Electron microscope studies of climb of dissociated dislocations

The mechanism of climb of dissociated dislocations in f.c.c. metals and alloys is not well understood. Climb of dislocations by absorption or emission of vacancies at existing jogs in dissociated dislocations has been observed using the “weak-beam” technique of electron microscopy, but the mechanism of nucleation of jogs is not clear. In this paper we report some results of experiments designed to study the nucleation problem, and more generally the mechanism of absorption of point defects under conditions of high supersaturation.Thin (111) sections of deformed single crystals of Cu-Al alloys, of various compositions, have been electron irradiated in an AEI EM7 HVEM up to 1 MeV, either at room temperature, or elevated temperatures up to 200°C, using a goniometer heating stage. Observations under weak beam conditions have been made a) in situ in the HVEM b) at 100kV in an JEM100B, following irradiation in the HVEM. Interstitials produced by the irradiation are expected to be preferentially attracted to the dislocations because of the strong dislocation-interstitial interaction.

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Mechanism of climb of dissociated dislocations

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1980.0077 ◽

1980 ◽

Vol 371 (1745) ◽

pp. 213-234 ◽

Cited By ~ 20

Keyword(s):

Electron Microscopy ◽

Point Defects ◽

Electron Irradiation ◽

Elevated Temperatures ◽

Beam Electron ◽

Microscopy Technique ◽

Weak Beam ◽

High Supersaturation ◽

Edge Component ◽

The Individual

The ‘weak-beam’ electron microscopy technique has been used to study the climb of dissociated dislocations in a C u-13.43 % A1 alloy under conditions of high supersaturation of point defects introduced by electron irradiation at room and elevated temperatures. Prismatic loops (assumed to be of the interstitial type because of the dislocation ‘bias’) are found to be nucleated on the individual partials. The Burgers vectors of the nucleated loops are a function of the dislocation character, and are such as to minimize the elastic energy of the resultant configuration (partial plus loop), and to maximize the edge component of the loops. For orientations other than pure edge, climb involves the generation of Burgers vectors different from those of the original partials. The complex dislocation configurations formed by climb at elevated temperatures can be understood in terms of the nucleation of prismatic loops and their growth in directions controlled by the climb force on the parts of the prismatic loops not lying in the glide plane of the dislocations.

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In-Situ Heating Observations on Superlattice Dislocation in A Ni3(Al, Zr) Single Crystal

MRS Proceedings ◽

10.1557/proc-364-321 ◽

1994 ◽

Vol 364 ◽

Author(s):

Yi Liu ◽

Yuefeng Gu ◽

Dongliang Lin ◽

Shipu Chen ◽

Xiaoning Zhao ◽

...

Keyword(s):

Single Crystal ◽

Significant Variation ◽

Room Temperature ◽

Peak Temperature ◽

Burgers Vector ◽

Superlattice Dislocation ◽

Weak Beam ◽

In Situ Heating ◽

Beam Technique

AbstractThe TEM weak-beam technique has been used to investigate the behavior of dissociated superlattice dislocation in Ni3Al single crystal as a function of temperature. The observed dislocation with the Burgers vector of [110] partly dissociated on the (001) plane forming Kear-Wilsdorf (KW) lock. The dissociated pair did not indicate significant variation of separation in the temperature range from room temperature to 773K. but turned to form a jog at 773K. At 898K, which is near the peak temperature, the dissociated segment constricted completely. The experimental observations are discussed.

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Tem Study of Dislocations in Plastically Deformed AlN

MRS Proceedings ◽

10.1557/proc-242-475 ◽

1992 ◽

Vol 242 ◽

Cited By ~ 1

Author(s):

V. Audurier ◽

J. L. Demenet ◽

J. Rabier

Keyword(s):

Electron Microscopy ◽

Room Temperature ◽

Compound Semiconductors ◽

Burgers Vector ◽

Weak Beam ◽

Deformation Substructure ◽

Transmission Electron ◽

Doping Effects ◽

Electronic Doping ◽

Beam Technique

ABSTRACTAlN ceramics were plastically deformed using uniaxial compression under hydrostatic pressure between room temperature (RT) and 800°C. Deformation microstructures have been studied by Transmission Electron Microscopy (TEM) using the weak beam technique. The deformation substructure at RT is characterized by perfect glide loops with 1/3<1120> Burgers vector in (0001) elongated in the screw direction. When deformation temperature increases, the screw character is associated to cross slip events and dislocation dipolesare found. In the investigated temperature range, slip of dislocations with 1/3<1120> Burgers vector is also evidenced on prismatic planes. Weak beam observations failed to evidence any dislocation splitting. Some of these dislocation properties, similar to those of III-V compound semiconductors, suggest that electronic doping effects could be used to control plastic behaviour of covalent ceramics.

