US3745337A

US3745337A - Apparatus for separating charged particles according to their respective ranges

Info

Publication number: US3745337A
Application number: US00142465A
Authority: US
Inventors: H Koike
Original assignee: Jeol Ltd
Current assignee: Jeol Ltd
Priority date: 1971-05-12
Filing date: 1971-05-12
Publication date: 1973-07-10
Anticipated expiration: 1990-07-10

Abstract

An apparatus for separating charged particles according to their respective energies. The charged particles are decelerated and passed through a long cylindrical electrode having a focusing coil. Since the velocity of the particles differs according to their respective energies, the particles are separated in the electrode and exit the electrode at different times.

Description

United States Patent 1 Koilte [111 3,745,337 [451 July 10,1973

[52] US. CL, ..250/4l.9 TF, 250/49.5 AE, 250/495 PE [51] Int. Cl. H01j 39/34 [58] Field of Search 250/419 TF, 49.5 R, 250/495 PE, 49.5 AB

[56] References Cited UNITED STATES PATENTS 3,582,648 6/1971 Anderson 250/419 TF BULRCE 7/1957 Hendee 250/419 TF 3/I970 Castaing 250/495 PE OTHER PUBLICATIONS Electron Velocity Micro-Analyzer," Shahbender RCA TN No. 310, November, 1959.

Primary Examinerlames W. Lawrence Assistant Examiner-C. E. Church I Attorney-Webb, Burden, Robinson & Webb [5 7] ABSTRACT An apparatus for separating charged particles according to their respective energies. The charged particles are decelerated and passed through a long cylindrical electrode having a focusing coil. Since the velocity of the particles differs according to their respective energies, the particles are separated in the electrode and exit the electrode at different times.

3 Claims, 8 Drawing Figures 40 4 4 1 33 20 k 6 5 g MAGNETIC FIELD CONTROL CIRCUIT Patented July 10, 1973 4Shecs-Sheet 1 /ZHIGH ,VOLTAGE GENERATOR VOLTAGE SUPPLY 2 46 g a a N m A .F'g J h )4 f l r J5 T Y DETECTOR FF 49 D|sPLAY I DEVICE AMPLIFIER b 1 AC Patented July 10, 1973 3,745,337

4 Sheets-Sheet 2 DETECTOR E 3 I SYNCHROSCOPE a q j j EAMPLIFIER SOURCE SOURCE EEIW 33 20 f4 4 3,? 1 I l. wwn w DETECTOR AMPLIFIER 4 Sheets-Shoot 1 Zap/H 1 Sheets-Sheet 1 CCC CIFbIillZll :L \r

womnow- APPARATUS FOR SEPARATING CHARGED PARTICLES ACCORDING TO THEIR RESPECTIVE RANGES This invention relates generally 'to an apparatus for separating charged particles according to their respective energies and more particularly to an apparatus for separating charged particles whose respective energies vary with time.

In the usual technique forseparating charged particles, they are caused to traverse either an electric or magnetic field. In either case, the charged particles traverse the field at a certain velocity and their trajectory or flight path varies according to the energy of the respective particles or groups of particles. Particles having the required energy exit the field via a slit in a baffle which is positioned so as to intercept the particles having energies greater or less than that required. The particles that would be intercepted are then made to pass through the slit in sequence either by moving the slit up and down or by varying the intensity of the electric or magnetic field.

In the prior art the energy difference capable of separation (i.e., resolution) has been limited to about l mev. The resolution is controlled by the characteristics of the electric or magnetic field and the width of the slit.

In the present invention, the velocity of the charged particles is reduced and the retarded or decelerated particles are passed through a long cylindrical electrode. As the velocity of the particles differs according to their respective energies, the particles are spatially separated along their path in the electrode and, therefore, exit the electrode at different times. In this way, the energy difference capable of separation is reduced below mev.

It is an advantage of apparatus according to this invention that they are capable of precisely separating charged particles according to their respective energies. It is another advantage that they are capable of separating charged particles according to their respective energies dependent upon time.

