Patent Application
20110291005
The invention relates to a mass spectrometer arrangement.
Mass spectrometric measuring methods are currently applied in manifold type and manner in the field of process engineering, technology and product development, medicine and in scientific research. Typical application areas are herein leakage testing of structural parts in various industrial fields, quantitative determination of the composition and purity of process gases (partial pressure determination of gas fractions), complex analyses of reactions on surfaces, investigation and process monitoring in chemical and biochemical procedures and processes, analyses in the area of vacuum engineering, for example of plasma processes, such as, for example, in the semiconductor industry, etc.
For this purpose a multiplicity of different methods for the physical mass separation of particles has been developed and, correspondingly, measuring instruments for practical use have been realized. All of these measuring instruments have in common that they require vacuum for their operation. The neutral particles to be analyzed are inducted into the vacuum of the system and ionized in a reaction zone. This component is conventionally referred to as ion source. The ionized particles are subsequently conducted out of this zone with the aid of an ion optics and supplied to a system for mass separation. There are various concepts for the mass separation. For example, in one case the ions are deflected via a magnetic field, wherein, depending on their mass, the particles are subject to large deflection radii which can be detected. Such a system is known by the name sector field mass spectrometer. In a further, very widely used system the mass filter is comprised of an electrostatic system of four rods into which the ions are shot. On the rod system is impressed a high-frequency alternating electrical field, whereby the ions execute oscillations of different amplitude and trajectory, which can be detected and separated. Among experts this system is known as a quadrupole mass spectrometer. This mass spectrometer has various advantages such as, in particular, high sensitivity, wide measuring range, high measurement repetition rate, small dimensions, arbitrary mounting orientation, direct compatibility in important applications in vacuum engineering and good operability.
The ion sources of these known mass spectrometers conventionally employ a thermionic cathode which includes a heated filament, thus an incandescent cathode, for the generation of electrons which ionize the neutral particles under bombardment. While on this conceptual basis, the quality, for example of the quadruple spectrometer, is already quite good, the thermionic cathodes utilized, however, have various disadvantages which then also have an overall negative effect on the mass spectrometer.
One problem is that from an incandescent cathode, material of the filaments is also always vaporized and thereby undesirable particles are superimposed on the particles to be measured, which increases the so-called signal noise and consequently negatively effects the measuring accuracy or falsifies the measurement signal.
A further problem consists in that on or in the proximity of the hot filament chemical reactions take place with the particles to be measured and thereby the measurement is falsified and the resolution decreased. The emission of light, thus of photons which can interact, is herein of disadvantage. The hot arrangement leads additionally to increased temperature fluctuations which result in increased drift behavior and poor reproducibility of the measurement results. A filament, moreover, is vibration-sensitive, which can lead to undesirable signal fluctuations (microphony) or even to breakage under severe shock.
The present invention addresses the problem of eliminating or reducing the disadvantages of the prior art. The problem in particular is involved by providing a mass spectrometer arrangement which permits generating an undisturbed spectrum of the gas to be measured at a better signal/noise ratio, which permits higher resolution and sensitivity and to achieve this in particular for quadrupole mass spectrometer arrangements. The mass spectrometer arrangement, additionally, is to be economically producible.
The problem is resolved with the mass spectrometer arrangement of the invention.
According to the invention the mass spectrometer arrangement comprises a cathode configuration for the emission of electrons, a reaction zone, which is connected with an entrance opening for the supply of neutral particles, wherein this opening is operatively connected with the cathode configuration, for the ionization of neutral particles, an ion extraction system, which is disposed such that it communicates with the effective region of the reaction zone, means for guiding ions to a detection system within the mass spectrometer arrangement and means for evacuating the mass spectrometer arrangement. The cathode configuration herein includes a field emission cathode with an emitter surface, wherein at a short distance from this emitter surface is disposed an extraction grid for the extraction of electrons, which grid substantially covers the emitter surface. The emitter surface herein encompasses at least partially a hollow volume, such that a tubular structure is formed.
The formation according to the invention of the field emission cathode configuration within the mass spectrometer arrangement permits the cold operation without photon emission in the ion source avoiding the problems listed above, which leads to the corresponding substantial improvement of the properties of the mass spectrometer. Such a cathode and ion source is, moreover, simpler to construct and fewer measures need also to be expended in the remaining parts and in the electronic evaluation circuitry for error compensation. This leads to greater economy of production of the entire measuring system and offers better capabilities for analyzing the results, such as the generated spectra.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure and are entirely based on Swiss priority application no. 1380/06 filed Aug. 29, 2006, and International application PCT/CH2007/000371 filed Jul. 27, 2007, and U.S. patent application Ser. No. 12/376,542 filed Feb. 5, 2009, the PCT and U.S. applications being incorporated here by reference.
In the following the invention will be described schematically and by example in conjunction with the drawings wherein:
A mass spectrometer arrangement according to the invention comprises substantially an ion source 6, 4, 5, an ion optics 4, 1, 10, 11 for the extraction and guidance of the ions 22, as well as an analyzer system 12, as is depicted in longitudinal section in
The ion source includes a cathode configuration 6 which includes an emitter surface 7 as field emitter, which is formed as a two-dimensional field emission cathode and at a short distance in front of this surface 7 an extraction grid 9 is disposed which is impressed with a voltage source 24 at a voltage VG with respect to the emitter surface 7 for the formation and extraction of electrons 21, as is also shown in detail in
The distance between the extraction grid 9 and the emitter surface 7 should be set to a value in the range of 1.0 μm and 2.0 mm, advantageously to a value in the range of 5.0 μm and 200 μm, which simplifies the structuring. The selected value is advantageously to be substantially uniformly employed over the entire emitter surface.
