US 2771568 A
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Nov-. 20, 1956 K. H. STEIGERWALD 2,771,568
UTILIZING ELECTRON ENERGY FOR PHYSICALLY AND CHEMICALLY CHANGING MEMBERS Filed Nov. 28, 1951 2 Sheets-Sheet l INVENTOR. In: lelnzfmaaem 8/? fzpC 0a Nov. 20, 1956 K H. STEIGERWALD 2,771,568
UTILIZING ELECTRON ENERGY FOR PHYSICALLY AND CHEMICALLY CHANGING MEMBERS Filed Nov. 28, 1951 2 Sheets-Sheet 2 p x S 22 a w I 27 27 27A 32 c E. in
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I /W BY mu Z N M d Train 5K5 United States Patent UTILIZING ELECTRON ENERGY FOR PHYSI- CALLY AND CHEMICALLY CHANGING MEMBERS Karl Heinz Steigerwald, Mosbaeh, Germany, assignor, by
mesne assignments, to Carl Zeiss, Wurttemburg, Germany Application November 28, 1951, Serial No. 258,671
6 Claims. (Cl. 31531) My invention relates to a novel electrical apparatus for and methods of utilizing energy stored in an electron beam for performing work on bodies.
More specifically my invention contemplates concentrating an electron beam into a relatively high current density as for example at the focus plane of the electron beam. I may with this concentrated electron beam generate heat on a body located substantially in this focus plane. Generally, I transfer the kinetic energy stored in electrons moving at high velocities into an object which is to receive this energy and is to be physically, mechanically or chemically altered.
Heretofore if it was desired to vaporize a metal such as tungsten, the only practical means has been to apply heat by means of an adjacent heating element. The heating element being itself at a high temperature introduced impurities into the tungsten vapor stream.
I have discovered that I can overcome this disadvantage by generating localized heat at a relatively small spot in the tungsten body to be vaporized by impinging upon the tungsten body an electron beam which has been focused at the plane where the body is located. By this means, I can generate sufiicient heat to vaporize the tungsten while maintaining the areas adjacent the area of impingment at substantially lower temperature.
Accordingly, an object of my invention is to provide a novel arrangement of an electron beam for producing a high current density concentration of electrons on an object such as tungsten for vaporizing the metal therefrom.
I may then use such vapors for producing coatings on objects of any desired thickness including thicknesses of the order of the wave length of light and down to an atom thickness. I
Accordingly, a further object of my invention is to provide a novel apparatus and methods for using the energy of an electron beam to coat surfaces to any desired thickness.
Heretofore in controlling the path of an electron'beam the first focus plane thereof has been placed at a point interposed between the electron emitter and the anode. In this area there exist electric fields. Any attempt to place the material to be treated in this area would disturb the electric fields and accordingly would cause a distortion of the electric field and therefore of the electron beam. Moreover when the focus plane of the electron beam is between the emitter and anode the picture plane is wider and therefor produces insufiicient current density for useful work.
I have discovered an arrangement for placing the first focusing plane of the electron beam at a point which is outside the region between the electron emitter and the anode; in this region there are no electric fields to be distorted and sufficient space may be made available for vaporizing the material and coating another surface.
Moreover, by such an arrangement I may under my control extend the length from the electron emitter to -the work at a critically exact position at the focusing plane.
Accordingly a further object of my invention is to provide a novel arrangement for placing the first focus. plane of the electron beam beyond the anode with respect to the electron emitter.
In the control electrodes heretofore employed, the electrodes were usually placed in a plane at right angles to the axis of the electron beam. This caused the electron beam to focus close to the electron emitter and always between the emitter and the anode.
I have found that by a proper shape of the control electrode I produce a novel distribution of the equipotential lines which provide a sharply limited current density distribution over the area of the electron beam and which provides a longer focusing distance of my electron beam system.
Accordingly a further object of my invention is to provide a novel construction of control electrode.
