Annular dark-field image simulation of the YBa2Cu3O7−δ/BaF2 interface

2000 ◽  
Vol 84 (1-2) ◽  
pp. 65-74 ◽  
Author(s):  
J.L Lee ◽  
J Silcox
Keyword(s):  
Dark Field Image ◽  
Dark Field ◽  
Image Simulation ◽  
Annular Dark Field

EM of rapidly solidified permanent magnets

1992 ◽  
Vol 50 (1) ◽  
pp. 198-199
Author(s):  
Raja K. Mishra
Keyword(s):  
Melt Spinning ◽  
Permanent Magnets ◽  
Dark Field Image ◽  
Dark Field ◽  
Maximum Energy ◽  
Quench Rate ◽  
Maximum Energy Product ◽  
Energy Product ◽  
Annular Dark Field ◽  
Rapidly Solidified

The discovery of a new class of permanent magnets based on Nd2Fe14B phase in the last decade has led to intense research and development efforts aimed at commercial exploitation of the new alloy. The material can be prepared either by rapid solidification or by powder metallurgy techniques and the resulting microstructures are very different. This paper details the microstructure of Nd-Fe-B magnets produced by melt-spinning.In melt spinning, quench rate can be varied easily by changing the rate of rotation of the quench wheel. There is an optimum quench rate when the material shows maximum magnetic hardening. For faster or slower quench rates, both coercivity and maximum energy product of the material fall off. These results can be directly related to the changes in the microstructure of the melt-spun ribbon as a function of quench rate. Figure 1 shows the microstructure of (a) an overquenched and (b) an optimally quenched ribbon. In Fig. 1(a), the material is nearly amorphous, with small nuclei of Nd2Fe14B grains visible and in Fig. 1(b) the microstructure consists of equiaxed Nd2Fe14B grains surrounded by a thin noncrystalline Nd-rich phase. Fig. 1(c) shows an annular dark field image of the intergranular phase. Nd enrichment in this phase is shown in the EDX spectra in Fig. 2.

Simulation of high-resolution annular dark field STEM images

1995 ◽  
Vol 53 ◽  
pp. 40-41
Author(s):  
E. J. Kirkland
Keyword(s):  
Electron Beam ◽  
Atomic Layer ◽  
Fresnel Diffraction ◽  
Dark Field ◽  
Objective Lens ◽  
Image Simulation ◽  
Small Probe ◽  
Annular Dark Field ◽  
Stem Image ◽  
Uniform Plane

In a STEM an electron beam is focused into a small probe on the specimen. This probe is raster scanned across the specimen to form an image from the electrons transmitted through the specimen. The objective lens is positioned before the specimen instead of after the specimen as in a CTEM. Because the probe is focused and scanned before the specimen, accurate annular dark field (ADF) STEM image simulation is more difficult than CTEM simulation. Instead of an incident uniform plane wave, ADF-STEM simulation starts with a probe wavefunction focused at a specified position on the specimen. The wavefunction is then propagated through the specimen one atomic layer (or slice) at a time with Fresnel diffraction between slices using the multislice method. After passing through the specimen the wavefunction is diffracted onto the detector. The ADF signal for one position of the probe is formed by integrating all electrons scattered outside of an inner angle large compared with the objective aperture.

HREM and HAADF Studies of Precipitates in the Mg-Y-Nd Alloy System

2007 ◽  
Vol 561-565 ◽  
pp. 275-278
Author(s):  
Wei Sun ◽  
Li Sun ◽  
Lin Lin Liu ◽  
Ze Zhang
Keyword(s):  
Structural Model ◽  
Imaging Technique ◽  
Dark Field Image ◽  
Alloy System ◽  
Dark Field ◽  
Orthorhombic Unit Cell ◽  
Characteristic Distribution ◽  
Transmission Electron ◽  
Annular Dark Field ◽  
Image Technique

By means of high resolution transmission electron microscopy (HREM) and high-angle annular dark-field image technique (HAADF), morphological, structural and compositional characteristics of the precipitates in the Mg-4Y-3Nd alloy aged at 200°C for different periods of time have been studied. On the basis of HREM observations, an atomic structural model for the β’-precipitate with an orthorhombic unit cell has been proposed. The characteristic distribution of the precipitates which are rich in rare-earth elements (Y, Nd) has been clearly revealed by the HAADF imaging technique.

