Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J49/00—Particle spectrometers or separator tubes
  • H01J49/02—Details
  • H01J49/10—Ion sources; Ion guns
  • H01J49/16—Ion sources; Ion guns using surface ionisation, e.g. field-, thermionic- or photo-emission
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J27/00—Ion beam tubes
  • H01J27/02—Ion sources; Ion guns
  • H01J27/26—Ion sources; Ion guns using surface ionisation, e.g. field effect ion sources, thermionic ion sources
• • 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
  • H01J49/40—Time-of-flight spectrometers

Definitions

• the invention relates to a mass spectrometer for the analysis of secondary ions and post-ionized neutral secondary particles with an ion source for generating a pre-ion beam for irradiating a sample and for generating secondary particles, which source has a heatable ion emitter which is in the field exposed area with a liquid metal Layer is coated, which contains an ionizable metal, which is emitted and ionized as a pri ion beam, the primary ion beam containing metal ions with different ionization levels and cluster states, and with a spectrometer unit for mass analysis of the secondary particles.
• the invention also relates to the ion source for such a mass spectrometer.
• Bismuth was successfully tested in the intensive search for further cluster-forming substances with only a natural isotope for secondary ion mass spectroscopy.
• Bismuth is an anisotopic element with a melting point of 271.3 ° C.
• bismuth alloys such as Bi + Pb, Bi + Sn and Bi + Zn, are known which have a lower melting point (46 ° C - 140 ° C) than pure bismuth. Pure bismuth is preferred for a liquid metal ion source.
• JP 03-084435 also specifies a calibration alloy for a secondary ion mass spectroscope, with which mass spectra can be obtained with high resolution.
• the elements V, Ge, Cd, Os and Bi are mentioned as elements with a high negative secondary ionization.
• the isotope curves (patterns) with the aforementioned elements result in characteristic, repeatable spectra.
• this document does not speak of cluster formation or a liquid metal ion source.
• bismuth is particularly suitable for cluster generation.
• the object of the invention is therefore to develop an ion source with an improved yield of cluster ions for the operation of secondary ion mass spectrometers in order to achieve a high efficiency of secondary ion formation with simultaneously high data rates and thus short analysis times.
• the proposed improvement combines a high efficiency E of secondary ion formation from unchanged sample surfaces with high cluster currents and leads to a corresponding reduction in the analysis times.
• the value of the efficiency E corresponds to the number of secondary particles detected by the spectrometer, which can be recorded per surface unit ⁇ TOXI of a fully consumed monolayer. Efficiency can therefore be used to calculate how many secondary ions can be detected in a small-area chemical analysis under the chosen bombardment conditions. It is particularly advantageous if the ions filtered out for a mass-pure ion beam belong to one of the following types: Bi 2 + , Bi 3 + , Bi 3 2+ , Bi 4 + , Bi 5 + , Bi s + , Bi 5 2+ or Bi 7 2+ . It is preferable to work with an ion type that makes up a relatively high proportion of the total number of ions.
• the mass spectrometer is preferably operated as a time-of-flight secondary ion mass spectrometer (TOF-SIMS), since there is a lot of experience with this type and the test operation has shown that the greatest user potential lies here.
• TOF-SIMS time-of-flight secondary ion mass spectrometer
• an ion emitter equipped with a nickel-chromium tip is a favorable solution for bismuth coatings in terms of wettability, stability and workability.
• the average current intensity during operation of the secondary ion mass spectrometer is chosen between 10 "8 and 5xl0 " 5 A for the emission current.
• a metallic alloy of bismuth is chosen instead of pure bismuth, one is preferably determined which has a low melting point with a high bismuth content.
• bismuth alloys with one or more of the following metals can be used as the liquid metal coating: Ni, Ag, Pb, Hg, Cu, Sn, Zn, an alloy preferably having a melting point below the melting point of the pure bismuth ,
• FIG. 1 is a diagram of the structure of a generation system of a liquid metal ion source
• FIG. 3 shows different images of a lateral dye distribution (413u and 640u) of a color filter array with different primary ion speci fi ces, 25 keV primary ion energy with a field of view of 50 ⁇ 50 ⁇ m 2 being chosen as analysis conditions.
• TOF-SIMS The general structure of a TOF-SIMS is generally known, so that reference is made here only to FIG. 1 and the associated description of DE 44 16 413 AI by the applicant.
• FIG. 1 A liquid metal ion source suitable for a TOF-SIMS is shown in FIG. 1.
• Liquid metal ion sources are used very widely for material processing and surface analysis. These ion sources have a very small virtual source size of approximately 10 nm and a high angular intensity. Due to these properties, liquid metal ion sources can be focused very well, whereby up to 7 nm beam diameter can be achieved with simultaneously relatively high beam currents.
• FIG. 1 shows schematically the generation system for ions from a liquid metal ion source with an emitter unit 1.
• the carrier unit 7 carries a stiff lead wire 6 at each of its two ends, with a heating current whose strength is adjustable being fed via the lead wires 6; both lead wires 6 are connected to a reservoir 5, in which a supply of molten bismuth is located when the emitter unit 1 is in operation.
• An emitter needle 1 projects centrally from the reservoir 5. The emitter needle 1 can thus be kept at a temperature at which the bismuth remains melted and the needle wets.
• the emitter needle 1 consists of a nickel-chromium alloy and is wetted with liquid bismuth 4 up to its tip.
• the emitter needle has a wire diameter of approximately 200 ⁇ m and a radius of curvature at the tip of 2 to 4 ⁇ m.
• the emitter needle 1 is positioned centrally in front of an extraction diaphragm 2 and surrounded by a suppression unit 3.
• FIG. 2 shows the emission current components for bismuth and gold, normalized to the atomic, simply charged ions for AuGe and Bi emitters with an emission current of 1 ⁇ A.
• the cluster components shown in FIG. 2 relate to a total emission current of 1 ⁇ A. Since the cluster shares are dependent on the emission current, the cluster current can be increased depending on other parameters for bismuth.
• the same liquid metal ion mass spectrometer was used to analyze the same organic surfaces with different types of primary ions (cf. FIG. 3).
• the sample is a color filter (color filter array) that is placed, for example in digital cameras, in front of a light-sensitive CCD area in order to provide the color information.
• This sample is very well suited as a standard of comparison because it is manufactured very homogeneously and reproducibly.
• the differences achieved between the primary ion species are quite typical and can be qualitatively transferred to other molecular solid surfaces.
• the series of images shown in FIG. 3 show the lateral distribution of two dyes used with the masses 413u and 64lu. Due to the increasing destruction of the surface as a result of the primary ion bombardment, the signal intensity decreases continuously. The total signal intensity is shown for all primary ion species of the type described, with the same degree of damage to the surface (l / e drop in signal intensity). The signal intensity achieved is therefore a measure of the efficiency of the analysis.
• the primary ion currents can be increased by a factor of 4 to 5 compared to Au 3 + . Due to the slightly increased yield, the increase in data rates is even higher.
• the l / e drop in signal intensity is seen after 750s with Au 3 + primions and after a significantly shorter analysis time of with Bi 3 + primions Reached 180s.
• the reduction in the measurement time is essentially due to the increased Bi 3 + cluster currents.
• the choice of Bi 3 ++ also leads to similarly short measuring times.
• An increase in efficiency can be achieved by using larger clusters, such as Bi ++ , but these cluster flows are only relatively small, so that the analysis times are extended overall.
• bismuth emitters have advantages over gold emitters with regard to the stability of the emission with small emission currents and the mass separation of the emitted ion types. The advantages described therefore indicate that bismuth emitters have significant economic and analytical advantages that were not readily expected.

