US3284629A - Mass filter having an ion source structure with preselected relative potentials applied thereto - Google Patents

Mass filter having an ion source structure with preselected relative potentials applied thereto Download PDF

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Publication number
US3284629A
US3284629A US255769A US25576963A US3284629A US 3284629 A US3284629 A US 3284629A US 255769 A US255769 A US 255769A US 25576963 A US25576963 A US 25576963A US 3284629 A US3284629 A US 3284629A
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Prior art keywords
ion
field
potential
ions
ion source
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US255769A
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English (en)
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Zahn Ulf Von
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Siemens Schuckertwerke AG
Siemens Corp
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Siemens Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J49/00—Particle spectrometers or separator tubes
    • H01J49/26—Mass spectrometers or separator tubes
    • H01J49/34—Dynamic spectrometers
    • H01J49/42—Stability-of-path spectrometers, e.g. monopole, quadrupole, multipole, farvitrons
    • H01J49/4205—Device types
    • H01J49/421—Mass filters, i.e. deviating unwanted ions without trapping

Definitions

  • My invention relates to the separation of ions of respectively different charge-to-mass ratios in periodically Varying electric fields whose potential is a square function of the space coordinates.
  • the travelling ions may perform two kinds of motion. In one kind they follow stable paths, that is, the ions oscillate about the center of symmetry of the field with amplitudes not exceeding a maximum value which is different for each ion. In the other kind of motion, the amplitudes increase with time so that, after a sufficient dwell of travel time in the field, the corpuscles impinge upon the field-producing electrodes or upon other neighboring components of the device and are thus separated. They then follow instable paths.
  • Increasing the number n of cycles of ion travel may be accomplished by operating with a very high frequency at which f(t) oscillates; by providing long and extensive fields; or by using slow ions.
  • f(t) oscillates By providing long and extensive fields; or by using slow ions.
  • the high frequency power for operating a mass filter of this type increases rapidly with frequency.
  • the increase in energy demand is proportional to the fifth power of the frequency. In practice, therefore, an increased frequency is advantageous only within very narrow limits.
  • the acceleration voltage with which the ions are extracted from the ion source must be low. Hence, the extracted ion current is also low.
  • This difiiculty can be partly overcome by initially using a high voltage for extracting the ions and then decelerating them before they pass into the analyzer field.
  • many ions, thus decelerated enter the analyzer field at a considerable angle to the shoot-in direction so that most of them are not subjected to mass separation because many of the ions travelling along theoretically stable paths are also separated and impinge upon the field electrodes.
  • the maximum oscillation amplitude of such ions is greater than the distance of 'the field electrodes from the field axis. The efiiciency and resolving power of such mass filters, therefore, is rather poor.
  • Another object of my invention is to provide an ion separating method and means of higher resolving power than has hitherto been available with similar equipment, particularly at corresponding ion currents.
  • Yet another object of my invention is to provide an ion separating method and means having a higher ion current than that obtainable with conventional methods and apparatus of similar size and power, particularly with corresponding resolving power. More specifically, the invention aims at increasing the separated ion current, obtainable with conventional methods and apparatus, by more than one order of magnitude.
  • Another object of the invention is to improve i-on separating methods and means and achieve an increase in the resolving power, of the ion current or both, with conventional apparatus only slightly modified.
  • Another object of the invention is to provide an ion separating method and means which is advantageous despite considerable energy inhomogeneity in the ions utilized and which does not restrict the applicability of the general separating processes and means.
  • I vary the location width of the stable or instable ranges by varying the amplitude, the frequency and/ or the oscillatory form of the field-producing voltages.
  • I superimpose further alternating voltages having small amplitudes.
  • FIG. 1 is a schematic and block diagram of a mass filter system according to the invention
  • FIG. 2 is a schematic illustration of part of a mass or spectroscopic filter.
  • FIGS. 2a, 2b, 2c are graphs of the potentials appearing within the filter of FIG. 2;
  • FIGS. 3 and 3a are schematic representations of two circuits suitable for energizing the field electrodes of the mass filter in FIG. 2;
  • FIG. 4 is a graph showing measurements of the ion collector current and of the resolving power (m/Am) relative to the effective energizing voltage of the apparatus in FIG. 11.
  • the mass-filter cell 1 is provided 'with an envelope 5 which contains an ion source 2, and a group of rod-shaped deflector electrodes 3 having individually a circular cross section.
  • Located at the end of the ion-beam path is a cup-shaped collector electrode 4.
  • the ion source 2 and the collector electrode 4 are coaxially spaced from each other and thus define a center axis for the ion beam issuing from the source 2 toward the electrode 4.
  • the electrode rods 3 are uniformly distributed about the ion-beam axis and extend parallel thereto. A total number of four such electrodes are used.
  • the above-mentioned envelope 5 of the cell 1 is vacuum-tightly sealed and has a nipple or neck 6 connected with a tank 7 containing the gaseous mixture to be investigated.
  • the rod electrodes 3 are electrically connected in pairs to a high-frequency generator 8 which supplies electric energy of suitable voltage and frequency.
  • the current due to the ions impinging upon the collector 4 is amplified by an amplifier 9 and supplied to a recorder 10 or other indicating or measuring device.
  • Another measuring instrument 10 is provided for supervising the electron emission of the cathode in the ion source 2.
  • FIG. 2 is a detailed view of part of the filter cell or vessel 1 together with energizing components.
  • Comprising the ion source 2 is an ionization space 21 with an exit diaphragm 22, two intermediate diaphragms 23 and a shoot-in or entrace diaphragm 24.
  • the space 21 and diaphragms 23, 24 connect to respective potentials in the instrument 10 which also constitutes a grounded voltage source.
  • the high-frequency generator 8 applies to the rods 3 a voltage to produce a potential 4 plus the D.-C. potential as shown and discussed relative to FIGS. 2a, 2b, 2c, 3 and 3a.
  • the instrument 10' applies to exit diaphragm 22, 250 volts D.-C. and to the entrance diaphragm 24, 0 volts, or ground potential.
  • the high-frequency generator 8 in addition to the alternating field applies to the rods 3 a D.-C. potential of to 200 volts.
  • a diagram illustrating the potentials within the vessel 1 for these conditions is shown in FIG. 2a.
  • FIGS. 2b and 2c illustrate D.-C. voltage conditions according to two other embodiments of the present invention.
  • the abscissas represent distance along the vessel axis, the potential graphs being aligned vertically with the components corresponding to the potentials indicate-d.
  • FIG. 2a illustrates the embodiment where the entrance diaphragm is connected to ground. The formation of ions occurs at a high positive potential; the entire ion deceleration analyzer field being almost as high in potential.
  • the generation of ions is effected at a low positive potential (p and the analyzer field, just like in conventional methods, is symmetrical with respect to ground. In this case, however, a strong negative potential (p is applied to the entrance diaphragm.
  • the ions are generated at zero potential. They are then accelerated towards the entrance diaphragm 24 which has a high negative bias voltage, and then again decelerated to the 'low negative potential of the analyzer field.
  • FIGS. 3 and 3a illustrate respectively two embodiments of the high frequency generator 3 connected to the rods 3 as exemplified in FIGS. 2 and 2a.
  • the analyzer rods 3 are supplied with voltage by a high-frequency oscillator 12 and by a constant voltage source 13.
  • Parallel-resonant filter circuits 16 prevent the high frequency from reaching the direct-voltage source.
  • a potentiometer 14 is centrally tapped and connected to ground via a constant voltage source 15. The latter achieves the potential pTIF of FIG. 2a.
  • the constant voltage source is omitted and the potential (p of FIG. 2a is achieved by shifting the tap of the voltage divider out of its central position.
  • the source 15 in FIG. 3 is reversed, and the position of the tap in FIG. 3a of divider .14 is shifted to the other side of the center.
  • the value of the voltage is according to the values of FIG. 20.
  • the potential distribution in accordance with FIGS. 2a and 2c is effected by supplying the constant voltage portion U of the function f(t) to the mass filter in an asymmetrical relationship with respect to ground, rather than in the usual symmetrical relationship with respect thereto. This is achieved by the bias voltage 15 (FIG. 3) or by the asymmetrical ground connection (FIG. 3a).
  • the ions were generated in a normal electron impact source at a potential (p and were accelerated towards a ground-connected entrance diaphragm 24. They entered the analyzer field through said diaphragm with respective energies of 70, 20 or 17.5eV.
  • the deceleration potential (p was superimposed upon t-he analyzer field so that the ions travelled through the analyzer field with an energy wherein e is the :unit charge.
  • FIG. 4 is a graph of resolving power m/Am and ion current relative to effective voltage U for three values of potential (p namely 17.5, 20, and 70 volts.
  • the present invention achieves the same resolving power as the conventional method, provided that the energy of the ions in the analyzer field is the same.
  • the fact that the curves do not exhibit a completely continuous or monotonous path is due to the specific construction of the apparatus as used. Measurements indicate that the energy homogeneity of the ions was not substantially altered by the decelerating action of the present invention. Consequently, the method of the present invention is adapted to improve considerably the performance of mass filters, particularly for a small apparatus wherein it is difficult to reach the required number n.

