Interference Experiments with a Field Emission Source

1970 ◽  
Vol 28 ◽  
pp. 534-535
Author(s):  
A. V. Crewe ◽  
J. Saxon
Keyword(s):  
Field Emission ◽  
Spherical Aberration ◽  
Electron Gun ◽  
Partial Coherence ◽  
Vacuum System ◽  
High Brightness ◽  
Small Spot ◽  
Tungsten Tip ◽  
Effective Source ◽  
Better Than

Field emission from a tungsten tip provides a source with very high brightness and high partial coherence. An electron gun of low spherical aberration is used to focus the electrons from the tip to a small spot about 100 Å in diameter. Since the voltages applied to the tip and gun are stable to better than 5 ppm, the temporal coherence is limited by the energy spread of the source, about 200 mv.Using the focused spot a few centimeters below the gun as an effective source, a metalized quartz fiber about 2 μ in diameter is positioned a few centimeters below the source, as shown in Fig. 1. Two cylindrica11y symmetric magnetic lenses are used to magnify the resulting Fresnel diffraction pattern. The image is produced on a fluorescent coating deposited on the vacuum side of a fiber optic window. The image is recorded directly on film placed against the window outside the vacuum system.

Optical characteristics of the hitachi HF-2000 cold field-emission TEM

1993 ◽  
Vol 51 ◽  
pp. 1076-1077
Author(s):  
L. F. Allard ◽  
E. Völkl ◽  
T. A. Nolan
Keyword(s):  
Field Emission ◽  
Recent Literature ◽  
Electron Gun ◽  
High Brightness ◽  
Condenser Lens ◽  
Illumination System ◽  
High Resolution Images ◽  
Imaging Mode ◽  
Better Than ◽  
Illuminating System

The illumination system of the cold field emission (CFE) Hitachi HF-2000 TEM operates with a single condenser lens in normal imaging mode, and with a second condenser lens excited to give the ultra-fine 1 nm probe for microanalysis. The electron gun provides a guaranteed high brightness of better than 7×l08 A/cm2/sr, more than twice the guaranteed brightness of Schottky emission guns. There have been several articles in the recent literature (e.g. refs.) which claim that the geometry of this illumination system yields a total current which is so low that when the beam is spread at low magnifications (say 10 kX), the operator must “keep his eyes glued to the binoculars” in order to see the image. It is also claimed that this illuminating system produces an isoplanatic patch (the area over which image character does not vary significantly) at high magnification which is so small that the instrument is ineffective for recording high resolution images.

High Brightness Electron Gun Using a Field Emission Cathode

1968 ◽  
Vol 26 ◽  
pp. 294-295
Author(s):  
A. N. Broers
Keyword(s):  
Field Emission ◽  
Electron Gun ◽  
Field Emission Cathode ◽  
High Brightness ◽  
Probe Size ◽  
Test Grid ◽  
Two Stages ◽  
Emission Cathode ◽  
Scanning Electron ◽  
Better Than

A field emission cathode electron gun with two stages of acceleration has been built in order to measure the electron beam brightness that can be produced in practice from a tungsten field emission cathode. The gun is similar to that reported by A. Crewe except that the accelerating electrodes are plane, rather than shaped, apertures, and the cathode is located by a gimbal mechanism which allows the cathode to be tilted over an arc of 70° in any direction and positioned laterally. The gun electrodes have been precisely machined with the apertures round within 0.25 micron and aligned with respect to each other to better than 10 micron. The second accelerating electrode is followed by scan plates, a test grid, and an electron detector which together allow the probe size to be measured in the usual scanning electron microscope mode.

Electron Holography and the Correction of Spherical Aberration

1971 ◽  
Vol 29 ◽  
pp. 12-13
Author(s):  
A. V. Crewe ◽  
J. Saxon
Keyword(s):  
Fiber Optic ◽  
Spherical Aberration ◽  
Reference Beam ◽  
Electron Gun ◽  
Vacuum System ◽  
Electron Holography ◽  
Parallel Beam ◽  
Positive Potential ◽  
Total Magnification ◽  
Image Position

Division of wavefront electron holograms have been recorded using a field emission source and electrostatic biprism to get an off axis reference beam. A schematic diagram of the apparatus used is shown in Fig. 1. The electron beam is focused to a point above the specimen and biprism fiber by a specially designed electron gun. With positive potential applied to the fiber the Fresnel diffraction pattern of the specimen is superimposed on the interference pattern of the two effective sources forming the hologram. Two standard magnetic projector lenses are used to magnify the hologram which is recorded outside the vacuum system directly on film in contact with a phosphor-coated fiber optic faceplate. A He-Ne laser is used for the reconstruction as shown in Fig. 2. Following Meier's analysis it is found that when a parallel beam is used to reconstruct the wavefront, the real image will be in focus a distancein front of the hologram where m is the total magnification of the hologram and μ is the ratio of the illuminating to recording wavelengths.

Development of a 200kV field emission TEM

1989 ◽  
Vol 47 ◽  
pp. 112-113
Author(s):  
S. Isakozawa ◽  
Y. Kashikura ◽  
Y. Sato ◽  
T. Takahashi ◽  
M. Ichihashi ◽  
...  
Keyword(s):  
Field Emission ◽  
Crystal Orientation ◽  
Electron Gun ◽  
Objective Lens ◽  
General View ◽  
Virtual Source ◽  
Lens System ◽  
Separate Paper ◽  
Small Probe ◽  
Tungsten Tip

We have completed development of a 200kV field emission TEM. Fig. 1 is a general view of the instrument showing the electron gun and illumination lens system. The electron gun is reported in a separate paper in details. The high voltage accelerator is of 6-stage with aluminum oxide insulators. It allows stable 200kV operation achieving a voltage stability of 1.5 х 10−6/min. The field emitter is a polished tungsten tip having a crystal orientation of (310). It is operated at an ambient temperature without heating. The illumination lens system has been designed and built with permalloy to suite the small virtual source and to minimize external magnetic field disturbances. The objective lens has been designed to allow a point resolution of 0.23 nm and a small probe of 1 nm diameter. The probe has an intensity of 1 х 109A/cm2 sr. or higher as measured on the specimen.

