POLARIZED PULSED FRONT-END BEAM SOURCE FOR ELECTRON MICROSCOPE

Abstract

A method and an electron source are provided for generating polarized electrons for an electron microscope. The electron source includes a photoemissive cathode and a low-power drive laser. The geometry of the photoemissive cathode uses a generally planar emission surface, which is imaged to approximately 1/100 its initial size via electrostatic focusing elements. The virtual emitter, or image spot, then is used as an electron source by a conventional microscope column.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention together with the above and other objects and advantages may best be understood from the following detailed description of the preferred embodiments of the invention illustrated in the drawings, wherein:

FIG. 1 is a schematic and block diagram illustrating an exemplary electron source for an electron microscope in accordance with a preferred embodiment;

FIG. 2 is a schematic diagram illustrating another exemplary electron source for an electron microscope with lines of constant voltage for an exemplary lens array in accordance with a preferred embodiment; and

FIGS. 3 and 4 are charts illustrating exemplary operation of an electron source in accordance with a preferred embodiment.

Claims

1. An electron source for generating polarized electrons for an electron microscope comprising: a photoemissive cathode;a low-power drive laser providing a pulsed laser beam to said photoemissive cathode;said photoemissive cathode generating pulsed, polarized electrons responsive to said pulsed laser beam; andelectrostatic focusing elements for focusing said pulsed, polarized electrons to an image spot, said image spot being used as the electron source for a microscope column.

2. An electron source for generating polarized electrons as recited in claim 1 wherein said photoemissive cathode has a generally planar emission surface.

3. An electron source for generating polarized electrons as recited in claim 1 wherein said photoemissive cathode is made of gallium arsenide (GaAs).

4. An electron source for generating polarized electrons as recited in claim 3 wherein said photoemissive cathode includes predefined cessation of the surface, and said applied pulsed laser beam producing electrons emerging from the surface with a defined polarization or spin orientation.

5. An electron source for generating polarized electrons as recited in claim 1 includes a cathode holder supporting said photoemissive cathode.

6. An electron source for generating polarized electrons as recited in claim 5 includes a set of insulators coupled between a grounded shell containing said cathode and said cathode holder.

7. An electron source for generating polarized electrons as recited in claim 6 includes a high voltage power supply providing a high voltage potential to said photoemissive cathode.

8. An electron source for generating polarized electrons as recited in claim 7 includes a high voltage feed-through extending through said grounded shell for coupling the high voltage potential to said photoemissive cathode.

9. An electron source for generating polarized electrons as recited in claim 6 includes a focusing anode extending from said grounded shell and spaced from said photoemissive cathode.

10. An electron source for generating polarized electrons as recited in claim 6 wherein said low-power drive laser is provided external to said grounded shell.

11. An electron source for generating polarized electrons as recited in claim 6 includes a laser port defined within said grounded shell for providing a laser light path from said low-power drive laser to said photoemissive cathode.

12. A method for generating polarized electrons for an electron microscope comprising the steps of: providing an external electron source using a photoemissive cathode and a low-power drive laser for providing a pulsed laser beam to said photoemissive cathode;generating pulsed, polarized electrons from said photoemissive cathode responsive to applying said pulsed laser beam; andfocusing said pulsed, polarized electrons to an image spot, said image spot being used as the electron source for a microscope column.

13. A method for generating polarized electrons for an electron microscope as recited in claim 12 wherein providing said external electron source using said photoemissive cathode and said low-power drive laser includes providing said photoemissive cathode having a generally planar emission surface.

14. A method for generating polarized electrons for an electron microscope as recited in claim 12 wherein providing said external electron source using said photoemissive cathode and said low-power drive laser includes providing said photoemissive cathode made of gallium arsenide (GaAs).

15. A method for generating polarized electrons for an electron microscope as recited in claim 12 wherein providing said external electron source using said photoemissive cathode and said low-power drive laser includes providing a cathode holder supporting said photoemissive cathode.

16. A method for generating polarized electrons for an electron microscope as recited in claim 15 includes providing a set of insulators coupled between a grounded shell containing said photoemissive cathode and said cathode holder.

17. A method for generating polarized electrons for an electron microscope as recited in claim 16 includes providing a high voltage power supply providing a high voltage potential to said photoemissive cathode.

18. A method for generating polarized electrons for an electron microscope as recited in claim 16 includes providing a focusing anode extending from said grounded shell and spaced from said photoemissive cathode.

19. A method for generating polarized electrons for an electron microscope as recited in claim 12 wherein providing said external electron source using said photoemissive cathode and said low-power drive laser includes providing said photoemissive cathode with predefined cessation of the surface, and said applied pulsed laser beam producing electrons emerging from the surface with a defined polarization or spin orientation.