A Directional Analyzer for Ion and Electron Velocity Distributions

The two basic difficulties usually encountered in multigrid retarding-potential analyzers have been identified and effectively overcome. The frequently experienced difficulty with such probes caused by the continually changing work function of metal surfaces due to a more or less evanescent sorption of ions has been eliminated by coating the nickel surfaces with a bonded graphite dispersion that leaves the surface microscopically rough and that is peculiarly free of transient sorbed films. The very divergent electric field near the wires of grids on which retarding potentials are applied defocuses the charged particle streams and interferes with the proper application of retarding potentials unless the fields near such grids are kept small. Double grids are used where necessary in order to insure minimum field penetration from the interior of the analyzer to the medium under study, and from one region to the next inside the analyzer. The device is versatile in that it can be used as a classical analyzer or as a filter-type analyzer. The amount of lens-effect defocusing of the charged particles is different for the two modes and, for most applications, the filter mode is preferable. The performance of the device is experimentally evaluated.