There are two general categories for most ESD-related experimental studies:
To measure properties of the desorbing species, include the measurements of:
Total desorption yields
Energy and angular distributions
Mass spectra
Radiation emitted by electronically excited metastables
To investigate changes in characteristics of the surface due to electron bombardment
Work function and elemental composition determination
Observations of differences in LEED patterns and TPD spectra
Vibrational spectroscopic studies of surface-bound ESD products.
Measurement of angular distributions of ions and electronically excited neutrals produced in ESD
Fig. 1.
A example is represented schematically in fig. 1. An electron beam strikes the surface of a single crystal at glancing incidence, and a small fraction of the ions ejected from the surface are collected by a channeltron mounted on a motor-driven, computer-controlled goniometer. The detector can traverse a spherical surface and map out ESD ion intensity angularly. Digital data is displayed in three-dimensional form, and digital background subtraction can be utilized to enhance the appearance of ESDIAD patterns.
Fig. 2.
Another approach is the digital ESDIAD imaging system presented in fig. 2. Particles ejected encounter a four-grid electrostatic lens array. All positive ion and neutral ESD species pass through the grid system, striking the first of two multi-channel plates (MCP). Then produce about one million electrons for each positive ion (or excited-state neutral). This electron pulse is accelerated into a resistive anode, causing an expanding ring of charge, centered at the pulse arrival point, to propagate across the thin conductive film. The position analysis computer translates it into a 3-dimensional image.