Monochromators energy resolution

HREELS experiments [66] were performed in a UHV chamber. The chamber was pre-evacuated by polyphenylether-oil diffusion pump the base pressure reached 2 x 10 Torr. The HREELS spectrometer consisted of a double-pass electrostatic cylindrical-deflector-type monochromator and the same type of analyzer. The energy resolution of the spectrometer is 4-6 meV (32-48 cm ). A sample was transferred from the ICP growth chamber to the HREELS chamber in the atmosphere. It was clipped by a small tantalum plate, which was suspended by tantalum wires. The sample was radia-tively heated in vacuum by a tungsten filament placed at the rear. The sample temperature was measured by an infrared (A = 2.0 yum) optical pyrometer. All HREELS measurements were taken at room temperature. The electron incident and detection angles were each 72° to the surface normal. The primary electron energy was 15 eV. 

Comparison between the core-level X-ray absorption spectroscopy (XAS), emission (XES), and X-ray photoemission spectroscopies (XPS) usually shows that the spectral edges rarely coincide with each other and with the Fermi level. It is common practice, however, to place F at the emission threshold which corresponds to a fully relaxed ion core (16). For defining the structure of the edge, an energy resolution of at least 1-2 eV is required in the range of 5-20-keV X-ray photons. This can be achieved with Bonse-Hart channel-cut silicon monochromator crystals. 

For the studies presented in Sections IV and V, measurements were taken at IBM Beamline U8B (12) at the National Synchrotron Light Source. Monochromator energy resolution at the carbon K-edge was 0.2 eV. A display analyzer (13) with channel plates was used to detect secondary electrons in an 8 eV window centered at 42 eV. This energy was selected so that only the most surface-sensitive (minimum escape depth) electrons were detected. 

Following the heat-load monochromator, the X-ray bandwidth is narrowed to approximately 1 eV and centered on the nuclear resonance energy (14.4 kev for Fe). The high-resolution monochromator further reduces the X-ray bandwidth to about 1 meV and motorized scanning of this monochromator tunes the energy over a range (typically within 100 meV of the resonance) adequate to explore excitation or annihilation of vibrational quanta. The X-ray flux at the sample is about 10 photons/s ( 10 tW), which is very low compared to typical milliwatt beam powers in laser-based Raman experiments see Vibrational Spectroscopy). Additional X-ray optics may reduce the beam size. The cross section of the beam at the sample point is currently about 0.5 x 0.5 mm at station D of beam line 3ID at APS. 

For second row transition metals, the corresponding Is 4d transition requires very high energies. Low monochromator resolution and short core-hole lifetimes hinder the ability to detect this transition in many cases. Other options to obtain information for these metals rely on intensity estimations of the 2p 4d (allowed) transitions at the f Cn.iii) edges. Another promising approach, mentioned in... 

The application of X-ray photoelectron spectroscopy (XPS) [1, 20-22], has considerably extended the possibilities. The main advantage of XPS is that, in contrast to the spectroscopic techniques mentioned above, it can in principle provide information on all valence levels. A drawback is that the energy resolution of spectra of solid samples is low, especially when a non-monochromated X-ray source (A1 Ka radiation with a natural width of 1 eV) is used. 

In 1971 a new variation on the transmission method was introduced by Sanche and Schulz (13). The technique incorporated the trochoidal monochromator of Stamatovlc and Schulz (14) and a modulation scheme to obtain the derivative of the electron current transmitted through a gas cell. This combination provides a relatively simple and very sensitive means of locating resonances as they appear in the total scattering cross section. In particular the energy resolution (20-50 meV), which is substantially better than that found in most trapped electron and SFg scavenger studies, is sufficient to observe the vibrational structure possessed by anions long lived enough to... 

The energy resolution as a function of the detector distance from a Si(3II) monochromator is clearly seen by the attenuation of the strong white line at the arsenic K-edge of a chalcogenide sample As2S3 (Fig. 4). The position of the monochromatic... 

Another important parameter that may affect the resolution is the higher harmonic contribution from the Bragg reflector. A fused quartz mirror behind the monochromator has been currently used to reject this high harmonic contribution. Therefore, the energy resolution of the spectrometer is just limited by the Darwin width of the rocking curve and the spatial resolution of the position-sensitive detector [8]. 

The flux is limited for this type of optics by the energy resolution of the monochromator (e.g. AE/E w 3 10-4 for Ge(lll)). Such an energy resolution is, however, not necessary for most SAXS-experiments. Thus the width — w — of a reflection in the diffraction plane may be written at small angles as [1]... 

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