Cylindrical mirror electron energy

Figure 5.30. Schematic diagram of a cylindrical mirror electron energy analyser.

Our earliest alkali halide studies were performed with cesium halides, since the prevailing evidence (Table I) indicated that the vapor would be predominantly monomeric, and hence simplest to interpret. The apparatus employed for these studies (Figure 1) consisted of a cylindrical mirror electron energy analyzer, a non-inductively wound oven for generating the cesium halide vapor, and a helium resonance lamp. The spectra we obtained ( ) for the cesium halides are displayed in Figure 2. They reveal a clearly resolved doublet for Csl, a partially resolved doublet for CsBr, and broad single peaks for CsCl and CsF. We shall briefly reproduce here the arguments we used to interpret these spectra. 

Figure 1. Cylindrical mirror electron energy analyzer (2> ).

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 HREELS, Auger electron spectroscopy (AES) and thermal desorption spectrometry (TDS) experiments were carried out in a UHV chamber described previously.6 Briefly, the chamber was equipped with a HREELS spectrometer for vibrational analysis, a single-pass cylindrical mirror analyzer for AES measurements and a quadrupole mass spectrometer for TDS measurements. The HREELS spectra were collected in the specular direction with an incident energy of 3.5 eV and with a spectroscopic resolution of 50-80 cm-1. The TDS data were obtained by simultaneously monitoring up to 16 masses, with a typical heating rate of about 1.5 K s-1. 

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. 

For time-resolved 2PPE spectroscopy, a combined set-up of an ultrafast laser system and an ultrahigh-vacuum photoemission spectroscopic system is indispensable. Typical electron energy analyzers have been used as the spectrometer, such as a cylindrical mirror analyzer, a hemispherical analyzer and a time-of-flight (TOF) analyzer. The TOF analyzer is mainly used for low repetition rate (<1 kFlz) laser sources, and the others are used for the lasers with multi-kldz or MHz repetition rates [11-14]. 

Surface analysis (AES/XPS) Electron spectroscopy for elemental analysis of surfaces, sensitive to as low as two atomic layers. Physical electronics model PHI-570 Auger Electron Spectroscopy/X-ray Photoelectron Spectroscopy System is a double pass cylindrical mirror energy analyzer with dual anode (Mg/Al) X-ray source and has a rapid sample introduction probe. It can detect elements at the first five to ten atomic layers of sample and detect all elements except H and He. 

Figure 3 demonstrates the electron spectrometer part of a depth-resolved conversion electron MOssbauer spectrometer specially designed for such measurements in our laboratory (10, 11). The electron spectrometer is of the cylindrical mirror type back-scattered K conversion electrons from resonantly excited Fe nuclei are resolved by the electrostatic field between the inner and outer cylinders (cylindrical mirror analyzer) and then detected by a ceramic semiconductor detector (ceratron). The electron energy spectra taken with this spectrometer indicate that peaks of 7.3-keV K conversion electrons, 6.3-keV KLM Auger electrons, 5.6-keV KLL Auger electrons, etc., can be resolved well, with energy resolution better than 4%. 

CMA cylindrical mirror analyzer DTA differential thermoanalysis EELS electron energy loss spectroscopy EDTA ethylenediaminetetraacetic acid... 

All experiments result in a spectriun which represents the energy distribution of photo electrons convoluted with instrumental functions from the analyzer and the detector system. These functions are fundamentally different for the two common analyzer types these are the cylindrical mirror analyzer (CMA) and the hemispherical analyzer (HSA). A description of the function of both devices can be found in the literature [2]. In commercial analytical instnunents, the HSA is more common than the CM A and all further discussion is limited to this device. 

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