Development of a User Adjustable Pole-piece Gap Objective-lens

2021 ◽  
Author(s):  
Lewys Jones ◽  
Keyword(s):  
Objective Lens ◽  
Pole Piece

Modification of a TEM for ultra-high-vacuum reflection-EM (UHV-REM) applications

1995 ◽  
Vol 53 ◽  
pp. 582-583
Author(s):  
Tung Hsu ◽  
Min-Yi Shih ◽  
A. V. Latyshev
Keyword(s):  
Electron Microscope ◽  
High Vacuum ◽  
High Energy ◽  
Ultra High Vacuum ◽  
Objective Lens ◽  
Pole Piece ◽  
High Energy Electron ◽  
Normal Position ◽  
Crystal Surfaces ◽  
Specimen Holder

A JEOL JEM-100C electron microscope was modified by adding a cryogenic UHV specimen holder for studying clean crystal surfaces with the reflection high energy electron diffraction (RHEED) and REM techniques. The Si(111) (l×l) and (7×7) phase transitions have been successfully observed (Fig. 1). Further modification is in progress for better resolution and other functions. Fig. 2.a shows the unmodified specimen holder and the objective lens of the microscope. The cryogenic holder based on the Novosibirsk design is shown in Fig. 2.b. Liquid nitrogen is continuously pumped through the shell of the holder for achieving UHV inside. The tilt/rotation controls and the current for heating of the specimen are fed through the holder. In this modification, the specimen was not placed at the normal position of the lens and therefore is not at the best position for imaging and diffraction.A new holder is shown in Fig. 2.c. This holder is inserted into the pole piece to place the specimen at the normal position.

Two “improvements” for Philips 400 series microscopes

1986 ◽  
Vol 44 ◽  
pp. 624-625
Author(s):  
A. E. Greene ◽  
J. A. Eades
Keyword(s):  
Magnetic Flux ◽  
Objective Lens ◽  
Pole Piece ◽  
Optimum Size ◽  
Lens System ◽  
Operating Characteristics ◽  
Maximum Area ◽  
Loss Of Information ◽  
Convergent Beam ◽  
Transmission Microscope

The optimum size for the disks in a convergent-beam pattern is when the disks just touch. This provides the maximum area of useful pattern indside the disks and avoids the loss of information where they overlap. In a standard transmission microscope, the size of the disk is selected by the size of the condenser aperture. This provides only a few possible settings with rather coarse steps.We have modified Philips EM420 and EM400T microscopes to provide a continuous variation of the convergence of the incident illumination. This is accomplished by adding a control to vary the ‘Mini’ lens current. The mini lens is located inside the objective lens upper pole piece and by reversal of its magnetic flux, gives the objective lens system two distinct operating characteristics.

Magnetic Imaging Of Recording Media

1999 ◽  
Vol 5 (S2) ◽  
pp. 28-29
Author(s):  
Robert Sinclair ◽  
Kai Tang
Keyword(s):  
Magnetic State ◽  
Objective Lens ◽  
Recording Media ◽  
Pole Piece ◽  
Processing Conditions ◽  
Microstructural Parameters ◽  
Magnetic Performance ◽  
Magnetic Imaging ◽  
Ferromagnetic Domain ◽  
Local Direction

Magnetic recording forms the basis of one of the largest international industries. Electron microscopy has of course played a significant role in relating magnetic performance to the underlying microstructure. However, relatively little attention has been paid to the ways in which imaging of the magnetic structure can be correlated with processing conditions and microstructural parameters. The present research has been aimed to address this deficiency.A method was devised to prepare samples with large electron transparent areas (e.g., 250 microns square) from real computer hard discs. Fresnel TEM images were taken in a Philips CM20 FEG equipped with a special Lorentz pole piece, and with the objective lens off. Upon defocusing, the ferromagnetic domain structure strikingly appears. The characteristics of the recorded tracks depend on the magnetic state of the disc prior to magnetic “writing”, and much information about the local direction of magnetization could be obtained from the nature of the magnetic “ripple” structure.