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
US255769A 1962-02-03 1963-02-04 Mass filter having an ion source structure with preselected relative potentials applied thereto Expired - Lifetime US3284629A (en)

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DES0077876 1962-02-03

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US (1) US3284629A (de)
CH (1) CH409462A (de)
DE (1) DE1498971A1 (de)
GB (1) GB1035495A (de)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3767914A (en) * 1971-05-17 1973-10-23 Bendix Corp Continuous injection mass spectrometer
US4214160A (en) * 1976-03-04 1980-07-22 Finnigan Corporation Mass spectrometer system and method for control of ion energy for different masses

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2636990A (en) * 1949-12-14 1953-04-28 Atomic Energy Commission Ion source unit
US2939952A (en) * 1953-12-24 1960-06-07 Paul Apparatus for separating charged particles of different specific charges
US2950389A (en) * 1957-12-27 1960-08-23 Siemens Ag Method of separating ions of different specific charges

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2636990A (en) * 1949-12-14 1953-04-28 Atomic Energy Commission Ion source unit
US2939952A (en) * 1953-12-24 1960-06-07 Paul Apparatus for separating charged particles of different specific charges
US2950389A (en) * 1957-12-27 1960-08-23 Siemens Ag Method of separating ions of different specific charges

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3767914A (en) * 1971-05-17 1973-10-23 Bendix Corp Continuous injection mass spectrometer
US4214160A (en) * 1976-03-04 1980-07-22 Finnigan Corporation Mass spectrometer system and method for control of ion energy for different masses

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DE1498971B2 (de) 1970-10-29
CH409462A (de) 1966-03-15
GB1035495A (en) 1966-07-06
DE1498971A1 (de) 1969-01-30

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