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US 4,107,526 AGranted
Ion scattering spectrometer with modified bias
AssigneeMinnesota Mining and Manufacturing Company
InventorsJames T. McKinney, Thomas W. Rusch
Life of this patent
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Abstract
An ion scattering spectrometer (ISS) providing enhanced sensitivity, reduced background, and preferential detection of low-mass scattered ions over that of high-mass sputtered ions is disclosed. These advantages are accomplished by a biasing arrangement which maintains a potential difference between the analyzer exit and the detector input at less than 30 volts and substantially eliminates the high potential provided on detector inputs of prior art ion scattering spectrometers which attracted and thereby accelerated ions prior to impinging on the inputs.
Claims10
In an ion scattering spectrometer comprising
- (a) means for supporting a specimen, a surface of which is to be analyzed,
- (b) means for directing a beam of ions having a preselected atomic mass and a preselected energy toward the surface,
- (c) analyzing means comprising an entrance section for receiving ions from the surfaces, analyzing section for selecting such ions passing through the entrance section at a given angle as have a predetermined energy, and an exit section for passing said selected ions, and
- (d) detecting means comprising a material having an electron emissive surface for receiving and detecting passed ions from the analyzing means by converting an ion current associated with said passed ions into a corresponding electron signal,
- the improvement wherein the spectrometer further comprises (e) biasing means to control the energy of ions impinging upon the electron emissive surface, to result in
- (i) the preferential detection of low-mass scattered ions having relatively high velocities over high-mass sputtered ions having relatively low velocities,
- and for maintaining a potential on said electron emissive surface within 30 volts of that maintained on said exit section of the analyzer means resulting in
- (ii) the absence of a force tending to attract electrons emitted from the emissive surface toward the analyzing means, and
- (iii) the absence of a force tending to attract such ions having an energy outside the pass-band of the analyzer through the exit section of the analyzing means to the emissive surface, such that there is produced an appreciably stronger electron signal corresponding to scattered ions, and a corresponding reduction in the background of the electron signal corresponding to the detection of heavier sputtered ions and spurious scattered ions not within the pass-band of the analyzer, said detecting means further comprising means for indirectly coupling said electron signal from the output portion to an amplifier means operating near ground potential, such that said output section may be maintained at a positive potential to cause electrons emitted from said emissive surface to drift into the detecting means.
6 more elements
In an ion scattering spectroscopic method for investigating the composition of a surface of a material comprising the steps of
- (a) supporting a specimen, the composition of a surface of which is to be analyzed,
- (b) directing a beam of ions having a preselected atomic mass and a preselected energy toward the surface,
- (c) analyzing ions received from the surface by passing ions received from the surface at a given angle through an entrance section, by subsequently selecting ions having a predetermined energy in an analyzer section and passing the selected ions through an exit section, and
- (d) detecting the passed ions in a detecting means comprising a material having an electron emissive surface by impinging the passed ions on the emissive surface and converting an ion current associated therewith into a corresponding electron signal,
- The improvement wherein the method further comprises the step of
- (e) biasing said emissive surface to control the energy of ions impinging on the emissive surface, resulting in
- (i) the preferential detection of low-mass scattered ions having relatively high velocities over high-mass sputtered ions having relatively low velocities, and to maintain a potential thereon within 30 volts of that maintained on said exit section resulting in
- (ii) the absence of a force tending to attract electrons emitted from the emissive surface toward said exit section, and
- (iii) the absence of a force tending to attract such ions having an energy outside the pass-band of the analyzer through the exit section toward the emissive surface, such that there is produced an appreciably stronger electron signal corresponding to scattered ions, and a corresponding reduction in the background of the electron signal corresponding to the detection of heavier sputtered ions, and spurious scattered ions not within the pass-band of the analyzer.
6 more elements
Dependencies are inferred from the claim text.