JPS6059635A - Ion source - Google Patents

Abstract

PURPOSE:To obtain a small large-capacity ion source having a high efficiency of leading out positive ions as well as negative ions by installing a sample-holding electrode having a hole in the middle between a thermion-radiating body and an ion-leading-out electrode. CONSTITUTION:After a solid or liquid sample is either placed on or applied to a sample-holding electrode 21, thermions 23 accelerated by the potential difference between the electrode 21 and a filament 20 are caused to become incident upon the electrode 21. After negative ions 25 liberated from a sample 24 are taken out together with electrons by ion-leading-out voltage applied across electrodes 21 and 22, the electrons are separated and qualitative and quantitative analysis of the negative ions is performed by means of a mass analyzer 26. When taking out positive ions 27, the potential distribution between electrodes 30 and 31 is changed. Electrons 35 passing through the small holes of the electrode 30 are reflected in the space formed between the electrodes 30 and 31 and finally strike against the surface of the electrode 30, thereby increasing the efficiency of the production and liberation of positive ions 27.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an apparatus for generating anions and cations, and is particularly applicable to mass spectrometry of extremely small amounts of solid or liquid samples, and hydrogen ion generation for nuclear fusion reactions. It can be used as an ion source suitable for the fields of ion generation, implantation of ions into semiconductor materials, and the like.

[Background of the invention]

Figure 1(a) shows an example of a conventional ion source of this type (Sa
ndstYom ej al, ,J,Chem ,
PhyS'+48.5683.1968).

Here, 1, 2.3 are grid electrodes in the form of wire mesh, 4 is a tungsten filament for thermionic emission, and 5 is a tungsten ribbon for adsorbing sample molecules. Thermionic electrons 6 emitted from the filament 4 are accelerated by a potential difference by a power source 7 and are incident on the surface of the ribbon 50. As a result, the cations 9 (e.g., CO+) generated and released from the sample 8 (e.g., CO) adsorbed on the surface of the ribbon 50 are Jl
(b) As shown in the figure, the voltage is drawn out by the potential difference caused by the power source 7. Then, after being further accelerated in the direction of the electrode 2, it is sent to the mass analyzer 10. According to this method, due to the potential difference between the filament 4 and the ribbon 5,
There is an advantage that the electrons 6 and the ions 9 can be accelerated simultaneously. However, it is difficult to extract anions (for example, O-) generated by electron impact from the ribbon 5 and send them toward the grid 2 because the polarity direction of the electric field is reversed.
It's completely impossible.

As a measure to alleviate such difficulties, for example, the method shown in Figure 2(a) (Hiroyuki Kono et al., Joint Conference of the Chugoku-Shikoku Branch and Kyushu Branch of the Chemical Society of Japan, Shinyo University, November 1982)
April, lecture number A217, lecture proceedings, page 101) was devised. Here, 11 is a flat plate electrode for holding a sample (for example, an aqueous solution of NaCl), 12 is a tungsten filament for thermionic emission, 13 is a cylindrical electrode for electron acceleration, 14 is a slit electrode for ion extraction, 15 is thermionic electron, 16 is the coated sample (e.g. NaCt), 1
7 is an anion (for example, Ct-), and 1B is a mass analyzer. In this conventional example, it is extremely easy to accelerate the thermoelectrons 15 in the direction of the electrode 11 due to the potential difference between the filament 12 and the electrode 11. but,
The anions 17 are efficiently drawn out from the electrode 11 and
It is very difficult to send it out in the direction of 4. The main reason is that the thermionic emitter 12p; electrode 11 and electrode 14
This is because the electric field for accelerating the electrons 15 tends to act as a blocking electric field for the anions 17, as shown in FIG. 2(b).

As described above, in the conventional embodiments, it is either impossible or extremely difficult to efficiently extract anions generated by electron impact, and therefore, the drawback is that they are impractical as an anion source. there were.

