Electrostatic hemispherical analyzer

Most of the spectrometers are based on an electrostatic hemispherical analyzer, equipped with electrostatic lenses to collect, focus, retard or accelerate the photoelectron beam. 

Figure 17.3.5 Schematic diagram of X-ray photoelectron spectrometer with an electrostatic hemispherical analyzer. The detector is usually a channel electron multipher. [From J. J. Pireaux and R. Sporken in M. Grasserbauer and H. W. Werner, Eds., Analysis of Microelectronic Materials and Devices, Wiley, New York, 1991, with permission.]...

The electrostatic hemispherical analyzer (HSA), also called concentric hemispherical analyzer (CHA), is now fitting all commercial XPS spectrometers (i in Fig. 7). It consists of two concentric hemispheres of radius Ri and/f2 respectively a section comprising the entrance slit and the center is shown in Fig. 8. Electrical potentials V and V2 are applied, so that the electrons are attracted by hemisphere 1 and repelled by hemisphere... 

In electron spectroscopic techniques—among which XPS is the most important—analysis of the energies of electrons ejected from a surface is central. Because of the low kinetic energies involved in the techniques, analyzers using magnetic fields are undesirable. Therefore the energy analyzers used are exclusively of the electrostatic deflection type. The two that are now universally employed are the concentric hemispherical analyzer (CHA) and the cylindrical mirror analyzer (CMA). Since both have been used in XPS, both are described here, although in practice the CHA is more suitable for XPS, and the CMA for AES. 

Fig. 7 X-ray photoelectron spectrometer. Left schematic view of a SSX 100/206 (Surface Science Instruments). Right, photographs of a Kratos Axis Ultra (Kratos Analytical) with the introduction and intermediate chambers (top) and analysis chamber (bottom), a, Turbomolecular pump b, cryogenic pump c, introduction chamber d, sample analysis chamber (SAC) e, transfer probe f, automatized X, Y, Z manipulator g, X-ray monochromator h, electrostatic lens i, hemispherical analyzer (HSA) j, ion gun k, aluminum anode (with monochromator) 1, aluminum-magnesium twin anode m, detector. Left channel plate. Right 8 channeltrons (Spectroscopy mode), phosphor screen behind a channel plate with a video camera (Imaging mode) n, spherical mirror analyzer (SMA) o, parking facility in the sample transfer chamber p, sample cooling device for the introduction chamber q, sample transfer chamber r, monitor interconnected with the video camera viewing samples in the SAC s, video camera in the SAC t, high temperature gas ceU (catalyst pretreatment)...

Modern EKEAs usually consist of a complex combination of electron transfer lenses and a hemispherical electrostatic deflection analyzer. Figure 16 shows a sketch of the analyzer and input lense system presently used on a VG ESCALAB 220iXL produced by VG Scientific . The input lens captures the maximum possible number of emitted phototelectrons and transfers them to the deflection analyzer. 

Figure 3.2.2.S Cross-sectional view of the Scienta R4000 hemispherical electrostatic energy analyzer equipped with a two-dimensional detector for parallel detection in energy and emission angle. Typical electron trajectories are shown for two different energies, starting at the sample surface and indicating both the focusing by the electrostatic lens and the hemispherical analyzer, as well as the energy dispersion on the detector plane. A similar dispersion takes place...

Figure 1.2.2.12 Schematic view of a three-dimensional spin polarimeter [39]. Electrons that are photoemitted from a sample are energy and angle selected by a hemispherical analyzer and detected in two orthogonal Mott polarimeters. In an electrostatic beam deflection system, the spin...

For the most versatile low-energy systems, a hemispherical electrostatic energy analyzer (Figure 3.3.7b) is used, which has much in common with the analyzers used in electron spectroscopies (see Chapter 3.2.2). This allows the detection of ions emitted in a particular direction in space with a weU-defined collection solid angle. This analyzer consists of two concentric hemispheres between which there... 

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... 

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-... 

Which interactions may be classified as the Lewis acid-Lewis base (La-Lb) ones First of all, the hydrogen bond which is the most often analyzed interaction since its key role in numerous chemical, physical and biochemical processes is very well known [29-33]. It is often identified as A-H...B where the A-H proton donating bond is the part of the Lewis acid subunit while B marks the Lewis base center possessing at least one free electron pair. The H...B contact is exactly that one between the Lewis acid and base centers the H-atom hemisphere is characterized by the positive electrostatic potential while the B-center by the negative electrostatic potential. Scheme 9.1 shows an example of the water dimer linked through the hydrogen bond. 

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