Various other objects and advantages of this invention will become apparent from the following detailed description read in conjunction with the drawings in which:

FIG. 1 shows an embodiment of this invention in which electrons are separated according to their respective energies;

FIG. 2 shows the wave forms of the voltages supplied to the deflecting means in the embodiment shown in FIG. 8 shows the deflecting voltage and distributions of the particles passed through the slits in the modified embodiment shown in FIG. 7.

Referring to FIG. I, an electron beam is produced by an electron gun comprising a cathode l, a Wehnelt electrode 2 and an anode 3. The Wehnelt electrode 2 is connected to the negative terminal of a high voltage generator 4 and to the cathode 1 via a bias resistor 5. By so doing, the electron beam current is maintained at a constant value. The electron beam, after passing through the Wehnelt electrode 2, is accelerated by the anode 3 which is grounded and then enters a first cylindrical electrode 6, also grounded.

An electrostatic or electromagnetic deflecting means l2 and a slit 13 are provided in the cylindrical electrode 6 in order to control the electron beam. The deflecting means may, for example, comprise a pair of parallel plates charged with opposite polarities or a pair of coils having facing ends of opposite polarities. A voltage supply source 16 supplies a controlling voltage or current to the deflecting means 12. When a voltage is applied to said deflecting means (e.g., V in FIG. 2a) the electron beam is deflected and intercepted by the baffle 13 containing a slit. On the other hand, when the voltage applied to the deflecting means 12 is zero, the electron beam passes through said slit in the baffle 13 and enters a second cylindrical electrode 8 to which a voltage, approximately the same as the voltage applied to the cathode 1, is supplied by a voltage regulator 11 comprising batteries 9 and a variable resistor 10. By so doing, the electrons constituting the electron beam are decelerated by a decelerating electric field produced between the first and second electrodes and, therefore, pass through the second electrode 8 at a reduced velocity. However, since the flow rate or speed of high energy electrons is higher than that of low energy electrons, the electrons are separated according to their respective energies. Further, in order to produce a uniform magnetic field along the center axis of the electrode 8 and, thereby, create a situation whereby the electrons move along the said axis repetitively and periodically, said electrode is equipped with a focusing coil 20. As a result, the energy of the electrons maintain their respective levels and, hence, their respective velocities. The length of the second electrode 8 defining.

an elongate passage through which the decelerated electrons pass is about 30 cm m.

The electrons, upon reaching the outlet of the electrode 8, are accelerated by an accelerating electric field produced between said electrode 8 and a third electrode 7 which is grounded. An electrostatic or electromagnet deflecting means 14 and a slit 15 are provided in the third electrode 7 in order to control the ac celerated electrons. The voltage supply source 16, as in the case of the deflecting means 12, supplies a controlled voltage to the deflecting means 14. When a voltage applied to the deflecting means (e.g., V in FIG. 2b) the electrons are deflected and intercepted by the baffle 15. On the other hand, when the voltage applied to the deflecting means 14 is zero, the electrons pass through the slit in baffle 15 and are detected by a detector 17. The detected signal is then amplified by an amplifier l8 and fed into a recorder or display means In the above arrangement, the electrons pass through the slit in baffle l3 and are decelerated by the decelerating electric field produced between the first and

second electrodes

6 and 8 during the period A 1'; that is to say, during the time no voltage is being applied to the deflecting means 12. During this period of time, the energy of the decelerated electrons traversing electrode 8 towards slit 15 is very low, for example, 10 mev. The period 1' during which the electrons pass from the slit in baffle 13 to the slit in baffle 1.5 is expressed as follows:

where V is the electron velocity, m is the electron mass, E is the electron energy and l is the distance between the two slits.

It is apparent from the above equation that 1 varies according to E. When E is large, T is short and conversely, when E is small, 7 is long. Therefore, by making A r extremely short as compared to 1' electrons having energy (velocity) substantially corresponding to T only pass through the slit in baffle 15.