[Purpose of the invention]

An object of the present invention is to provide a compact, large-capacity ion source that has high extraction efficiency not only for cations generated on the surface of a solid by electron bombardment but also for anions.

[Summary of the invention]

In conventional embodiments, since the thermionic emitter is installed in the middle between the sample holding electrode and the ion extraction electrode, it has been impossible or extremely difficult to extract anions. In order to solve this difficulty, in the present invention, the structure of the ion source is modified as shown in FIG. 3(a). Here, 19 is an electrode for back shielding, 20 is a filament for thermoelectron emission, 21 is a perforated electrode for holding a sample (transparent sponge, mesh, bamboo blind, gridiron, or perforated punched plate), and 22 is an ion extractor. electrode (mesh or slit plate).

After loading or applying a solid or liquid sample to the sample holding electrode 21, thermionic electrons 23 accelerated by the potential difference between the sample holding electrode 21 and the filament 20 are transferred to the sample holding electrode 21. Make it incident. As a result, the anions 25 desorbed from the sample 24 on the sample holding electrode 21 are
After being extracted along with electrons by an ion extraction voltage applied between the electrode 21 and the electrode 22, the mass analyzer 2
6, electron separation and qualitative/quantitative analysis of gap ions are performed.

FIG. 4 shows a case in which positive ions 27 are extracted using the above-described ion source according to the present invention. here,
28 is an electrode for back shielding, 29 is a filament for thermoelectron emission, 30 is a perforated electrode for holding a sample, 31 is an ion extraction electrode, 32 (is [4 pieces, 33 is a sample 7 immersed or coated, 34 is a I am using a mass analyzer.The position distribution between Naoto 30 and Napole 31 is different from that in Figure 3, but the structure and arrangement of the Napoles are the same. The 'Nariko 35 that passed through the small hole on the electrode 30
It was reflected in the window between ``Narigoku 31'' and finally 1 yen 3
Since the surface of 0 is titanized, it is useful for increasing the efficiency of generation and desorption of cations 27.

In the present invention, as mentioned above, since the perforated electrode for holding the sample is installed in the intermediate part between the thermionic emitter and the ion extractor, even desorbed cations or side columns of gap ions can be efficiently removed. Can be pulled out easily.

In addition, as a sample 1 pole, a thin mesh/yu, a see-through sponge, a fine blind, a gridiron with a narrow parallel 1@In and a wide width on each opposing surface, or a board with many small holes. etc., to hold the sample and generate and generate ions.
The narrow area that is effective for desorption can be very large within a narrow space. Therefore, it is possible to downsize the entire ion source.

As described above, the present invention can provide a simple ion source that can generate and extract ions from the negative and hot water sides with high efficiency. This feature was not found in conventional embodiments.

[Embodiments of the invention]

An embodiment according to the present invention will be described below with reference to FIG.

FIG. 5(b) is a schematic cross-sectional view of an ion source designed and manufactured for a mass spectrometer. FIG. 5(a) is a sectional view taken along the line -■ in FIG. 5(b). 36 is a back shield box made of stainless steel, and 37 is a spiral tungsten filament (diameter 0.1 mm) for thermionic emission.

Total length 3c1n), 38 is a stainless steel mesh with an aperture ratio of 50%, 39 is a stainless steel ion extraction slit polarization, 4o is a mesh mounting frame, 41 is a guide rail for attaching and detaching the mesh electrode with frame, 42 is a filament The mounting stems 43 and 44 are both insulators, and 45 is a screw for a solid bolt.

46 is a thermoelectron, 47 is a sample, 48 is an anion, and 49 is a cation. FIG. 5(C) shows the mesh 38 and the mesh attachment frame 40.