IMPROVED POLE PIECE CONSTRUCTION OF THE OBJECTIVE LENS OF A MAGNETIC ELECTRON MICROSCOPE

1940 ◽  
Vol 18a (11) ◽  
pp. 175-177 ◽  
Author(s):  
Albert Prebus
Keyword(s):  
Electron Microscope ◽  
Objective Lens ◽  
Pole Piece ◽  
University Of Toronto ◽  
New Form ◽  
The University ◽  
Magnetic Electron

The paper is a description of a new form of pole piece devised for the electron microscope developed at the University of Toronto.

Lorentz Microscopy: Effect of Tilting on Magnetic Domains in Single Crystal Iron Films

1968 ◽  
Vol 26 ◽  
pp. 388-389
Author(s):  
L. F. Allard ◽  
A. P. Rowe ◽  
P. L. Fan
Keyword(s):  
Single Crystal ◽  
Domain Walls ◽  
Magnetic Domain ◽  
Objective Lens ◽  
Pole Piece ◽  
Magnetic Domains ◽  
Iron Films ◽  
Lorentz Microscopy ◽  
Magnetic Domain Walls ◽  
Microscopy Techniques

In order to observe magnetic domain walls by Lorentz microscopy techniques it is often necessary either to operate the microscope with the objective lens off, thus severely limiting the magnification, or to move the specimen from its usual position or make some other modification so that the field to which it is subjected is not so strong that it saturates the specimen. However, conditions in the JEM-6A have proved favorable for observation of domains in single crystal iron films by the out-of-focus method without any modifications, using either the regular specimen stage with the small bore pole piece or the tilting stage with the large bore pole piece. The tilting stage is particularly useful for these studies because the domains are very sensitive to small differences in inclination in the field.

An environmental cell Transmission Electron Microscope

1990 ◽  
Vol 48 (4) ◽  
pp. 552-553
Author(s):  
D.K. Dewald ◽  
T.C. Lee ◽  
J.A. Eades ◽  
I.M. Robertson ◽  
H.K. Bimbaum
Keyword(s):  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Objective Lens ◽  
Pole Piece ◽  
Noticeable Effect ◽  
Plan View ◽  
Handling System ◽  
Transmission Electron ◽  
Environmental Cell ◽  
Cell Transmission

The ability to observe directly and at high spatial resolution the interactions between environments and materials affords the material scientist new and unique opportunities. This capability is realized in the Environmental Cell Transmission Electron Microscope Facility which has been installed as part of the Center for Microanalysis of Materials at the Materials Research Laboratory of the University of Illinois at Urbana-Champaign.The Facility is based on a JEOL 4000EX equipped with a specially designed pole piece. An aperture limited, differentially pumped, environmental cell has been installed in this pole piece. The system is shown schematically in Figures 1 and 2. Figure 1 is a plan view of a section through the objective lens pole-piece, with the microscope axis perpendicular to the plane of the paper, showing the cell enclosing the sample rod, the gas handling system and the location of the magnetically levitated Turbo-Molecular pumps. Figure 2 shows a cross-sectional view of the environmental cell and the gas handling system. As shown in Figure 2 the electron beam passes through a series of five apertures which allow the column vacuum to be maintained while the cell pressure is increased. The actual cell apertures are located at the apex of cones to minimize the gas path length, allow maximum tilt and still permit high- angle diffraction data to be obtained. Differential pumping of the cell is achieved by the four turbo- molecular pumps, the location of which can be seen in the Figures. With this arrangement the environmental cell is capable of supporting 400 torr of N2 gas which has no noticeable effect on the microscope operation. This allows the microscope to be operated with a LaB6 filament. The gas handling system was designed to handle a variety of environments including corrosive ones.

