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.

Cell structure properties during in situ creep experiments in the H.V.E.M.

1978 ◽  
Vol 36 (1) ◽  
pp. 574-575
Author(s):  
D. Caillard ◽  
J.L. Martin
Keyword(s):  
Tensile Axis ◽  
Cell Structure ◽  
Image Intensifier ◽  
Foil Thickness ◽  
Average Cell Size ◽  
Average Cell ◽  
Voltage Electron ◽  
Steady Stage ◽  
Stationary Creep

The behaviour of the dislocation substructure during the steady stage regime of creep, as well as its contribution to the creep rate, are poorly known. In particular, the stability of the subboundaries has been questioned recently, on the basis of experimental observations |1||2| and theoretical estimates |1||3|. In situ deformation experiments in the high voltage electron microscope are well adapted to the direct observation of this behaviour. We report here recent results on dislocation and subboundary properties during stationary creep of an aluminium polycristal at 200°C.During a macroscopic creep test at 200°C, a cell substructure is developed with an average cell size of a few microns. Microsamples are cut out of these specimens |4| with the same tensile axis, and then further deformed in the microscope at the same temperature and stain rate. At 1 MeV, one or a few cells can be observed in the foil thickness |5|. Low electron fluxes and an image intensifier were used to reduce radiation damage effects.

scholarly journals Electrochemical generation of 2,3-oxazolidinone glycosyl triflates as an intermediate for stereoselective glycosylation

2012 ◽  
Vol 8 ◽  
pp. 456-460 ◽  
Author(s):  
Toshiki Nokami ◽  
Akito Shibuya ◽  
Yoshihiro Saigusa ◽  
Shino Manabe ◽  
Yukishige Ito ◽  
...  
Keyword(s):  
Low Temperature ◽  
Electrochemical Oxidation ◽  
Low Temperatures ◽  
Protecting Group ◽  
Triflic Acid ◽  
Electrochemical Generation ◽  
Stereoselective Glycosylation

Glycosyl triflates with a 2,3-oxazolidinone protecting group were generated from thioglycosides by low-temperature electrochemical oxidation. The glycosyl triflates reacted with alcohols to give the corresponding glycosides β-selectively at low temperatures. However, α-selectivity was observed in the absence of base at elevated reaction temperatures. In situ generated triflic acid promotes the isomerization of β-products to α-products.

The Dissociation of Sessile Superdislocations at a Coherent Twin Eoundary in Ordered CU3AU During Plastic Deformation

1990 ◽  
Vol 186 ◽  
Author(s):  
F.D. Tichelaar ◽  
F.W. Schapink
Keyword(s):  
Plastic Deformation ◽  
Shear Stress ◽  
Electron Microscope ◽  
Slip System ◽  
Tensile Axis ◽  
Slip Systems ◽  
Coherent Twin Boundary ◽  
Cube Plane ◽  
Transmission Electron ◽  
The Matrix

AbstractThe glide behaviour of superdislocations at a coherent twin boundary in ordered Cu3Au was examined in a transmission electron microscope for the case when the superdislocations are sessile in the boundary. Possible schemes for dissociation of a superdislocation in the boundary were analysed geometrically. The leading superpartial of each superdislocation dissociated into a superpartial in the matrix and a residual Shockley partial in the boundary of glissile type. The trailing superpartial remained undissociated in the boundary. The superpartial in the matrix glided on a cube plane, and a ribbon of APB connected to the boundary was left in its trail. The cube slip occurs as a result of (i) a maximal resolved shear stress for the observed slip system and (ii) the geometric criteria for slip applied to all possible slip systems in the matrix. The Schmid factors for the slip systems in the matrix could be calculated by assuming a uniform tensile axis in the foil. The tensile axis was deduced from the observed slip systems in the twin.