Still a further object of my invention is to provide a novel arrangement of the control electrode with respect to the electron emitter.
These and other objects of my invention will be more clearly understood in connection with the specification which is to follow in connection with the drawings in which:
Figure 1 is a cross section of one embodiment of'my invention.
Figure 2 shows the equipotential lines produced by my novel control electrode.
Figure 2a shows a full range of equipotential lines be tween the cathode and anode.
Figure 3 is a detail of the control electrode.
In the drawing, the electron gun 11 comprising a tu-" 7 amperes.
Also mounted within the electron gun 11 in any suitable manner is a control electrode 19 having its upper portion 20 in the form of a cylinder and having an integral extension 21 of conical construction with an opening at its apex 22. A further integral extension 23 of the control electrode is cylindrical in shape.
The control electrode is connected over the conductor 24 to a potential source. The cathode is maintained at a potential of approximately 50,000 volts with respect to ground, and the control electrode is maintained over conductor 24 to a higher negative potential than the cathode by approximately to 300 volts. These voltages may be suitably regulated in any well known manner.
It will be noted that the electron emitter 15 protrudes through the apex opening 22 of the conically shaped extension 21 of the control electrode. In practice, I have found that the cathode is preferably a hairpin shape having a wire diameter of 0.15 mm. For my purposes, I have found that the electron emitter should protrude beyond the opening at the apex of the cone 21 by a distance prise preferably six conicaljsectors 25, insulated frc'vnl 2,771,568 Patented Nov. 20,1956,
each other as shown .in Figure 3. Each sector is maintained at suitable potential between each other and cathode of the order of 500 volts.
It will of course now be understood that the voltages of each of these sectors with respect to ground remain of the order of 50,000 volts.
To maintain these potential differences between the sectors, individual conductors corresponding to 24 are connected to each of the sectors 25 each having predetermined potentials applied thereto. Correspondingly, the
. cylindrical section 23 is also connected over its individual conductor cor-responding to conductor 24 for applying a predetermined voltage thereto.
The cylindrical section 23 may be also formed of a plurality of sectors, insulated from each other and each maintained at suitable potentials with respect to each other.
In the present illustrations however, the conical portions and the cylindrical portions are unitary members maintained at a common potential.
In Figure 2 I have shown in considerably magnified form a portion of the electron emitter, the equipotential lines andthe electron beam in the region of the control electrode.
As will be .seen, the cathode 15 protrudes beyond the conically shaped control electrode 21 by a distance equal to the diameter of the emitter wire. Adjacent to the electron emitter 15 there exists as is well known in the art, a space charge. The equipotential lines produced by the potential between the control electrode and anode assume theshapes shown by the lines 27, 27'.
It will be seen from Figure 20 that the equipotential lines follow the values of their adjacent electrodes.
The .-.50,000 volt equipotential line which is at the cathode or electron emitter potential follows generally theform of the cylindrical electrode 23 and the conical electrode 21. In Figure 2 the line closest to the cathode has a slight hump 27" adjacent the space charge zone at the cathode tip. The negatively charged electrons in the space charge zone are pulled out by this shape of the potential line, The equipotential lines thereafter rapidly straighten out this. hump and assume complete convex forms as. shown at 27 Figure 2a. The curvature of these lines further away from the cathode bccome'st-raight as a t 27l, Figure 2, and then concave as at- 27.
Because these potential lines apply an accelerating force to the electrons in a direction normal to the potential, the-electron stream is at'first widened as at 32' and. then accelerated inwardly slowly as at 32" by the potential lines 27 to produce a large distance to the focal p an.
It will ofcoursebe understood. that the equipotential linesin Figures 2 and 2a necessarily are not shown in their true dimensions as this is not possible in illustrating theprineipal functions of these lines.
