Claims
- 1. A method of efficiently extracting for quantitative spectroscopic analysis a selected atomic component removed from a sample held at a sample electric field potential relative to a spectrometer housing electric field potential, comprising the steps of:
- generating near said sample a volume containing said selected atomic component;
- applying a predetermined electric field potential near said sample, said predetermined electric field potential comprising regions of slowly diminishing and rapidly diminishing field potential, said slowly diminishing field potential exhibiting an averaged change of potential over a portion of the region between said sample and the electric field generating lens element nearest said sample and said averaged change of potential for said region of slowly diminishing field potential being less than about ten to twenty percent of the difference between said sample electric field potential and said spectrometer housing potential and said predetermined electric field potential further including said region of rapidly diminishing field potential exhibiting an averaged change of potential extending contiguously beyond said slowly diminishing field potential region and said averaged potential change being greater than about ten to twenty percent of the difference between said sample potential and said spectrometer housing potential
- ionizing said selected atomic component substantially in said slowly diminishing field potential region; and
- extracting said ionized atomic component responsive to entering said rapidly diminishing field potential region, said extracted atomic component subsequently undergoing said quantitative spectroscopic analysis.
- 2. The method as defined in claim 1 wherein said slowly and rapidly diminishing field potential regions comprise electric field potentials decreasing with the perpendicular distance from said sample.
- 3. The method as defined in claim 2 wherein said electric field potential diminishes about 5 to 100 volts over said slowly diminishing field region.
- 4. A method of efficiently extracting for quantitative spectroscopic analysis a selected atomic component removed from a sample held at a sample electric field potential relative to a spectrometer housing electric field potential, comprising the steps of:
- generating near said sample a volume containing said selected atomic component;
- generating an electric field potential on said sample for selectively repelling ions from the vicinity of said sample;
- applying a predetermined electric field potential near said sample, said predetermined electric field potential comprising regions of slowly diminishing and rapidly diminishing field potential, said slowly diminishing field potential exhibiting an averaged change of potential over a portion of the region between said sample and the electric field generating lens element nearest said sample and said averaged change of potential for said region of slowly diminishing field potential being less than about ten to twenty percent of the difference between said sample electric field potential and said spectrometer housing potential and said predetermined electric field potential further including said region of rapidly diminishing field potential exhibiting an averaged change of potential extending contiguously beyond said slowly diminishing field potential region and said averaged potential change being greater than about ten to twenty percent of the difference between said sample potential and said spectrometer housing potential;
- ionizing said selected atomic component substantially in said slowly diminishing field potential region; and
- extracting said ionized atomic component responsive to entering said rapidly diminishing field potential region, said extracted atomic component subsequently undergoing said quantitative spectroscopic analysis.
- 5. The method as defined in claim 4 wherein said step of generating said electric field potential comprises applying a pulsed electric field to said sample while applying said predetermined electric field potential, said pulsed electric field potential repelling ions from the vicinity of said sample.
- 6. A method of efficiently extracting for quantitative spectroscopic analysis a selected atomic component removed from a sample held at a sample electric field potential relative to a spectrometer housing electric field potential, comprising the steps of:
- generating near said sample a volume containing said selected atomic component;
- applying a predetermined electric field potential near said sample, said predetermined electric field potential comprising regions of slowly diminishing and rapidly diminishing field potential, said slowly diminishing field potential exhibiting an averaged change of potential over a portion of the region between said sample and the electric field generating lens element nearest said sample and said averaged change of potential for said region of slowly diminishing field potential being less than about ten to twenty percent of the difference between said sample electric field potential and said spectrometer electric field housing potential and said predetermined electric field potential further including said region of rapidly diminishing field potential exhibiting an averaged change of potential extending contiguously beyond said slowly diminishing field potential region and said averaged potential change being greater than about ten to twenty percent of the difference between said sample potential and said spectrometer housing potential said step of applying a field potential performable by electric field means having structures appropriately shaped for minimizing redeposition probability of the atoms from said electric field means onto said sample;
- ionizing said selected atomic component substantially in said slowly diminishing field potential region; and
- extracting said ionized atomic component responsive to entering said rapidly diminishing field potential region, said extracted atomic component subsequently undergoing said quantitative spectroscopic analysis.
