Electrostatic focusing

Electron impact (El) ion sources are the simplest type. O2, Ar, or another (most often noble) gas flows through an ionization region similar to that depicted in Eig. 3.30. Electrons from an incandescent filament are accelerated to several tens of eV by means of a grid anode. A 20-100 eV electron impact on a gas atom or molecule typically effects its ionization. An extraction cathode accelerates the ions towards electrostatic focusing lenses and scanning electrodes. 

Two types of ion source produce high enough brightness (> 106 A/cm2.ster., 20 keV) for them to be considered for semiconductor fabrication applications the field ion source (56) and the liquid metal source (57,58). The field ion source produces relatively small energy spread (<3 eV) and when combined with a short focal length (< 1 cm) electrostatic focusing system should be able to produce beam sizes as small as 10 nm with adequate current (10-11 amp) for laboratory microfabrication experiments. As with field emission electron sources, the field ion source only produces a limited total current and the maximum beam current is limited to about 1 10 amp. 

Novakoski, L.V. and McClelland, G.M. (1987). Orientation of CHF3 desorbed and scattered from Ag(lll) measurements using electrostatic focusing, Phys. Rev. Lett., 59, 1259-1262. 

A schematic representation of the apparatus [21] is shown in Fig. 2. An electrostatically focused beam (105 e+/s at 65 eV) enters a section of waveguide (2.3cm x 1.0cm) and strikes a polycrystalline molybdenum target attached to the opposite inner wall... 

The SO3 flux was such that no masses corresponding to more than one SO3 molecule in a cluster were detected. Electrostatic focusing demonstrated that the SC O adduct, expected to be the initial product, rapidly isomerized to H2SO4. 

The molecular beam filtered out electrons and small ions since no electrostatic focusing was used. Applied deflection voltage less than about 0.1 V had no effect on the current arriving at the Faraday cage, which indicates that ions smaller than about 300 100 amu were not in the beam. 

MicroChannel Electrostatic focusing piate Collector and acceleration lens ... 

As determined by their chemical stability, the relative proportions of molecular ion and fragment ions are reasonably reproducible. Positive ions are repelled or drawn out of the ionization chamber by an electrical field. The cations are then electrostatically focused and introduced into the mass analyzer. 

Double focusing Electrostatic focusing followed by magnetic field deflection. Trajectories depend on m/z values. 

ISPD. Electrostatically focused MCPs are better in this respect. Proximity-focused HCP intensifiers show an average gain reduction of 40-50% after 2-3,000 hours of non-stop exposure to varying low light levels. This is equivalent to approximately 1-1.5 years of continuous operation (4 hours/day). Also, the gain can be raised again, resulting in a real lifetime of 6,000-8,000 hours. 

SIT ISIT. Array is flat. Curved formats are not available. Electrostatic focusing causes pin-cushion distortion and a loss of geometric resolution at the detector s edges. 

SIT ISIT. Spectral response depends on the selection of the photocathode and can be optimized for the blue or the near IR. Typical photocathodes are S-20 and S-20R (extended red multialkali) which allow an adequate response up to 900 nm. Because the electrostatically focused image section requires a special optical-fiber faceplate window (curved inside to match the focusing field contours) made out of glass, the cut-off... 

Again, whenever a new reaction class is presented, analyze the examples given on the basis of electrostatics. Focus on the logical con.sequcnccs of oppositely charged or polarized atoms attracting each other. Do this now for the examples in the reaction table in the text section. 

Figure 6 Schematic of electrostatically focused electron-beam furnace.

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