On the influence of specimen thickness in TEM images of super-conducting vortices

1996 ◽  
Vol 54 ◽  
pp. 724-725
Author(s):  
J. Bonevich ◽  
D. Capacci ◽  
G. Pozzi ◽  
K. Harada ◽  
H. Kasai ◽  
...  
Keyword(s):  
Flux Line ◽  
Analytical Form ◽  
Realistic Model ◽  
Electron Holography ◽  
Specimen Thickness ◽  
Flux Tubes ◽  
Analytical Expression ◽  
Flux Lines ◽  
Normal Core ◽  
Two Parameters

The successful observation of superconducting flux lines (fluxons) in thin specimens both in conventional and high Tc superconductors by means of Lorentz and electron holography methods has presented several problems concerning the interpretation of the experimental results. The first approach has been to model the fluxon as a bundle of flux tubes perpendicular to the specimen surface (for which the electron optical phase shift has been found in analytical form) with a magnetic flux distribution given by the London model, which corresponds to a flux line having an infinitely small normal core. In addition to being described by an analytical expression, this model has the advantage that a single parameter, the London penetration depth, completely characterizes the superconducting fluxon. The obtained results have shown that the most relevant features of the experimental data are well interpreted by this model. However, Clem has proposed another more realistic model for the fluxon core that removes the unphysical limitation of the infinitely small normal core and has the advantage of being described by an analytical expression depending on two parameters (the coherence length and the London depth).

Real-time observation of vortex lattices in a superconductor

1993 ◽  
Vol 51 ◽  
pp. 1050-1051
Author(s):  
K. Harada ◽  
T. Matsuda ◽  
J.E. Bonevich ◽  
M. Igarashi ◽  
S. Kondo ◽  
...  
Keyword(s):  
Real Time ◽  
Flux Line ◽  
Electron Holography ◽  
Lorentz Microscopy ◽  
Vortex Lattices ◽  
Flux Lines ◽  
Magnetic Flux Lines ◽  
Time Observation ◽  
Thin Superconductor ◽  
Real Time Observation

Previous observations of magnetic flux-lines (vortex lattices) in superconductors, such as the field distribution of a flux-line, and flux-line dynamics activated by heat and current, have employed the high spatial resolution and magnetic sensitivity of electron holography. And recently, the 2-D static distribution of vortices was also observed by this technique. However, real-time observations of the vortex lattice, in spite of scientific and technological interest, have not been possible due to experimental difficulties. Here, we report the real-time observation of vortex lattices in a thin superconductor, by means of Lorentz microscopy using a 300 kV field emission electron microscope. This technique allows us to observe the dynamic motion of individual vortices and record the events on a VTR system.The experimental arrangement is shown in Fig. 1. A Nb thin film for transmission observation was prepared by chemical etching. The grain size of the film was increased by annealing, and single crystals were observed with a thickness of 50∼90 nm.

Flux-line observation by electron Holography

1993 ◽  
Vol 51 ◽  
pp. 1024-1025
Author(s):  
Akira Tonomura
Keyword(s):  
Electron Microscopy ◽  
Electron Beam ◽  
Magnetic Flux ◽  
Transition Region ◽  
Flux Line ◽  
Electron Holography ◽  
Phase Measurements ◽  
Flux Lines ◽  
Magnetic Flux Lines ◽  
Line Observation

In electron microscopy, the intensity of an electron beam transmitted through an object can be observed. While in electron holography, the phase of the electron beam can also be observed and displayed as an interference micrograph. Using a technique unique to holography, the precision of phase measurements can be increased to 1/100 of the electron wavelength. An interference micrograph of a magnetic object can be interpreted in a straightforward way: Contour fringes directly indicate projected magnetic flux lines and a constant magnetic flux of h/e (= 4 × 10-15 Wb) flows between two adjacent fringes (See Fig. 1).Examples of magnetic recordings are shown in Fig. 2. Flux lines inside and outside of the magnetic tapes, recorded in different ways, can directly and quantitatively be observed as interference micrographs. Figure 2 (a) shows an example of in-plane magnetic recording. Two magnetization streams, pointed in opposite directions, merge and produce vortices in the transition region similar to those produced by streams of water.

