Radiant energy – Electron energy analysis
Reexamination Certificate
1998-07-14
2001-02-06
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Electron energy analysis
Reexamination Certificate
active
06184523
ABSTRACT:
TECHNICAL FIELD
The present invention relates to charged particle-energy detecting cylindrical mirror analyzers generally, and more particularly to an easily positionable, compact, small diameter, high resolution charged particle-energy detecting, multiple sequential stage, retractable cylindrical mirror analyzer system which, in use, enables charged particles, which have energies within specified bands, to be detected with an improved resolution, as compared to that possible where only a single stage is utilized.
BACKGROUND
The use of cylindrical mirror analyzers to enable detection of charged particles of a specific energy, (i.e. particle-energy), is well known. Generally, cylindrical mirror analyzers allow charged particles with energies within a certain range of energies, (but not charged particles with energies outside said certain range of energies), which enter thereinto at an angle within an acceptance range of angles, to exit therefrom and be directed into a detector. The presence of a charged particle which transverses a cylindrical mirror analyzer at a detector is a “count-like” indication that said charged particle had an energy within a certain range of energies and entered said cylindrical mirror analyzer at an angle thereto within an acceptance range of angles. In use, parameters of operation, (e.g. applied voltage as discussed supra herein), can be user adjusted and thus allow selection of:
“energy—charged-particle—angle of entry”
combinations that can pass through a relatively fixed geometry cylindrical mirror analyzer system, and be subsequently detected.
To aide with understanding of the present invention it must be understood that cylindrical mirror analyzers generally comprise two finite length, elongated, concentric essentially tubular shaped elements, (i.e. outer and central-most), which two finite length elongated concentric essentially tubular shaped elements are typically of a functional, essentially equal, length. Each of said two elongated concentric essentially tubular shaped elements is preferably, but not necessarily, essentially circular shaped in cross-section, and the central-most concentric essentially tubular shaped element has holes through the tubular wall thereof near each longitudinally opposed end thereof, such that in use, charged particles can enter and exit the formed annular space between said outer and central-most elongated concentric essentially tubular shaped elements through holes at first and second ends, respectively, of said central-most concentric essentially tubular shaped element.
In use, a voltage is applied between the outer and central-most concentric essentially tubular shaped elements such that an electric field is effected in said formed annular space therebetween, and such that charged particles which enter into said annular space at some energy related velocity and trajectory locus angle, via said a hole through the first end of the tubular wall of said central-most elongated concentric essentially tubular shaped element, are guided in their further trajectory locus through, and out of, said annular space. Entering charged particles with an energy, (i.e. velocity), within a range which is determined by the applied voltage across the two elongated concentric essentially tubular shaped elements, (and the roughly the distance from said first hole, to a second hole through the central-most essentially tubular shaped element wall), will be guided so as to exit said annular space between said outer and central-most essentially tubular shaped elements, through a second hole through the wall of said central-most elongated concentric essentially tubular shaped element, at the opposed longitudinal, (e.g. second), end of the central-most elongated concentric essentially tubular shaped element. A detector for detecting charged particles is typically positioned to intercept said exiting charged particles. Charged particles which do not enter the annular space, or which enter at other than an angle within a range of acceptance angles, or which have an energy outside the “detection” range, (which again is determined by the applied voltage and distance between said first and second holes through the wall of the central-most elongated concentric essentially tubular shaped element), will not be guided in their trajectory locus so as to exit the annular space through said hole through the wall of said at the opposed, second, longitudinal end of the central-most elongated concentric essentially tubular shaped element. Instead such charged particles with energies outside the “detection” range etc. will typically collide with, for instance, the inner surface of the essentially tubular shaped wall of the outer elongated concentric essentially tubular shaped element, or the outer surface of the essentially tubular shaped wall of the central-most elongated concentric essentially tubular shaped element. Assuming a charged particle has an entry trajectory locus angle within a range of acceptance angles, it can then be appreciated that only particles which have an energy, (i.e. mass, charge and velocity), within a “detection” range, and which enter the identified annular space, can be expected to reach the indicated detector through a cylindrical mirror analyzer. It should also be appreciated that the “detection” range of energies of charged particle which are guided into the detector for detecting charged particles of a given charge, is easily user determined by adjustment of the voltage applied between the two, (outer and central-most), concentric essentially tubular shaped elements and the electric field formed in said annular space as a result. Within limits, this is the case regardless of fixed physical distance between the first and second holes in the wall of the central-most elongated concentric essentially tubular shaped element, as voltage applied between the two, (outer and central-most), concentric essentially tubular shaped elements is continuously adjustable over a practical range. It is also noted that charged particles have associated therewith mass, and because the trajectory of a charged particle moving in an electric field is effected by said charged particle mass, cylindrical mirror analyzers can, alternatively, be employed as a mass-spectrometer, similar to a time of flight mass-spectrometer, where the magnitude of the charge present is known.
Representative, non-limiting sources of energetic charged particles which can be analyzed by cylindrical mirror analyzers include Auger, electron photoemission, and low energy positive ion scattering systems. That is, particles with either positive or negative charge can be detected. A particularly relevant source of charged particles is a material sample system which is caused to be bombarded by a source of energetic excitation, such as a beam of electrons, photons or ions. As a result of interaction between said bombarding particles, or photons, and said material sample system, charged particles are emitted from said material sample system.
Until recently, typical known cylindrical mirror analyzers were large and bulky and required fixed placement, or placement on a bulky position manipulator. This was the case as to attain high resolution charged particle-energy detecting, large diameter elongated concentric essentially tubular shaped elements, (i.e. outer and central-most), were thought to be necessary. A 1996 Patent to Dowben et al., U.S. Pat. No. 5,541,410, however, described a single pass cylindrical mirror analyzer of a relatively reduced diameter and size, which reduced size single pass cylindrical mirror analyzer, could be easily mounted on a flange mounted linear motion feedthrough, such that insertion and retraction of said reduced size single pass cylindrical mirror analyzer, to and from a position at which charged particles to be detected were present, the energies of which charged particles are to be investigated, could be easily achieved utilizing, for instance, a bellows-type linear motion feedthrough means. This ease of adjustment, it is noted, provided a major a
Dowben Peter A.
McAvoy Tara J.
McIlroy David N.
Waldfried Carlo
Board of Regents of the University of Nebraska
Nguyen Kiet T.
Welch James D.
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