GLOW DISCHARGE SYSTEM, ION EXTRACTION STRUCTURE THEREOF, AND GLOW DISCHARGE MASS SPECTROSCOPE

There is provided a glow discharge mass spectroscope having a higher analytical sensitivity by increasing an amount of extracted ion beams without a significant change in device construction and drive conditions of conventional glow discharge systems. An extraction plate 25 that is disposed at an ion extraction port of a discharge cell 20 and functions as an extraction electrode includes a first plate 26 that has a projection 26a projected toward a discharge region 27 in an opening 25a and that is disposed on the discharge region 27 side, and a second plate 28 that is connected to the first plate 26 in an outer circumferential edge and that is disposed with a gap provided between the first plate 26 and the second plate 28.

TECHNICAL FIELD

The present invention relates to a glow discharge system, an ion extraction structure thereof, and a glow discharge mass spectroscope using the glow discharge system.

BACKGROUND ART

A glow discharge mass spectroscope (GDMS) is known as an analyzer for various solid samples such as metals, semiconductors, and insulating materials. Such analyzer is a device that sputters a surface of a solid sample utilizing glow discharge and measures ionized constituent atoms of the solid sample with a mass spectrometer.

The analyzer has a glow discharge system in which, as disclosed in Patent Literature 1, a solid sample is placed so that a surface of the solid sample is exposed within a discharge cell, an inert gas is introduced into the discharge cell to generate glow discharge by which the solid sample is sputtered, and discharged atoms are ionized within the discharge cell, followed by extraction of ionized atoms as ion beams through an opening formed in the discharge cell.

Prior Art Reference

Patent Literature

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

In a glow discharge mass spectroscope, what is desired for an enhancement in analytical sensitivity is to increase a beam (ion) amount of ion beams extracted from the glow discharge system.

An object of the present invention is to provide a glow discharge mass spectroscope having a higher analytical sensitivity by increasing an amount of extracted ion beams without a significant change in device construction and drive conditions of a conventional glow discharge system.

Means for Solving the Problem

According to a first aspect of the present invention, there is provided an ion extraction structure of a glow discharge system used for a glow discharge mass spectroscope, the glow discharge system comprising:

an electroconductive cell body that forms a discharge region; and

an electroconductive extraction plate that is connected to the cell body with at least an insulating member provided between the cell body and the extraction plate and that has an ion extraction port, wherein

the extraction plate includes a first plate and a second plate that are connected to each other in an outer circumferential edge,

the first plate is disposed on a side of the discharge region and has a projection that is cylindrically projected from the ion extraction port toward the discharge region, and

any one of the first plate and the second plate is projected toward the other in the outer circumferential edge, and the first plate and the second plate are disposed in a region excluding the outer circumferential edge with a gap provided between the first plate and the second plate.

The ion extraction structure of a glow discharge system of the present invention includes a preferred embodiment wherein an electroconductive slit plate having a slit and an electroconductive end plate having an opening are disposed in that order between the cell body and the insulating member, and

the end plate has a shape in which a projection that is cylindrically projected toward an outside is provided in a flat plate having the opening at a position spaced apart from the opening by a predetermined distance on an outer circumferential side.

According to a second aspect of the present invention, there is provided a glow discharge system comprising the ion extraction structure of a glow discharge system according to the above present invention.

According to a third aspect of the present invention, there is provided a glow discharge mass spectroscope comprising:

a glow discharge system that extracts ion beams of constituent atoms of a solid sample from the solid sample by glow discharge; and

a mass spectrograph that performs a mass spectroscopic analysis of ions contained in the ion beams, wherein the glow discharge system is the glow discharge system according to the above present invention.

The glow discharge mass spectroscope of the present invention includes a preferred embodiment wherein a magnetic field system that separates and selects target ions from the ion beams extracted from the glow discharge system, and an electric field system that focuses energy of ion beams selected in the magnetic field system are further provided.

Effects of the Invention

The glow discharge system of the present invention can extract ion beams in an amount that has been significantly increased compared with the conventional glow discharge system by adopting a specific structure as an ion extraction structure. Thus, according to the present invention, an amount of ion beams to be analyzed in a mass spectrograph can be increased by slightly modifying an apparatus construction, thereby realizing a higher sensitivity in mass spectroscopic analysis of the solid sample than the prior art.

