US3876305A - Demountable sputtering cathode for atomic absorption spectroscopy - Google Patents

Demountable sputtering cathode for atomic absorption spectroscopy Download PDF

Info

Publication number
US3876305A
US3876305A US389088A US38908873A US3876305A US 3876305 A US3876305 A US 3876305A US 389088 A US389088 A US 389088A US 38908873 A US38908873 A US 38908873A US 3876305 A US3876305 A US 3876305A
Authority
US
United States
Prior art keywords
sample
gas
vacuum chamber
discharge
vacuum
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US389088A
Other languages
English (en)
Inventor
David Samuel Gough
Peter Hannaford
Alan Walsh
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Commonwealth Scientific and Industrial Research Organization CSIRO
Original Assignee
Commonwealth Scientific and Industrial Research Organization CSIRO
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Commonwealth Scientific and Industrial Research Organization CSIRO filed Critical Commonwealth Scientific and Industrial Research Organization CSIRO
Application granted granted Critical
Publication of US3876305A publication Critical patent/US3876305A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H3/00—Production or acceleration of neutral particle beams, e.g. molecular or atomic beams
    • H05H3/02—Molecular or atomic-beam generation, e.g. resonant beam generation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/66—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light electrically excited, e.g. electroluminescence
    • G01N21/67—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light electrically excited, e.g. electroluminescence using electric arcs or discharges
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/71—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light thermally excited
    • G01N21/74—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light thermally excited using flameless atomising, e.g. graphite furnaces

