Concentric hemispherical analyzer

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 electron spectroscopic techniques - among which XPS is the most important -analysis of the energies of electrons ejected from a surface is central. Nowadays universally employed is the concentric hemispherical analyzer (CHA). 

Concentration standards, 75 750-751 Concentrators, sulfuric acid, 23 787 Concentric annular reactors, 23 544 Concentric cylinder viscometer, 27 733 Concentric hemispherical analyzer (CHA), 24 103-104, 105 energy resolution of, 24 106 Conching, milk chocolate, 6 363-364 Concomitant polymorphism, 8 69 CONCORD program, 6 10 76 752 Concrete(s)... 

Multichannel analyzer (MCA), 26 434 Multichannel detection, in concentric hemispherical analyzers, 24 106 Multiclient studies, 15 635-636 Multicollector-I CP-MS (MC-ICP-MS), archaeological materials, 5 743 Multicolor displays, LEDs in, 22 175 Multicompartment drum filters, 11 357 Multicomponent copolymerization, 7 619-620... 

Figure 7.8 Working principles of a concentric hemispherical analyzer.

The CMA as shown is used for Auger electron spectroscopy. For XPS, two CMAs in series are used to obtain the required energy resolution. This design is called a double pass CMA. The transmission of electrons through a double pass CMA is good, but the resolution is poorer than that obtained using the concentric hemispherical analyzer described subsequently. 

Fig. 1. ScheiQatic cross section of a typical UHV system for multi-technique surface studies as employed in the authors laboratory (1) sample, (2) vibrating Kelvin probe, (3) quadrupole mass spectrometer, (4) LEED screen, (5) electron energy analyzer (electron lens system), (6) electron gun, (7) viewport, (8) concentric hemispherical analyzer, (9) electron detection system (electron multiplier). The system is also equipped with an ion sputter gun, a specimen manipulator and various gas inlet and pumping facilities.

Figure 12.29 Diagram of a Concentric Hemispherical Analyzer (CHA) for XPS with a standard input lens system, which transfers an image of the analysed area on the sample onto the entrance slit to the analyzer, with slight magnification to permit removing the sample from close proximity to the entrance slit of the analyzer permitting greater working space around the sample. Source Reprinted with permission from Coxon P, Krizek J, Humpherson M, Warden IRM, Relat Phenomena, 52, 821, 1990. Copyright 1990, Elsevier.

There are many different designs of electron energy analyzers but the preferred option for photoemission experiments is a Concentric Hemispherical Analyzer (CHA), which uses an electric field between two hemispherical surfaces to disperse the electrons according to their kinetic energy (Fig. 5.9). 

XPS analyses were performed using a PHI 5700 spectrophotometer equipped with a concentric hemispherical analyzer in the standard configuration (Physical Electronics, Eden Prairie, MN, USA). The vacuum system consists of a turbo-molecular pump, ion pump, and a titanium sublimation pump. The base pressure before the analysis was better than 10 Pa. The X-ray source was A1K0 (1486.6 eV), run at 300 watts. The incident angle was 54.7° and the emission angle was 45° with respect to the sample surface normal. All the spectra were obtained in digital mode. A constant energy of 23.50 eV was set across the hemispheres of the electron analyzer operated in the Fixed Analyzer Transmission (FAT) mode for the detailed spectra the survey spectra have been acquired with 187.85 eV pass... 

XPS Measurements. X-ray photoelectron spectra were acquired with a VG Thetaprobe spectrophotometer (Thermo Electron Corporation, West Sussex, U.K.) equipped with a radian lens, a concentric hemispherical analyzer, and a 2D channel-plate detector with 112 energy and 96 angle chatmels. A monochromatic Al Ka source with a spot size of400pm was used. Electrons were emitted at 53 with respect to the surface normak and the acceptance angle was 30. The instrument was operated in standard lens mode, and the analyzer in constant-analyzer-energy mode. Pass energies used for survey scans and detailed scans were 200 and 100 eV, respectively, for Au 4f, C Is, F Is, O Is, and... 

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. 

An example of the arrangement of a single-stage CMA in a modem system for AES analysis is shown in Figure 32, taken from [128]. The double-pass CMA described in Section 27.2.2.4 (see Fig. 8) can also be used for AES by grounding the spherical retardation meshes and the inner cylinders and by setting the variable internal apertures to minimum. Although the double-pass CMA is not ideal for either AES or XPS, use of the same analyzer, in its different modes of operation, for both techniques is very convenient. Similarly, the concentric hemispherical analyzer... 

Meanwhile, the chemical binding state of the nanostrips near the surface of the tri-bofihns was examined by XPS analysis. Photoelectrons were excited by monochromatic Al-Ka (1486.6 eV) and detected with a concentric hemispherical analyzer. The x-ray tube was operated at 40 W. The pass energy of Concentric Hemispherical Analyzer (CHA) was 58.7 eV for scan spectra. The analyzed area was 20 x 20 pm and was located in the center of the irradiated area. The take-off angle was 45°. The binding energies of the spectra were calibrated by setting the Cls peak at 284.6 eV. 

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... 

Figure 8. Schematic diagrams of (a) a double-pass cylindrical mirror analyzer (DPCMA) (from Ref. 19), and (b) a concentric hemispherical analyzer (CHA) (from Ref. 16).

FIGURE 7 Concentric hemispherical analyzer (CHA) diagram. [Reproduced with permission from D. Roy and J.-D. Carette, Canadian Journal of Physics, Vol.49, p. 2141,1971 Copyright 1971, NRC Research Press.]... 

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