JPH0530240B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a device that generates a convergent high-speed atomic beam. [Prior art] Conventionally, devices that generate convergent high-speed atomic beams are
The configuration was as shown in the figure. In the figure, 1 is an ion source, 2 is an electrostatic lens, 3 is an ion beam,
4 is a charge exchanger, 5 is a gas inlet, and 6 is a convergent high-speed atomic beam. The ion source 1, the electrostatic lens 2, and the charge exchanger 4 are arranged in a row in the vacuum container 7. . 8 is a vacuum pump for the vacuum container 7. The operation of this device is as follows. First, the vacuum container 7 is sufficiently evacuated using the vacuum pump 8. An ion source 1 generates a high-speed ion beam 3, which is guided to an electrostatic lens 2 and converged to form a convergent high-speed ion beam 3. This is further guided to a charge exchanger 4. Gas is introduced into the charge exchanger 4 through a gas inlet 5. Inside the charge exchanger 4, the following charge exchange reaction proceeds due to collision between the ion beam 3 and gas molecules. Ions constituting the ion beam 3 are represented by M ⁺ or M ^- , and gas molecules are represented by A. () When the ion is positively charged, M ⁺ +A → M+A ⁺ ...(1) A ⁺ + wall of charge exchanger → A ...(2) Gas molecule A has electron affinity such as H ₂ , He, Ar, Hg, etc. A small one. () When the ion is negatively charged M ^- + A → M + A ^- ... (3) A ^- + wall of charge exchanger → A ... (4) Gas molecule A has electron affinity such as F ₂ , O ₂ , Cl ₂ The big one. Through the reactions (1) to (4) above, the ions lose their charge and become atomic beams 6, which are ejected from the charge exchanger 4. [Problems to be Solved by the Invention] The above conventional device has the following problems. Because ions collide with gas molecules with large mass, there is a large loss of kinetic energy, making it difficult for the atomic beams formed to reach sufficient speed. Collisions with gas molecules of large mass greatly disturb the direction of ion motion, resulting in poor convergence of atomic beams. In order to introduce gas into the charge exchanger, it is difficult to maintain a high vacuum or an ultra-high vacuum inside the vacuum container. The present invention solves these conventional problems. [Means for Solving the Problems] In order to solve the above conventional problems, the present invention includes an ion neutralizer that traps electrons in the path of a negatively charged ion beam, and collides the negatively charged ion beam with the electrons. By removing the charge from ions, a convergent high-speed atomic beam is efficiently generated. [Example] Hereinafter, an example of the present invention will be described based on FIGS. 1 and 2. In the figure, parts similar to those of the above-mentioned conventional example are given the same reference numerals. That is, 1 is an ion source, 2 is an electrostatic lens, 3 is an ion beam, 6 is an atomic beam, 7 is a vacuum container, and 8 is a vacuum pump. In the vacuum container 7, an ion neutralizer 9 and deflectors 10 and 11 to which a voltage is applied are arranged side by side after the electrostatic lens 2. Note that here, a device that neutralizes a negatively charged ion beam and obtains an atomic beam is called an ion neutralizer. The configuration of the ion neutralizer 9 is shown in FIG. In the figure, 12 is a metal cylindrical envelope, 13 is a filament for generating thermionic electrons arranged inside the envelope 12, 14 is a DC power supply,
15 is a power source for filament ignition, 16 is a metallic cylindrical mesh electrode, and 17 is a DC power source for accelerating thermionic electrons. The cylindrical mesh electrode 16 and the envelope 12 are arranged so that their respective central axes substantially coincide. The filament 13 is ignited by the power source 15 and emits thermoelectrons. The mesh electrode 16 is maintained at a positive potential of 70 to 200 V with respect to the filament 13 by a DC power supply 17, and the thermoelectrons generated in the filament 13 are attracted to this potential and accelerated in the direction of the mesh electrode 16. Ru. The thermoelectrons that reached the mesh electrode 16 are
A part of it collides with the mesh electrode 16 and is absorbed therein, and the rest passes through the mesh electrode 16, enters its interior, and then passes through the mesh electrode 16. The envelope 12 is kept at a certain negative potential with respect to the filament 13 by the DC power supply 14, and therefore the thermoelectrons that have passed through the mesh electrode 16 are stopped at the edge of the inner wall surface of the envelope 12. , and begin to be accelerated toward the mesh electrode 16. In this way, the mesh electrode 16
The inside of is filled with electrons that are moving back and forth with a kinetic energy of 70 to 200 eV, forming an electron cloud. Next, the operation will be explained. First, the vacuum container 7 is sufficiently evacuated using the vacuum pump 8. Then, an ion source 1 generates a high-speed negatively charged ion beam, which is guided to an electrostatic lens 2 to become a focused high-speed ion beam 3. This is led to an ion neutralizer 9. As described above, the net electrode 16 in the neutralizer 9 is filled with thermoelectrons as an electron cloud, and the focused high-speed negatively charged ion beam 3 is incident thereon. This incident ion collides with electrons of 70 to 200 eV, strips off its negative charge, and becomes an atomic beam 6. This is because the outermost electrons of the negatively charged ions are repelled by the electrons or negatively charged ions and are repelled, resulting in neutralization. At this time, since the mass of the electron is extremely small compared to the ion, the kinetic energy of the ion is not lost due to collision with the electron, and the direction of the ion's motion is not disturbed. Therefore, regarding the kinetic energy and convergence of the atomic beam 6, the kinetic energy and convergence of the ion beam 3 before entering the ion neutralizer 9 are preserved. Note that since the envelope 12 is kept at a negative potential with respect to the mesh electrode 16, the electron cloud inside the mesh electrode 16 does not flow out in the direction of the entrance and exit of the ion neutralizer 9. It is always confined inside the mesh electrode 16, increasing the efficiency of neutralization. The atomic beam 6 then passes between deflectors 10 and 11. A voltage is applied between the deflectors 10 and 11, and if any ions remain in the high-speed atomic beam 6 passing between them, they are removed and a pure high-speed atomic beam is formed. By the way, the DC voltage for accelerating electrons is 70~
The reason for using 200V is that it has been experimentally confirmed that this value is suitable for stripping off electrons attached to ions. If it is lower than this value, the electron detachment probability will decrease, and if it is higher than this, the outer shell electrons of the formed atom will be stripped off and become positive ions, both of which will reduce the efficiency of conversion from negative ions to atoms. become bad. Table 1 below shows an experimental comparison of the degree of convergence of high-speed atomic beams between the conventional charge exchange method and the present invention.

