Brightness and virtual source size of a supersonic deuterium beam

The remarkable achievement of atomic resolution by low voltage point projection microscopy has revived interest in this instrument, and, since resolution is approximately equal to virtual source size, demonstrates field-emission from tip regions of atomic dimensions. Ray-tracing calculations show the aberration coefficients and size of the virtual source to be subnanometer. The brightness of such a nanotip has been measured to be 7.7 × 1010 A cm -2 sr -1 (at 100 kV), somewhat greater than conventional cold field emitters or synchrotrons. The images require the theory of transmission LEED for interpretation and are always out of focus by the tip to sample distance zl. Their relationship to HREM images and coherent CBED is discussed elsewhere The instruments hold promise for imaging small organic molecules (across holey carbon grids), LB and other thin organic films where radiation damage is dominated by inner-shell processes.

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Development of a conical anode Fe-gun for low voltage SEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100106958 ◽

1988 ◽

Vol 46 ◽

pp. 978-979

Author(s):

T. Miyokawa ◽

S. Norioka ◽

S. Goto

Keyword(s):

High Resolution ◽

Field Emission ◽

Low Voltage ◽

Irradiation Damage ◽

Cold Cathode ◽

Virtual Source ◽

Source Position ◽

Electrostatic Lens ◽

Electrostatic Lenses ◽

Wide Range

Field emission SEMs (FE-SEMs) are becoming popular due to their high resolution needs. In the field of semiconductor product, it is demanded to use the low accelerating voltage FE-SEM to avoid the electron irradiation damage and the electron charging up on samples. However the accelerating voltage of usual SEM with FE-gun is limited until 1 kV, which is not enough small for the present demands, because the virtual source goes far from the tip in lower accelerating voltages. This virtual source position depends on the shape of the electrostatic lens. So, we investigated several types of electrostatic lenses to be applicable to the lower accelerating voltage. In the result, it is found a field emission gun with a conical anode is effectively applied for a wide range of low accelerating voltages.A field emission gun usually consists of a field emission tip (cold cathode) and the Butler type electrostatic lens.

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Electron sources: Past, present, and future

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100149659 ◽

1993 ◽

Vol 51 ◽

pp. 764-765

Author(s):

David C Joy

Keyword(s):

Glass Tube ◽

Source Size ◽

Electron Gun ◽

Operating Parameters ◽

Operational Parameters ◽

Electron Sources ◽

Difficult Decision ◽

Probe Size ◽

Wide Range ◽

Overall Performance

The electron source is the most important component of the Scanning electron microscope (SEM) since it is this which will determine the overall performance of the machine. The gun performance can be described in terms of quantities such as its brightness, its source size, its energy spread, and its stability and, depending on the chosen application, any of these factors may be the most significant one. The task of the electron gun in an SEM is, in fact, particularly difficult because of the very wide range of operational parameters that may be required e.g a variation in probe size of from a few angstroms to a few microns, and a probe current which may go from less than a pico-amp to more than a microamp. This wide range of operating parameters makes the choice of the optimum source for scanning microscopy a difficult decision.Historically, the first step up from the sealed glass tube ‘cathode ray generator’ was the simple, diode, tungsten thermionic emitter.

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