Some Applications of Plasma-Cathode Electron Sources

AbstractThis paper presents a review of physical principles, design, and performances of plasma-cathode direct current (dc) electron beam guns operated in so called fore-vacuum pressure (1–15 Pa). That operation pressure range was not reached before for any kind of electron sources. A number of unique parameters of the e-beam were obtained, such as electron energy (up to 25 kV), dc beam current (up 0.5 A), and total beam power (up to 7 kW). For electron beam generation at these relatively high pressures, the following special features are important: high probability of electrical breakdown within the accelerating gap, a strong influence of back-streaming ions on both the emission electrode and the emitting plasma, generation of secondary plasma in the beam propagation region, and intense beam-plasma interactions that lead in turn to broadening of the beam energy spectrum and beam defocusing. Yet other unique peculiarities can occur for the case of ribbon electron beams, having to do with local maxima in the lateral beam current density distribution. The construction details of several plasma-cathode electron sources and some specific applications are also presented.

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Plasma cathode electron sources and their applications

25th Anniversary, IEEE Conference Record - Abstracts. 1998 IEEE International Conference on Plasma Science (Cat. No.98CH36221) ◽

10.1109/plasma.1998.677647 ◽

2002 ◽

Author(s):

E. Oks

Keyword(s):

Plasma Cathode ◽

Electron Sources

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A Stable Field Emission Electron Source

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100077918 ◽

1977 ◽

Vol 35 ◽

pp. 58-59

Author(s):

W.R. Bottoms ◽

G.B. Haydon

Keyword(s):

Field Emission ◽

Signal To Noise Ratio ◽

High Brightness ◽

Electron Sources ◽

Brightness Field ◽

Current Densities ◽

Properties Of Materials ◽

Stable Field ◽

Stable Current ◽

Careful Design

There is great interest in improving the brightness of electron sources and therefore the ability of electron optical instrumentation to probe the properties of materials. Extensive work by Dr. Crew and others has provided extremely high brightness sources for certain kinds of analytical problems but which pose serious difficulties in other problems. These sources cannot survive in conventional system vacuums. If one wishes to gather information from the other signal channels activated by electron beam bombardment it is necessary to provide sufficient current to allow an acceptable signal-to-noise ratio. It is possible through careful design to provide a high brightness field emission source which has the capability of providing high currents as well as high current densities to a specimen. In this paper we describe an electrode to provide long-lived stable current in field emission sources.The source geometry was based upon the results of extensive computer modeling. The design attempted to maximize the total current available at a specimen.

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Low-workfunction field-emission source for high-resolution EELS

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100125592 ◽

1987 ◽

Vol 45 ◽

pp. 132-133

Author(s):

P. E. Batson

Keyword(s):

High Resolution ◽

Energy Loss ◽

Electron Probe ◽

Collection Efficiency ◽

Electron Sources ◽

Wien Filter ◽

Half Angle ◽

Thermal Emitter ◽

Electron Energy Loss ◽

Intrinsic Energy

In recent years,instrumentation for electron energy loss spectroscopy (EELS) has been steadily improved to increase energy resolution and collection efficiency. At present 0.40eV at 10mR collection half angle is available with commercial magnetic sectors (e.g. Gatan, Inc. and VG Microscopes, Ltd.), and 70meV at 10mR has been demonstrated by use of a Wien filter within a large deceleration field. When these high resolution spectrometers are coupled to the modern small electron probe instrument, we obtain a tool which promises to reveal local changes in bandstructure and bonding near defects and interfaces in heterogeneous materials.Unfortunately, typical electron sources have intrinsic energy widths which limit attainable spectroscopic resolution in the absence of some monochromation system. For instance, the W thermal emitter has a half width of about 1eV.

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Electron holography of interfaces in electroceramics

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100151271 ◽

1993 ◽

Vol 51 ◽

pp. 1088-1089

Author(s):

Vinayak P. Dravid ◽

V. Ravikumar ◽

Richard Plass

Keyword(s):

Space Charge ◽

Direct Evidence ◽

Materials Science ◽

Theoretical Work ◽

Electron Holography ◽

Resolution Limit ◽

Interference Phenomenon ◽

X Ray ◽

Electron Sources ◽

Science Community

With the advent of coherent electron sources with cold field emission guns (cFEGs), it has become possible to utilize the coherent interference phenomenon and perform “practical” electron holography. Historically, holography was envisioned to extent the resolution limit by compensating coherent aberrations. Indeed such work has been done with reasonable success in a few laboratories around the world. However, it is the ability of electron holography to map electrical and magnetic fields which has caught considerable attention of materials science community.There has been considerable theoretical work on formation of space charge on surfaces and internal interfaces. In particular, formation and nature of space charge have important implications for the performance of numerous electroceramics which derive their useful properties from electrically active grain boundaries. Bonnell and coworkers, in their elegant STM experiments provided the direct evidence for GB space charge and its sign, while Chiang et al. used the indirect but powerful technique of x-ray microchemical profiling across GBs to infer the nature of space charge.

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Quantitative analysis by reconstruction of HREM focal series

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100171432 ◽

1994 ◽

Vol 52 ◽

pp. 740-741

Author(s):

W. Coene ◽

A. Thust ◽

M. Op de Beeck ◽

D. Van Dyck

Keyword(s):

Phase Retrieval ◽

Image Plane ◽

Initial Guess ◽

Recursive Least Squares ◽

Objective Lens ◽

Electron Wave ◽

Electron Sources ◽

Original Algorithm ◽

Coherent Field ◽

Direct Interpretation

Compared to conventional electron sources, the use of a highly coherent field-emission gun (FEG) in TEM improves the information resolution considerably. A direct interpretation of this extra information, however, is hampered since amplitude and phase of the electron wave are scrambled in a complicated way upon transfer from the specimen exit plane through the objective lens towards the image plane. In order to make the additional high-resolution information interpretable, a phase retrieval procedure is applied, which yields the aberration-corrected electron wave from a focal series of HRTEM images (Coene et al, 1992).Kirkland (1984) tackled non-linear image reconstruction using a recursive least-squares formalism in which the electron wave is modified stepwise towards the solution which optimally matches the contrast features in the experimental through-focus series. The original algorithm suffers from two major drawbacks : first, the result depends strongly on the quality of the initial guess of the first step, second, the processing time is impractically high.

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