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Oct, l, 1946.e
ART
P. c. SMITH
2,408,487
ASCERTATNING THE ATOMIC STRUCTURE OF MATERIALS
Filed Feb. 29, 1944
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'Perry l’.
Cîîtorneg
Patented Oct. 1, 1946
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2,408,487
orricla:A
f Urufrsov STATES PATENT
2,408,487
ART OF ASCERTAINING THE ATOMIC
`
STRUCTURE 0F MATERIALS
'
‘
Perry C. Smith, Moorestown, N. J., assignor to
Radio Corporation of America, a corporation _.
of _ Delaware
Application rFebruary 29, 1944, Serial -No.’524_,42_4
l
_ y4 claims. (cl. 25o-49.5)
This invention relates to the art of ascertain
ing theßatomic -structure of materials> and has
special reference to the rprovision of an improved
method of and means for producing, recording
and interpreting diiîraction patterns.
In the usual diffraction apparatus for deter
mining the atomic structure, of materials, the
electrons or- other rays (e. g., X-I‘ays) which
strike, are which emanate from, the specimen are
focused upon a photographic plate or film. Prop
erly interpreted, the spacingand intensity ofthe
rings in the resulting photograpic image or “pat
tern” provide .an indication of the atomic struc
ture of the specimen and this makes it possible
to ascertain changes in the specimen material
when the said material is subjected to various
treatments and chemical processes. ,
~
2
` Certainv details of procedure and construction,
together withv other objects and' advantages willk
be apparent and the invention itself- will be best
understood by reference to Atheti-‘ollowing speciñ- l
cation
and to the
accompanying drawing,v
wherein:
Figure 1>> is a schematic View of an electron
__ - dif-~
fraction “camera” embodying the invention andv
including certain Vauxiliary translating and re-.
cording
apparatus,
_
_
_
_
_
,
,.
..
,
Figure 2 is a graph of a diiîraction pattern-pro
duced in the “camera” of Fig. 1, and ,
Y _
Fig. 3 is a schematic view showing the arrange
ment of the electrodes of the electron multiplier
“pick-up” in the diiïracticn instrument >of Fig. 1..
In Fig. l of the ydrawing there is shown an elec
tron dilïraction camera, indicated generally at |-,
comprising an >evacuable chamber 3 c_:ontainingga'y
vThe examination 3 and interpretation ofsuch
photographs requires the use of a precision inf
cathode 5, a beam forming anode 1, a specimen
strument, such for example as a >microph‘otom 20. holder 9, an .electron lens system_ (exemplified by
eter, and can be entrusted only to the most skilled
an electro-magnet)- l lV and a pivotedfluorescent
technicians..r Further, such work is very tedious
and is complicated and limited not only by hu
man frailities and mechanical inaccuracies in the
screen orv cassette I3„all,arranged in-_spacedarray
in the order named along ,theccntralagispfztha
chamber 3. The elements thusfar described may
measuring instrument, but also by “light scat 25 be of any conventional design (see for example
tering” and other undesired phenomena peculiar
U. S. Patent No. 2,275,234) and are adapted to
to the particular photographic emulsion em-v
produce a beam l5 made up of electrons diiiracted
ployed.
Accordingly. the principal object of the present
invention is to obviate the foregoing and other
less apparent objections to present day methods
of and means for producing, recording and inter
_ preting diffraction patterns.
from the specimen. As is Well known to those
skilled in the art, the invisible rays of which the
beam l5 is comprised, are converted into a visible
image> of the diffraction ray pattern when the
plate I3 is moved into the path of said rays or
“beam." In the instant case however, the screen
or plate I3 is shown swung upwardly out of the
As will hereinafter more fully appear, the ob
jects of the present invention are achieved by 35 path of the beam; thus, the only diñraction pat
producing a diiïraction ray pattern in space, then
tern now present within the Vacuum chamber 3
translating the rays of which the pattern is com
exists merely in space. (Such a pattern would
prised into an electric current (or voltage) of a
be invisible to an observer looking into the cham
value proportionate to the intensity of said rays
ber through one of the Viewing windows or ports
at diil’erent points along a radius of said pattern 40 I1 with which the “camera” is provided.)
and then plotting or otherwise recording a graph
In carrying the present inventioninto effect,
of said current as a function of said radius. The
the evacuable chamber 3 is provided with an elec
translation or conversion of the rays (of which
tronic amplifier device I 9 such for example as
the diffraction pattern is comprised) into an elec
the electrode assembly of an “electron multiplier”
tric current is effected directly or by means of a 45 (say an RCA type 931A), capable of converting
-secondarily-emissive electrode assembly and the
the rays l5 of which the diffraction pattern 1s
plotting and recording of the current may be done
comprised into an electric current (or voltage) of
either manually, with the aid of a suitable meter,
a Value proportionate to the intensity of said
or automatically as by means of a facsimile re
rays. This electrode assembly I9 is mounted for
corder or analogous device. In any event, the 50 movement as on a micrometer screw 2l along a
resulting graph or curve contains all of the in
radius of the beam and is provided with a mask
formation required to be known in the interpre
23 having a slot 23a therein which is arranged
tation of a diffraction pattern and may be read
in register with the first multiplying stage 4| of
by an unskilled observer without the aid of addi
the device. The vacuous space about the ampliñer
tional equipment.