Modification Of a Conventional TEM (CTEM) for Lorentz Microscopy

1998 ◽  
Vol 4 (S2) ◽  
pp. 390-391
Author(s):  
M. Wall ◽  
S. Bajt ◽  
C. Cerjan
Keyword(s):  
Excited State ◽  
Magnetic Fields ◽  
Magnetic Materials ◽  
Objective Lens ◽  
High Magnification ◽  
Pole Piece ◽  
Lorentz Microscopy ◽  
Better Than

We have modified a CTEM in order to perform Lorentz microscopy experiments at high magnification and resolution on magnetic materials. The modification consists of the adaptation of a second side entry goniometer (SEG) to the CTEM (JEOL 200CX STEM) column above the objective lens, in a region of the column where the measured residual magnetic fields are < 0.5 Gauss with the objective lens in a fully excited state (see Figure 1).With the specimen positioned above the objective lens, it is necessary to increase the excitation of the lens by approximately 20% in order to bring the image into focus. This combination of a specimen positioned above the object pole piece, and the higher objective lens excitation, affects several changes in the optics. First, if a specimen is positioned within the pole piece gap and the objective lens is turned off for Lorentz microscopy purposes, the highest typical magnification achievable is approximately 1,000 X and the resolution is not much better than 0.1μm.

Design of an Objective Lens with Minimum Chromatic Aberration Coefficient

1997 ◽  
Vol 3 (S2) ◽  
pp. 1083-1084
Author(s):  
K. Tsuno ◽  
D. A. Jefferson
Keyword(s):  
Magnetic Flux ◽  
Spatial Frequency ◽  
High Voltage ◽  
Spherical Aberration ◽  
Wave Length ◽  
Finite Size ◽  
Chromatic Aberration ◽  
Magnetic Flux Density ◽  
Objective Lens ◽  
Pole Piece

The Schelzer resolution is defined as the highest spatial frequency which is transferred into the image with the same phase as all lower frequencies. The resolution of the information limit is, however, determined by the information from the specimen which is equal to the degree of noise. The Schelzer resolution is determined by the wave length and the spherical aberration coefficient Cs of the objective lens. It reached 0.1 nm at 1250 kV. The limit of the resolution has been calculated numerically and it is written as d = 4.65(BsVr)−1/4 (nm), where Bs (in T) is the saturation magnetic flux density of the pole-piece material and Vr the relativistically corrected accelerating voltage. The resolution of the information limit is determined by the axial chromatic aberration coefficient Cc and incoherent effects such as the finite size of the source, beam divergence, energy spread, instabilities of the high voltage and lens current. The limit of the resolution is not clear. Most of the objective lenses of commercial microscopes are designed to optimize Cs rather than Cc. In this investigation, however, we describe the limit of Cc for 200 kV microscopes.

Microstructural Damage Evolution in "Triple-Beam" Ion-Irradiated Fe-10% Cr*

1982 ◽  
Vol 40 ◽  
pp. 588-589
Author(s):  
L. L. Horton ◽  
J. Bentley
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Magnetic Materials ◽  
Damage Evolution ◽  
Objective Lens ◽  
Pole Piece ◽  
Graaff Accelerator ◽  
Microstructural Damage ◽  
Transmission Electron ◽  
Accelerator System

The evolution of the damage microstructures which result from fusion environment irradiation of Fe— 10% Cr has been characterized with transmission electron microscopy (TEM). Disk specimens (3 mm diameter) were bombarded at 850 K in the ORNL dual Van de Graaff accelerator system with a “triple beam” of He+, D+, and 4 MeV Fe++ to fluences of 0.3, 1, 3, 10, 30 and 100 dpa with 10 at. ppm He/dpa and 41 at. ppm D/dpa. The specimens were prepared for TEM using standard electrolytic “sectioning” and “back-thinning” techniques with a sectioning depth of 0.9 μm. TEM examination was performed at 120 kV in a JEM 120C equipped with a special objective lens pole-piece (AMG) for the observation of magnetic materials.

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