Development of a Field Emission Stem and its Application to Element Analysis

1976 ◽  
Vol 34 ◽  
pp. 524-525
Author(s):  
S. Nomura ◽  
H. Todokoro ◽  
T. Komoda
Keyword(s):  
Field Emission ◽  
Collection Efficiency ◽  
Scanning Transmission Electron Microscope ◽  
Electron Gun ◽  
High Signal ◽  
Element Analysis ◽  
Signal Collection ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Tungsten Tip

The Scanning Transmission Electron Microscope (STEM) has made possible specimen observation with a number of advantages such as high signal collection efficiency. In addition, STEM also permits element analysis of micro-areas, when it is used in conjunction with X-ray and/or electron spectrometers. These advantages become more effective by using a high brightness electron gun.The authors have developed a field emission STEM. The schematic diagram of the instrument is shown in Fig. 1. Electrons emitted from the tungsten tip are focused on a specimen by one electro-static and two magnetic lenses. The field emission tip is surrounded by ion pumps, and the vacuum of the gun chamber is maintained at better than 5xlO-10torr.

Single-Crystal LaB6 as Thermal Field Emitter for Electron Microscope

1990 ◽  
Vol 48 (1) ◽  
pp. 196-197
Author(s):  
Ken Harada ◽  
Haruto Nagata ◽  
Ryuichi Shimizu ◽  
Takayoshi Tanji ◽  
Keiji Yada
Keyword(s):  
Electron Microscope ◽  
Single Crystal ◽  
Field Emission ◽  
Thermal Field ◽  
Thermionic Emission ◽  
Electron Gun ◽  
Field Evaporation ◽  
Good Reproducibility ◽  
High Brightness ◽  
Evaporation Technique

Thermal field emission (T.F.E.) properties of single crystal LaB6 -tips has been investigated by observing emission patterns. Applying field evaporation technique we succeeded to get the clean pattern consisting of <310> spots with very good reproducibility. This investigation has led to conclusion;, the <310> spot is promising electron source of high brightness provided that the tip is operated at tip temperature∽ 1000-1050°C in vacuum of 10−9 Torr region.As a preliminary experiment of brightness-measurement, we mounted the <310> LaB6-tip in a commercial type TEM, JEM-100CX-FEG, attached with an electron gun system for T.F.E. of <100> W-tip, being operated at 10−9 Torr region without Schottky shield electrode. The LaB6-tip, however, can not be operated without the Schottky shield because thermionic emission (T.E.) from the LaB6-tip is considerably high even though the tip is operated at lower than ∽1000 °C. In the present experiment, therefore, we manufactured a Schottky shield electrode as shown in Fig.l and performed the measurement of brightness by setting the Schottky shield electrode, applied the same voltage as the tip since the electron gun system has no extra feed-throughs for bias-voltage.

Development of 350-KV holography electron microscope equipped with magnetic type field-emission electron gun

1989 ◽  
Vol 47 ◽  
pp. 104-105
Author(s):  
J. Endo ◽  
T. Kawasaki ◽  
T. Masuda ◽  
A. Tonomura
Keyword(s):  
Electron Microscope ◽  
Field Emission ◽  
High Sensitivity ◽  
Beam Current ◽  
Electron Gun ◽  
Electron Holography ◽  
Electron Microscopic ◽  
Magnetic Lens ◽  
High Brightness ◽  
Emission Electron

A field-emission electron gun is one of the most epoch-making technologies in an electron microscopic world. In a transmission electron microscope, a high brightness of this beam has been effectively employed for electron-holographic measurements, though the value is not still high enough. Development of a higher brightness beam will promise to open up unattained application possibilities of electron holography such as high resolution and high sensitivity interferometry.We developed the field emission electron microscope for electron holographic applications. Special attentions were paid for high brightness, large beam current and easy operation. Figure 1 is a schematic diagram of the electron gun. In order not to deteriorate the original high-brightness feature of the beam by the aberrations in the gun and the condenser lenses, a magnetic lens was installed between the tip and the extraction anode so that the total aberration effect might be minimized. Field emitted electron beam is converged by the magnetic and the electrostatic lenses, and accelerated in a ten-stage accelerator which is made of porcelain.

Interference Experiments with a Field Emission Electron Miscroscope

1974 ◽  
Vol 32 ◽  
pp. 386-387
Author(s):  
J. Munch ◽  
E. Zeitler
Keyword(s):  
Electron Microscope ◽  
Field Emission ◽  
Design Principles ◽  
Electron Gun ◽  
University Of Chicago ◽  
Emission Electron ◽  
The University ◽  
Better Than

We have modified a Hitachi HU 12 electron microscope by replacing the thermionic electron gun with a field emission gun. The design principles of this gun are substantially the same as those used in the scanning microscopes developed at the University of Chicago by A. V. Crewe and his collaborators. To accommodate the field emission gun in the conventional column two differentially pumped stages were employed, assuring a vacuum of better than 2 x 10−10 Torr in the tip region.

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