Preferably the cross section of the electron beam should be circular. This is determined by the shape of the cathode, the space charge adjacent .thereto and the shape and potentials. of the various conical sectors 25. If because of an unsymmetrical shape of the electron emitter, the cross sectional area of the electron stream in the first instanceis elliptical, I have found that by a proper distribution of potentials applied to the individual conical sectors, I can reconstruct the;cross sectional shape of the electron stream to restore it to a circle.
Thus for example, in the case of an original elliptically shaped electron stream, I would increase the relative potential of those sectors opposite the long axis of the conical shaped electron stream causing the long axis to be reduced. I also decrease the potential of the sectors opposite the small axis of the sectors which enlarges thesmall axis and restores the cross sectional circular shape of the electron stream.
By using potential-distributions between the sectors which are. not chosen symmetrical to the optical-axis, one
can also secure deflections of the electron beams direc tion.
It will, of course, be understood that in referring to an increase ordecrease of potentials at the conical sectors, I am here referring to the relative voltages with respect to each other.
The diameter of the electron stream at its widest point for useful cases is between 0.5 to. 1.5 mm. For the smaller diameter of electron stream, that is, 0.5 mm., the focal point of the electron stream will be approximately 10 cm. from the electron emitter, whereas for the electron stream having a diameter of 1.5 mm. the focal point will be 30 cm. from the emitter.
As the potential between the electron emitter and the control electrode increases, the diameter of the cross section through the electron stream adjacent the cathode decreases and the length to the focusing plane of the electron s-tream correspondingly decreases. As a result the current density increases until a critical point is reached. A further increase in the potential ditference between the; electron emitter and .the control electrode withdraws the hump 27 from the space charge region and the current density decreases.
I have given below a table in which such relative values are set forth. It will be understood, however, that these values are not exactly reproduced but are given solely for purposes of illustration.
The anode 11 which is the lower end of the tubular member 11 is provided with an aperture 34 through which the. electron 'beam 32 passes. Anode 11' is adjustalbly: mounted on the base 361 by means of theadjusting screws 37' and'z38 which permit adjustments of the anode 11 in, an angular direction in a plane at right angles to the drawing. Correspondingly adjusting screws 41 and 42' permit an adjustment of the anode at any desired tilt in the plane of the drawing. In each of these adjustments, any desired number of adjusting screws may be employed.
Adjustment of'the anode by the adjusting screws41 and 42, may by the tilting action change the direction of" the long'axis ofthe electron beam to direct it in any desired WHYL It-will be noted that the anode 11"is grounded-in any suitable manner as, for example, in the illustration here shown through the adjusting screws and to the grounded base member 43-. The member 43 carries the entire electron gun through the adjusting screws and is provided with a rubber ring seal 45. The entire mechanism includ ing the base 43 and the electron gun construction hereinafter described is evacuated in any suitable manner.
The base member 43 has a neck portion which iscylindrical in shape and is provided at its lower end with anintegral portion 46 having a cylindrical shape. Integral" with the base 43' is an internal tubular section 47 having a hollow inner space 48 through which the electron beam passesinto the drum shapedmember 46.
- The cylindrical wall 47 made of metal and grouhdedj as shown captures any impurities which may have entered the electron stream. Such impurities may have originated from metal vapors produced at the electron emitter and which tend to fly off from the electron stream at angles thereto to adjacent. bodies. Any such impurities which" still remaininthe stream would, particularly because of the close proximity of the inner cylindrical wall 47 be retained thereby before any collision can occur with otherparticles which would re-directthese particles back-into the electron stream.
It will be understood in this connection, however, that although an elongated tubular opening 47 as close to the electron stream as possible is provided, care must be taken so that in any adjustment of the electron gun described hereinabove, the electron stream does not contact the tubular member. If desired, the tubular member 47 may be constructed as a part of the electron gun. It will be further understood that the tubular member 47 is only necessary where an exceedingly high degree of purification of the electron stream is desired.