On the Calculation of the Phase Shift of a Superconducting Flux Line Lattice

2000 ◽  
Vol 6 (S2) ◽  
pp. 1032-1033
Author(s):  
M. Beleggia ◽  
G. Pozzi ◽  
A. Tonomura
Keyword(s):  
Magnetic Field ◽  
Electron Beam ◽  
Phase Shift ◽  
Flux Line ◽  
Realistic Model ◽  
Regular Lattice ◽  
Transmission Experiment ◽  
Line Lattice ◽  
Flux Tubes ◽  
London Model

Recently out-of-focus, low angle electron diffraction and Foucault experiments have been carried out on superconducting specimens in a range of applied magnetic fields where the fluxons form a more or less regular lattice. Let us recall that in order to describe the effect on the electron beam in a transmission experiment of a fluxon in a tilted specimen, the fluxon itself has been approximated by a suitable bundle of straight flux tubes, relying on the important result that the phase shift of the flux tube can be calculated analytically even in the tilted specimen geometry. In this way, it is only necessary to convolute this phase shift with the chosen projected magnetic field distribution (in our case a London model with a phenomenological penetration depth of 50 nm) in order to obtain a fairly realistic model. Therefore, in order to interpret the main features of the experimental results,

Electron holography observation of flux-line dynamics

1992 ◽  
Vol 50 (1) ◽  
pp. 68-69 ◽  
Author(s):  
Takaho Yoshida ◽  
Tsuyoshi Matsuda ◽  
Akira Tonomura
Keyword(s):  
Magnetic Field ◽  
Thin Films ◽  
Spatial Resolution ◽  
Flux Line ◽  
Electrical Current ◽  
Electron Holography ◽  
Video Tape ◽  
Flux Lines ◽  
Flux Motion ◽  
Individual Flux

With the sufficient spatial resolution and magnetic sensitivity, Electron holography has opened a new way to directly observe the flux lines in superconductors. It has successfully shown the detailed magnetic field distribution of individual flux lines penetrating Pb thin films. This technique also excels at observing flux line dynamics. By taking the holograms with a TV camera and recording them on a video tape, it became possible to observe the flux motion microscopically and continuously. Using this technique, the present study will demonstrate the thermally excited and the electrical current induced flux line dynamics.

Flux Line Dynamics with Electron Holography

1994 ◽  
Vol 332 ◽  
Author(s):  
Akira Tonomura
Keyword(s):  
Flux Line ◽  
Interference Microscopy ◽  
Electron Holography ◽  
Temperature Changes ◽  
Lorentz Microscopy ◽  
Flux Lines ◽  
Electron Interference ◽  
Time Observation ◽  
Real Time Observation ◽  
Line Movement

ABSTRACTFlux lines in superconducting thin films are observed statically in a holographic electron interference micrograph, and dynamically in a Lorentz micrograph with a “coherent” and 300kV electron beam. In interference microscopy, projected magnetic lines of force in a tilted Nb thin film are observed quantitatively as contour fringes drawn on an in-focus electron micrograph. Whereas in Lorentz microscopy, flux lines are observed as spots with bright and dark contrast pairs due to defocusing of the image. Although the image is blurred due to a large amount of defocusing, this method is suitable for real-time observation. By making the best use of this feature, flux line movement can be observed when the applied magnetic field or the film temperature changes.

The effect of core size on the holographic interference images of superconducting fluxons in tilted specimens

1993 ◽  
Vol 51 ◽  
pp. 1224-1225
Author(s):  
G. Pozzi ◽  
J.E. Bonevich ◽  
A. Tonomura
Keyword(s):  
Electron Holography ◽  
Electron Optics ◽  
Core Size ◽  
Flux Tubes ◽  
Lorentz Microscopy ◽  
Flux Lines ◽  
Advanced Phase ◽  
Transmission Electron ◽  
Phase Sensitive ◽  
Set Up

Recently, observations of quantized flux lines in thin superconducting specimens have been successfully carried out in transmission electron microscopy by means of standard methods of Lorentz microscopy and also by electron holography. The breakthrough with respect to the previous unsuccessful attempts is represented by the fact that the specimen is observed tilted with respect both to the electron beam and the ancillary magnetic field that is used to introduce and stabilize the fluxons in the specimen.Although a reduction of the phase difference with respect to the optimum situation of fluxons perpendicular to the beam is expected in this set-up, it has nonetheless been possible to ascertain by means of a simple model that this reduction is not below the detectability limit that can be reached by the most advanced phase sensitive methods available today in electron optics, such as electron holography. However calculations have been carried out so far either for the single fluxon case, taking into account also its core structure, or for an array of 25 flux tubes (i.e. fluxons with negligible core size) arranged in a triangular lattice.

Practical Importance of Spatial Resolution and Analytical Sensitivity in AEM X-ray Microanalysis

1990 ◽  
Vol 48 (2) ◽  
pp. 432-433
Author(s):  
J. Zhang ◽  
D.B. Williams ◽  
J.I. Goldstein
Keyword(s):  
Spatial Resolution ◽  
Practical Importance ◽  
Beam Current ◽  
Specimen Thickness ◽  
Analytical Sensitivity ◽  
Related Factors ◽  
X Ray ◽  
Probe Size ◽  
Excitation Volume ◽  
Two Parameters

Analytical sensitivity and spatial resolution are important and closely related factors in x-ray microanalysis using the AEM. Analytical sensitivity is the ability to distinguish, for a given element under given conditions, between two concentrations that are nearly equal. The analytical sensitivity is directly related to the number of x-ray counts collected and, therefore, to the probe current, specimen thickness and counting time. The spatial resolution in AEM analysis is determined by the probe size and beam broadening in the specimen. A finer probe and a thinner specimen give a higher spatial resolution. However, the resulting lower beam current and smaller X-ray excitation volume degrade analytical sensitivity. A compromise must be made between high spatial resolution and an acceptable analytical sensitivity. In this paper, we show the necessity of evaluating these two parameters in order to determine the low temperature Fe-Ni phase diagram.A Phillips EM400T AEM with an EDAX/TN2000 EDS/MCA system and a VG HB501 FEG STEM with a LINK AN10 EDS/MCA system were used.

