In-Situ Tem Dynamic Magnetizing Experiments Used To Identify The Pinning Centers In Hard Magnets Re13.75fe80.25b6 (Re=Nd, Pr).

1999 ◽  
Vol 5 (S2) ◽  
pp. 20-21
Author(s):  
V.V. Volkov ◽  
Y. Zhu
Keyword(s):  
Control Mode ◽  
Objective Lens ◽  
In Situ Tem ◽  
Soft Magnets ◽  
Pinning Centers ◽  
Resolution Electron ◽  
High Resolution Electron Microscope ◽  
Hard Magnets ◽  
Free Environment

The new JEOL 3000F high resolution electron microscope at BNL has been optimized for Lorentz imaging. The necessary field-free environment around the sample is obtained by switching off the objective lens in the free-lens control mode, and the associated reduction in magnification is compensated for by a Gatan post-column image filter (GIF) at ∼ 20x magnification. Fresnel imaging is obtained by defocusing with objective mini-lens (OM). The use of low angle diffraction with an aperture located at the back focal plane makes it possible to obtain Foucault images.In-situTEM dynamic magnetizing experiments combined with Lorentz magnetrc microscopy both in Fresnel and Foucault modes were used to characterize the magnetic structure of some hard and relatively soft magnets, Nd13.75Fe80.25B6 and Pr13.75Fe80.25B6, prepared by different processing routes. The goal of these in-situexperiments was to develop a reliable and effective procedure to search for, identify, and classify the different pinning centers present in real magnets that accord with their “pinning power” versus applied magnetic field.

HREM In-Situ Studies of Electron Irradiation Effects in Oxides

1988 ◽  
Vol 100 ◽  
Author(s):  
D. E. Luzzi ◽  
L. D. Marks ◽  
M. I. Buckett ◽  
J. W. Strane ◽  
B. W. Wessels ◽  
...  
Keyword(s):  
Electron Irradiation ◽  
Point Of View ◽  
Irradiation Damage ◽  
Original Material ◽  
Irradiation Effects ◽  
Resolution Electron ◽  
Wide Range ◽  
Electronic Irradiation ◽  
High Resolution Electron Microscope

ABSTRACTHigh resolution electron microscope (HREM) studies provide the ability to study desorption and sputtering from the perspective of the analysis of the resultant materials, their structure, composition and atomic registry (orientation with respect to the original,material and the irradiation). This is a neglected facet of surface irradiation effects research, yet it is the most important from the technological point of view. In the current study, surface electron irradiation processes in oxides were studied in-situ in a Hitachi H-9000 HREM operated at incident electron energies of 100–300 keV. It was found that a wide range of processes occur in the HREM which are dependent on the energy and flux of the incident electrons and on the material properties. Both ballistic and electronic irradiation damage was observed and the material responses included surface sputtering, amorphisation, chemical disordering, desorption of O and metal surface layer creation, surface roughening and bulk defect creation.

Development of High Resolution Electron Microscope, JEM-100B

1968 ◽  
Vol 26 ◽  
pp. 298-299
Author(s):  
M. Watanabe ◽  
T. Yanaka ◽  
M. Yamamoto ◽  
S. Suzuki ◽  
Y. Nagahama ◽  
...  
Keyword(s):  
Electron Microscope ◽  
Spherical Aberration ◽  
Point Of View ◽  
Resolving Power ◽  
Objective Lens ◽  
Stage Of Development ◽  
Resolution Electron ◽  
Microscopic Studies ◽  
High Resolution Electron Microscope ◽  
The Stability

The JEM-100B electron microscope has been developed with a view to the possibility of obtaining an ultimate resolving power at a beam accelerating voltage of 100kev. Prom the very nature of the instrument, the stability is fully ensured from a mechanical and electrical point of view. In the electron optical system, since highly excited lenses are utilized, image formation under the lowest aberration condition are ensured. The image forming system is of the 4-stage type which greatly expands the range of application not only in microscopic studies but also in the study of electron diffraction. Furthermore, with a view to simplifying instrument operation, various problems have been solved this enabling the instrument to be fully automated. The JEM-100B exhibits the following features.Objective Lens: At the present stage of development, fo=1.6mm. However, so as to be able to incorporate a lens (T. Yanaka et al, 1967) possessing an extremely small spherical aberration coefficient in the future, lens excitation has been made sufficiently high (8kA) and the movable aperture control knob and the specimen device have been designed accordingly.

Magnetic Domains and Domain Wall Pinning in Nanocrystalline Ni-P

2001 ◽  
Vol 7 (S2) ◽  
pp. 1242-1243
Author(s):  
J.P. Zhang ◽  
Y.X. Guo ◽  
J.S. Speck
Keyword(s):  
Magnetic Domain ◽  
Control Mode ◽  
Objective Lens ◽  
Magnetic Domains ◽  
Lorentz Microscopy ◽  
Domain Structures ◽  
Resolution Electron ◽  
Alloy Material ◽  
Electron Imaging ◽  
Fcc Structure

Magnetic domain structures in a Ni-5at%P alloy have been examined using Lorentz microscopy in Fresnel mode in a JEOL 2010TEM. with electron diffraction and high resolution electron imaging, the Ni-P alloy material is seen to be of FCC structure and composed of nanometer-sized grains (< 4nm in diameter), which is about 2 orders less in size than that of a single magnetic domain.The TEM specimen was prepared using jet polishing method. Before introducing the specimen into the microscope, the objective lens was turned off in a free lens control mode to ensure that the domain structures in the specimen remain unaffected. The objective mini-lens was used to perform Lorentz imaging with out-focus method.Stripe domains were observed. The width of these stripes is about 0.2 micron. But the length of these domains varies, sometime up to several microns. The stripe domains are grouped, which are near parallel one to the other.