Definitions

  • ABSTRACT Techniques and apparatus for measuring the concentration of elements in a solid metal sample by atomic absorption and fluorescence are described.
  • a silica disc with an annular dischargcsuppressing gap surrounding the sample area and an O-ring seal are used to locate a surface of the sample for sputtering. and gas passages in the disc allow sputtered atoms to be swept into the body of a vacuum chamber for convenient analysis.
  • the flame method also suffers to a greater or lesser extent from other disadvantages, including pressure broadening of absorption lines, quenching of fluorescence radiation, compound formation in the flame, and opacity of the flame gases to vacuum-ultraviolet light.
  • the sputtered atoms rapidly come to thermal equilibrium with the gas, and sputtering and diffusion rates are such that relatively large steady-state concentrations accumulate in the region around the cathode.
  • the negative glow is relatively well confined, and the anode glow and positive column can be virtually eliminated by positioning the anode at the edge of the negative glow.
  • large concentrations of relatively emissionfree sputtered vapours, in thermal equilibrium with the gas, are available in the region just beyond the negative glow.
  • the invention provides a method and apparatus whereby samples for spectrochemical analysis by sputtering may be interchanged rapidly.
  • the invention avoids the contamination difficulties associated with the introduction of the whole sample into the vacuum chamber by allowing the bulk of the sample, if it is a solid block, to remain outside the chamber.
  • the sample may be in the form of a solid piece of metal, for example a disc of about 4 cm diameter, or may be formed on the surface of a similar solid block of holding material.
  • sample body the area on the surface from which sample atoms are sputtered will be referred to as the "sample area.”
  • sample area the area on the surface from which sample atoms are sputtered.
  • the sample area, and a small part of the surrounding surface, are the only portions of the sample body subjected to the vacuum; the remainder being left in contact with the surrounding air.
  • vacuum as used in this specification is intended to cover a partial vacuum, and pressures inside the vacuum chamber are typically of the order of 1-10 torr.
  • the vacuum chamber is provided with an aperture in one of its walls.
  • the sample area can then form the cathode of a sputtering discharge between itself and an anode located inside the vacuum chamber.
  • Interference may be produced because the material then sputtered may be left over from previous samples, and even if the samples are the same, the relative distribution of atoms in the atomic vapour may be quite different to that in the samples because there is no compensation for different sputtering rates; and furthermore, different current densities characteristic of a new discharge path may result in different discharge conditions. Even more extreme interference can result with a heavy build-up of sputtered material on the walls because eventually a conductive path can form between the anode and cathode. short-circuiting the discharge.
  • the invention comprises apparatus for providing an atomic vapour for spectrochemical analysis from a sample area on the surface of a sample body.
  • the sample area in use forming the cathode of a sputtering discharge.
  • a vacuum chamber having an apertured wall. an anode lying in side the chamber. and apertured sample locating means around the wall aperture comprising an outer annular portion adapted in use to abut the surface of the sample body and an inner annular portion electrically insulated from said outer portion and said anode adapted in use to lie opposite the surface of the sample body but spaced therefrom a short distance to form an annular gap surrounding the sample area.
  • the gapwidth being large enough to electrically isolate the opposed sur faces thereof but smaller than the width of the cathode dark space for the sputtering discharge.
  • inner and outer annular portions should be understood as being electrically insulated from each other if one or both are made from electrically insulating material. including the case where they are formed integrally from eleetri cally insulating material.
  • the vacuum chamber is purged with clean inert gas while maintaining the vacuum level appropriate to the glow discharge so that impurity atoms are swept from the volume.
  • the invention provides gas passages within the disc so that purge gas is directed into the area of the discharge in such a way that atoms sputtered from the sample area are carried away from the discharge region towards the body of the vacuum chamber to facilitate spectrochemical analysis.
  • the sample 10- eating means is in the form of a separate flat disc with a central aperture and an inwardly stepped inner annular portion on one face.
  • FIG. I is a diagrammatic representation of apparatus for spectrochemical analysis according to the invention'.
  • FIG. 2 shows a cross section of a sample holding arrangement of the invention
  • FIG. 3 shows in plan view a disc used in the sample holding arrangement
  • FIGS. 4A and 4B show exploded plan views of a disc according to a further embodiment of the invention.
  • FIGS. 5A and 5B show section views through the disc shown in FIGS. 4A and 48;
  • FIG. 6 shows a section view of a further sample holding arrangement according to the invention.
  • FIG. 7 shows a typical warm-up trace of fluorescence radiation intensity obtained from a surface with no prior sputtering treatment.
  • the sample body 1 is located against an aperture (not shown) in vacuum chamber 2.
  • the sample body is electrically conductive and is connected to a negative supply voltage line 3, and a discharge is struck between it and an anode inside the chamber connected to positive voltage line 4.
  • a spectral lamp 5, operated to emit a pulsed highintensity spectral line characteristic of the element being estimated. is located so that it illuminates the atomic vapour created inside chamber 2. If fluorescence radiation is being examined.
  • a photodetector 6 is arranged to receive light emitted by the sample vapour in a direction at right angles to the incident radia tion. If atomic absorption is being examined.
  • a photodetector of monochromator 7 is arranged in line with the incident radiation.
  • lenses may be ar ranged to focus incoming and outgoing light relative to the vacuum chamber.
  • light baffles may be used to mini mize the interference due to stray light reflections, and filters may be interposed in the light paths to select appropriate regions of the spectrum.
  • the detectors 6 and/or 7 are preferably arranged in synchromous demodulation circuits. so that light pulses originating from lamp 5 are selectively detected.
  • a fuller description ofcircuit and optical arrangements may be found in our Australian patent specification No. 163,586 in relation to atomic absorption and in the specification of the aforementioned Australian patent application No. 37.1254/68 in relation to fluorescence.
  • FIG. 2 a preferred sample holding means of the invention is shown in more detail. Portions of the wall of the chamber 2 of FIG. 1 are shown at 8.8. with an aperture at 9.
  • Anode 10 is located inside the chamber at a point about 1 cm below the cathode formed by sample area 11, the distance of 1 cm corresponding roughly to the edge of the negative glow in order to eliminate as far as possible background interference from an anode glow and positive column.
  • the discharge causes sputtering of sample atoms from the cathode to form an atomic vapour. and the preferred location at which this vapour is examined spectroscopically is about 2 cm below the cathode. thus minimizing the contribution of the negative glow to interfering background radiation.
  • the sample area 11 is located on the surface 12 of the sample body 13.
  • Surface 12 is preferably ground flat and is pressed against the wall 8.8 by a retaining member 14 assisted by outside air pressure when the chamber 2 is evacuated.
  • a sample locating means 15 and a resilient sealing member 16.