- 7. The method as defined in claim 6 wherein said appropriately shaped structures comprise truncated conical portions.
- 8. A method of efficiently extracting for quantitative spectroscopic analysis a selected atomic component removed from a sample held at a sample electric field potential relative to a spectrometer housing electric field potential, comprising the steps of:
- generating near said sample a volume containing said selected atomic component;
- applying a predetermined electric field potential near said sample, said predetermined electric field potential comprising regions of slowly diminishing and rapidly diminishing field potential, said slowly diminishing field potential exhibiting an averaged change of potential over a portion of the region between said sample and the electric field generating lens element nearest said sample and said averaged change of potential for said region of slowly diminishing field potential being less than about ten to twenty percent of the difference between said sample electric field potential and said spectrometer electric field housing potential and said predetermined electric field potential further including said region of rapidly diminishing field potential exhibiting an averaged change of potential extending contiguously beyond said slowly diminishing field potential region and said averaged change of potential being greater than about ten to twenty percent of the difference between said sample potential and said spectrometer housing potential;
- ionizing said selected atomic component substantially in said slowly diminishing field potential region; and
- extracting said ionized atomic component responsive to entering said rapidly diminishing field potential region, said extracted atomic component subsequently undergoing said quantitative spectroscopic analysis.
- 9. The method as defined in claim 8 wherein said step of generating a volume of said selected atomic component comprises generating an energetic particle beam and bombarding said sample with said particle beam.
- 10. The method as defined in claim 9 wherein said energetic particle beam comprises an ionized particle beam.
- 11. The method as defined in claim 8 wherein said step of ionizing comprises applying at least one laser beam pulse to said atomic component, said laser beam pulse having a predetermined energy spectrum for achieving selected non resonance ionization, resonance and autoionization resonance states for said selected atomic components.
- 12. The method as defined in claim 9 wherein said energetic particle beam comprises a neutral particle beam.
- 13. The method as defined in claim 9 wherein said energetic particle beam comprises a photon beam.
- 14. A method of efficiently extracting for quantitative spectroscopic analysis a selected atomic component removed from a sample held at a sample electric field potential relative to a spectrometer housing electric field potential, comprising the steps of:
- generating near said sample a volume containing said selected atomic component;
- applying a predetermined electric field potential near said sample, said predetermined electric field potential arising from a combination of electrodes with the electrode nearest said sample generating a first electric field potential more positive than the electric field potential on said sample and said first electric field potential combining with at least a second electric field potential arising from at least one other electrode causing formation of a slowly diminishing electric field potential over a portion of the region near said sample, said slowly diminishing field potential exhibiting an averaged change of potential beyond said sample of less than about ten to twenty percent of the difference between said sample potential and said spectrometer housing potential and within said slowly diminishing field potential ionized forms of said selected atomic component are formed with at least one other remaining electrode generating a rapidly diminishing electric field potential contiguous to said slowly diminishing electric field potential;
- ionizing said selected atomic component substantially in said slowly diminishing field potential region; and
- extracting said ionized atomic component responsive to entering said rapidly diminishing field potential region, said extracted atomic component subsequently undergoing said quantitative spectroscopic analysis.
