	US 7,332,345 B2
	Chemical sensor system
Murray R. Darrach, Valencia, Calif. (US); and Ara Chutjian, La Crescenta, Calif. (US)
Assigned to California Institute of Technology, Pasadena, Calif. (US)
Filed on Nov. 12, 2002, as Appl. No. 10/293,966.
Application 10/293966 is a continuation in part of application No. 09/283008, filed on Mar. 31, 1999, abandoned.
Application 09/283008 is a continuation of application No. 09/235046, filed on Jan. 20, 1999, abandoned.
Claims priority of provisional application 60/072179, filed on Jan. 22, 1998.
Prior Publication US 2005/0170523 A1, Aug. 04, 2005
Int. Cl. H01J 49/04 (2006.01); G06F 17/50 (2006.01); G01N 33/22 (2006.01); B01D 59/44 (2006.01)

U.S. Cl. 436—173 [250/281; 250/282; 250/288; 250/427; 436/96; 436/98; 436/104; 436/107; 436/110; 436/124; 703/13; 703/22]

33 Claims

1. A method for generating a negative ion in a reversal region, the method comprising:

a) providing an electron emitter comprising a non-planar electron-emitting surface for generating an electron beam comprising electrons;

b) providing a lens stack comprising 1) an electron extractor for electrostatically focusing the emitted electrons of the electron beam along an axis to a reversal region and 2) an electrostatic mirror for neutralizing the kinetic energy of the electrons of the electron beam;

c) determining the fields and trajectories for the electrons of the electron beam at the electrostatic mirror, wherein the trajectories of the electrons at the electrostatic mirror are calculated in an electric-field configuration at the electrostatic mirror that is matched to the geometry of the electron-emitting surface and the space charge of electrons in the electron beam is accounted for;

d) determining the number of reflections to be made by the electron beam in the reversal region;

e) modifying the geometry of the lens stack in light of the results obtained in c) and the results obtained in d) to provide an electron kinetic energy of 2 meV or less for the electrons of the electron beam and at least 5 reflections of the electron beam at the reversal region; and

f) intersecting the reversal region with a target molecular gas beam comprising a target molecule, wherein electrons of the electron beam attach to the target molecule to form a negative ion.