After loading or coating a small amount of solid (for example, LIH, KF, etc.) or liquid (for example, C82, TiCl2, etc.) sample on the surface of the mesh electrode 38 in the order of μg to mg, the airlock device 50 moves the guide rail It is attached to 41 parts. Next, heat the filament 37 to about 1900° with the heater power supply 51 and
Thermionic electrons of A are emitted and accelerated to 150 eV using an electron acceleration power source 53 together with a back shielding power source 52.
The light is made incident on the mesh electrode 38. Desorbed anion 48
Alternatively, the positive ions 49 are accelerated to 300 e by the ion extraction power source 55 connected to the polarity changeover switch 54 and then sent to the mass analyzer 56 .

Generally, there are currently no simple ion sources that can efficiently generate anions such as atoms and molecules with low electron affinity from a small amount of solid sample. If you can,
The electron mirror oroka of Mizubuki atom and lithium atom is 0, respectively.
．． H-
It is generally difficult to generate Li- or Li-. Therefore, when we selected 1 m g of LiH as a solid sample, operated the ion source as described above, and observed the mass spectrum with a single focusing mass spectrometer, we found that the sharp peak spectrum of H- and Li- was observed. It was found that it was easy to see and the lifetime of the sample was over 5 hours. This result shows that (1) in contrast to the case of a spark discharge type ion source for solid samples, the energy width of the desorbed ions is relatively narrow; In addition, (2) the ion source according to the present invention can be applied to atoms with low electron affinity, in contrast to conventional surface electrode detachable anion sources for solid samples. anion can be easily generated from a solid sample, and further,
(3) Compared to the conventional electron impact ion source, which vaporizes a solid sample in a vacuum device and then bombards the vapor with electrons,
that the ion source according to the invention has very low loss of non-ionized sample, thus helping to improve detection sensitivity;
There are characteristics such as. Note that by maintaining good vacuum conditions inside the ion source, no generation of packed ground ions such as C", C2-, C2H-, etc. was observed.

FIG. 6 illustrates the performance of the ion source according to the present invention. The mesh '[electrode 38 (size 0.2
After loading about 10 mg of NaH on the surface of the filament 37 (X O,5 cA ), the filament 37 is heated to 1900°K, and an electron current of about 2 mA is made to enter the single pole 38 . A 180 degree magnetic field deflection type single focusing mass spectrometer was used to measure the amount of desorbed water 5+1 ions. The horizontal axis in FIG. 6 is the kinetic energy of electrons that bombarded the sample, and the vertical axis is the radiation current value of hydrogen anions. In this graph, the aperture ratio is approximately 50% and the width is 0. From the climax of L ct&, 60μA
1i- ions are emitted from the scale. The lifespan (continuous operation time) of this ion source is, for example, about 1
When loaded with 0 mg of NaH, an H-current of approximately 0.1 μA can be extracted for over 8 hours. Also,
The utilization efficiency of loaded NaH is approximately 1 mg/load density.
When crl, it was about 5%.

FIG. 7(a) shows an example of an ion source to which the present invention is applied for fields that require generation of a powerful ion beam, such as an ion source for heating neutral particles in a nuclear fusion reactor. 7th
FIG. 7(b) is a sectional view taken along the line ■-■ in FIG. 7(a). 57
58 is a semi-cylindrical electrode for back shielding, and 58 is a spiral tungsten filament (diameter 0.1 t) for thermoelectron emission.
ea, total length 150 crn), 59 and 60 are semi-cylindrical mesh electrodes for sample holding, 61 is a flat mesh electrode for ion extraction, 62° 63 and 64 are mesh mounting frames,
65 is an insulator, 66 is a screw for assembling electrodes, 67 is a semicircular side cover, 68 is a stem for attaching a filament, 69 is an insulator, and 70 is a screw for attaching the side cover. Further, 71 is a thermoelectron, 72 is an anion, 73 is a sample, 74 is a magnet for electron separation, 75 is a filament heating power source, 76 is an electron reflection power source, 77 is an electron acceleration power source, 78 and 79 are ions The extraction power supplies 80 and 81 are switches for changing the polarity of the ion extraction voltage.