- 15. A method of efficiently extracting for quantitative spectroscopic analysis a selected atomic component removed from a sample held at a sample electric field potential relative to a spectrometer housing electric field potential, comprising the steps of:
- generating near said sample a volume containing said selected atomic component;
- applying a predetermined electric field potential near said sample, said predetermined electric field potential comprising regions of slowly diminishing and rapidly diminishing field potential, said slowly diminishing field potential exhibiting an averaged change of potential over a portion of the region between said sample and the electric field generating lens element nearest said sample and said averaged change of potential for said region of slowly diminishing field potential being less than about ten to twenty percent, per mm distance from said sample, of the difference between said sample electric field potential and said spectrometer housing potential and said predetermined electric field potential further including said region of rapidly diminishing field potential exhibiting an averaged change of potential extending contiguously beyond said slowly diminishing field potential region with said averaged potential change being greater than about ten to twenty percent, per mm distance from said sample, of the difference between said sample potential and said spectrometer housing potential;
- ionizing said selected atomic component substantially in said slowly diminishing field potential region; and
- extracting said ionized atomic component responsive to entering said rapidly diminishing field potential region, said extracted atomic component subsequently undergoing said quantitative spectroscopic analysis.
- 16. A method of efficiently extracting for quantitative spectroscopic analysis a selected atomic component removed from a sample held at a sample electric field potential relative to a spectrometer electric field housing potential, comprising the steps of:
- generating near said sample a volume containing said selected atomic component;
- generating an electric field potential on said sample for selectively repelling ions from the vicinity of said sample;
- applying a predetermined electric field potential near said sample, said predetermined electric field potential comprising regions of slowly diminishing and rapidly diminishing field potential, said slowly diminishing field potential exhibiting an averaged change of potential over a portion of the region between said sample and the electric field generating lens element nearest said sample and said averaged change of potential for said region of slowly diminishing field potential being less than about ten to twenty percent, per mm distance from said sample, of the difference between said sample electric field potential and said spectrometer housing potential with said predetermined electric field potential further including said region of rapidly diminishing field potential exhibiting an averaged change of potential extending contiguously beyond said slowly diminishing field potential region and said averaged potential change being greater than about ten to twenty percent, per mm distance from said sample, of the difference between said sample potential and said spectrometer housing potential;
- ionizing said selected atomic component substantially in said slowly diminishing field potential region; and
- extracting said ionized atomic component responsive to entering said rapidly diminishing field potential region, said extracted atomic component subsequently undergoing said quantitative spectroscopic analysis.
- 17. A method of efficiently extracting for quantitative spectroscopic analysis a selected atomic component removed from a sample held at a sample electric field potential relative to a spectrometer housing electric field potential, comprising the steps of:
- generating near said sample a volume containing said selected atomic component;
- applying a predetermined electric field potential near said sample, said predetermined electric field potential comprising regions of slowly diminishing and rapidly diminishing field potential, said slowly diminishing field potential exhibiting an averaged change of potential over a portion of the region between said sample and the electric field generating lens element nearest said sample and said averaged change of potential for said region of slowly diminishing field potential being less than about ten to twenty percent, per mm distance from said sample, of the difference between said sample electric field potential and said spectrometer electric field housing potential and said predetermined electric field potential further including said region of rapidly diminishing field potential having an averaged change of potential extending contiguously beyond said slowly diminishing field potential region with said averaged potential change being greater than about ten to twenty percent, per mm distance from said sample, of the difference between the sample potential and the spectrometer housing potential;
- ionizing said selected atomic component substantially in said slowly diminishing field potential region; and
- extracting said ionized atomic component responsive to entering said rapidly diminishing field potential region, said extracted atomic component subsequently undergoing said quantitative spectroscopic analysis.
BACKGROUND OF THE INVENTION
This is a divisional of co-pending application Ser. No. 870,437 filed on June 4, 1986, abandoned.
The present invention relates generally to a charged particle spectrometer. More particularly the invention relates to an ion spectrometer having a lens system configured to extract from a sample ionized atomic components having well controlled energy and also to provide precise spatial manipulation of the various ion beams, enabling highly sensitive detection of the ionized atomic components. Improvement of signal to noise ratio is also achieved by exciting the atomic components to autoionization states before performing energy and angular refocusing time of flight (hereinafter, "EARTOF") mass spectrometric analysis.