Mounted on the tubular member 46 are a pair of insulators 51 and 52 which in turn carry a cylindrical member 53 having openings at 54, 55 and '56. The member 53 in turn supports a pair of shutters 57 and 58 suitably mounted as by means of the screws 61 in slots in the shutter members 57 and 58. These shutters may then be moved through an angle and screw members 61 after adjustment in the slot can be locked in position for purposes to be described hereinafter.
Also mounted on the member 53 is an insulator 62 which carries a supporting base 63 on which is mounted the work member 64. In the example hereinabove described, the member 64 may be tungsten from which metal vapors are to be withdrawn. It will be noted that a point 66 on the upper surface of the tungsten 64 has been placed in the focal plane of the electron beam 32. The concentration therefore of heat at this point will now in a matter of from ten to twenty seconds produce a coating of 0.001 mm. when the velocity of the electron stream corresponds to 50,000 electron volts and when the current density has a value of about ten amperes per square centimeter.
The metal vapors now produced from the tungsten 64 will take a straight line path as shown at 71.
Suitably mounted on the wall 46 is a swivel 171 which carries a supporting member 72. By adjustment the member 72 may be turned to any desired angle. Member 72 in turn carries a member 73 on which the desired coating is to be made.
In the present example this may be a glass plate on which a tungsten coating is to be made. Adjacent to the base member 72 is a pin 74 protruding through the wall 46 and carrying at its inner end a shutter or shadow member 75 which may be moved from the position shown at the right hand into a position in which it covers the glass plate 73 so as to prevent coating thereof as is illustrated in the second unit at 81. By this means, any desired number of members may be or may not be coated. It will further be understood that by adjustment of the shadow members 57 and 58 the area over which the coating is applied may be varied. Thus any partial shadowing of the surface 73 to be coated may be obtained.
In order to further protect the coating from any impurities, the inner cylindrical body 53 may be connected to a potential source over the conductor 82. The base member 63 may have a different potential applied thereto over the conductor 83. This difference in potential between the base 63 and the inner tubular member 53 will result in an attraction or repulsion of any charged ions which may have been extracted from the tungsten body.
Summarizing the above, it will now be understood that although an example of one form of utility for my invention has been described in connection with tungsten, any other body may be similarly vaporized by the use of my novel electron stream arrangement. Moreover, although I have here described my invention in connection with applying coatings other uses of the vaporized particles may similarly be made.
It will further be understood that the particular embodiment I have here chosen for illustrating the 'basic principle is only one example for carrying out my invention.
In general, I have provided an arrangement by which the electronic control of the electron beam to concentrate it into a relatively small area is achieved before the electron beam is called upon to perform work. Thus I have provided an electronic tube construction in one region at 11 of my device. In this region I have performed all of the focusing operations upon the electron beam.
Thereafter, the electron beam is caused to leave the region of electron optical action and to pass on to a second region 46 which is for all practical purposes isolated from the electron optical region. In this region I apply the electron beam to perform the work, in this case, of evaporating a minirnus area of a member placed in the remote focal plane of the electron beam.
In this example, I have further shown the electron beam having generally a conical shape with its focus plane at the apex of the conical member for the purpose of the illustration of my invention.
The treatment of the work material should preferably be placed where the electron beam has the smallest cross section. This may be at the focal plane as here illustrated or at the image plane as more fully described in my copending application S. N. 258,672, filed November 28, 1951, hereby made a part of this specification.
While I have illustrated my system, which does not require focusing electrodes they may be used in the manner described in the above mentioned application.
It will be further understood that although for purposes of illustrating this invention, I have described a particular shape of the control electrode that I have done this for the purpose of illustrating the production of a particularly desired form of equipotential lines which will extend the focusing plane of the electron beam to a region beyond the anode where I may now place the work without interference with or by the electron optical system.
Although I have described my invention using electron energy, I may also carry out my invention with ions in the manner described in my copending application S. N. 258,673, filed November 28, 1951, hereby made a part of the present application.
