Extraction lens

The bombarding of the specimen surface by the primary beam of high energy ions leads to the ejection (sputtering) of both neutral and charged (+/—) species from the surface. The ejected species may include atoms, clusters of atoms and molecular fragments. The ions enter an extraction lens and the polarity of the applied voltages determines the polarity of the secondary ions that enter the analyser. 

Analysis of terrestrial samples demonstrated that the tuning of the ion extraction system, and consequently the amount of instrumental mass fractionation, was very sensitive to charge build-up on the sample, the position of the primary beam relative to the spectrometer optic axis, and the position of the sample relative to the extraction lens. To optimize reproducible tuning of the extraction system from sample to sample, we developed the following criteria (1) resistance of the sample (Au-coated) to ground less than 106 fi (2) alignment of the primary beam to within 10 pm using... 

The ions formed are extracted by the extraction lens, EL, perpendicular to the electron beam. Due to the low energy spread of ions formed in an electron ionization source (< 1 eV) one single-focusing magnetic sector field mass spectrometer or quadrupole analyzer is sufficient for... 

Extraction Lens Vacuum Housing Conversion Dynode (—15kV)... 

Figure 9 Layout of the inductively coupled plasma time-of-flight mass spectrometer (ICP-TOF-MS) with improved vacuum chamber and ion optics. SI, second-stage extraction lens / , repeller C, Faraday cup Gl, G2, TOF-MS entry grids FI, Y2, steering plates D1, D2, deflection plates G3, reflectron entrance grid / 1, deceleration grid / 2, reflecting grid MCP, microchannel plate. (From Ref. 27.)...

The extraction lens, held at a negative voltage, attracts the positive ions as they emerge from the skimmer cone. The negative ions are repelled and the neutral species diffuse away. The accelerated positive ions are focused by the ion-lens stack and then enter the quadrupole region. Positioned between the extraction lens and the first ion... 

In the example of ions A, B, and C above, by delaying the extraction voltage relative to ion formation, the ions are allowed to expand, as a function of their inherent velocities, within the source under field-free conditions. Ion A therefore moves away from the extraction lens, ion C moves toward the extraction lens, and ion B remains stationary When the extraction voltage is applied, ions A and C will have moved to regions of higher and lower extraction potential respectively, relative to their initial positions within the source (see Fig. 20b). Because of this, the turnaround time for ion A will decrease, and the additional voltage push for ion C will be minimized. This ultimately improves mass resolution because the ion source residence time differentials between A, B, and C are minimized. 

Praphairaksit, N. and Houk, R. S. 2000. Reduction of mass bias and matrix effects in inductively coupled plasma mass spectrometry with a supplemental electron source in a negative extraction lens. Anal Chem 72, 4435 1440. 

Lens 1—circular geometry extraction lens Lens 2—transfer optics Y lens Lens 3—Z lens... 

The beam leaving the expansion chamber via the skimmer aperture is electrically neutral and heavily dominated by neutral Ar atoms, forcing all entities to move with the same velocity [21, 22]. A negatively charged extraction lens selectively attracts the positive ions and repels the negatively charged entities (electrons and ions), which are removed by the vacuum system together with the neutral particles, which... 

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