Significant advances have been made in the quantitative analysis of atomic components in a sample. For example, resonance ion spectrometers have demonstrated considerable sensitivity for the detection of atoms of a predetermined component. (See, for example, U.S. Pat. Nos. 4,442,354 and 3,987,302 (Hurst et al.) and U.S. patent application Ser. No. 691,825, which are incorporated by reference herein). In practice, however, these previous resonance ion spectrometers still have significant limitations in terms of achieving sensitivities in the part per trillion range because of severe difficulties encountered in discriminating low level signals to be measured from noise made up of competing, undesired and extraneous signals.
It is therefore an object of the invention to provide an improved spectrometer for quantitative analysis of selected atomic components.
It is another object of the invention to provide a novel ion spectrometer wherein a predetermined electric field is applied to ions enabling improved detection sensitivity of selected atomic components from a sample.
It is an additional object of the invention to provide an improved resonance ion and an autoionization spectrometer wherein a pulsed electric field is applied to a sample for repelling unwanted ions prior to extraction of photo ions generated by laser beam pulse excitation of selected atomic components.
It is another object of the invention to provide an improved spectrometer lens system having appropriately shaped lens structures for minimizing the redeposition probability of unwanted impurities from the lens system onto a sample.
It is an additional object of the invention to provide a novel spectrometer lens system enabling both the focusing of a primary ion beam along a path perpendicular to a sample and extraction of ions from a sample along a path also perpendicular to the sample and leading to a detector at the end of the spectrometer.
It is a further object of the invention to provide an improved device for generating predetermined electric field boundary conditions to achieve a required electric field potential for the desired use, such as the EARTOF analysis.
It is another object of the invention to provide a mass spectrometer construction having two complementary electrostatic analyzers with spherical electrical fields and an interposed telescopic lens for analyzing charged particle beams, such as the ionized selected atomic components.
A significant feature in accordance with the instant invention lies in the provision of an improved spectrometer having enhanced sensitivity for detecting selected atomic components of a sample. A lens system is configured to provide a predetermined slowly diminishing electric field region for a volume containing a large portion of the ionized form of the selected atomic components, thereby minimizing the energy spread of the volume of the ionized selected atomic components which are subsequently extracted for spectroscopic analysis, such as in an EARTOF spectrometer. The relatively small energy spread makes the spectroscopic analysis substantially more accurate and increases the signal to noise ratio. In another aspect of the invention, the lens system also applies a pulsed electric field to the sample to remove some of the unwanted secondary ions from the volume containing neutral ones of the selected atomic components prior to their ionization. The pulsed electric field also places some of the unwanted secondary ions into high energy escape orbits, causing the secondary ions to be rejected in subsequent stages of the spectrometer 10. Once the unwanted ions are removed from the volume, the selected atomic components are excited to an ionized state, including selected autoionization states which provide enhanced discrimination of unwanted ionized species.
In an additional aspect of the invention, the lens system is adapted to perform a number of different spatial manipulations of various charged particle beams. For example, the lens system can guide a primary ion beam perpendicular to the surface of the sample, while also adapted for extracting ions of the selected atomic component perpendicular to the sample surface along a path leading to the detector at the end of the spectrometer.
In a further aspect of the invention, the final stages of the lens system include two complementary spherical electric field sections. A preselected resistive thick film configuration is disposed on an insulator substrate for generating predetermined electric field boundary conditions for any one of a number of uses. In particular, the resistive thick film configuration is used in conjunction with the spherical electrostatic analyzers, achieving the required electric field potential necessary for accurate EARTOF spectrometer analysis and minimization of signal loss.
Further objects and advantages of the present invention, together with the organization and manner of operation thereof, will become apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings wherein like reference numerals designate like elements in the several views.
CONTRACTUAL ORIGIN OF THE INVENTION
The U.S. Government has rights in this invention pursuant to Contract No. W-31-109-ENG-38 between the U.S. Department of Energy and Argonne National Laboratory.
US Referenced Citations (8)
Divisions (1)
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Number |
Date |
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870437 |
Jun 1986 |
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Patent Grant
4855596