Formation of a Ni3O4 Spinel Phase on the Surface of NiO During Electron Irradiation

1988 ◽  
Vol 129 ◽  
Author(s):  
Mary I. Buckett ◽  
L. D. Marks
Keyword(s):  
Surface Science ◽  
Electron Irradiation ◽  
Structural Changes ◽  
Science Studies ◽  
Spinel Phase ◽  
Preparation Conditions ◽  
Variable Voltage ◽  
Resolution Electron ◽  
High Resolution Electron Microscope

ABSTRACTStructural changes occurring at the surface of NiO during electron irradiation were examined in-situ with a variable voltage high resolution electron microscope. The interaction of the specimen with the electron beam was found to be highly dependent on the state of the surface prior to irradiation. It was observed that by varying the sample preparation conditions, the Ni on the surface of NiO could either be oxidized to Ni304 spinel phase or reduced to islands of metallic Ni. The formation of the Ni3O4 spinel phase is in agreement with previous surface science studies, where chemical shift information identified the presence of Ni3+ species at the surface. This has previously been interpreted as the formation of Ni203

Complete HREM autotuning using automated diffractogram analysis

1992 ◽  
Vol 50 (1) ◽  
pp. 96-97
Author(s):  
O.L. Krivanek ◽  
G.Y. Fan
Keyword(s):  
Amorphous Materials ◽  
Processing Time ◽  
Ccd Camera ◽  
Objective Lens ◽  
Optical Bench ◽  
Single Image ◽  
Resolution Electron ◽  
Starting Point ◽  
High Resolution Electron Microscope ◽  
Human Operators

Complete autotuning of a high resolution electron microscope (HREM) aligns the electron illumination along the true axis of the objective lens (autoalignment), corrects the astigmatism (autostigmation) and sets the focus to a user-selected value (autofocusing). We have developed a new method which performs complete autotuning with just 3 images, and is faster and more accurate than the best human operators.Our method uses diffractograms of images of amorphous materials recorded with a slow-scan CCD camera (SSC) at magnifications of 200-800 kx. Diffractograms computed from SSC images have better quality than diffractograms formed in an optical bench from a micrograph recorded on film, and are the perfect starting point for the autotuning procedure. The diffractograms are analyzed by an automatic routine described previously. The analysis yields the defocus, astigmatism, and astigmatism direction, and the computer then applies the needed corrections to the microscope. A single image recorded in typically 0.5 - 1.0 sees plus about 8 sees of processing time on a Macintosh Quadra are therefore sufficient for complete autostigmation and autofocusing. This time is likely to decrease in the future simply because of the increasing power of new generations of computers.

HREM autotuning on crystalline materials

1995 ◽  
Vol 53 ◽  
pp. 24-25
Author(s):  
M. Pan ◽  
O.L. Krivanek
Keyword(s):  
High Resolution ◽  
Amorphous Materials ◽  
Optical Axis ◽  
Amorphous Layer ◽  
Objective Lens ◽  
Crystalline Materials ◽  
Crystalline Sample ◽  
Resolution Electron ◽  
High Resolution Electron Microscope ◽  
Electron Microscopes

Complete autotuning of a high resolution electron microscope has been well established. It performs the following tasks: align the electron beam along the true electron-optical axis of objective lens (autoalignment), correct the astigmatism (autostigmation), and set the defocus to a user defined value (autofocus). It can also characterize the coefficient of 3-fold astigmatism while performing the autoalignment. Based on diffractogram analysis current HREM autotuning algorithm only works on amorphous materials. In reality, however, most of the HREM practice is performed on crystalline materials. Therefore it is highly desirable to extend the current HREM autotuning algorithm to crystalline specimens. In this abstract we report preliminary studies on attempting to analyze diffractograms from a mix of crystalline and amorphous materials.For crystalline specimens observed in most high resolution electron microscopes, except under UHV conditions, there is typically a thin layer of amorphous contamination due to either sample preparation or poor vacuum conditions. This amorphous layer can be easily seen at the edge of a crystalline sample in the microscope.

Surface studies with a UHV-TEM

1992 ◽  
Vol 50 (1) ◽  
pp. 326-327
Author(s):  
David J. Smith ◽  
M. Gajdardziska-Josifovska ◽  
M.R. McCartney
Keyword(s):  
Electron Microscope ◽  
Surface Profile ◽  
High Energy ◽  
Operating Modes ◽  
Transmission Imaging ◽  
Transmission Electron ◽  
Resolution Electron ◽  
Reflection Electron Microscopy ◽  
High Resolution Electron Microscope

The provision of ultrahigh vacuum capabilities, as well as in situ specimen treatment and annealing facilities, makes the transmission electron microscope into a potentially powerful instrument for the characterization of surfaces. Several operating modes are available, including surface profile imaging, reflection electron microscopy (REM), and reflection high energy electron diffraction (RHEED), as well as conventional transmission imaging and diffraction. All of these techniques have been utilized in our recent studies of surface structures and reactions for various metals, oxides and semiconductors with our modified Philips-Gatan 430ST high-resolution electron microscope.

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