55 I9 and in the chamber 3 is continuous; hence the
2,408,487
3
rays l5 which pass through the open slot 23a
impinge directly upon the electrode 4I and gen
erate a secondary-electron current proportionate
to the intensity of the rays at the particular point
on the radius of the image to which the »said elec
trode 4l is presented. As indicated in Fig. 3 the
secondary-electrons emitted from the “cathode”
4| are directed by ñxed electrostatic ñelds along
fixed paths to the dynode (secondary-emitter)
42. The electrons impinging on this dynode sur;
face produce many other electrons;A the number.`Y
depending on the energy of the impingingîelec:
trons.
These secondary electrons are then di
rected to the next dynode 53 and‘knock out moref
new electrons.
This multiplyingprocess is-> re
peated in each successive stage (44 to 50 inclu»
sive) until those emitted íromth'enlast dynode,_
From the foregoing it is apparent that the pres
ent invention provides a simple and reliable
method of and means for producing recording
and interpreting diffraction patterns.
I claim as my invention:
l. In combination, means for producing a dif
fraction ray pattern ofj'a specimen, in a plane
spaced from said specimen, means mounted for
movement along a radius of said pattern for con
-' verting the diffracted rays which fall along said
radius'intofan electromotive force, and means for
measuring'l said electromotive force as a function
of »said radius.
2i In“combination;V means for producing a dif
fraction ray pattern of a specimen in a plane
spaced from said specimen, means mounted for
moyementalongïaradius of said pattern for con
vertingvthe di?fracted rays which fall along said
50, are collected by the anode 5I and constitute
radius into an electric current, and means for re
the current utilized in the output circuit;
The relative position of the amplifier I9 along 20 cording a graph of said current as a function of
said'radius.
’
the radius of thediffraction pattern; lâfisfindi
3:. Electron diiîraction apparatusvcomprising anv
cated uponk a» scale 25 whichY is `read in> conjunc=
evacuable chamberk containing» means for creat@
tion with a pointer ‘21’ on the screw> I9’.-- The out`ing'an electron’beam Aand- for directing said beam»
putl of’ the ampliñerl I9" is~ shown connected
upon a specimen, an electron lens for; forming
25:
through a switch 29î'to a recorder 3l which will
the electrons diffracted fromesaidëspecimen into
be understood to be driven in eynchronism vwith
an electron diffraction vpattermand'for-- projecting
the screw 2 I. The recorder 3| thus automatically
saidv pattern towarda plane in‘said evacuab'le
plots av graph orcurve -showing the current gen
chamber, aA secondary-electron emissive ampliñ’er
erated bythe ampliñer I9'V as a' function' of the
mountedl forl movementN in said' piane4 alongv a
radius of the diffraction pattern |5î Alterna 30 radius of said diffraction pattern andiresponsive
tively, the output of the translating' device i9
to the impress of‘said'diiîractedïelectrongthereon;
may be connected through the switch 29 to a
means for moving> saidgampliîñer along< said radius
suitableemeter‘33', and 'thel meter‘ readings plotted
against thelscal’e 251 In either event'a graphy
intensity andfspa'cing ofthe diffractionrings and
in said plane, and rnean's'for‘indicatingztliev outr
put of said amplifier.
4. The invention asf'set`forth' in claimßl and
thus ' contains all’of ‘the informationv necessary to
type and is adapted to-,recordthe'outputof said
(see Fig; 2) `, is »obtained which shows‘the' relative
beknown in the interpretation off av diiîractiorr
pattern. The ordinatev of the curve of Fig; 2ïand-
wherein said indicating means' isxof- the recording:
ampliiier as a function of‘the radius ofV said/elec
the-markings of "the sca1e`25 Fig. l, areß’shown 40 tron diffraction pattern..
calibrated in fractions of- an inch; obviously; how--
ever', they may becalibrated in¢Angstrom-units
of ‘atomicspacing-g if desired.’ .
PERRY." C. , SMITH."
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