In the above description I have given specific values for the various voltages and for the dimensions of electrodes. These are provided to illustrate a specific application of my invention as, for example, in the treatment of tungsten hereinabove given. Obviously I may treat other materials which may require different values of electron volts or time of operation or temperatures to achieve vaporization and I do not intend to be limited by these specific examples hereinabove given but only as set forth by the appended claims.
1. In an electron gun, a source of electrons, means for causing said electrons to move in a given direction, a
control electrode surrounding said source of electrons, said control electrode comprising a conical and a cylindrical section, said conical section having its apex positioned downstream with respect to its base, said cylin drical section extending external of said conical section from the base thereof toward and beyond the said apex, and said source of electrons protruding from the apex of said conical section.
2. In an electron gun, a source of electrons, means for causing said electrons to move in a given direction, a control electrode surrounding said source of electrons, said control electrode comprising a conical and a cylindrical section, said conical section having its apex positioned downstream with respect to its base, said cylindrical section extending external of said conical section from the base thereof toward and beyond the said apex, said source of electrons protruding from the apex of said conical section, said means including an anode spaced from said source and control electrode, and means ineluding said source of electrons and said control elec-.
trode for first diverging and converging said electrons for essentially focusing said beam of electrons at a point beyond said anode and at a relatively great distance from said electron source.
3. In an electron gun, a source of electrons, means for causing said electrons to move in a given direction, a control electrode adjacent said source of electrons at a point at which said electrons have relatively low velocity in the given direction, said control electrode comprising a conical and a cylindrical section, said conical section having its apex positioned downstream with respect to its base, said cylindrical section extending external of said conical section from the base thereof toward and beyond the said apex.
4. In an electron gun, a source of electrons, means for causing said electrons to move in a given direction, a control electrode surrounding said source of electrons, said control electrode comprising a conical and a cylindrical section, said conical section having its apex positioned downstream with respect to its base, said cylindrical section extending external of said conical section .from the base thereof toward and beyond the said apex.
said source of electrons prortuding from the apex of said conical section, said means including an anode spaced from said source and control electrode, and means including said control electrode and said source of electrons for first diverging said electrons in the region adjacent said source of electrons and then converging said electrons in the region of said control electrode for essentially focusing said electrons at a point beyond said anode and at a relatively great distance from said source of electrons.
5. In an electron gun, a source of electrons, means for causing said electrons to move in a given direction, a control electrode surrounding said source of electrons, said control electrode comprising a conical and a cylindrical section, said conical section having its apex positioneddownstream with respect to. its, base, saidlcylindrical. section extending, external ofsaidconical section from the base thereof toward and. beyond. thesaid apex, and said source of electrons protruding from the apex of said conical section, said means including an anode spaced from said source and control electrode.
6. In an electron gun, a source of electrons, means for causing said electrons to move in a given direction, a control electrode surrounding said source. of electrons, said control electrode comprising a conical and a.v cylindrical section formed of a plurality of angularly spaced segments, said conical section having its apex positioned downstream with respect to its base, said cylindricalfsection extending external of said conical .section from the base thereof toward and beyond the said apex, said source of electrons protruding from the apex, of said conical section; said angularly spaced segments being, individually connectible to sources of control potential; said sources of control potential being adjustable for adjusting the shape of said equipotential surfaces to thereby control the cross-sectional shape of the beam of said electrons.
References Cited in the file of this patent UNITED STATES PATENTS 1,326,794 Sinding-Larsen Dec. 30, 1919 2,272,353 Ruska Feb. 10, 1942 2,391,780 Hillier Dec..25, 1945 2,428,868 Dimmick Oct. 14, 1947 2,436,265 Pohle et al. Feb. 17, 1948 2,506,660 Blattmann et al May 9, 1950 2,549,926 Pride et al. Apr. 24, 1951 2,600,151 Backus June 10, 1952