The intervals between the electrodes 62, 63, and 64 are all 5 squares, and the electrode 59
and 60 are between 101+II+1 and 20, respectively. When generating a negative ion beam, the electrode 59
The potential is gradually increased in the order of →60 →61.

A solid sample (e.g. CaHz) is placed on the surface of the electrodes 59 and 60.
After loading filament 58, 19
It is heated to 00°K to emit thermoelectrons with a current value of 600 mA, accelerated to 150 ev, and impacts the electrodes 59 and 60. The ion 72 emitted from the electrode 59 is extracted by the electrode 60, and then further accelerated and focused by the electrode 61 and extracted.

On the other hand, the anions desorbed from the electrode 60 are accelerated and focused by the electrode 61. According to this embodiment, the surface area where anions are generated is much larger than in the case of the method shown in FIG. 5, and the utilization rate of electron current is high.
Since it is possible to extract and focus negative ions at the same time, it is possible to easily generate a large current negative ion beam.

On the other hand, when generating positive ions, after loading and coating the sample only on the electrode 59, switch the polarity of the ion extraction voltage with switches 78 and 79, and lower the potential in the order of electrodes 59 → 60 → 61. In particular, the positive ions emitted from the electrode 59 can be extracted efficiently. Since the structure of the ion source is the same as in the case of generating anions, efficient ion generation effects can be obtained in the case of cations as well as in the case of anions.

In order to extract only the 1(- beam from the Li1(or NaH) homogeneous sample, the simultaneously generated Li- and Na-e
It is safe to separate with a Wien filter or mass filter, and therefore, in the process of this separation operation, the essential H-
This will cause the beam to lose its singing. However, C
When aH2 is used, Ca has a negative electron affinity, so no Ca- is generated. Therefore, CaH
The negative ions generated by the electron bombardment in step 2 are only H-, and a pure H- beam can be easily extracted by simply removing the electrons with a weak magnetic field. Therefore, approximately 1 mg/di of CaH was added to the surfaces of electrodes 59 and 60 in FIG.
After loading 2, when bombarded with 150 eV thermionic electrons, 5
The H-ion current of about 1 μA/crll was changed over an hour. This production density is only about 8% and 0.2% compared to LIH and NaH, respectively. However, by (1) increasing the effective area of the sample holding electrode (approximately 30 crA) as shown in Figure 7, and (2) employing multiple ion sources in parallel, A powerful H-beam component can be extracted efficiently.

Effects of the Invention] According to the invention, the following effects (1) to (6) can be obtained.

(1) Expanding the range of sample selection For example, surface ionization type ion sources are widely used as a method for generating anions from solid samples.

However, according to this method, the electron affinity is generally 2 eV.
Only the atoms and atomic groups mentioned above can be subjected to negative ionization. Therefore, the range of application of the surface ionization type anion source is narrow, and its effectiveness is limited to specific samples such as halogen compounds.

However, the ion source of the present invention has an electron affinity of 0.7.
There is a percentage sign that even H atoms at 5 eV and Li atoms at 0.62 eV can be easily anionized. This is because the surface characteristics of the solid sample itself (active sites with relatively small work functions can generally exist on the surface of compounds) can be effectively utilized. Therefore, adoption of the ion source has the effect of increasing both the types of anions that can be produced and the types of solid samples that can be adopted.

(2) Improving ionization efficiency Electron impact ion sources that use gas or vapor as a sample have been widely used. However, since the probability that gas molecules and electrons collide in the gas phase is very small, generally more than 99% of the sample is wasted and exhausted.

However, in the ion source of the present invention, since electrons are irradiated onto the '-polar surface where the sample exists two-dimensionally, the probability of collision between electrons and sample molecules is high. For example, NaH at 150eV
If the ion yield when irradiated with an electron beam is defined as the ratio of the emitted ion current to the incident electron bottom current, the value reaches 4%.

