Cryo-electron microscope with high field superconducting lense

Fernandez-Moran, H.

English

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LOW TEMPERATURE ELECTRON MICROSCOPY WITH 
HIGH FIELD SUPERCONDUCTING LENSES 
Paper to be presented at the Sixth International 
Congress for Electron Microscopy 
Kyoto, Japan 
August 27 - September 4, 1966 
H. Fernandez-Moran /-' 
Department of Biophysics 
University of Chicago 
Chicago, Illinois U.S.A. 
Following our first successful electron microscopy experiments with 
high field superconducting lenses operating at liquid helium tempera- 
ture (la), a comprehensive research program is being pursued with dif- 
ferent types of cryo-electron microscopes concentrating on 2 approaches: 
1. Cryo-electron microscope optical bench system (Fig. 1) using high 
field superconducting niobium-zirconium solenoid lenses in liquid helium 
Dewars, operating at 4 to 32 kG without pole pieces, and with modified 
objective, and objective-projector pole pieces. An additional current 
vernier control circuit for the superconducting objective solenoid is 
used in conjunction with a 25 A regulated power supply to permit adjust- 
able current changes of for achieving reproducible j!superfine" r 
focusing, orders of magnitude better than conventional systems. This 
device, specially developed for our lenses by D. Kasun and associates of 
Westinghouse Cryogenics Div., consists of a low field two-winding super- 
conducting toroid with its secondary connected in series with the main 
solenoid. 
in the solenoid circuit, altering the persistent current value, and 
results in an incremental change of field in the main solenoid. After 
optimum focusing adjustment is achieved, bransfer of t o r o i d  primary t o  
persistent mode places the entire system in a lossless, completely stable 
condition, Improved point cathode sources and highly stabilized 50 kV 
accelerating potential were used, taking special precautions t o  minimiz-e 
Once gorrec6 
focus of test specimens at electron optical magnifications of ~OOX-~O:OOOX 
is attained, the superconducting solenoid system,is switched into persis- 
tent current mode. 
maintained without any external lens current source are of an unprecedented 
i 
Energizing the toroid primary changes the t o t a l  flux linkage 
1, magnetic and electrical field perturbations. 
c 
The high quality images (50-100 8, resolution) thus 
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https://ntrs.nasa.gov/search.jsp?R=19680009752 2020-03-12T09:30:27+00:00Z
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4 
aegree of stability, permitting exposures of up to several minutes with 
lolw intensity illumination for direct photographic recording on high 
resolution films. The same area can be contfinuously recorded at 5-15 
mirlute &intervals over a 10-hour period under carefully controlled con- 
ditions without detectable image changes, demonstrating typical long- 
term superstability (Fig. 2a, b) . Combination of this unique stability 
af superconducting lenses with coherent micpobeam illumination - appears 
promising for practical realization of Gabor's wavefront-reconstruction 
microscopy. 
2. Special superconducting ob.iective lens in liauid helium cryostat 
which may be used as integral part of cryo-electron microscopes or re- 
place the objective lens in modified high resolution commercial electron 
microscopes. 
(Figs. 3, 4), designed- and built t o  our specifications by Westinghouse 
Co., comprises a main Nb-Zr coil (27,220 ampere-turns) with vernier coil, 
superconducting stigmators, persistent current switches and improved cur- 
rent control devices. Specimens are mounted on microstages of special 
design maintained at 4.2OK together with pole pieces of different types, 
including short focal length, single field condenser-objective pole 
pieces of iron or dysprosium, and trapped-flux Nb Sn lenses. Our micro- 
scope (Fig. 3) mounted on a 10-ton vibration isolated base, features ex- 
tensive magnetic shielding, ultrahigh vacuum ion pump system, improved 
field and T-F emission source, image intensifier and photographic record- 
ing. It is primarily designed for high resolution electron microscopy of 
biological specimens, examined preferably in the frozen hydrated state 
under ideal low-temperature conditions of minimized specimen contamination, 
radiation damage and thermal noise. 
The superconducting objective lens in a special Dewar 
3 
The valuable collaboration of A. Peuron, D. Kasun, F. Lins of 
Westinghouse Cryogenics Div., in key aspects of this work, the technical 
assistance of L. Ouwerkerk, R. Vicario, H. Krebs and discussions with 
Dr. K. Yada are gratefully acknowledged. This work was supported by 
National Institutes of Health Grant GM-13243, U. S. Atomic Energy Commission 
Contract AT( 11-1) -1344, National Aeronautics and Space Administ 
NsG 4-41-63 and the L. Block Fund of the University of Chicago. 
-.' 
1. H. 
H. 
REFERENCES 
Prdc. Natl. Acad. Sei., 53, 445, 
Fernandez-Moran: Science, - 148, 665, (1965r 
Fernandez-Moran: 
e *  Low Temperature Electron Microscopy with High Field Superconducting Lenses 
H.Fernandez-Moran,Dept.Biophysics, University of Chicago 
c 
Pig. 1. Cryo-electron microscope com- 
prising liquid helium Dewar with 
high field K b Z r  superconducting so- 
lenoid objective-projector lenses, 
supercoriductirig circuitry and power 
supply controlsj50 kV gun with 
point cathode;essential magnetic 
shielding arid accesscry cryogenic: 
equipmelit . 
- 
2 160line c. / ~ m  di TI" rac 5 i on c r o s s - 
grating replica reccrded at 5OkV, 
10,000 x eIectr.opt.(top);zO,OOOx 
(be1ow)with supei-cord. lens in per- 
sistent current mode continuously 
over lohour period.Unaltered images 
of first(a)and final(b)scries de- 
y,lonstraie unique long-term stabili- v. 
ELECTRICAL LEADS 
- 30mm 
SUPERCONDUCTING OBJECTIVE LENS AND ClOUiV HELIUM COLO STACE ASSENEL1 
FOR CRY0 ELECTRON YlCROSCOPE 
Fi-g.3.Special high resolution elec- 
tron microscope(mo2ified ~~-115) 
with supercorLductirig objective lens 
assembly, power supply and c o n i r o l s ,  
ultrahigh v4cuum ior, pmp(U1tek) 
system, extensive magnetic shielding 
image intensif'ier.I/loimted on 10 
ton vibration isolated base, 
Fig.4. Sketch of special supercon- 
ducting obJective lens in liquid 
helium Dewar (West inghou s e C ryoge- 
riic Div. )ccmprising:iron-encased 
: Ib-Zr  main coil with supercon4uct- 
iiig stigmators, vernier control 
circuitry,and central cryostat 
space for specimen microstage and 
'pole pieces I 


Low Temperature Electron Microscopy with High Field Superconducting Lenses

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