Electrostatic electron spectrometry apparatus

• US 8,013,298 B2
• Filed: 07/14/2009
• Issued: 09/06/2011
• Est. Priority Date: 07/14/2008
• Status: Active Grant

• Current Assignee: National University of Singapore
• Original Assignee: National University of Singapore
• Inventors: Khursheed, Anjam
• Primary Examiner(s): Kim; Robert
• Assistant Examiner(s): SMITH, DAVID E
• Application Number:
  US12/502,707
• Publication Number:
  US 20100127168A1
• Time in Patent Office: 784 Days
• Field of Search: 250305-307, 250310-311, 250396 R-397
• US Class Current: 250/305
• CPC Class Codes: H01J 49/48 using electrostatic analysers, e.g. cylindrical sector, Wien filter

Abstract

An apparatus for spectrometry that includes a spectrometer configured for second order focusing and capable of 2π azimuthal collection.

Claims

1. An electrostatic electron spectrometry apparatus, comprising:

a spectrometer that includes,

a first deflection plate having a convex surface with a first radius of curvature;

a second deflection plate having a concave surface with a second radius of curvature larger than said first radius of curvature, said convex surface facing but spaced from said concave surface to define a curved space for passage of scattered electrons, said curved space having an electron entrance and an electron exit;

a first biasing source coupled to said first deflection plate to bias said first deflection plate to a first voltage; and

a second biasing source coupled to said second deflection plate to bias said second deflection plate to a second voltage, said second voltage being different from said first voltage to generate electric field lines inside said curved space;

wherein said spectrometer is configured so that said scattered electrons enter said curved space through said electron entrance along any trajectory residing in a predefined angular spread, are focused once at a first point inside said curved spaced, and focused subsequently at a second point outside said electron exit.

2. The electrostatic electron spectrometry apparatus of claim 1, wherein said electron entrance is arranged to receive scattered electrons in a full azimuthal direction.

3. The electronic electron spectrometry apparatus of claim 1, wherein, when said first and said second deflection plates are biased to first and second voltages, scattered electrons are deflected radially on a plane that includes said first radius of curvature and said second radius of curvature.

4. The electrostatic electron spectrometry apparatus of claim 1, wherein said curved space is semi-toroidal.

5. The electrostatic electron spectrometry apparatus of claim 1, further comprising a plurality of herzog shunts at said electron entrance.

6. The electrostatic electron spectrometry apparatus of claim 1, further comprising a plurality of herzog shunts at said electron exit.

7. The electrostatic electron spectrometry apparatus of claim 1, further comprising a plurality of detectors arranged to intercept electrons exiting said electron exit.

8. The electrostatic electron spectrometry apparatus of claim 6, further comprising a filter disposed between said electron exit and said detector, said filter including an aperture to allow passage of electrons therethrough.

9. The electrostatic electron spectrometry apparatus of claim 1, wherein said angular spread can range between 12 degrees and 20 degrees.

10. The electrostatic electron spectrometry apparatus of claim 1, further comprising a pre-focusing lens disposed in the path of said scattered electrons before said electron entrance.

11. The electrostatic electron spectrometry apparatus of claim 1, wherein said spectrometer includes a plurality of sectors.

12. The electrostatic electron spectrometry apparatus of claim 1, further comprising a detector having a detection plane that intercepts electrons at said second point.

13. The electrostatic electron spectrometry apparatus of claim 1, wherein said scattered electrons are focused at a plurality of first points inside said curved space and subsequently focused at a plurality of respective second points outside said curved space, wherein a detector having a detection plane is positioned so that said detection plane intercepts said second points.

14. The electrostatic electron spectrometry apparatus of claim 1, further comprising an electron accelerator disposed before said electron entrance.

15. The electrostatic electron spectrometry apparatus of claim 1, further comprising an electron decelerator disposed before said electron entrance.

16. A method for spectrometry, comprising:

generating an electric field around a central point and extending along a curved path between an electron entrance region and an electron exit region, said electric field including a plurality of spaced, curved equipotential lines, each line having a respective radius of curvature passing through said central point along a common radial direction; and

passing scattered electrons through said electron entrance and into said electric field to perform first order focusing before said electrons reach said electron exit region and second order focusing after said electrons reach said electron exit region.

17. The method of claim 16, further comprising selectively accelerating or decelerating said scattered electrons before said electrons reach said electron entrance region.

18. The method of claim 16, wherein said electric field is generated by biasing a first deflection plate to a first voltage and a second deflection plate to a second voltage, said first and said second deflection plates being spaced from one another to define said curved path.

19. The method of claim 16, wherein said scattered electrons travel along trajectory paths having an angular spread, said angular spread being defined by an aperture in a solid body that is disposed between said scattered electrons and said electron entrance.

20. The method of claim 16, wherein said angular spread is between 12 degrees and 20 degrees.

21. The method of claim 16, further comprising prefocusing said scattered electrons before said electrons pass through said electron entrance region.