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• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Plasma & Fusion (AREA)
• Combustion & Propulsion (AREA)
• Electron Tubes For Measurement (AREA)
• Electron Sources, Ion Sources (AREA)
• Other Investigation Or Analysis Of Materials By Electrical Means (AREA)

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• 2003
  • 2003-08-25 DE DE10339346A patent/DE10339346B8/de not_active Withdrawn - After Issue
• 2004
  • 2004-07-01 US US10/568,832 patent/US20060202130A1/en active Granted
  • 2004-07-01 JP JP2006524234A patent/JP5128814B2/ja not_active Expired - Lifetime
  • 2004-07-01 WO PCT/EP2004/007154 patent/WO2005029532A2/fr active IP Right Grant
  • 2004-07-01 US US10/568,832 patent/US9378937B2/en active Active
  • 2004-07-01 EP EP04740521A patent/EP1658632B1/fr not_active Revoked
  • 2004-07-01 AT AT04740521T patent/ATE408891T1/de not_active IP Right Cessation
• 2011
  • 2011-09-06 JP JP2011193692A patent/JP5416178B2/ja not_active Expired - Lifetime
• 2012
  • 2012-01-11 US US13/347,792 patent/US20120104249A1/en not_active Abandoned
• 2013
  • 2013-10-04 JP JP2013208935A patent/JP2014006265A/ja active Pending
• 2016
  • 2016-05-12 US US15/152,757 patent/US20160254134A1/en not_active Abandoned

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