  • Sample locating means 15, shown in plan view in FIG. 3, in one embodiment. takes the form of a solid disc of insulating. heat-resisting material such as quartz. with a central aperture 17. In use. this aperture is aligned with aperture 9 in wall 8,8 of the vacuum chamber.
  • the disc is relatively flat on the side which is placed against wall 8,8 of the chamber. and on its other side has two annular portions, the inner portion 18 being stepped inwardly relative to the outer portion 19.
  • the ratio of the thickness of the disc to that of sealing member 16, preferably an O-ring, is set so that when the sample body is forced against the disc. the O-ring is sufficiently compressed to form a vacuum-tight seal between the surface I2 and the wall 8,8.
  • the annular gap 20, formed between the surface 12 and the inner annular portion 18, is approximately 0.2 mm wide, and extends approximately 5 mm parallel to surface I2.
  • the sample body 13 may be cooled to predetermined temperature by means of a water jacket 21, and gas, preferably argon may be passed through chamber 2 via gas inlet and outlet connections (not shown).
  • gas preferably argon
  • the gas connections are preferably arranged on opposite sides of the chamber relative to the sample area so that a flow of pure argon across the cathode surface may be maintained to sweep impurity molecules away from the viewing area.
  • disc 15 instead of being solid may be provided with internal gas flow passages to direct gas into the area ofthe discharge in such a way that sputtered atoms are swept into the body of the vacuum chamber 2 to facilitate spectrochemical analysis.
  • FIGS. 4 6 of the accompanying drawings depict such an arrangement.
  • FIGS. 4A and 48 a disc 15 having internal gas passages is shown in two halves prior to assembly.
  • FIG. 5A represents a cross-section through the halves of disc I5 shown in FIGS. 4A and 48 along the lines AA, with the halves arranged in opposing relation.
  • FIG. 5B is a similar view along lines BB in FIGS. 4A and 4B.
  • a circular groove of rectangular crosssection is shown on the upper face of the lower half of the disc.
  • a corresponding groove 2I' can be seen on the lower face of the upper half of the disc.
  • grooves 21 and 21' when aligned opposite each other form a gas circulation passage within the composite disc 15.
  • a gas inlet port 22 can be seen in FIGS. 4A and 58 leading into gas circulation passages 21,21.
  • the disc 15 is arranged as shown in FIG. 6 with a gas inlet tube inserted partially into hole 22 so that argon. at a suitably low flow rate is directed into the region of the sputtering discharge through gas outlet ducts 24 (shown in FIG. 5A). It has been found unnec essary in practice for a leak free connection to be made between gas inlet tube 25 and inlet port 22, as adequate sweeping of atoms, and molecules, out ofthe discharge region has been attained with quite loose connections.
  • the argon preferably in a purified form, passes from the discharge region to a vacuum pump, shown schematically in FIG. I, which is kept running while the sputtering discharge is operating.
  • the gas circulation passage 21,21 may be connected to a series of duets leading into the region of the annular gap 20 shown in FIG. 2, so that gas then passes out from this region, through aperture I7 in sample locating means 15 and into the body of the vacuum chamber 2, and thence to the vacuum pump.
  • the chamber is brought up to atmospheric pressure with dry argon before being opened, and a fresh sample is placed on the disc 15 over the aperture 9.
  • the chamber is pumped down to a vacuum of approximately 5 microns over about 1 minute to clear as much contamination from the sample and chamber as possible.
  • the pressure of argon is then let up to about 5 torr, and a steady flow of argon of about 0.2
  • FIG. 4 shows a typical warm-up trace of the intensity of fluorescence radiation emitted from an atomic vapour derived from the surface which had received no prior sputtering treatment. As can be seen, the signal reaches a peak value after only about 5 seconds, and then approaches a final equilibrium value after 1 minute or so.
  • the annular gap 20 has been found to contain the discharge to the aperture 17 without any fringing into the gap, and material sputtered on the disc and wall surfaces outside the annular gap has not become electrically connected to the cathode.
  • Apparatus for providing an atomic vapour for spectrochemical analysis from a sample area on the surface of a sample body, the sample area in use forming the cathode ofa sputtering discharge, comprising a vacuum chamber having an apertured wall, an anode lying inside the chamber and below the wall aperture.
  • sample locating means lying outside the chamber around the wall aperture and comprising an outer annular portion adapted in use to abut the surface of the sample body and an inner annular portion electrically insulated from the outer portion and the anode, adapted in use to lie opposite the surface of the sample body but spaced therefrom a short distance to form an annular gap surrounding the sample area, the gapwidth being large enough to electrically isolate the opposed surfaces thereof but smaller than the width of the cathode dark space for the sputtering discharge.
  • the vacuum chamber includes means whereby a stream of gas may be introduced into the vacuum chamber while vacuum is maintained by a vacuum pump, such that impurity atoms and molecules may be swept out of the chamber while the sputtering discharge is operating.
  • sample locating means is provided with at least one internal gas passage for directing at least part of the stream of gas into the region of the sputtering discharge so that sputtered atoms are thereby carried away from the discharge region towards the body of the vacuum chamber to facilitate spectrochemical analysis.
  • the sample locating means has a gas circulation passage into which at least part of the stream of gas may be directed. and at least one gas outlet duct leading into the aper ture in the sample locating means.
  • the sample locating means has a gas circulation passage into which at least part of the stream of gas may be directed, and at least one outlet duct leading into the annular gap between the sample locating means and the surface of the sample body.
  • Apparatus for spectrochemical analysis of a sample by means of a sputtering discharge comprising in combination;
  • a vacuum chamber having an apertured wall.
  • a disc-shaped centrally apertured sample locating means disposed outside and around the wall aperture having a surface facing the sample with an outer annular portion abutting the surface of the sample and an inner annular portion electrically insulated from the outer annular portion and the anode. stepped away from the sample surface a distance large enough to electrically isolate the opposed surfaces of the gap so formed but smaller than the width of the cathode dark space for the sputtering discharge;
  • a sealing member in the form of an O-ring disposed around the periphery of the sample locating means and between the sample and the vacuum chamber wall so as to effect a vacuum seal therebetween;
  • a spectral lamp providing light containing at least one spectral line characteristic of an element under analysis
  • photodetector means for providing an indication of the degree to which the characteristic spectral line is absorbed by atoms sputtered from the sample by the discharge.
  • Apparatus for spectrochemical analysis of a sample as claimed in claim 7 in which the degree of absorbance is determined by measuring the fluorescent light re-emitted by the sputtered atoms.
  • Apparatus for spectrochemical analysis as claimed in claim 7 including means whereby a stream of gas may be introduced into the vacuum chamber while vacuum is maintained by a vacuum pump such that impurity atoms and molecules may be swept out of the vacuum chamber while the sputtering discharge is operat ing.
  • the sample locating means is provided with at least one internal gas passage for directing at least part of the stream of gas into the region of the sputtering discharge so that sputtered atoms are thereby carried away from the discharge region towards the body of the vacuum chamber to facilitate spectrochemical analysis.