Electron holography of catalysts

1995 ◽  
Vol 53 ◽  
pp. 416-417
Author(s):  
A. K. Datye ◽  
D. S. Kalakkad ◽  
L. F. Allard ◽  
E. Völkl
Keyword(s):  
Heterogeneous Catalysts ◽  
High Surface ◽  
High Surface Area ◽  
Atomic Scale ◽  
Nano Particles ◽  
Phase Image ◽  
Electron Holography ◽  
Specimen Thickness ◽  
Phase Information ◽  
Particle Structure

The active phase in heterogeneous catalysts consists of nanometer-sized metal or oxide particles dispersed within the tortuous pore structure of a high surface area matrix. Such catalysts are extensively used for controlling emissions from automobile exhausts or in industrial processes such as the refining of crude oil to produce gasoline. The morphology of these nano-particles is of great interest to catalytic chemists since it affects the activity and selectivity for a class of reactions known as structure-sensitive reactions. In this paper, we describe some of the challenges in the study of heterogeneous catalysts, and provide examples of how electron holography can help in extracting details of particle structure and morphology on an atomic scale.Conventional high-resolution TEM imaging methods permit the image intensity to be recorded, but the phase information in the complex image wave is lost. However, it is the phase information which is sensitive at the atomic scale to changes in specimen thickness and composition, and thus analysis of the phase image can yield important information on morphological details at the nanometer level.

Off-axis electron holography applied to the study of interfaces

1992 ◽  
Vol 50 (1) ◽  
pp. 244-245
Author(s):  
J.K. Weiss ◽  
M. Gajdardziska-Josifovska ◽  
M. R. McCartney ◽  
David J. Smith
Keyword(s):  
Electric Fields ◽  
Resolution Enhancement ◽  
Interfacial Structure ◽  
Atomic Scale ◽  
Bulk Property ◽  
Electron Holography ◽  
Specimen Thickness ◽  
Composition And Structure ◽  
Chemical Segregation ◽  
Diffraction Effects

Interfacial structure is a controlling parameter in the behavior of many materials. Electron microscopy methods are widely used for characterizing such features as interface abruptness and chemical segregation at interfaces. The problem for high resolution microscopy is to establish optimum imaging conditions for extracting this information. We have found that off-axis electron holography can provide useful information for the study of interfaces that is not easily obtained by other techniques.Electron holography permits the recovery of both the amplitude and the phase of the image wave. Recent studies have applied the information obtained from electron holograms to characterizing magnetic and electric fields in materials and also to atomic-scale resolution enhancement. The phase of an electron wave passing through a specimen is shifted by an amount which is proportional to the product of the specimen thickness and the projected electrostatic potential (ignoring magnetic fields and diffraction effects). If atomic-scale variations are ignored, the potential in the specimen is described by the mean inner potential, a bulk property sensitive to both composition and structure. For the study of interfaces, the specimen thickness is assumed to be approximately constant across the interface, so that the phase of the image wave will give a picture of mean inner potential across the interface.

scholarly journals What are the Radio Filaments Near the Galactic Center?

1996 ◽  
Vol 169 ◽  
pp. 247-261 ◽  
Author(s):  
Mark Morris
Keyword(s):  
Magnetic Field ◽  
Galactic Center ◽  
Galactic Plane ◽  
Local Source ◽  
Flux Tubes ◽  
Flux Lines ◽  
Magnetic Flux Tubes ◽  
The Magnetic Field ◽  
Relativistic Particles ◽  
Projected Distance

A population of nonthermally-emitting radio filaments tens of parsecs in length has been observed within a projected distance of ∼130 pc of the Galactic center. More or less perpendicular to the Galactic plane, they appear to define the flux lines of a milligauss magnetic field. The characteristics of the known filaments are summarized. Three fundamental questions raised by these structures are discussed: 1) Do they represent magnetic flux tubes embedded within an ubiquitous, dipole magnetic field permeating the inner Galaxy, but which have been illuminated by some local source of relativistic particles, or are they instead isolated, self-sustaining current paths with an approximately force-free magnetic configuration in pressure equilibrium with the interstellar medium? 2) What is the source of either the magnetic field or the current? and 3) What is the source of the relativistic particles which provide the illuminating synchrotron radiation? We are nearer an answer to the the last of these questions than to the others, although several interesting models have been proposed.

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