MODE FOR CARRYING OUT THE INVENTION

Although, for the present invention, embodiments will be described in more detail appropriately with reference to the drawings, the present invention should not be construed to be limited by the following embodiments. Well-known or publicly known techniques in the technical field can be applied to portions not specifically described in the following description and portions not specifically illustrated in the drawings.

The glow discharge system of the present invention is a system for a glow discharge mass spectroscope and is characterized by an ion extraction structure thereof. The glow discharge system of the present invention includes an electroconductive cell body forming a discharge region, and an electroconductive extraction plate that is connected to the cell body with at least insulating member provided between the cell body and the extraction plate and that has an ion extraction port. The present invention is characterized in that a beam amount of ion beams extracted from the glow discharge system is significantly increased by virtue of a construction of an extraction plate including a first plate having a projection projected from an ion extraction port toward a discharge region, and a second plate with a gap provided between the first plate and the second plate at the side of the ion extraction port.

At the outset, a conventional glow discharge system is illustrated inFIG. 2.FIG. 2is an end view that schematically illustrates a construction of a conventional glow discharge system and that is a cross section including a central axis of ion beams extracted from the glow discharge system.

The glow discharge system illustrated inFIG. 2includes a sample holder10that holds a solid sample30, and a discharge cell20that generates glow discharge to extract ion beams (not illustrated) from the solid sample30.

The sample holder10includes a front plate14that has an opening14aand that is disposed on a frame11with an insulating ring12provided between the frame11and the front plate14, and a solid sample30is held by being pressed against a sample isolator13by a plunger16that is a holding member with one main surface of the solid sample30facing the opening14a. A part of the main surface of the solid sample30is exposed within the opening14a. The frame11and the plunger16are formed of an electroconductive material, for example, aluminum, the insulating ring12is formed of an insulating material, for example, polyether ether ketone (PEEK), the sample isolator13is a plate that has an opening in communication with the opening14a, that is formed of an insulating material, for example, alumina, and the front plate14is formed of an electroconductive material, for example, tantalum.

The discharge cell20includes a cell body21that is cylindrical with one of openings being adjacent to an opening14aside of a front plate14that is an opening of a sample holder10, in contact with the front plat14, while the other opening side is an ion extraction port side. The cell body21has a discharge region27in its interior and has a gas introduction hole21afor introducing a discharge gas at a side wall. In the other opening of the cell body21, a slit plate22, an end plate41, a cell mounting plate24, and an extraction plate42are disposed in that order and each have an opening for extraction of ions to the outside. In the drawing,22adenotes a slit formed in the slit plate22. The discharge region27is a closed system except for the gas introduction hole21aand the slit22a. All of the cell body21, the slit plate22, and the end plate41are formed of an electroconductive material, for example, tantalum. The cell mounting plate24is an insulating member formed of an insulating material, for example, an insulating resin such as PEEK.

In the construction, an inert gas, for example, a high-purity argon gas (purity: 99.9999% or higher), is introduced through the gas introduction hole21ainto the discharge region27, and a predetermined voltage is applied by using the solid sample30as a negative electrode through the frame11and the plunger16, and using the cell body21, the slit plate22, the end plate41, and the front plate14as a positive electrode. Further, the extraction plate42functions as an extraction electrode for extraction of ions from the discharge region27and sets a potential in a range of minus several tens of volts to minus 1000 volts to the cell body21. In the discharge region27, glow discharge is generated, ions of a discharge gas sputter a surface of the solid sample30, emitted constituent atoms of the solid sample30are ionized by plasma in the discharge region27, and ionized atoms are passed through a slit22aand openings41a,42aand are extracted as ion beams.

The ion beams extracted from the glow discharge system are subjected to separation and selection of ions for analysis purposes in a magnetic field system not illustrated, the selected ion beams are subjected to beam energy focusing in an electric field system not illustrated, and a mass spectroscopic analysis for ions contained in the ion beams is performed in a mass spectrograph not illustrated to determine a composition of the solid sample30. Double-focusing mass spectrometers are preferred as the mass spectrograph.

Next, the glow discharge system of the present invention will be described with reference toFIGS. 1 and 3.FIG. 1is a diagram schematically illustrating a construction of an embodiment of a glow discharge system according to the present invention and is an end view of a cross section including a central axis of ions beams extracted from the glow discharge system, andFIG. 3is an enlarged view of a discharge cell20inFIG. 1.