Landscapes

  • Health & Medical Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Pathology (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Immunology (AREA)
  • Chemical & Material Sciences (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Environmental & Geological Engineering (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Investigating, Analyzing Materials By Fluorescence Or Luminescence (AREA)
US389088A 1972-08-18 1973-08-17 Demountable sputtering cathode for atomic absorption spectroscopy Expired - Lifetime US3876305A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
AUPB014772 1972-08-18

Publications (1)

Publication Number Publication Date
US3876305A true US3876305A (en) 1975-04-08

Family

ID=3765268

Family Applications (1)

Application Number Title Priority Date Filing Date
US389088A Expired - Lifetime US3876305A (en) 1972-08-18 1973-08-17 Demountable sputtering cathode for atomic absorption spectroscopy

Country Status (6)

Country Link
US (1) US3876305A (cs)
JP (1) JPS5713817B2 (cs)
CA (1) CA1020905A (cs)
DE (1) DE2341204A1 (cs)
GB (1) GB1435597A (cs)
NL (1) NL7311382A (cs)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4824249A (en) * 1986-04-16 1989-04-25 Chamber Ridge Pty. Ltd. Systems for the direct analysis of solid samples by atomic emission spectroscopy
EP0407030A1 (en) * 1989-05-31 1991-01-09 Clemson University Method and apparatus for analysing solid samples
US5064204A (en) * 1988-06-22 1991-11-12 Outokumpu Oy Analyzer sealing member
US5325021A (en) * 1992-04-09 1994-06-28 Clemson University Radio-frequency powered glow discharge device and method with high voltage interface
US20080280135A1 (en) * 2007-05-10 2008-11-13 Wook-Seong Lee Dc plasma assisted chemical vapor deposition apparatus in the absence of positive column, method for depositing material in the absence of positive column, and diamond thin layer thereby
US9536725B2 (en) 2013-02-05 2017-01-03 Clemson University Means of introducing an analyte into liquid sampling atmospheric pressure glow discharge

