Electrostatic energy analyzers

FIGURE 3.12 Schematic diagram of the quadratic reflectron mass spectrometer of Yoshida. (Reprinted from reference 18). 

FIGURE 3.13 The monopole reflectron of Davis and Evans (a) construction and (b) diagram showing the equipotential lines. (Reprinted from reference 19). 

Nonetheless, electrostatic energy analyzers have played a significant role in time-of-flight design. One approach, exemplified by the ETOF mass spectrometer developed at 

FIGURE 3.14 Diagram of the gridless reflectron described by Wollnik et al. ° showing the equipotential lines. (Reprinted with permission from reference 20). 

Electric sectors have not enjoyed anywhere near the same popularity as reflectrons in time-of-flight design. Isochronous systems, particularly those involving multiple sectors, are more difficult to design. In addition, reflectron instruments provide an important opportunity for recording the structural information provide by postsource decay, which is now being utilized for the amino acid sequencing of peptides. 

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If electromagnetic radiation with a sufficiently short wavelength hits a specimen, then electrons may be excited and leave its surface. By the use of X-rays, also electrons of core levels may be emitted. X-ray Photoelectron Spectroscopy (XPS) examines the kinetic energy of these photo-emitted electrons in an electrostatic energy analyzer. A simple energy balance permits the evaluation of the binding energy Eg of the level from which the electron is emitted. 

Figure 11 Schematic diagram of (a) an electrostatic energy analyzer and (b) a Bessel box energy analyzer. (From Ref. 19.)...

Fig. 120. Glow discharge mass spectrometry. A Sector field based instrument (a) glow discharge source (b) magnetic sector field (c) electrostatic energy analyzer (d) Daly detector (e) ...

Figure 5.15 The experimental arrangement of a photoelectron photoion coincidence (PEPICO) set-up. Electron energy analysis is accomplished by an electrostatic energy analyzer, by electron TOP when the light source is pulsed, or by angular discrimination against energetic electrons. Taken with permission from Baer (1986).

There is only one rigorous solution to this problem, albeit a tedious one. Use of an electrostatic energy analyzer resolves the energy spectrum... 

Physical Basis. In XPS, the sample inside a high vacuum system (pressure <10 Pa or 10 torr) is irradiated with soft X rays, usually Mg Ka (1253.6 eV) or A1 Ka (1486.6 eV). The primary event is photoemission of a core electron, but relaxation processes also lead to emission of Auger electrons or photons, as shown in Figure 1. The emitted electrons are collected by an electrostatic energy analyzer and detected as a function of kinetic energy Ey, producing a spectrum such as illustrated in Figure 2. 

There are several v/ays to record a low-energy electron Mossbauer spectrum. Initial attempts used electrostatic energy analyzers to filter the electrons of the desired energy. This is indeed possible but it is rather costly and presents experimental difficulties. A more simple approach is to use a channeltron as electron detector and to apply a positive bias between the cone entrance of the channeltron and the sample. The detection efficiency of channeltrons for electrons with energies lower than 100 eV is small. They present a much higher detection efficiency for electrons with energies in... 

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