Ion source for soft electron ionization and related systems and methods

Patent metadata

Field	Value
Publication number	US-2016172146-A1
Application number	US-201514950983-A
Country	US
Kind code	A1
Filing date	Nov 24, 2015
Priority date	Dec 12, 2014
Publication date	Jun 16, 2016
Grant date	—

Abstract

An ion source is configured for soft electron ionization and produces a low electron-energy, yet high-intensity, electron beam. The ion source includes an electron source that produces the electron beam and transmits it into an ionization chamber. The electron beam interacts with sample material in the ionization chamber to produce an ion beam that may be transmitted to a downstream device. The electron source is configured for generating a virtual cathode upstream of the ionization chamber, which enhances the intensity of the electron beam.

First claim

What is claimed is:

1 . An ion source, comprising:
a body surrounding an ionization chamber; an electron extractor configured for accelerating electrons into the ionization chamber; an electron source outside the ionization chamber and comprising an electron repeller, a thermionic cathode, and an electron lens between the thermionic cathode and the electron extractor; and a voltage source configured for applying respective voltages to the electron repeller, the thermionic cathode, the electron lens, and the electron extractor effective for: emitting electrons from the thermionic cathode; accelerating the electrons toward the ionization chamber; and generating a potential valley at the electron lens effective for decelerating the electrons and forming at the electron lens a virtual cathode comprising the decelerated electrons.

2 . The ion source of claim 1 , comprising a sample inlet leading into the ionization chamber.

3 . The ion source of claim 1 , comprising a magnet assembly surrounding the body and configured for generating an axial magnetic field in the ionization chamber.

4 . The ion source of claim 1 , wherein the ionization chamber comprises an ion outlet oriented orthogonally to the electron extractor, or aligned with the electron extractor along an axis.

5 . The ion source of claim 1 , wherein the ionization chamber comprises an ion extractor configured for directing an ion beam out from the ionization chamber.

6 . The ion source of claim 1 , wherein the thermionic cathode has a configuration selected from the group consisting of: the thermionic cathode is positioned between the electron repeller and the electron extractor; the thermionic cathode is oriented orthogonally to the electron repeller; and both of the foregoing.

7 . The ion source of claim 1 , wherein the voltage source is configured for decelerating the electrons to near zero velocity in the potential valley.

8 . The ion source of claim 1 , wherein the electron lens comprises a first electron lens between the thermionic cathode and the electron extractor, and a second electron lens between the first electron lens and the electron extractor, and wherein the voltage source is configured for applying respective voltages to the first electron lens and the second electron lens effective for:
accelerating the electrons from the thermionic cathode toward the second electron lens; and generating the potential valley and forming the virtual cathode at the second electron lens.

9 . The ion source of claim 1 , wherein the electron extractor comprises an ion repeller, the body, or both an ion repeller and the body.

10 . A mass spectrometer (MS), comprising:
the ion source of claim 1 ; and a mass analyzer downstream from the ionization chamber.

11 . A method for producing an electron beam for electron ionization, the method comprising:
producing electrons; accelerating the electrons toward an ionization chamber; decelerating the electrons to a level effective for forming a virtual cathode outside of the ionization chamber, the virtual cathode comprising the decelerated electrons; and accelerating the electrons from the virtual cathode into the ionization chamber.

12 . The method of claim 11 , comprising producing the electrons at an electron energy of about 20 eV or lower.

13 . The method of claim 11 , comprising decelerating the electrons to near zero velocity at a region where the virtual cathode is formed.

14 . The method of claim 11 , wherein accelerating the electrons toward the ionization chamber comprises applying a voltage to an electron extractor, and decelerating the electrons comprises applying a voltage to an electron lens of lesser magnitude than the voltage applied to the electron extractor, and wherein the virtual cathode is formed at the electron lens.

15 . The method of claim 14 , wherein producing the electrons comprises applying a voltage to a thermionic cathode, and wherein the voltage applied to the electron lens is of lesser magnitude than the voltage applied to the thermionic cathode.

16 . The method of claim 14 , wherein the electron extractor comprises an ion repeller, a body surrounding the ionization chamber, or both an ion repeller and a body surrounding the ionization chamber.

17 . The method of claim 11 , wherein accelerating the electrons toward the ionization chamber comprises applying respective voltages to a first electron lens and an electron extractor, and decelerating the electrons comprises applying a voltage to a second electron lens between the first electron lens and electron extractor, and wherein the voltage applied to the second electron lens is of lesser magnitude than the voltage applied to the electron extractor and the virtual cathode is formed at the second electron lens.

18 . The method of claim 17 , wherein the voltage applied to the second electron lens is of lesser magnitude than the voltage applied to the first electron lens.

19 . The method of claim 17 , wherein producing the electrons comprises applying a voltage to a thermionic cathode, and wherein the voltage applied to the first electron lens is of greater magnitude than the voltage applied to the thermionic cathode.

20 . A method for analyzing sample material, the method comprising:
producing an electron beam according to the method of claim 11 ; producing ions by directing sample material into the ionization chamber toward the electrons; and transmitting the ions from the ionization chamber to a mass analyzer.

Assignees

• Agilent Technologies Inc

Inventors

• Wang Mingda

Classifications

• H01J49/147 Primary

  with electrons, e.g. electron impact ionisation, electron attachment (H01J49/145 takes precedence) · CPC title

• H01J27/205 Primary

  with electrons, e.g. electron impact ionisation, electron attachment · CPC title

• H01J49/168 Primary

  field ionisation, e.g. corona discharge (atmospheric pressure corona discharge per se H01T19/00) · CPC title

• H01J49/0027

  Methods for using particle spectrometers · CPC title