Hemispherical analyser

The hemispherical analyser shown in Figure 8.5(d) works on a similar principle buf has fhe advanfage of collecting more phofoelecfrons. An analyser consisting of two concentric plates which are parts of hemispheres, so-called spherical sector plates, is often used in a spectiomefer which operafes for bofh UPS and XPS. 

Figure 8.5 (a) Slotted grid, (b) spherical grid, (c) 127° cylindrical and (d) hemispherical analysers... 

The energy of the photoelectrons leaving the sample are determined using a Concentric Hemispherical Analyser (CHA), and this gives a spectrum with a series of peaks whose energy values are characteristic of each element. A schematic diagram of a CHA is shown in Figure 2.3. 

Higher resolution is offered by dispersive analysers of which the main types are the 127° (27), the hemispherical (28), and the cylindrical mirror analyser (29). The various types will not be discussed here and the reader is referred to the useful summaries by Eland (4) and Sevier (30). At least two commercial companies offer uhv photoelectron spectrometers for surface work combining hemispherical analysers with discharge lamps. Bradshaw and Menzel describe (25) a system for surface studies, whereby other techniques can be combined with photoelectron spectroscopy (see Fig. 3). 

Figure 3.13 Electrostatic positron beam system S = source assembly, T = target, HSA = hemispherical analyser LA = LEED/ Auger...

For XPS characterisation, we used an Omicron UHV system with hemispherical analyser [27]. Spectra were obtained with Mg K excitation at room temperature and were corrected for differences in contact potential. Elemental ratios were calculated fi om the XPS intensities, modified with the specific atomic sensitivity factors (ASFs) when necessary [28]. 

ICP analyses were performed by Plasma Absorption Emission Spectroscopy (ICP-AES). BET surface areas were measured with a Micromeritics TriStar 3000 instrument after degassing the samples at 150 C under a 0.13 Pa vacuum overnight. XPS analyses were performed on a SSI X-probe spectrometer (SSX-100/206 photoelectron spectrometer Fisons) equipped with a monochromatized microfocused Al Ka X-ray source (1486.6 eV) and a hemispherical analyser. The binding energies were calculated relative to the C-(C, H) component of the adventitious Cls carbon peak fixed at 284.8 eV. Zeta potential measurements were carried out in a PENKEM Zeta Meter 500, using 25 mg of sample ultrasonically dispersed in 200 ml of an aqueous solution... 

Figure 13.9 Principle of electric- and magnetic-sector charged-particle analysers, here shown for a 180° sector (hemispherical analyser). Conceptually, electric sectors serve as kinetic energy analysers magnetic sectors (magnetic field perpendicular to the plane) constitute mass analysers...

Figure 5 The hemispherical analyser. R, R, R2 are the radius of the inner electrode, the midradius, and the radius of the outer electrode, respectively. Si and S2 are the entrance and exit slits, respectively.

Two types of PEPICO experiments have been carried out. In one the light source has a fixed energy (e.g. the He(I) source at 21.2 eV) and the electron energies are selected by a dispersive analyser such as a hemispherical analyser. In the more versatile... 

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