ◽  
Optical Magnification ◽  
Zinc Crystal ◽  
And Migration

As was demonstrated by the present authors that atomic structure of simple crystal can be photographed by the conventional 100 kV electron microscope adjusted at “aberration free focus (AFF)” condition. In order to operate the microscope at AFF condition effectively, highly stabilized electron beams with small energy spread and small beam divergence are necessary. In the present observation, a 120 kV electron microscope with LaB6 electron gun was used. The most of the images were taken with the direct electron optical magnification of 1.3 million times and then magnified photographically.1. Twist boundary of ZnSFig. 1 is the image of wurtzite single crystal with twist boundary grown on the surface of zinc crystal by the reaction of sulphur vapour of 1540 Torr at 500°C. Crystal surface is parallel to (00.1) plane and electron beam is incident along the axis normal to the crystal surface. In the twist boundary there is a dislocation net work between two perfect crystals with a certain rotation angle.

Growth of hematite by surface oxidation of olivine

1988 ◽  
Vol 46 ◽  
pp. 800-801
Author(s):  
S. McKernan ◽  
C. B. Carter
Keyword(s):  
Electron Microscope ◽  
Surface Oxidation ◽  
Thin Foil ◽  
Nucleation And Growth ◽  
Ion Milling ◽  
Annealed Material ◽  
Thin Foils ◽  
Natural Olivine ◽  
Approximate Composition ◽  
Second Phases

The oxidation of natural olivine has previously been performed on bulk samples and the reactions followed by preparation of TEM specimens from the annealed material. These results show that below ∼1000°C hematite and amorphous silica are formed, particularly around dislocations. At higher temperatures magnetite and some enstatite-like phase are formed. In both cases the olivine is left almost totally Fe depleted. By performing the oxidation on characterized thin TEM specimens it is possible to obtain more information on the nucleation and growth of the second phases formed. The conditions in a thin foil, however, are very different from those in the bulk especially with regard to surface effects. The nucleation of precipitates in particular may be expected to occur differently in these thin foils than in the bulk.TEM specimens of natural olivine (approximate composition Mg+Fe+Si2o4) which had been annealed at 1000°C for 1 hr were prepared by mechanical polishing and dimpling, followed by Ar ion milling to perforation. The specimens were characterized in the electron microscope and then heated in air in alumina boats to 900°C for between 30 and 180 minutes.

In situ Tensile Experiments at Low Temperatures on Niobium Single Crystals by H.V.E.M.

1975 ◽  
Vol 33 ◽  
pp. 58-59
Author(s):  
F. H. Louchet ◽  
L. P. Kubin
Keyword(s):  
Electron Microscope ◽  
Transition Temperature ◽  
Low Temperature ◽  
Slip System ◽  
Low Temperatures ◽  
Tensile Axis ◽  
Image Intensifier ◽  
Screw Dislocations ◽  
Source Operation

Experiments have been carried out on the 3 MeV electron microscope in Toulouse. The low temperature straining holder has been previously described Images given by an image intensifier are recorded on magnetic tape.The microtensile niobium samples are cut in a plane with the two operative slip directions [111] and lying in the foil plane. The tensile axis is near [011].Our results concern:- The transition temperature of niobium near 220 K: at this temperature and below an increasing difference appears between the mobilities of the screw and edge portions of dislocations loops. Source operation and interactions between screw dislocations of different slip system have been recorded.

A TEM study of the microstructure of avian eggshells

1992 ◽  
Vol 50 (2) ◽  
pp. 1102-1103
Author(s):  
S. Q. Xiao ◽  
S. Baden ◽  
A. H. Heuer
Keyword(s):  
Electron Microscope ◽  
Calcium Carbonate ◽  
Nucleation And Growth ◽  
Growth Mechanisms ◽  
Shell Surface ◽  
Thin Sections ◽  
Polycrystalline Metals ◽  
Transmission Electron ◽  
Nucleation And Growth Mechanisms

The avian eggshell is one of the most rapidly mineralizing biological systems known. In situ, 5g of calcium carbonate are crystallized in less than 20 hrs to fabricate the shell. Although there have been much work about the formation of eggshells, controversy about the nucleation and growth mechanisms of the calcite crystals, and their texture in the eggshell, still remain unclear. In this report the microstructure and microchemistry of avian eggshells have been analyzed using transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS).Fresh white and dry brown eggshells were broken and fixed in Karnosky's fixative (kaltitanden) for 2 hrs, then rinsed in distilled H2O. Small speckles of the eggshells were embedded in Spurr medium and thin sections were made ultramicrotome.The crystalline part of eggshells are composed of many small plate-like calcite grains, whose plate normals are approximately parallel to the shell surface. The sizes of the grains are about 0.3×0.3×1 μm3 (Fig.l). These grains are not as closely packed as man-made polycrystalline metals and ceramics, and small gaps between adjacent grains are visible indicating the absence of conventional grain boundaries.

Observation of dislocations in dynamically loaded Cu-SiO2

1986 ◽  
Vol 44 ◽  
pp. 424-425
Author(s):  
D. S. Pritchard
Keyword(s):  
Electron Microscope ◽  
Strain Rate ◽  
Single Crystal ◽  
Transmission Electron Microscope ◽  
Volume Fraction ◽  
Screw Dislocations ◽  
Spherical Inclusions ◽  
Transmission Electron ◽  
Crystal Dispersion ◽  
Strain Rate Loading

The effect of varying the strain rate loading conditions in compression on a copper single crystal dispersion-hardened with SiO2 particles has been examined. These particles appear as small spherical inclusions in the copper lattice and have a volume fraction of 0.6%. The structure of representative crystals was examined prior to any testing on a transmission electron microscope (TEM) to determine the nature of the dislocations initially present in the tested crystals. Only a few scattered edge and screw dislocations were viewed in those specimens.

Microstructure and microanalysis of sintered Fe-Nd-B permanent magnets

1990 ◽  
Vol 48 (4) ◽  
pp. 990-991
Author(s):  
Mahesh Chandramouli
Keyword(s):  
Electron Microscope ◽  
Liquid Phase ◽  
Permanent Magnets ◽  
Phase Distribution ◽  
Energy Dispersive Spectrometer ◽  
Nucleation And Growth ◽  
Liquid Phase Sintering ◽  
Domain Wall Energy ◽  
Oxide Phases ◽  
Scanning Electron

Magnetization reversal in sintered Fe-Nd-B, a complex, multiphase material, occurs by nucleation and growth of reverse domains making the isolation of the ferromagnetic Fe14Nd2B grains by other nonmagnetic phases crucial. The magnets used in this study were slightly rich in Nd (in comparison to Fe14Nd2B) to promote the formation of Nd-oxides at multigrain junctions and incorporated Dy80Al20 as a liquid phase sintering addition. Dy has been shown to increase the domain wall energy thus making nucleation more difficult while Al is thought to improve the wettability of the Nd-oxide phases.Bulk polished samples were examined in a JEOL 35CF scanning electron microscope (SEM) operated at 30keV equipped with a Be window energy dispersive spectrometer (EDS) detector in order to determine the phase distribution.

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