DE10248055B4 - Method for excitation of optical atomic emission and apparatus for spectrochemical analysis - Google Patents

Abstract

Device for exciting solid samples, comprising - an ion beam cannon with two concentrically arranged tubes (2, 3) made of non-conductive material and with acceleration electrodes (4), and - a generator (7) for generating high-frequency high voltages with unidirectional or bidirectional current profiles, characterized that - a main counter-electrode (1) is arranged in the inner of the two tubes (2) of the ion beam gun, - a grounded sample table (8) is provided, - between the main counter-electrode (1) and the sample table (8) the Acceleration electrodes (4) are provided, and - a protective gas (5) flows between the outer tube (3) and the inner tube (2).

Description

1. Field of the invention

The invention described below relates to the use of optical emission spectroscopy (OES) for spectrochemical analysis, in particular to the use of an ion beam gun (ISK) and a generator for generating the ion beam as an excitation source in optical emission spectrometers , as well as methods of OES when using the ISK and the generator.

2. Background of the invention

The OES involves exciting the chemical elements (analytes) of a sample to emit their characteristic optical spectra. In the application of the OES for samples of solids, especially metals, the analytes are usually caused by the excitation by means of an electric spark discharge, an electric arc or a glow discharge to send out their characteristic spectra. All of these methods are based on the use of direct currents or low frequency pulsed currents for sample excitation. The stimulating discharge occurs between the sample and a counter electrode.

Due to the nature of the excitation, the above methods are only suitable for conducting samples. Another problem is the contamination of the counter electrode, which is only a few millimeters away from the sample, with the vaporized material, which falsifies a subsequent analysis. Furthermore, the discharges are not stationary, that is to say that each individual excites a different sample spot and thus the discharge channel in front of the entrance slit or light guide of the spectrometer is in a different position than the preceding, which suffers the reproducibility of the measurements.

According to the invention, in contrast to the above-mentioned methods, medium to high-frequency currents are used at high voltages for the indirect excitation of the solid samples. However, the distance between the counter electrode and the sample is in the range of 40 to 100 mm, so that the above-mentioned contamination is virtually eliminated and "memory effects" are absent from the previous measurement. The ion beam generator has the ability to generate high frequency sequential, triangular or rectangular current waveforms at high voltages that ionize a gas, preferably argon, as it passes through the ISK. Subsequently, the ionized gas atoms in the ISK experience a high acceleration in the direction of the sample due to the generated voltages. In the further course, in contrast to the above excitation methods, the highly accelerated ions strike the surface of the sample and there dissolve material which is excited by the ion beam through the mentioned current pulses and multiple collisions between argon ions and sample atoms.

Because of the high frequency currents or voltages generated by the generator, the ion beam system is capable of accomplishing several millions of stripping and excitation processes per analysis. Such a high number of individual optical signal events significantly improves the analytical results. The very well-defined, round and uniform focal spot also allows the thickness of several layers of a sample surface to be sequentially measured by determining the time to penetrate a layer. Therefore, the ion beam excitation method, according to the claim of the invention, combines the advantages of spark and glow discharge systems.

3. Description of the invention

1 schematically shows the ISK and the arrangement of the ion beam generator. The ISK consists essentially of two concentrically arranged glass tubes ( 2 ) and ( 3 ). To determine the outflow velocity of the ion beam gas ( 10 ), preferably argon, is the diameter of the upper tube part ( 2 ) greatly reduced. As a result, the outflowing ion beam ( 10 ) Speeds of preferably several tens of meters per second, which ensures a very well defined, round and uniform focal spot on the sample surface. The outer protective gas tube ( 3 ) is protected by inert gas ( 5 ) flows through, preferably nitrogen or argon, to the ion beam ( 10 ) after having left the ISK ( 11 ) and thereby shield him from the ambient atmosphere. The flow velocity of the protective gas ( 11 ) should be on the order of preferably several meters per second.

The ion beam generator ( 7 ) provides the means for generating high voltages at high frequencies, with which the main counterelectrode ( 1 ) and the accelerating electrodes ( 14 ) 15 ) with grounded sample table ( 8th ) 12 ). Furthermore, the ion beam generator ( 7 ) the possibility to choose between pre-programmed, preferably triangular or rectangular, current waveforms, with which the electrode ( 1 ) over the connection ( 13 ) is supplied.

The between the electrodes ( 1 ) 4 ) and the sample ( 9 ) high-frequency high-voltage ionizes the passing gas ( 5 ) and accelerates the gas atoms after ionization, whereby the ion beam ( 10 ) arises. The acceleration of the positively charged, heavy (argon) ions on their way to the sample surface ( 9 ) is capacitively coupled by the acceleration electrodes ( 4 ).

The heavy ions hit the sample surface after acceleration ( 9 ) and support the current pulses during the detachment of the sample material for subsequent excitation. The current pulses, in combination with multiple bursts of ions, excite the atoms detached from the sample to emit their characteristic optical spectra. The light spectrally distributed according to the sample composition is transmitted via an optical recording system ( 16 ) to a spectrometer, by means of which the light is decomposed into its spectral components and analyzed.

