Dual-detection residual gas analyzer

1. A detector in a residual gas analyzer (RGA), the detector configured to receive ions traveling in a downstream direction of a beamline, the detector comprising:

a) a steering electrode offset from the beamline;

b) a first ion-receiving electrode arranged at least partly on the opposite side of the steering electrode from the beamline;

c) a second ion-receiving electrode at least partly offset from the beamline and arranged at least partly across the beamline from at least a portion of the steering electrode and at least partially upstream of at least a portion of the steering electrode;

d) a shielding electrode arranged at least partly between the beamline and the second ion-receiving electrode; and

e) a source for applying a potential to the shielding electrode.

2. The detector according to claim 1 , wherein the shielding electrode is arranged oblique to the beamline.

3. The detector according to claim 1 , further including an electron multiplier having the first ion-receiving electrode and a channel electrically connected to the first ion-receiving electrode.

4. The detector according to claim 1 , further including a readout electrode electrically connected to both the first ion-receiving electrode and the second ion-receiving electrode.

5. The detector according to claim 1 , further including a supply for selectively applying a potential to the first ion-receiving electrode.

6. The detector according to claim 1 , wherein the first ion-receiving electrode includes a conductive cone having a farthest-downstream collection point and the shielding electrode extends at least partly upstream of the farthest-downstream collection point.

7. The detector according to claim 1 , further including a steering supply for selectively applying a potential to the steering electrode.

8. The detector according to claim 1 , further including a multichannel plate including the steering electrode and having a farthest-downstream collection point.

9. The detector according to claim 8 , wherein the shielding electrode extends at least partly upstream of the farthest-downstream collection point.

10. The detector according to claim 1 , wherein the second ion-receiving electrode is arranged fully off the beamline.

11. The detector according to claim 1 , wherein the steering electrode and the shielding electrode include respective grids.

12. A residual gas analyzer (RGA), comprising:

a) an ion source;

b) an analyzer having an aperture, the analyzer defining a beamline passing through the aperture; and

c) a detector configured to receive ions traveling in a downstream direction through the aperture, the detector comprising:

i) a steering electrode offset from the beamline;

ii) a first ion-receiving electrode arranged at least partly on the opposite side of the steering electrode from the beamline;

iii) a second ion-receiving electrode at least partly offset from the beamline and arranged at least partly across the beamline from at least a portion of the steering electrode and at least partially upstream of at least a portion of the steering electrode;

iv) a shielding electrode arranged at least partly between the beamline and the second ion-receiving electrode; and

v) a source for applying a potential to the shielding electrode.

13. The RGA according to claim 12 , wherein:

a) the detector further includes an electron multiplier having the first ion-receiving electrode and a collector plate, and a readout electrode electrically connected to both the second ion-receiving electrode and the collector plate; and

b) the RGA further includes a supply for applying a selected potential to the first ion-receiving electrode and a steering supply for applying a selected potential to the steering electrode of the detector.

14. The RGA according to claim 13 , further including a controller adapted to receive a mode command and operate the supply and the steering supply to direct ions departing the analyzer either towards or away from the first ion-receiving electrode of the electron multiplier in response to the mode command.

15. The RGA according to claim 13 , wherein the analyzer includes a quadrupole mass filter.

16. The RGA according to claim 12 , wherein the steering electrode and the shielding electrode include respective grids.

17. The RGA according to claim 12 , wherein the first ion-receiving electrode includes a conductive cone having a farthest-downstream collection point and the shielding electrode extends at least partly upstream of the farthest-downstream collection point.

18. The RGA according to claim 12 , further including a multichannel plate including the steering electrode and having a farthest-downstream collection point.

19. The RGA according to claim 18 , wherein the shielding electrode extends at least partly upstream of the farthest-downstream collection point.

20. A detector in a residual gas analyzer (RGA), the detector configured to receive ions traveling in a downstream direction of a beamline, the detector comprising:

a) a readout electrode;

b) a steering electrode arranged offset from the beamline;

c) a steering supply for selectively applying a potential to the steering electrode;

d) an electron multiplier including:

i) a first ion-receiving electrode arranged at least partly on the opposite side of the steering electrode from the beamline and having a farthest-downstream collection point;

ii) a collector plate electrically connected to the readout electrode and configured to collect electrons from the first ion-receiving electrode;

iii) and a supply configured to selectively apply a voltage to at least part of the first ion-receiving electrode;

e) a Faraday cup including a second ion-receiving electrode electrically connected to the readout electrode, the second ion-receiving electrode arranged at least partly offset from the beamline, at least partly across the beamline from at least a portion of the steering electrode, and at least partially upstream of at least a portion of the steering electrode;

f) a shielding electrode arranged at least partly between the beamline and the second ion-receiving electrode and extending at least partly upstream of the farthest-downstream collection point; and

g) a source for applying a potential to the shielding electrode.