US 4,139,773 A · Method and apparatus for producing bright high resolution ion beams

Abstract

A field ionization source includes a <110> oriented iridium emitter, the tip of which is initially built up in the <110> direction. A negative voltage is applied to the emitter after the emitter has been heated to approximately 2000.degree. C; thereafter, the emitter is cooled to approximately 1200.degree. C. Crystalline buildup of the pointed iridium tip occurs in the <110> direction. After buildup has occurred, the emitter is cooled sufficiently to "freeze" the tip in the built up configuration. The negative voltage is then removed. A gas containing molecules to be ionized is differentially pumped at relatively high pressure through a tube into a region immediately around the emitter tip enclosed by a cathode cap having an aperture through which the ion beam is accelerated. The iridium emitter is mounted in thermal contact with a liquid nitrogen reservoir, which maintains the emitter at near-cryogenic temperatures. The gaseous source of molecules is also maintained in thermal contact with the liquid nitrogen reservoir which cools the gas to near-cryogenic temperatures. A positive voltage of sufficient magnitude to cause ionization of molecules from the gas is applied to the emitter with respect to the cathode cap. The ions are accelerated through the aperture of the cathode cap by the electric field between the emitter and the cathode cap, thereby forming the ion beam.

Claims22

Dependent claims

A method for producing a high intensity beam of ions from a gas substantially confined within a region bounded by a conductive enclosing means having an aperture therein, said method including the steps of:

(a) heating an oriented crystalline emitter of <110>
iridium within the region to cause substantial surface mobility of iridium atoms at the tip of said emitter;
(b) applying a first voltage of sufficient negative potential with respect to the enclosing means to said emitter to cause <110>
build-up of the tip of said emitter;
(c) cooling said emitter to inhibit substantial surface mobility of iridium atoms at the tip of said emitter;
(d) maintaining the gas in an immediate region surrounding the tip of said emitter at a sufficiently high pressure and a sufficiently low temperature to increase the supply of low energy gas molecules available for ionization in said immediate region;
and
(e) applying a second voltage of sufficient negative potential with respect to the closing means to said emitter to ionize molecules of the gas in said immediate region and accelerate the resultant ions through the aperture in the enclosing means.

5 more elements

A field ion gun for producing a high intensity ion beam from gaseous molecules and for providing high resolution focusing of a portion of said in beam onto a predetermined spot, said gun comprising in combination:

(a) an oriented crystalline emitter having a longitudinally extending pointed tip;
(b) conductive means for substantially enclosing a region immediately surrounding said emitter including a limited aperture axially aligned with the longitudinally extending tip of said emitter;
(c) means for introducing gas into the region immediately surrounding said emitter;
(d) means for cooling said emitter and said gas to near-cryogenic temperatures;
(e) means for maintaining said gas in said immediate region at sufficiently high pressure to increase the supply of said molecules available for ionization;
(f) means for applying a first voltage of sufficient potential with respect to said conductive means to said emitter to ionize molecules of said gas in the region immediately surrounding said emitter and accelerate the resultant ions through the aperture in said conductive means to form the high intensity ion beam;
and
(g) an electrostatic lens system enclosed in a low pressure chamber for receiving the ion beam and focusing a portion of the ion beam onto a predetermined spot in response to selected control signals imposed upon said electrostatic lens system.

5 more elements

Dependencies are inferred from the claim text.

Method and apparatus for producing bright high resolution ion beams

Life of this patent

Method and apparatus for producing bright high resolution ion beams

Life of this patent

Abstract

Claims22