4. Execution of the ISK

• a) Die innere Glasröhre (2) wird von Argon (6) durchströmt, so dass der ausströmende und ionisierte Gasstrahl eine Geschwindigkeit im Bereich von 20 bis 50 m/s erreicht. Dieser Ionenstrahl hat einen Durchmesser von 1,5 bis 2 mm, wodurch auf der Probe ein Brennfleckdurchmesser von 3 bis 4 mm entsteht.
• b) Die äußere Glasröhre (3) dient zur Erzeugung einer Schutzgasummantelung (11) für den Ionenstrahl (10), welche ihn von der umgebenden Atmosphäre abschirmt. Die Ausströmgeschwindigkeit des Schutzgases (11) beträgt etwa 1 bis 2 m/s.
• c) Die innere (2) und die umgebende (3) Glasröhre sind in der Art angeordnet, dass der Abstand zwischen ihnen und der Probe (9) im Bereich von 40 bis 100 mm liegt.
• d) Die vom Ionenstrahl-Generator abgegebene Leistung für die hochfrequente Hochspannung liegt im Bereich von 100 bis 200 W.

The inventive apparatus of the ISK shows 1 ,

• a) The inner glass tube ( 2 ) is separated from argon ( 6 ) flows through, so that the effluent and ionized gas jet reaches a speed in the range of 20 to 50 m / s. This ion beam has a diameter of 1.5 to 2 mm, resulting in a focal spot diameter of 3 to 4 mm on the sample.
• b) The outer glass tube ( 3 ) is used to generate a protective gas jacket ( 11 ) for the ion beam ( 10 ), which shields him from the surrounding atmosphere. The outflow velocity of the protective gas ( 11 ) is about 1 to 2 m / s.
• c) The inner ( 2 ) and the surrounding ( 3 ) Glass tubes are arranged in such a way that the distance between them and the sample ( 9 ) is in the range of 40 to 100 mm.
• d) The power supplied by the ion beam generator for the high-frequency high voltage is in the range of 100 to 200 W.

5. Application examples

Attempts to verify analytical capabilities have been made with the apparatus described above. Below are some results to be shown.

5.1 Ablation speed of the ion-jet source

a) Appearance of the focal spot:

The ablation crater produced by the ion beam on the sample has a parabolic depth profile. At the edge of the crater, material is deposited during the ablation process, forming a wall around it.

b) Measurement results:

The penetration depths as a function of time, as well as the edge heights and the aspect ratio of edge height to penetration depth are given in Table 2 again.

c) Analytical results:

The table in 3 lists for some selected lines the detection limits (LOD) and Background Equivalent Concentrations (BEC) achieved using the ion beam source.

The results presented above are based on aluminum-based samples and are only preliminary results. Further optimization of the ion beam system will certainly further enhance analytical capabilities.

LIST OF REFERENCE NUMBERS

1

counter electrode

2

Glass tube for ion beam

3

Glass tube for inert gas flow

4

accelerating electrodes

5

Protective gas flow

6

Gas stream for ion beam

7

An ion beam generator

8th

Plate of the sample table

9

Solid sample

10

ion beam

11

Protective gas flow

12

Grounding connection

13

power line

14

Connection to the accelerating electrode

15

Connection to the accelerating electrode

16

Optical fiber to the spectrometer

Claims (7)

Device for exciting solid samples, comprising - an ion beam gun with two concentrically arranged tubes ( 2 . 3 ) made of non-conductive material and with accelerating electrodes ( 4 ), as well as - a generator ( 7 ) for the generation of high-frequency high voltages with unidirectional or bidirectional current characteristics , characterized in that - in the interior of the two tubes ( 2 ) of the ion beam gun a main counter electrode ( 1 ), - a grounded sample table ( 8th ), between the main counterelectrode ( 1 ) and the sample table ( 8th ) the acceleration electrodes ( 4 ) are provided, and Between the outer tube ( 3 ) and the inner tube ( 2 ) a protective gas ( 5 ) flows. Device according to claim 1, characterized in that the tubes ( 2 . 3 ) are made of quartz glass. Device according to one of the preceding claims, characterized in that the acceleration electrodes ( 4 ) on the outside of the inner tube ( 2 ) of the ion beam gun are mounted. Device according to one of the preceding claims, characterized in that the tubes ( 2 . 3 ) of the ion beam gun at its the sample stage ( 8th ) facing end have a reduced diameter to increase the flow velocity. Device according to one of the preceding claims, characterized in that the high-frequency high voltage current pulses with pre-programmed triangular or rectangular shape. Device according to one of the preceding claims, characterized in that the generator ( 7 ) has means for changing the frequency and current for supplying the sample-electrode system. Device according to one of the preceding claims, characterized in that the inside of the tube ( 2 ), ionized gas ( 6 ) via a capacitive coupling with the electrodes ( 4 ) is accelerated.

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