Stem Dark-Field Image Using A 200-kV AEM

1996 ◽  
Vol 54 ◽  
pp. 444-445
Author(s):  
T. Tomita ◽  
T. Honda ◽  
M. Kersker
Keyword(s):  
High Resolution ◽  
Field Emission ◽  
Thermal Field ◽  
Imaging System ◽  
Dark Field Image ◽  
Dark Field ◽  
Specimen Thickness ◽  
High Angle ◽  
Long Term Stability ◽  
Annular Dark Field

Interpretation of the high resolution transmission image typically requires simulation since the contrast changes in a complicated way due to changes in focus and specimen thickness. The contrast in images formed by collecting high angle forward scattered electrons in STEM does not change with changes in thickness or defocus.Until recently, high angle annular dark field (HADF) images were obtained only from instruments using cold field emission guns. Recently we have attempted to obtain HADF images using Schottky (ZrO/W(100)) thermal field emission and using a 200kV instrument designed as a comprehensive TEM/STEM. Advantages of the ZrO/W emitter are easy operation, very good short and long term stability, high brightness, and narrow energy spread. This microscope, The JEM2010F with thermal field emission, allows subnanometer analysis with EDS(spot, line, and mapping), EELS, holograms, etc, and has a standard TEM imaging system for high resolution imaging and for various diffraction modes, viz., CBED, selected area, Tanaka, etc.

Microdiffraction studies of small crystallites

1988 ◽  
Vol 46 ◽  
pp. 708-709
Author(s):  
S. A. Bradley ◽  
H. J. Robota
Keyword(s):  
Surface Area ◽  
High Surface ◽  
High Surface Area ◽  
Dark Field Image ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Angle Scattering ◽  
Dark Field Microscopy ◽  
Scanning Transmission ◽  
Annular Dark Field

Identification of nano-crystallites (<5 nm) on a high surface area support such as a catalyst is critical in the development of improved catalysts. Bright field imaging of small particles can be obscured by the phase contrast of the support. A common approach is to utilize annular dark field microscopy; however, wide angle scattering from the high surface area support can easily appear in the annular dark field image. Often one utilizes the energy dispersive detector to identify conclusively the nanosized metal crystallite, but this approach is troublesome when crystallites are very thin since counting times for imaging can become excessive. One technique for avoiding some of these difficulties is to utilize microdiffraction to identify the crystallite and then to image the crystallite by axial dark field microscopy.In the work reported here, the imaging was performed with a dedicated VG HB-5 scanning transmission electron microscope.

Developments in Processing Multisignal Imaging in STEM

1990 ◽  
Vol 48 (1) ◽  
pp. 118-119
Author(s):  
C. Jeanguillaume ◽  
P. Ballongue ◽  
M. Tencé ◽  
C. Colliex
Keyword(s):  
Signal To Noise Ratio ◽  
Dark Field Image ◽  
Beam Current ◽  
Dark Field ◽  
Annular Dark Field ◽  
Processing Modes ◽  
Electron Lens ◽  
Novel Processing ◽  
Dose Condition ◽  
Z Contrast

In an electron microscope, it is most important to optimize , for a given irradiation dose, the information extracted from the specimen . The STEM configuration is quite suited for such developments because it can easily be equipped with a set of detectors for recording simultaneous signals . When associated with novel processing modes, this multisignal imaging approach affords interesting developments in many fields of applications, as illustrated here on a simple example . A VG STEM with a magnetic spectrometer for energy loss studies, has been fitted with four different detection channels, as shown in Fig 1 . These are : the beam current measurement (Icur), the annular dark field image (Iadf), the unscattered (Iun ), and total inelastic signal (Iin ). These latter contributions are discriminated on two separate detectors after magnification of the EELS spectrum with a dedicated double gap electron lens, see (1) for complete description of the design. Before introducing these different data in the appropriate analytical expressions which involve sums, differences or ratios, it is necessary to evaluate their relative weights, i.e the ratios of their detection efficiencies. Following the general principle described in (2), a reconstructed image of the primary beam current is obtained as a suitable linear combination of the three other signals . New images can then be generated for : a) the enhancement of the signal to noise ratio in low dose condition; b) the separation of the elastic and inelastic contributions; c) the improvement of the Z contrast; d) the development of mass thickness measurements. These latter two aspects are illustrated in the present abstract.

scholarly journals The 1s-State Analysis Applied to High-Angle, Annular Dark-Field Image Interpretation—When Can We Use It?

2004 ◽  
Vol 10 (1) ◽  
pp. 4-8 ◽  
Author(s):  
Geoffrey R. Anstis
Keyword(s):  
Image Interpretation ◽  
Dark Field Image ◽  
Dark Field ◽  
High Angle ◽  
Atomic Column ◽  
Thermal Diffuse Scattering ◽  
Small Probe ◽  
Annular Dark Field ◽  
Electron Intensity ◽  
Thermal Diffuse

A small probe centered on an atomic column excites the bound and unbound states of the two-dimensional projected potential of the column. It has been argued that, even when several states are excited, only the 1sstate is sufficiently localized to contribute a signal to the high-angle detector. This article shows that non-1sstates do make a significant contribution for certain incident probe profiles. The contribution of the 1sstate to the thermal diffuse scattering is calculated directly. Sub-Ångstrom probes formed by Cs-corrected lenses excite predominantly the 1sstate and contributions from other states are not very large. For probes of lower resolution when non-1sstates are important, the integrated electron intensity at the column provides a better estimate of image intensity.

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