【table】

〔Effect of the invention〕

As explained above, the convergent fast atomic beam source according to the present invention is configured to generate an atomic beam by stripping off the charge attached to negatively charged ions with high-energy electrons, so it has good convergence. This method has the advantage that a high-speed atomic beam source can be obtained and that it can be operated in an ultra-high vacuum.

[Brief explanation of the drawing]

1 and 2 show an embodiment of the present invention,
FIG. 1 is a schematic block diagram of the main parts, FIG. 2 is a schematic block diagram of the entire structure, and FIG. 3 is a schematic block diagram of the entire conventional example. 3... Ion beam, 6... Convergent high-speed atomic beam, 9... Ion neutralizer, 12... Envelope, 13
... Filament for generating thermionic electrons, 16 ... Cylindrical mesh electrode.

Claims (1)

[Claims] 1. A convergent high-speed atomic beam source that passes a generated negatively charged ion beam through an ion neutralizer to create a convergent high-speed atomic beam, the ion neutralizer comprising:
a cylindrical envelope through which a negatively charged ion beam passes through the center; a thermionic generation filament provided inside the envelope to emit thermoelectrons; and a filament provided concentrically inside the envelope. a cylindrical mesh electrode that is held at a positive potential with respect to the filament and a negative charge with respect to the envelope to trap thermoelectrons emitted from the filament; A convergent high-speed atomic beam source characterized in that the charge of a negatively charged ion beam is stripped off by electrons inside the ion beam.