Hemispherical energy analyzer

In certain applications (e.g., X-ray photoelectron spectrometry) an electron beam must be analyzed by its kinetic energy using a 180° hemispherical energy analyzer consisting of two concentric hemispheres coupled to a wide-area charge-coupled detector (see Fig. 10.29). 

X-ray Photoelectron Spectroscopy. A PHI 5700 X-ray photoelectron spectrometer equipped with an monochromatic A1 Ka X-ray source (hv = 1486.7 eV) incident at 90° relative to axis of a hemispherical energy analyzer was used to obtain X-ray photoelectron spectra of the films at a photoelectron takeoff angle of 45° from the surface and a pass energy of 23.5 eV. The surface concentration of CF3 groups in the mixed monolayers was determined by integrating the F Is and Au 4f photoelectron peaks. Additional experimental details are provided in reference 13. 

These modes of operation ate used in conjunction with the two most popular energy analyzers, the cylindrical mirror analyzer (CMA) and the concentric hemispherical analyzer (CHA). The most common form of the CMA used today is the double-pass version diagramed in Eigute 21. This device consists of two perfectly coaxial cylinders of radii r and r. The outer cylinder is held at a potential of (— ) and the inner cylinder is held at ground. The... 

In 1979, the construction of an XPS system for the investigation of solids in gas atmospheres at pressures of up to 1 mbar was reported by Joyner and Roberts (1979a) this was later commercialized. One differential pumping stage around the high-pressure sample cell was used in combination with the commercial hemispherical electron energy analyzer ESCALAB of V.G. Scientific Ltd. Two "high-pressure" spectrometers of this type were supplied to the University of Wales (Cardiff, UK) and the Boreskov Institute of Catalysis (Novosibirsk, Russia). 

Figure 4 Analogy between the principles of optical and photoelectron holography. In optical holography (top), the incident laser beam is the reference wave, the reflected waves are the scattered waves, and a fllm is used as a detector. In photoelectron holography (bottom), the direct, photo-emitted waves are reference waves that interfere with the scattered waves from neighboring atoms, and a hemispherical, electron energy analyzer is used as a detector.

The UhV surface probes used in this study were x-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS) and temperature programmed desorption (TPD). XPS measurements were carried out with Mg K radiation (hv= 1253.6 eV) and a hemispherical electron energy analyzer set at 50 eV pass energy. ISS measurements were made with the same analyzer but with reversed polarity on the hemispheres and input lenses. The incident He + ion beam current was 5 x 10-9 amps at 500 eV. This beam energy and ion current... 

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]. 

As an illustrative example, the 2PPE system developed by our group is depicted in Figure 19.1 [15, 30]. The UHV chamber was equipped with a home-made TOF electron energy analyzer, a hemispherical electrostatic electron energy analyzer, an... 

In our x-ray photoemission studies, a monochromatized photon beam (A1 Ka, hv = 1486.6 eV) was focused onto the sample surface, and the emitted electrons were energy analyzed with a Surface Sciences Instruments hemispherical analyzer. The take-off angle of the photoelectrons relative to the surface normal was 60° unless otherwise specified. A position-sensitive detector with 128 channels was used with a dedicated HP9836C computer to facilitate data acquisition. (22.) ... 

Semi quantitative analyses of the calcium phosphate deposits were acquired using a Kratos Axis ULTRA XPS spectrometer incorporating a 165-mm hemispherical electron energy analyzer. The source of X-ray incident radiation was a monochromatic Al Ka (1486.6 eV) at 150 W (15 kV, 10 mA). Survey (wide) scans were taken at an analyzer pass energy of 160 eV. 

X-ray photoelectron spectra were recorded with a VG Escalab 200R electron spectrometer equipped with a Mg Ka X-ray source (hv = 1253.6 eV) and a hemispherical electron analyzer operating at constant transmission energy (50 eV). No reduction treatment of ICP catalysts was carried out before XPS measurements. The C Is peak at 284.6 eV was used as an internal standard for peak position measurement. 

Figure 3. Representation of an ESC A instrument using a hemispherical electron analyzer (Ephotoe ectron = hv — binding energy).

Most energy analyzers are of the type illustrated in Figure 21-4, in which the electron beam is dellected by the electrostatic field of a hemispherical capacitor. The electrons thus travel in a curved path from the lens to the multichannel transducer, I he radius of curvature depends on the kinetic energy of the electrons and the magnitude of the electrostatic field. An entire spec-... 

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