In this way, the ion source has the effect of increasing the ion production efficiency.

(3) Generation of a single-component gap ion beam If a compound containing only one type of element with a positive electron affinity value is selected as a sample, it is possible to generate a single-component exposed ion beam using only that element. be.

For example, if adopted as CaH++', the electron affinities of Ca and H are -1, 6 and 0.75 eV, respectively, so
Ca- is never generated. Therefore, such a sample selection method can be applied to the ion source of the present invention, and a weak magnetic field can be used for separating thermionic electrons without using a Wien filter or a mass filter. The effect of easily extracting a single-component warm ion beam can be achieved by simply using this method.

(4) Reducing the load on the exhaust system In the case of conventional ion sources that use gas as a sample, for example, when H- is generated by arc discharge in hydrogen gas, a large-sized ion source is used to exhaust the unionized hydrogen gas. An empty pump is required.

However, in the ion source of the present invention, for example, H- is replaced with NaH
Since the ion beam can be generated from solid samples such as

Therefore, by employing the ion source, the cost of the ion beam generation device can be reduced.

(5) Miniaturization of the device Since the present ion source has a simple structure, it is easy to reduce the overall size to within Lcm3. Therefore, it has the advantage that it can be easily incorporated into a relatively small-sized experimental device as a simple anion source or cation source.

(6) Expansion of the selection range of manufacturing materials When generating anions by surface ionization, the surface material for ion generation must have a small work function value (large in the case of cationization), and Melting point is 2000
It is generally necessary to employ special materials, such as metals or semi-metals, which are resistant to temperatures greater than 100°C.

However, when using the electron impact desorption method, the surface characteristics of the solid sample itself and the kinetic energy of the impact electrons are used to generate and desorb ions, so the selection of materials for the sample electrode is In this case, there is no need to consider heat resistance or the size of the work function. Therefore, with the exception of the thermionic emission filament, the material of the ion source has the advantage of being able to freely select metal materials that are inexpensive and have good workability, such as stainless steel and copper.

[Brief explanation of the drawing]

FIG. 1(a) is a cross-sectional view of a conventional cation source, FIG. 1(b) is its potential diagram, and FIG. 2(a) is a cross-sectional view of a conventional negative ion source. Figure Bb) is its potential diagram, Figure 3(a) is a cross-sectional view of the ion source for anions according to the present invention, Figure 3(b) is its potential diagram, and Figure 4(a) is the cation source according to the present invention. FIG. 4(b) is a cross-sectional view of the ion source for use, FIG. 4(b) is a potential diagram thereof, FIG. 5 is a cross-sectional view of an embodiment of the present invention, and FIG. 5(C) is a diagram showing the mesh in FIG. 5(b), FIG. 6 is an illustration of the performance of the ion source which is an embodiment of the present invention, and FIG. 7 is a diagram showing the mesh in FIG. 5(b). Other inventions! , 7(b) is a sectional view taken along the line V■--■ of FIG. 7(a). 19.28, 36.57... Electrode for back shield,
20.29, 37.58... Filament for thermionic emission, 21, 30.3B, 59.60... Perforated electrode for sample holding, 22, 31, 39.61... Ion attraction No. 1
Figure %z Figure YJ 3 Figure distance Amphibious Z 4 Figure large Flesh color"f) 5 Figure q) 5 Otsu Figure' (L↓7to07ton゛rutono

Claims (1)

[Claims] 1. A perforated electrode for holding a sample is installed between the ion extraction electrode and the thermionic emitter, and anions are generated by bombarding the sample with electrons from the back side of the perforated electrode. Or, an ion source characterized by efficiently generating and desorbing cations and extracting an ion beam using an ion extraction electrode. 2. Claim 1, characterized in that by electron bombarding a compound containing one or more elements with a positive electron affinity value as a sample, only anions of the element are generated with high efficiency. The ion source described in.