The glow discharge system of the present invention has the same basic construction as the conventional glow discharge system, except that, as will be described later, an ion extraction structure of the discharge cell has been changed. Thus, only portions different from the conventional glow discharge system will be described, and portions that are the same as the conventional glow discharge system will be omitted.

In the present invention, an extraction plate25that is an extraction electrode for ion extraction includes a first plate26and a second plate28that are connected to each other in an outer circumferential edge. The first plate26is disposed on a discharge region27side and has a projection26athat is cylindrically projected toward the discharge region27from an opening25athat is an ion extraction port. Further, any one of the first plate26and the second plate28is projected toward the other in an outer circumferential edge, and the first plate26and the second plate28are disposed with a gap t3being provided therebetween in the region excluding the outer circumferential edge. In the embodiments illustrated inFIGS. 1 and 3, the first plate26is projected toward the second plate28side in the outer circumferential edge to form a gap t3. In the present invention, however, the second plate28may be projected toward the first plate26side in the outer circumferential edge.

A beam amount of ion beams extracted by the glow discharge system of the present invention is increased by adopting the above structure.

More preferably, the end plate23disposed between the slit plate22and the cell mounting plate24, as illustrated inFIG. 3, has a shape in which a projection23bthat is cylindrically projected toward an outside is provided in a flat plate having the opening23aat a position spaced apart from the opening23aby a predetermined distance on an outer circumferential side. Specifically, in the conventional structure illustrated inFIG. 2, the end plate41is tapered so that an inner diameter of an opening41ais increased from the discharge region27toward the outside on the whole thickness direction. On the other hand, in the present invention, a part of the taper portion is deleted to form a step.

The shape of the end plate23contributes to a further increase in beam amount of ion beams extracted by the glow discharge system of the present invention.

In the glow discharge system illustrated inFIG. 1, the solid sample30is a circular flat plate, all of the cell body21, all of the projections23b,26aare cylindrical, and all of the opening14aand the openings23a,25aare circular. Further, the slit22ais in a linear form perpendicular to a paper surface. In the invention of the present application, the shapes are not always limited to those described above.

The glow discharge system illustrated inFIG. 1is a flat cell-type glow discharge system that uses a flat plate-shaped solid sample30. In the present invention, however, the glow discharge system is not limited to the flat cell-type and can also be applied to a glow discharge system of a type that analyzes a pin cell-type rod-shaped solid sample not illustrated.

In the present invention, an electric conductor or a semiconductor material can be directly analyzed as a solid sample30. Further, for the insulator, electric conductors such as gold, graphite, and silver can be mixed as a binder with an insulator and molded into a solid sample30, followed by analysis of the solid sample30. Further, even solid flat plate-shaped insulators can be analyzed by using an auxiliary electrode (not illustrated) as a negative electrode to generate glow discharge.

Examples

A glow discharge system in a glow discharge mass spectroscope “model VG9000Mk4” manufactured by Thermo Elemental limited was replaced with a glow discharge system of the present invention shown inFIG. 1, and a mass spectroscopic analysis of a solid sample of copper was performed. Further, the copper solid sample as used above was subjected to a mass spectroscopic analysis under the same conditions as described above, except that a conventional glow discharge system illustrated inFIG. 2was used in the glow discharge mass spectroscope. Respective site sizes were t1=0.5 mm, t2=2 mm, t3=0.5 mm, t4=0.5 mm, t5=2.0 mm, t6=0.5 mm, t7=1.5 mm, t8=1.0 mm, t11=0.5 mm, t12=1.5 mm, and t13=3.5 mm. The opening25ahad an inner diameter of 5.0 mm, and the slit22ahad a width of 0.16 mm and a length of 1.0 mm.

Copper contains Cu63 and Cu65 that are isotopes, at a mass ratio of Cu63:Cu65=7:3. For this reason, Cu63 having a high content has hitherto been measured for copper measurement. Also in this Example, a peak of Cu63 had a height of 1.0×10−9A in a mass spectroscopic analysis using the conventional glow discharge system.

On the other hand, in a mass spectroscopic analysis using a glow discharge system of the present invention, due to an excessively high peak as a result of Cu63 measurement, Cu65 having a low content was measured for detector protection purposes. As a result, the peak had a height of 1.1×10−9A that was 2.5×10−9A in terms of Cu63. This height was more than twice the peak height of Cu63 measured using the conventional glow discharge system. Analysis charts for the obtained Cu65 and Cu63 are illustrated inFIGS. 4 and 5.

EXPLANATION OF REFERENCE NUMERALS