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Sept. 24, 1946.,
2,408,287
c. H. BACHMAN
ELECTRON MICROSCOPE
Filed Feb. 1, ‘1944
'Fi
2.
F33.”
.30
3.9
33
Inventor“:
Charles H. Bachman,
61
Hus Attor‘neg.
2,408,287
Patented Sept. 24, 1946
~ UNITE-D STATE S PATIENT-‘OFFICE
~ Charles II.
General
Bachman,“ Scotia,'-YYN-.‘Y., assignor to I
Electric ‘Company, I a >7 corpor
tion ‘_ of
New York
vApplication February 1, 19411, _$erial Nor
' 5 Claims.v
'" '
(Cl. 250-495) ~
It is .an'objectvof the invention to provide a new
in the appended claims. The invention itself
together “with vfurther objects and advantages
thereof'may best be_understood- by reference to
the following description-taken in connection with
thegacco'mpanying' drawing in which Fig. 1 repre
and‘ improved ?uorescent screen for an electron '
sents ‘diagrammatically ‘an end section of an elec
microscope.‘
Fig.‘ 2 is‘ a cross-sectional view showing'the ?u
' The present invention relates to electron opti
cal apparatus particularly adapted for themiOl‘U
scopic examination of electron pervious objects.
_
_
v
tron optical system'employing my invention ‘and
p
f It, is known that objects may be microscopically
orescent"scre'en supporting arrangement of ‘the
examined by the rays of an electron beam which
transra'diates the object,’ ‘the, beam' ‘passing 710
invention.
’
'
'
‘
'
providedwith thelch'aracteristics thereof. Such
, “Referring ‘to Figs. 1" and 2 jointly‘, ‘there is
shown ‘an ‘electron microscope 'comprising an ‘
that there ‘are two fundamental limitations in
con?nes the" emitted electrons to a "narrow beam
throughithe object and in'this passage being
elongatedvacuum-t'ight container H] of a tubular
an "electron beam may be refracted by appro
metal‘ construction; Atone end’ of ‘the‘container,
priately conditioned ?elds and the’ beam may be
impinged upon a ?uorescent screen; an image 115 there isi'provided a glass insulator I l’ which serves
to support‘ an electron source in" the :form of ‘a
being‘ constructed on. the > screen, in accordance
?lamentary ‘cathode-121 The cathode I2 is sur
withthe characteristics given to 'the'bea'm in ‘its
rounded by ‘a tubularm‘etal member'l? which
passage ‘through the, object. It hasbeen observed.
'
with 'res'pect'to an
the use of ?uorescent screenin? electron micros- , 20 and is ‘cooperatively ‘positioned
M which is in contact with
copy where an‘ electron beamjis impingedjupon
' apertured electrode‘
I the metal envelope part l0.- The opposite end of
theen'velo'pe I0‘ is sealed ‘by ‘a glass window ‘I5.
are ‘thecsize of thejphosphor or fluorescent par
ticlesf and the" physical thickness'of the screen.‘ ' ' A-?uorescentviewing screen" I 6 is positioned with"
and passes through the ‘screen; ' These limitations
in thejtubel?- in front of vvthe window [5.
The limitations of course are of consequence only
when optical magni?cation of an’ image on ‘the
screen is desired7 In ‘this'case,>as;the_image_on
‘a ?uorescent screen
' Inthe'normal use of‘ the'apparatus, the en
velope l0 and the apertured electrode I4 ‘are
maintained at "g'round-potentialand the cathode
enlarged to magni?cations
of the order of, 25 diameters,_ thethickness 0f the
‘screen,‘that is,‘ the number of layers'of phosphor
or ?uorescentparticles causes the edges of the
is ‘maintained at a high negative potential, for
@330 example; being ‘connected to 'a ‘potential source
‘
hand,'the sizeof the individual phosphor particles
can beso controlled that this factor ‘does not enter
'as/a limitation of magni?cation until‘ enlarge
ments of the order of several hundreddiameters
'
"l1 "so that electrons
the cathode are promoted axially
of the contain‘er-with'the objector producing a
‘image tolbecome blurred or fuzzy. ' Onthe other
35
' are‘ reached.’ Improved magni?cation may be at
visible image ‘on the fluorescent vscreen l8.
