Cylindrical mirror analyser

The energies of the Auger electrons leaving the sample are determined in a manner similar to that employed for photoelectrons already described in chapter 2 Section 4. Modern instruments nearly always incorporate cylindrical mirror analysers (CMA) because their high transmission efficiency leads to better signal-to-noise ratios than the CHA already described. 

The structure, crystallinity and phase of the films were studied by X-ray diffraction (Cu Ka filtered radiation) and by reflection and transmission high energy electron diffraction (RHEED and THEED), with 50 keV incident electron beams. The composition and the purity of the films was determined by Auger electron spectroscopy (AES). A cylindrical mirror analyser with a coaxial electron gun was placed at 30° with respect to the normal surface. 

Fig. 1.10. The fully electrostatic high-brightness positron beam developed by the Brandeis group. The positron Soa gun is located near B. The beam is deflected at C using a cylindrical mirror analyser and focussed onto a remoderator in chamber D. The extracted beam is then focussed and remoderated at the lower left of D. The double brightness-enhanced beam is then transported into the target chamber, E. Reprinted from Nucl. Instrum. Methods B143, Charlton, Review of Positron Physics, 11-20, copyright 1998, with permission from Elsevier Science.

To measure relative partial cross sections a, it is advantageous to avoid the dependences on the polarization quantities Sj and A and on the angular distribution parameter / . This can be achieved with the experimental set-up shown in Fig. 1.16 where a cylindrical mirror analyser CMA (see Section 4.2) is used which accepts all electrons around the -direction. This corresponds to a <1>-integration in the above formula and yields... 

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). 

Another advantage of AES is the speed of the analysis. Cylindrical mirror analysers possess the ability to examine the complete Auger spectrum in less than a second and rapid data acquisition may be critically important in kinetic studies. This very high-speed analysis is most important in the presence of electron beam induced desorption and damages, which are one of the major drawbacks of AES. 

A commercial x-ray photoelectron spectrometer uses a fixed anode x-ray source, typically producing magnesium Ka or aluminium Ka radiation, which directs a beam at the sample surface. The sample chamber is held at ultra-high vacuum and the resulting photoelectrons are collected and their energy analysed in an electrostatic analyser such as a cylindrical mirror analyser. 

Portion of an Auger spectrum from a (111) surface of a Cd doped AgCl crystal taken with a cylindrical mirror analyser. The primary beam has a diameter of i l ram and is incident at 27° to the surface. Primary current lOpA, modulation voltage 2.8 V peak to peak, frequency 15 kHZ, sweep rate 1 V/sec. 

Figure 7 Schematic diagram of a DCEM spectrometer based on the electrostatic cylindrical mirror analyser. Forward scattering geometry is used. 6- and O2, minimal and maximal angles for the input slit edge positions Pb, lead shielding.

The following part is restricted to the description of some frequently used electrostatic analysers, namely the radial cylindrical the hemispherical and the cylindrical-mirror analysers. 

Figure 6 The axial focusing cylindrical mirror analyser. and / 2 are the radius of the inner and the outer cylinder, respectively N is the axial extent of the source, L is the source-detector distance.

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