Now, if two electrons having energies of E and E I A E respectively enter the second electrode 8, the time taken (r 7 for each electron to pass from the slit in baffle 13 to the slit in baffle 15 is given as follows:

Thus, the time differential 'r, 1 can be expressed as follows:

Further, since the time taken for the respective electrons to pass from the slit in baffle 13 to the slit in baffle l5 varies, the energy distribution of said electrons is recorded by or displayed on the recorder or display means 19 as a differential loss curve by varying the voltage supplied to the second electrode 8 or the frequency of the signal supplied to the deflecting means 12. Still further, by keeping the voltage and frequency applied to said electrode constant, the apparatus can be used as a monochromater.

FIG. 3 shows another embodiment of the apparatus heretofore described. In the figure, a beam of charged particles emanating from a source 21 is deflected by a deflecting means 22 so as to scan a slit plate 23 provided with a minute opening. Said particles which pass through the opening periodically are directed to a cylindrical electrode 24 similar to the second electrode 8 shown in FIG. 1 and separated according to their respective energies therein. The separated particles are then accelerated by an accelerating electrode 25 and detected by a detector 26, the output signal of which is fed into a synchroscope 28 via an amplifier 27. In this embodiment, since there is no deflecting means and slit at the output side of the electrode 24, the separated particles are free to enter the detector continuously.

The resultant energy distribution curve produced on the synchroscope is shown in FIG. 6.

FIG. 4 shows a further embodiment of this invention. In this case,

control electrodes

29 and 30, to which a bias voltage is supplied from a control circuit 31, are provided at each end of the long cylindrical electrode 24. Normally, a bias voltage is applied to both electrodes in order to intercept the particles, so that it is only during the short periods when said bias voltage is zero that the particles pass through the electrodes. It is possible to discard electrode 30 as required. It is also possible to utilize the control electrode of a charge particle source; e.g., the electron gun Wehnelt electrode in FIG. 1 to which said bias voltage is applied instead of electrode 29.

FIG. 5 shows yet another embodiment of this invention. In the figure, the charged particles emanating from the source 21 are deflected by the deflecting coil 22 and scan the slit plate 23 in the same way as in the embodiment shown in FIG. 3. The particles passed through said slit plate then enter a magnetic field 32 (shown as its optical analog) wherein the particles are directionally changed so as to direct them into an electrode 33 maintained at ground potential. The particles are decelerated by a decelerating electric field produced between

electrodes

33 and 24, thus causing the particles to travel along the cylindrical electrode 24 at an extremely low velocity. A mirror electrode 34 is placed at the end of the long cylindrical electrode 24 so that a reflecting electric field of the particles is produced in front of said mirror electrode. The particles reaching the end of the electrode 24 are reflected by said reflecting field and then travel along the electrode 24 in the reverse direction. The reflecting particles are accelerated by the electrode 33, again directionally changed by the magnetic field 32 and then detected bp the detector 26. The detected signal is fed via amplifier 27 into a sampling scope or synchroscope 28 which displays an energy distribution curve of the separated particles as shown in FIG. 6.

In the above embodiment, since the particles traverse the cylindrical electrode 24 twice, the effective passage length is doubled. Therefore, the separability of this embodiment is twice as good as the embodiments shown in FIGS. 1, 3 and 4. It is also possible to place a deflecting means and a slit between the magnetic field 32 and the detector 26 so as to detect only one portion of the separated particles.

FIG. 7 shows a modified embodiment of the embodiment shown in FIG. 5. In this case, two

slits

40 and 41 and a deflecting means 42 to which a controlled voltage is applied from a control circuit 43 are arranged 'between the magnetic field 32 and the electrode 33. An example of said control voltage'is shown in FIG. 8a. When the voltage is zero; namely, at time 1- the particles pass through both slits. FIG. 8b shows the distribution of the particles passed through the slits. Said particles are decelerated by the decelerating field produced between

electrodes

33 and 24, thereby traveling along electrode 24 at a very low velocity. The particles reaching the end of said electrode are reflected in the reverse direction by the mirror electrode 34. The reflecting particles are accelerated by the electric field produced between

electrodes

24 and 33, pass through slit 41 and are then directed to the deflecting means 42.