Kinetically asymmetric charge and discharge behavior of LiNi0.5Mn1.5O4 at low temperature observed by in situ X-ray diffraction

2014 ◽  
Vol 2 (37) ◽  
pp. 15414-15419 ◽  
Author(s):  
Ikuma Takahashi ◽  
Haruno Murayama ◽  
Kenji Sato ◽  
Takahiro Naka ◽  
Koji Kitada ◽  
...  
Keyword(s):  
Low Temperature ◽  
Low Temperatures ◽  
X Ray Diffraction ◽  
X Ray ◽  
Discharge Behavior

Thermodynamically reversible LiNi0.5Mn1.5O4 electrodes kinetically behave asymmetrically during charging and discharging at low temperatures.

scholarly journals Сильная связь экситонов в микрорезонаторах GaN гексагональной формы

2020 ◽  
Vol 54 (1) ◽  
pp. 85
Author(s):  
А.В. Белоновский ◽  
Г. Позина ◽  
Я.В. Левитский ◽  
К.М. Морозов ◽  
М.И. Митрофанов ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Spatial Distribution ◽  
Electron Microscope ◽  
Low Temperature ◽  
Spatial Localization ◽  
Rabi Splitting ◽  
Hexagonal Shape ◽  
Radiation Probability ◽  
Scanning Electron

The GaN planar hexagonal microcavities were grown by a selective vapor phase epitaxy. The spectra were measured by the low-temperature cathodoluminescence method in-situ scanning electron microscope. The obtained spectra show a huge Rabi splitting (in order of 100 meV). Numerical simulation of the spatial distribution of the modes’ intensities of a hexagonal resonator is shown. Some modes can have strong spatial localization, leading to strong coupling with the exciton and huge Rabi splitting. Theoretically, we calculated the fraction of excitons in polariton modes, which correlates with the intensity of exciton radiation associated with these modes, for microcavities of a hexagonal shape. Thus, we have obtained the form of the dependence of the radiation probability on the eigenfrequencies of the structure.

Thin Film Nucleation and Growth Under Controlled Conditions

1968 ◽  
Vol 26 ◽  
pp. 378-379
Author(s):  
Helmut Poppa
Keyword(s):  
Electron Microscope ◽  
Image Intensifier ◽  
Nucleation And Growth ◽  
Nucleation Kinetics ◽  
Extraction Replica ◽  
In Situ Deposition ◽  
Theoretical Predictions ◽  
Experimental Approaches ◽  
Film Nucleation

Results of controlled in-situ nucleation experiments inside the electron microscope were reported recently. The experimental technique employed permitted detailed quantitative studies of the nucleation kinetics which led to a comparison of test results with nucleation theoretical predictions. However, the background pressures were still of the order of 10-7 to 5x10-8 torr and the experimental arrangement did not provide for producing and maintaining clean single-crystal substrates. It was therefore necessary to limit the choice of substrate-overgrowth material combinations, delete epitaxial studies completely, and defer meaningful investigations of the effect of residual gases on nucleation and growth processes. In addition, the influence on the experimental results of the high-intensity imaging electron beam could only be assessed in a qualitative manner.A research program involving two methodically different experimental approaches has since been initiated that promises to eliminate most of the previous test restrictions. The two approaches entail the use of a modified low-energy electron diffraction (LEED) system in conjunction with extraction replica electron microscopy, and a newly designed ultrahigh-vacuum (UHV) electron-microscope specimen chamber in combination with a microscope image intensifier system for in-situ deposition studies.

Lamellae and their organization in melt-crystallized polymers

1994 ◽  
Vol 348 (1686) ◽  
pp. 29-43 ◽  
Keyword(s):  
Fine Structure ◽  
Thermal Properties ◽  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Molecular Mechanisms ◽  
Mechanical And Thermal Properties ◽  
Screw Dislocations ◽  
Transmission Electron ◽  
Gain Material

Significant advances in knowledge of lamellae and their organization in meltcrystallized polymers have stemmed from the ability to examine internal morphologies systematically with the transmission electron microscope. Spherulites form because the first-forming (dominant) lamellae branch repetitively, often at giant screw dislocations, then diverge substantially creating a skeleton to which later-forming lamellae must accommodate. This sequence promotes chain-folding, invites fractional crystallization and modulates chemical, mechanical and thermal properties of spherulites at the inter-dominant spacing. The key feature of lamellar divergence at screw dislocations is present in individual crystals, probably deriving from pressure of uncrystallized molecular cilia; growing lamellae will also distort very substantially to gain material. If necessary, spacefilling is achieved without lamellar and crystallographic continuity by nucleating new growth at large misorientations. Individual melt-grown crystals have been studied both after extraction from a quenched matrix and in situ in thinned specimens. For polyethylene different lamellar profiles have been placed in context while their fine structure provides insights into molecular mechanisms of growth.

Sign in / Sign up

Export Citation Format

Share Document