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Application of analytical electron microscopy to the study of partitioning of silicon in a 2 wt% Si eutectoid steel

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100110222 ◽

1978 ◽

Vol 36 (1) ◽

pp. 616-617

Author(s):

N. Ridley ◽

S.A. Al-Salman ◽

G.W. Lorimer

Keyword(s):

Electron Microscopy ◽

Electron Microscope ◽

Analytical Electron Microscopy ◽

Eutectoid Steel ◽

Minimum Diameter ◽

Thin Foils ◽

Analytical Electron ◽

Analytical Electron Microscope ◽

Transformation Front

The application of the technique of analytical electron microscopy to the study of partitioning of Mn (1) and Cr (2) during the austenite-pearlite transformation in eutectoid steels has been described in previous papers. In both of these investigations, ‘in-situ’ analyses of individual cementite and ferrite plates in thin foils showed that the alloying elements partitioned preferentially to cementite at the transformation front at higher reaction temperatures. At lower temperatures partitioning did not occur and it was possible to identify a ‘no-partition’ temperature for each of the steels examined.In the present work partitioning during the pearlite transformation has been studied in a eutectoid steel containing 1.95 wt% Si. Measurements of pearlite interlamellar spacings showed, however, that except at the highest reaction temperatures the spacing would be too small to make the in-situ analysis of individual cementite plates possible, without interference from adjacent ferrite lamellae. The minimum diameter of the analysis probe on the instrument used, an EMMA-4 analytical electron microscope, was approximately 100 nm.

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Remote On-Line Control of a High-Voltage in situ Transmission Electron Microscope with A Rational User Interface

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100164386 ◽

1996 ◽

Vol 54 ◽

pp. 384-385

Author(s):

M.A. O’Keefe ◽

J. Taylor ◽

D. Owen ◽

B. Crowley ◽

K.H. Westmacott ◽

...

Keyword(s):

Electron Microscopy ◽

Electron Microscope ◽

User Interface ◽

Transmission Electron Microscope ◽

High Voltage ◽

Materials Science ◽

Transmission Electron ◽

On Line ◽

Electron Microscopes

Remote on-line electron microscopy is rapidly becoming more available as improvements continue to be developed in the software and hardware of interfaces and networks. Scanning electron microscopes have been driven remotely across both wide and local area networks. Initial implementations with transmission electron microscopes have targeted unique facilities like an advanced analytical electron microscope, a biological 3-D IVEM and a HVEM capable of in situ materials science applications. As implementations of on-line transmission electron microscopy become more widespread, it is essential that suitable standards be developed and followed. Two such standards have been proposed for a high-level protocol language for on-line access, and we have proposed a rational graphical user interface. The user interface we present here is based on experience gained with a full-function materials science application providing users of the National Center for Electron Microscopy with remote on-line access to a 1.5MeV Kratos EM-1500 in situ high-voltage transmission electron microscope via existing wide area networks. We have developed and implemented, and are continuing to refine, a set of tools, protocols, and interfaces to run the Kratos EM-1500 on-line for collaborative research. Computer tools for capturing and manipulating real-time video signals are integrated into a standardized user interface that may be used for remote access to any transmission electron microscope equipped with a suitable control computer.