The emitter surface 7 is formed as an arcuate surface and encompasses at least partially a hollow volume 13 such that a tubular structure is formed. It can also be divided into sector elements, thus have discontinuities. In this case only the emitter surface 7 as a layer can itself be divided and not the support or the support can also be divided. However, preferred is a substantially nondivided surface which is self-closing and thereby the hollow volume 13, at least on the wall of the tubular structure, is also closed. The tubular structure is advantageously formed substantially cylindrically. This simplifies the structuring and permits better signal optimization.
The dimension of the emitter surface 7 should be in the range from 0.5 cm2 to 80 cm2, the range from 1.0 cm2 to 50 cm2 being preferred. The diameter of the formed hollow volume 13 is in the range between 0.5 cm and 8.0 cm, preferably in the range from 0.5 cm to 6.0 cm. The length of the hollow volume 13 in the axial direction is in the range between 2.0 cm and 8.0 cm.
The emitter surface 7 is comprised of an emitter material or is produced as a coating from this material, this material containing at least one of the materials of carbon, metal or a metal mixture, a semiconductor, a carbide or mixtures of these materials. Preferred are herein metals, in particular molybdenum and/or tantalum. Especially preferred are corrosion-resistant steels. Mixtures of these metals can also be employed. If the emitter surface 7 is deposited as a thin layer onto the wall 2 of a support, vacuum processes are preferred, such as chemical vapor deposition (CVD) and physical vapor deposition (PVD).
An especially advantageous implementation of the emitter surface 7 comprises that this surface is comprised of the material of the wall 2 of the support itself and covers at least a portion of the surface of the housing wall 2 thus formed, preferably however assumes, if possible, the entire surface of wall 2 which encompasses the hollow volume 13. The housing wall 2 comprises in this case one of the above listed metals itself or a metal alloy, preferably a corrosion-resistant steel. The wall 2 could also be covered with a type of sleeve of the emitting material. If the housing wall 2 and the emitter surface 7 are comprised of the same material, the arrangement can be realized more simply and better. The housing wall can in this case also be formed directly as a vacuum housing, whereby a further simplification is attained. It is then also of advantage if the housing wall 2, and therewith the emitter surface 7, is electrically at ground potential, as is shown in
The surfaces of said coating or the surface of the solid material of the housing wall 2 must be roughened such that a suitable emitter surface 7 is formed, which subsequently has field emission properties, such that it is capable of emitting sufficient electrons 21 at the low grid extraction voltage VG. The roughening can be carried out mechanically, preferably by etching, such as plasma etching or preferably through chemical etching. Hereby in extremely simple manner a multiplicity of irregularly distributed prominences is generated, which are sharp-edged and/or tip-like with dimensions in the nanometer range, whereby field emission of electrons is possible even at low field strengths. Such prominences have heights compared to the mean base surface within a range of 10 nm to 1000 nm, preferably within 10 nm to 100 nm.
Known field emitters, such as Spint Mikrotips, are structured, for example, as an array-form uniformly distributed tip arrangement. This takes place through multiple, complex erosion and application of material. For this purpose complex and expensive multi-stage structuring processes are necessary. Such processes can also not take place on any surface, such as for example on inner surfaces of small tubular parts.
In contrast, in the present invention the present surface is roughened simply. The roughening herein takes place exclusively using a single structuring step, such that the desired sharp-edged or tip-like elements are formed, which permit the desired field emission. In the mechanical working of the surface this is generated, for example, through a grinding process. In the preferred etching this is generated through the inherently present grain structure of the basic material. The emitting tips are thereby distributed stochastically.
The electrons 21 generated in such manner with the cathode configuration 6 and accelerated impinge within a reaction zone 3 onto the neutral particles 20 which are here ionized. The reaction zone 3 is thus connected with an entrance opening 14 for the supply of neutral particles 20.
In an embodiment of the invention, such as depicted in
The neutral particles 20 in this formation are admitted into this reaction volume 3 radially with respect to the axis, laterally of the reaction volume 3 through the entrance opening 14. The extracted ions 22 are guided through the ion optics 4, 1 onto a focusing means 10, 11 and subsequently into the analyzer 12. In the preferred quadrupole mass spectrometer the ion optics includes, for example, an extraction lens 4 and a further lens 1, here shown as base plate at ground potential and the succeeding focusing means includes a focusing lens 10 and an injection aperture plate 11, as well as the detection system as a four-fold rod system. In
The entire arrangement is, in addition, developed such that for operation it can be evacuated, be that by flanging it to pumped vacuum systems and/or by providing it with its own pumps.
A further preferred embodiment of the invention is depicted in
The neutral particles 20 to be analyzed are admitted through an entrance opening 14 into the hollow volume 13 of the tubular cathode configuration. This entrance opening is located at the end side with respect to the tubular hollow volume 13, opposite to the ion extraction lens 4. The tubular cathode configuration 6 with the ion extraction lens 4 is advantageously axially oriented, thus in line with respect to the longitudinal axis of the quadrupole mass spectrometer arrangement. The motion direction 23 of the extracted ions 22 leads here along the longitudinal axis in the direction of the analyzer 12.
A further preferred arrangement according to the invention is shown in
Through the arrangement according to
This is a continuation of U.S. patent application Ser. No. 12/376,542 filed Feb. 5, 2009 and now U.S. Pat. No. ______, which is a 371 application of PCT/CH2007/000371 filed Jul. 27, 2007, which two applications are incorporated herein by reference, and which claims priority from Swiss patent application no. 1380/06 filed Aug. 29, 2006, which claim of priority is repeated here.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12376542 | Feb 2009 | US |
| Child | 13205925 | US |