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4845041A (en) * 1985-11-20 1989-07-04 Analyte Corporation Atomic-absorption sputtering chamber and system
DE3605911A1 (de) * 1986-02-24 1987-08-27 Ges Foerderung Spektrochemie Glimmentladungslampe sowie ihre verwendung

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3644045A (en) * 1968-05-01 1972-02-22 Commw Scient Ind Res Org Atomic absorption spectroscopy

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3644045A (en) * 1968-05-01 1972-02-22 Commw Scient Ind Res Org Atomic absorption spectroscopy

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4824249A (en) * 1986-04-16 1989-04-25 Chamber Ridge Pty. Ltd. Systems for the direct analysis of solid samples by atomic emission spectroscopy
US5064204A (en) * 1988-06-22 1991-11-12 Outokumpu Oy Analyzer sealing member
EP0407030A1 (en) * 1989-05-31 1991-01-09 Clemson University Method and apparatus for analysing solid samples
US5325021A (en) * 1992-04-09 1994-06-28 Clemson University Radio-frequency powered glow discharge device and method with high voltage interface
US20080280135A1 (en) * 2007-05-10 2008-11-13 Wook-Seong Lee Dc plasma assisted chemical vapor deposition apparatus in the absence of positive column, method for depositing material in the absence of positive column, and diamond thin layer thereby
US8334027B2 (en) * 2007-05-10 2012-12-18 Korea Institute Of Science And Technology Method for DC plasma assisted chemical vapor deposition in the absence of a positive column
US9536725B2 (en) 2013-02-05 2017-01-03 Clemson University Means of introducing an analyte into liquid sampling atmospheric pressure glow discharge
US10269525B2 (en) 2013-02-05 2019-04-23 Clemson University Research Foundation Means of introducing an analyte into liquid sampling atmospheric pressure glow discharge

Also Published As

Publication number Publication date
JPS5713817B2 (cs) 1982-03-19
NL7311382A (cs) 1974-02-20
CA1020905A (en) 1977-11-15
GB1435597A (en) 1976-05-12
DE2341204A1 (de) 1974-02-28
JPS4987389A (cs) 1974-08-21

Similar Documents

Publication Publication Date Title
US4830492A (en) Glow-discharge lamp and its application
Mavrodineanu Hollow cathode discharges: Analytical applications
Slevin et al. The hollow cathode discharge as a spectrochemical emission source
CN109755097B (zh) 一种四极杆质谱仪及其使用方法
Gough et al. The application of cathodic sputtering to the production of atomic vapours in atomic fluorescence spectroscopy
US3876305A (en) Demountable sputtering cathode for atomic absorption spectroscopy
Houpt Physical phenomena and analytical applications of helium microwave discharges
Loving et al. Simultaneous analysis of an abnormal glow discharge by atomic absorption spectrometry and mass spectrometry
Jonkman et al. Low-temperature secondary positive ion mass spectrometry of neat and argon-diluted organic solids
US3218459A (en) Fluid sample holders for x-ray spectrometers under vacuum
US3591289A (en) Atomic absorption sample cell
US3521054A (en) Analytical photoionization mass spectrometer with an argon gas filter between the light source and monochrometer
Lazik et al. Effect of directed (radial) gas flow on sputtering and emission characteristics in radio frequency powered glow discharge devices
US3635561A (en) Apparatus and method for determining the content of chemical elements in a solid sample
US3809479A (en) Sputtering method and apparatus for quantitative and qualitative analysis of materials
Falk et al. Furnace atomisation with non-thermal excitation—Experimental evaluation of detection based on a high-resolution échelle monochromator incorporating automatic background correction
US3430041A (en) Far ultraviolet non-dispersive analyzer utilizing resonant radiant energy from the periphery of the vapor cloud of the source
Hannaford et al. Sputtered atoms in absorption and fluorescence spectroscopy
Van Gelder New high-intensity spectral source with a narrow line profile
Trivedi et al. Physical properties of a planar magnetron glow discharge
Broekaert et al. Investigations of a jet-assisted glow discharge lamp for optical emission spectrometry
US5153674A (en) Semiconductor production control and/or measuring unit
US3596127A (en) Glow discharge lamps for use in spectroscopic analyzers
Milazzo Versatile Hollow-Cathode Light Source for Spectrochemical Analysis in the Vacuum Ultraviolet
EP0729174B1 (en) Atmospheric seal and method for glow discharge analytical instrument