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Characterization of Ti/SnO2 Interface by X-ray Photoelectron Spectroscopy

Nanomaterials ◽

10.3390/nano12020202 ◽

2022 ◽

Vol 12 (2) ◽

pp. 202

Author(s):

Miranda Martinez ◽

Anil R. Chourasia

Keyword(s):

Photoelectron Spectroscopy ◽

Room Temperature ◽

Chemical Interaction ◽

Photoelectron Spectra ◽

X Ray ◽

Increasing Trend ◽

Substrate Temperatures ◽

Beam Technique

The Ti/SnO2 interface has been investigated in situ via the technique of x-ray photoelectron spectroscopy. Thin films (in the range from 0.3 to 1.1 nm) of titanium were deposited on SnO2 substrates via the e-beam technique. The deposition was carried out at two different substrate temperatures, namely room temperature and 200 °C. The photoelectron spectra of tin and titanium in the samples were found to exhibit significant differences upon comparison with the corresponding elemental and the oxide spectra. These changes result from chemical interaction between SnO2 and the titanium overlayer at the interface. The SnO2 was observed to be reduced to elemental tin while the titanium overlayer was observed to become oxidized. Complete reduction of SnO2 to elemental tin did not occur even for the lowest thickness of the titanium overlayer. The interfaces in both the types of the samples were observed to consist of elemental Sn, SnO2, elemental titanium, TiO2, and Ti-suboxide. The relative percentages of the constituents at the interface have been estimated by curve fitting the spectral data with the corresponding elemental and the oxide spectra. In the 200 °C samples, thermal diffusion of the titanium overlayer was observed. This resulted in the complete oxidation of the titanium overlayer to TiO2 upto a thickness of 0.9 nm of the overlayer. Elemental titanium resulting from the unreacted overlayer was observed to be more in the room temperature samples. The room temperature samples showed variation around 20% for the Ti-suboxide while an increasing trend was observed in the 200 °C samples.

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In situ transmission electron microscope measurements of solid Al-solid Pb and solid Al-liquid Pb surface-energy anisotropy in rapidly solidified Al-5% Pb (by mass)

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1987.0156 ◽

1987 ◽

Vol 414 (1847) ◽

pp. 499-507 ◽

Cited By ~ 54

Keyword(s):

Electron Microscope ◽

Melting Point ◽

Surface Energy ◽

Transmission Electron Microscope ◽

Room Temperature ◽

Transmission Electron ◽

Increasing Temperature ◽

Rapidly Solidified ◽

Al Matrix

Alloys of Al-5% Pb and Al-5% Pb-0.5% Si (by mass) have been manufactured by rapid solidification and then examined by transmission electron microscopy. The rapidly solidified alloy microstructures consist of 5-60 nm Pb particles embedded in an Al matrix. The Pb particles have a cube-cube orientation relation with the Al matrix, and are cub-octahedral in shape, bounded by {100} Al, Pb and {111} Al, Pb facets. The equilibrium Pb particle shape and therefore the anisotropy of solid Al-solid Pb and solid Al-liquid Pb surface energies have been monitored by in situ heating in the transmission electron microscope over the temperature range between room temperature and 550°C. The anisotropy of solid Al-solid Pb surface energy is constant between room temperature and the Pb melting point, with a {100} Al, Pb surface energy about 14% greater than the {111} Al, Pb surface energy, in good agreement with geometric near-neighbour bond energy calculations. The {100} AI, Pb facet disappears when the Pb particles melt, and the anisotropy of solid Al-liquid Pb surface energy decreases gradually with increasing temperature above the Pb melting point, until the Pb particles become spherical at about 550°C.

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Electron microscopy of interphase chromosomes in situ; binding of permanganate to chicken erythrocytes

Journal of Cell Science ◽

10.1242/jcs.20.2.289 ◽

1976 ◽

Vol 20 (2) ◽

pp. 289-307

Author(s):

H.G. Davies

Keyword(s):

Electron Microscopy ◽

Electron Microscope ◽

Chemical Composition ◽

Protein Interaction ◽

Phosphotungstic Acid ◽

Intact Cell ◽

Anomalous Behaviour ◽

Protein Protein Interaction ◽

Chicken Erythrocytes

From quantitative electron-microscope observations on the binding of permanganate to regions of erythrocytes and reticulocytes of known chemical composition, it is concluded that KMnO4, like phosphotungstic acid (PTA), binds preferentially to sites on proteins. Compared with PTA, KMnO4 binding exhibits less anomalous behaviour. The data support the hypothesis previously put forward that the 2 regions, or phases, in condensed chromatin differ in both molecular composition and concentration. The increase in binding to protein which occurs during nuclear haemolysis is interpreted in terms of protein-protein interaction in the chromatin of the intact cell.

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