Between the cathode I2 and the image-‘repro
ducing'screenl‘lt there is provided object
sup
l‘9.c In the
‘porting- means ' indicated generally at
intended use of the apparatus, this means is to~be
tained, therefore; if asu?iciently thin fluorescent
screen,“ preferably consisting of: a single player of 1 employed as a support for an object to be trans
‘?uorescent particles, may be constructed satis :40 radiated *by an electron beam, the beam being
‘factorily without the occurrence of tiny‘ holes due
to ‘incomplete coverage of a screen surface dele
teriously a?ecting satisfactory‘imaging of ‘the '
passed-through the object and in the passage as
suming the characteristics of the object. A sup
porting ‘structure may ‘be ‘provided in connection
~
7
.withr-the object supporting means l9 and may
:It is an .iobject of my invention to provide im- _, rlikewise employ appropriate clamps or other
"proved' means by which very thin - ?uorescent ‘ 'means (notshown) forholding an object with its
'magnified object.’ 1
screens may be successfully‘emplo'yed in electron
‘optical studies or .objects.‘ ‘
~
.I
'"An‘ important feature ‘of the invention consists
vinran apparatus arrangement by which thin ?u
crescent screens used in electron
optical' studies‘ a
‘are movedilaterally' to effect a smoothing out of
Tall irregularities in the screen structure'and with
surface, in exposed position to the electron
beam20.
‘I
,
v
y.
_
.
.
,
V
In order that the electron beam,_after modi?
cation in accordance with the structural charac
ter ofrthe object under investigation as the beam
caused to pro
'transradiate's' the-object,
may' beofthe
visible
image
object in
videv an enlarged
the micro
l-s'u?lcient frequency to eliminate visual effects. '
accordance with the ‘intended: use ofthrough‘
the
' ' The features of the'inv'ention' whichIdesi‘re to 155 “scope; the beam 20,v after passing
\protect herein‘ are pointed out with particularity:
2,408,287
3
object, is caused to pass through an electron lens
system of known character. In the drawing, the
lens system is illustrated as of the electrostatic
type, although a lens system of the magnetic type
may be ‘employed. The lens system comprises a
series of three diaphragms, numbered 22-24, in
clusive. The diaphragms 22 and 24 are main
production of the electron image are encoun
tered.
To eliminate any possible visual defects in the
reproduction of the electron image, as the screen
I6 is moved laterally, the frequency of motion
of screen l6 Of course must be greater than the
?icker frequency of the human eye. To this end,
a frequency ofv 20 cycles-per second or greater
at ground potential and the intermediate dia
phragm 23 may be insulatingly supported and is _10_ should be employed in movement of rod 35. Such
vibration of the rod 35 may be obtained by means
biased to cathode potential through a connection
'of an electrical coil 40 energized from a suit
25 which is brought into the microscope enclosure
able source of alternating voltage 4| through a
through an insulating bushing 26. Because of the ‘ ‘control
switch 42. An armature 43 may be pro
resultant di?‘erence in potential between the dia
vided at they lower. end of rod 36 to be vibrated
phragm 23 and diaphragms" 22 and 2‘, lens ?elds 15 by coil 40'.
~
are established between these diaphragms which
When the lens .system 29 is replaced by a cam
have the eifect of refracting the electron beam in
era for photographing the image produced on
a manner analogous to the refraction of a light
screen
IS, the need for eliminating ?icker effect
beam by an optical lens. Additional lens ?elds
is no longer present so that at such times the
may be employed in the electron microscope 20 frequency
of vibration of screen [6 may be re
where so desired.
duced
and
the screen may be moved manually
Means are provided for optical magni?cation
tained at the potential of the casing H1, that is,
during the exposure time.
of the image formed on the ?uorescent screen I6
and this means is represented conventionally as
»
'By the present invention, in an electron mi
croscope of the type described above, a ?uores
an optical lens 29 through which the beam of 25 cent screen may be employed. which is made up
visible radiation 28. projected through window
of a single layer of ?uorescent particles; Such
I5 from ?uorescent screen I6. is caused to pass.
a screen usually is not suitable for electron mi
The fluorescent screen I 5 shown in plan View
croscopic examinations, since the coverage of the
in Fig. 2 comprises a frame member 30 which
screen
under such conditions is only about 60%
Inav be either circular or recta'ngnlar in shape 30
complete. In the normal microscope, therefore,
and which supports a transparent window 3|
more effective coverage of the screen surface is
upon which is deposited a thin coating of a suit_
able ?uorescent material 32.
