Patent Number: 
Section: claims

1. Focused ion beam system at least adapted for one of CD-measurements or DR-measurements of a specimen, comprising:a gas field ion source, the gas field ion source having an emitter tip;the emitter tip having a base tip comprising a first material and a supertip comprising a material different from the first material,wherein the supertip is a single atom tip for emitting an ion beam;wherein the base tip is a single crystal base tip;a detector for detection of at least one of the group consisting of backscattered and secondary particles released from the specimen;an analyzer for performing at least one of the group consisting of analyzing, evaluating, and classifying structures on the specimen and being connected to the detector; anda probe current control device comprising a current measurement device and having a control loop adapted to trigger a probe current control action. 2. The focused ion beam device according to claim 1, wherein the supertip is a coating of the base tip. 3. The focused ion beam device according claim 1, wherein the supertip is a metal supertip. 4. The focused ion beam device according to claim 1, wherein the base tip consists of a material selected from the group of: tungsten, tantalum, rhenium, molybdenum, and niobium. 5. The focused ion beam device according to claim 1, wherein the supertip consist of a material selected from the group of platinum, rhodium, and palladium. 6. The focused ion beam device according to claim 1, further comprising a deflector directing the ion beam to the measurement device. 7. The focused ion beam device according to claim 1, wherein the probe current measurement device comprises a Faraday cup. 8. The focused ion beam device according to claim 1, wherein the probe current measurement device comprises a beam limiting aperture. 9. The focused ion beam device according to claim 1, further comprising a sample charge control. 10. The focused ion beam device according to claim 9, wherein the sample charge control comprises a surface charge measurement device. 11. The focused ion beam device according to claim 9, wherein the sample charge control comprises a spectrometer. 12. The focused ion beam device according to claim 9, wherein the sample charge control comprises a retarding field configuration. 13. Method of operating a gas field ion source assembly having an emitter tip with a base tip comprising a first material and a supertip comprising a material different from the first material, wherein the base tip is a single crystal base tip; an electrode for providing an extraction voltage; a single emission center by the supertip; a probe current control device comprising a current measurement device and having a control loop, the method comprising:emitting an ion beam comprising:applying a voltage between the single emission center of the supertip and the electrode, andsupplying a gas to the emitter tip;detecting a signal released from a specimen;performing at least one of the group consisting of analyzing, evaluating and classifying the structure of the specimen with the detected signal, and triggering a probe current control action by the control loop. 14. The method according to claim 13, wherein the single emission center is provided by a single atom supertip. 15. The method according to claim 13, wherein the gas is helium, hydrogen, neon, argon or methane. 16. The method according to claim 13, wherein a probe current is controlled. 17. The method according to claim 16, further comprising controlling the probe current changes when the changes have reached a predetermined limit. 18. The method according to claim 16, wherein the controlling of the probe current comprises measuring the probe current. 19. The method according to claim 17, further comprising using the measurement of the probe current as a signal for changing the beam current. 20. The method according to claim 13, wherein a sample charge is controlled. 21. The method according to claim 20, wherein the sample charge is measured and controlled during operation of the ion beam device. 22. The method according to claim 21, further comprising triggering compensation measures based on the measurement of the sample charge. 23. The method according to any of claim 21, further comprising supplying a control voltage to the sample after measuring the sample charge.