Scanning microscope uses a field-emission tip for the electron source, an electron gun that simultaneously accelerates and focuses electrons from the source, and one auxiliary lens to produce a final probe size at the specimen on the order of angstroms

Chapman, G. L.

Jung, E. A.

Lewis, R. N.

Van Loon, L. S.

Welter, L. M.

English

NASA Technical Reports Server

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October 1969	 Brief 69-10603 
AEC-NASA TECH BRIEF 
FES
AEC-NASA Tech Briefs describe innovations resulting from the research and development program 
of the U.S. AEC or from AEC-NASA interagency efforts. They are issued to encourage commercial 
application. Tech Briefs are published by NASA and may be purchased, at 15 cents each, from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Flexible High-Voltage Supply for 
Experimental Electron Microscope 
Fig. 1. Block Oiog,o,o; Vi. Voltage Applied to 
Field-Emission Tip; VO. Accelerating Voltage 
The problem: 
To develop a power supply to operate a new scan-
fling electron microscope. Commercially available 
microscopes use high-voltage supplies typically 
providing output voltages ranging from 10 to 100 kv, 
output currents of 500 iza, and instabilities and 
ripples on the order of 10 parts per million (ppm).
A filament electron source, referenced to the high-
voltage terminal, is heated to the appropriate tem-
perature with radio-frequency power supplied through 
a high-voltage isolation transformer. The new scan-
ning microscopes, using field-emission sources and 
energy-analyzers, however, require modified power 
supplies.
(continued overleaf) 
This document was prepared under the sponsorship of the Atomic 
Energy Commission and/or the National Aeronautics and Space 
Administration. Neither the United States Government nor any per-
son acting on behalf of the United States Government assumes any
liability resulting from the use of the information contained in this 
document, or warrants that the use of any information, apparatus, 
method, or process disclosed in this document may not infringe pri-
vately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19690000557 2020-03-16T18:26:23+00:00Z
The solution: 
A system of power supplies for operating a new 
scanning electron microscope. The high-voltage 
supply is variable from 0 to 30 kv in steps of 0.58 v; 
it has a peak-to-peak ripple of 50 my and an insta-
bility of 4 ppm/hr. A corona-free "hot top" provides 
ample space for circuits referenced to the high-volt-
age output, and includes a 0.6-to-1.6-kv supply for 
a field-emission electron source. This supply exhibits 
an instability of 20 ppm/hr and a peak-to-peak ripple 
of 10 my. Use of rechargeable batteries as an energy 
source, within the hot top, eliminates noise and leak-
age problems typically encountered when high-volt-
age isolation transformers are used for this applica-
tion. 
How it's done: 
The new scanning microscope (Fig. 1) uses a field-
emission tip for the electron source, a new electron 
gun that simultaneously accelerates and focuses elec-
trons from the source, and one auxiliary lens to pro-
duce a final probe size at the specimen on the order 
of angstroms. Since electrons are emitted from the 
field-emission tip when the voltage is on the order of 
1 to 3 kv, the conventional filament supply can be 
eliminated and replaced with a d-c-voltage supply. 
This supply is specified to have an output voltage 
variable from 0.5 to at least 1.5 kv with the vernier 
control having a resolution of 100 m y, to have an in-
stability less than 20 ppm/hr and a peak-to-peak 
ripple less than 10 m y, to provide at least 100 ALa 
while in regulation and to current-limit at about 1 ma, 
and to produce no overshoot when activated and to be 
operative with the high voltage (VO) applied. 
The current from the field-emission tip usually 
ranges from 0.1 to 100 pta, but only a very small por-
tion is allowed to pass through the aperture in the 
first anode and is used as beam current. In fact the 
leakage current and beam current, which typically 
total less than 0.05 ia, make up the entire load cur-
rent on the VO supply. The VO supply is specified 
to be variable from 0 to 30 kv, with the vernier con-
trol having a resolution of at least 1 v, to have an 
instability less than 4 ppm/hr and a peak-to-peak
ripple less than 100 my, to provide at least 0.1 ia 
while in regulation, and to produce no overshoot when 
activated and to be undamaged by overloads. 
Normal operation of the new microscope requires 
the two voltage supplies specified above. In addition 
the surface of the field-emission tip eventually be-
comes contaminated and requires periodic cleaning 
to keep the emission current stable. This cleaning 
entails pulsation of a current through the filament 
upon which the tip is mounted; the contaminants are 
boiled off by conduction heating. The tip flasher is 
specified to deliver a current ranging from 6 to 10 
amps, to have a compliance voltage of at least 10 v, 
to provide a current pulse adjustable in width from 
0.05 to 0.5 second, and to be operative while the high 
voltage VO is applied. 
In addition the new power supply is easy to serv-
ice, includes an electrometer for monitoring leakage 
current or tip current, and provides space and power 
for additional circuits referenced to the high-voltage 
terminal. 
Notes: 
1. Manufacturers or modifiers of electron micro-
scopes may be interested. 
2. Inquiries concerning this innovation may be di-
rected to:
Office of Industrial Cooperation 
Argonne National Laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Reference: B69-10603 
Source: R. N. Lewis, E. A. Jung, L. M. Welter,
L. S. Van Loon, and G. L. Chapman
Electronics Division
(ARG- 10482) 
Patent status: 
Inquiries concerning rights for commercial use of 
this innovation may be made to: 
Mr. George H. Lee, Chief 
Chicago Patent Group 
U.S. Atomic Energy Commission 
Chicago Operations Office 
9800 South Cass Avenue 
Argonne, Illinois 60439
S 
Brief 69-10603	 Category 01., 02


Flexible high-voltage supply for experimental electron microscope

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