Preferably. the
obtained by adding additional layers of‘ ?uores
cent material. In a microscope, however, in
coating 32 consists of a minimum number of
lateral shaking of the screen is provided,
lavers of small particles Of'a suitable phosphor. 35 awhich
single layer of ?uorescent particles may be em
The frame 30 is suspended within member In by
ployed and the shaking produces the effect of
means of a set of swine members 33 which pro
a completely covered very thin screen having re_
virie a good conductive connection, between
duced light output because of the decreased
screen l6 and tube H). To one edge of the frame
number of ?uorescent particles.
'
30. there is attached a rod member 35 which ex 40
While
I
have
shown
a
particular
embodiment
tends through an opening 35 in tube 10 and
of my invention, it will of course be understood
passes through a bellows device 31. the bellows 31
that I do not wish to be limited thereto since
providing a seal across opening 36. The member
various modi?cations may be vmade, and I con
35 has a nnrtirm extending pwterio-rlv of the he]
lows 31 by which motion may be imparted to 45 template by the appended claims to cover any
such modi?cations as fall within the true spirit
screen [6 to produce lateral movement of this
and scope of my invention.
screen.
What I claim as new and desire to secure by
In order to prevent any motion imparted to
Letters Patent of the United States is:
screen I6 bv actuating rod 35 from producing
1. The combination, in an electron micro
axial motion of the screen to aiTect either the 50
scope, of a viewing screen coated with a thin
electronic or optical focus. a plurality of guide
layer of ?uorescent material and means for pro
members 39 are attached to the inner surface
ducing lateral motion of said screen to reduce
of container Ill. The guide members‘ 39 may be
blurring of images produced on said screen.
provided with slots or ?ngers at one of their ends
2. An electron microscope comprising an evac
and the screen I 6 may be restrained by these 55
uated container having a ?uorescent screen po~
?ngers from axial movement and yet permitted
sitioned therein, means for projectingv a beam
to move in a plane perpendicular to the axis of
of electrons upon said screen, means for sup
the container I0.
porting an object to be examined in the path
Bv the screen supporting arrangement de
of
said beam, and means for vibrating said screen
scribed, the screen 16 may be moved laterally 60
in a plane substantially transverse to said beam
and the eifect of any kind of screen irregulari
to reduce blurring of the image of said object
ties, such as holes, dirt specks, and similar de
produced on said screen.
‘
fects in the phosphor coating on screen l6, which
would normally produce distortion in optically
3. An electron microscope system comprising
enlarged images on the ?uorescent screen I 6 is 65 an evacuated container having a transparent
wall, a ?uorescent screen supported within said
eliminated, Since the electron beam 20 always
container‘ in front of said wall, means for pro
bombards the same points in space, as the screen
I6 is shifted in a plane perpendicular to the
beam, the effect of smoothing out all the irreg
ularities of the above-mentioned type in the 70
screen structure is obtained. So long as the mo
tion is con?ned to a lateral direction and there
is not su?icient axial motion to a?'ect either elec
tronic or optical focus, no ill effects inv the re
screen, means external of said container for pro
ducing optical enlargement of the' image on said
screen, and means for vibrating said screen in
75 a plane substantially transverse to said beam to
reduce blurring of said enlarged image due to
2,408,281
non-uniform distribution of ?uorescent particles
on said screen.
4. In combination, a viewing ‘screen coated
with a thin layer of fluorescent particles, means
for producing an image to be viewed on said
screen, optical means for enlarging said image
to a degree such that irregularities in the depo
sition of said particles on said screen produce
objectionable blurring of said enlarged image,
and means for vibrating said screen in a plane
transverse tov the optical axis of said optical
means to reduce said blurring.
5. The combination, in an electron microscope
having a vacuum-tight container, of a ?uorescent
screen resiliently supported within said con
' tainer, means for projecting an electron beam on
an image thereon, means
said screen to produce said image, and means for
for optically enlarging
vibrating said screen in a plane transverse to
' said beam to reduce
image.
blurring in said enlarged _
CHARLES H. BACHIVLAN.
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