FIG. 8c shows the distribution of the particles that would pass through the slit 41. At time 1- namely, when the voltage supplied to the deflecting means is zero, the particles pass through the deflecting means and the slit 40 without being deflected. FIG. 8d shows the distribution of the separated particles passed through the slit 40. The separated particles are directed to the detector by the magnetic field. In this arrangement, particles having the desired energy are detected by controlling a periodic time 2 1- of the voltage supplied from the circuit 43 to the deflecting means. When the accelerating voltage of the source 21 is varied continuously and the periodic time 2 T is fixed, the differential loss curve similar to FIG. 6 is obtained.

Further, if the frequency of the rectangular pulse supplied to the deflecting means 42 is varied, the differential loss curve as shown in FIG. 80 is obtained.

Having thus described my invention with the detail and particularity as required by the Patent Laws, what is desired protected by Letters Patent is set forth in the following claims.

I claim:

1. An apparatus for separating charged particles according to their respective energies comprising:

a. means for decelerating said particles;

b. an enclosure defining an elongate passage through which said decelerated particles pass and in which said particles are separated according to their respective energies;

c. a magnetic field for deflecting and directing unseparated charged particles into one end of said passage, said field also deflecting the separated particles emerging from said end; i

d. a reflecting means for reflecting the charged particles, said reflecting means being provided at the second end of said passage;

e. a control means for directing said particles into said passage via said magnetic field during a very short period of time; and, V

f. means synchronized with said control means for detecting the separated particles.

2. An apparatus for separating charged particles according to their respective energies comprising:

a. means for decelerating said particles;

b. an enclosure defining an elongate passage through which the said decelerated particles pass and in which said particles are separated according to their respective energies;

c. a magnetic field for deflecting and directing unseparated charged particles into one end of said passage, said field also deflecting the separated particles;

e. first and second spaced baffles having slits therein provided between said magnetic field and said passage;

f. a deflecting means provided between the baffles for deflecting the charged particles, said particles directed into said passage being controlled by said deflecting means and the second baffle, the charged particles separated in said passage being controlled by said deflecting means and the first baffle; and,

g. control means for causing the deflecting means to pass unseparated particles through beffles for a short interval and at a measured time later to pass separated particles through said baffles.

3. An apparatus according to claim 2 wherein said enclosure comprises a long cylindrical electrode having a focusing coil thereabout.

Claims

1. An apparatus for separating charged particles according to their respective energies comprising: a. means for decelerating said particles; b. an enclosure defining an elongate passage through which said decelerated particles pass and in which said particles are separated according to their respective energies; c. a magnetic field for deflecting and directing unseparated charged particles into one end of said passage, said field also deflecting the separated particles emerging from said end; d. a reflecting means for reflecting the charged particles, said reflecting means being provided at the second end of said passage; e. a control means for directing said particles into said passage via said magnetic field during a very short period of time; and, f. means synchronized with said control means for detecting the separated particles.

2. An apparatus for separating charged particles according to their respective energies comprising: a. means for decelerating said particles; b. an enclosure defining an elongate passage through which the said decelerated particles pass and in which said particles are separated according to their respective energies; c. a magnetic field for deflecting and directing unseparated charged particles into one end of said passage, said field also deflecting the separated particles; d. a reflecting means for reflecting the charged particles, said reflecting means being provided at the second end of said passage; e. first and second spaced baffles having slits therein provided between said magnetic field and said passage; f. a deflecting means provided between the baffles for deflecting the charged particles, said particles directed into said passage being controlled by said deflecting means and the second baffle, the charged particles separated in said passage being controlled by said deflecting means and tbe first baffle; and, g. control means for causing the deflecting means to pass unseparated particles through beffles for a short interval and at a measured time later to pass separated particles through said baffles.