Polarized X-ray

Detection limits for various elements by TXRF on Si wafers are shown in Fig. 4.13. Synchrotron radiation (SR) enables bright and horizontally polarized X-ray excitation of narrow collimation that reduces the Compton scatter of silicon. Recent developments in the field of SR-TXRF and extreme ultra violet (EUV) lithography nurture our hope for improved sensitivity down to the range of less than 10 atoms cm ... 

MCP experiments were performed at AR-NE1 station of KEK (National Laboratory of High Energy Physics), Japan, using circularly polarized X-rays with the incident X- ray energy of 60 keV emitted from the elliptical multipole wiggler. Figures 1 and 2 show MCPs ofUSe and UTe, which have been measured at 150 and 80 K, respectively. 

The applications of polarized x-ray absorption spectroscopy (PXAS) for structure determination in inorganic and bioinorganic systems are discussed. PXAS studies of oriented samples add angular detail to the information obtained from x-ray absorption edges and from EXAFS. In some cases, PXAS can be used to determine molecular orientation. In other cases, PXAS can be used to infer the details of electronic structure or of chemical bonding. Some of the potential future applications of PXAS are discussed. 

In this chapter, we briefly discuss the theoretical background of polarized x-ray absorption spectroscopy (PXAS). Many of the recent applications of synchrotron radiation to polarized absorption edge structure and to EXAFS are discussed, with particular emphasis being given to the study of discrete molecular systems. We present here some indication of the potential applications of PXAS to systems of chemical and biological interest. 

Electronic Structure Determination, Cox and Beaumont have studied the polarized x-ray absorption edge of a single crystal of Zn 2 (23), in which the Zn has tetragonal (D ) site symmetry. The observed anisotropic K-absorption edges were explained in terms of a ls+4p and a ls-K4p, 4p ) transition. 

Future Applications. These examples illustrate a few of the applications of polarized x-ray absorption edges to the deter-... 

Polar interaction between guest and cyclodextrin molecules, 32 428-432,434-435 Polarized X-ray absorption spectroscopy, 35 15-17... 

E of the incident polarized X-ray relative to the axis of the a and n orbitals. This, coupled with the fact that sharp core level excitations for elements C, N, O, and F occur in the soft X-ray spectral region, makes NEXAFS an ideal technique for probing molecular orientations of organic molecules. 

Information concerning the orientation of the molecule can be inferred from the polarization dependence. NEXAFS is sensitive to bond angles, whereas EXAFS is sensitive to the interatomic distances. Linearly polarized X-rays are best suited for molecules possessing directional bonds. This is best exemplified for flat 7T-conjugated molecules lying flat on surfaces. When the electric field vector E is aligned along the surface normal, features due to the out-of-plane tt orbitals... 

Jauncey has recently described a corpuscular quantum theory of the scattering of polarized X-rays, in which a formula for the intensity of the scattering in any direction is derived. From this formula an expression for the linear scattering coefl cient per unit solid angle in any direction 4> may be obtained. In particular this linear scattering coefficient for the case where plane polarized X-rays are scattered in the plane of the electric vector of the primary X-rays is given by... 

Here I0 is the intensity of the x-ray beam, r0 = e2/mc2 is the classical electron radius (2.82 x 10 15 m)., P(9,) is the polarization of the x-rays it depends on the angle between the polarization and the scattering vector. For horizontally polarized x-rays, it takes the form P(0, < >) = 1 - sin220 sin2t)>, where 20 is the scattering angle and < > the azimuthal angle with respect to the vertical direction. The formfactor ) is the Fourier transform of the atomic electron density ... 

In scattering theory this radius is interpreted as a maximum vibration amplitude. When set into vibration by a polarized X-ray plane wave of amplitude S, the electron becomes a source of secondary scattered waves of amplitude... 

Second, the velocity distribution function (VDF) of hot electrons was directly measured to clarify the energy deposition process using X-ray line polarization spectroscopy. When the plasma has electromagnetic field anisotropy, polarized X-rays corresponding to the magnetic quantum number are emitted. In the case of polarization spectroscopy in an electron beam ion trap (EBIT) [21], the polarization degree P is generally defined by... 

Fig. 10.8. Polarized X-ray spectra for the a a component without overcoating, b 7r component without overcoating, c a component with 0.05-p.m-thick Ch overcoating, and d -n component with 0.05-p.m-thick CH overcoating...

The experimental techniques used are optical and scanning electron microscopes, electron microprobe, potentiodynamic polarization, X-ray diffraction, Fourier transform infrared spectroscopy and transmission Mossbauer spectroscopy. 

Fig. 6.33. Polarized x-ray emission spectra (S Ap, and Mo LPj) obtained from a single crystal of MoS, (2H poly type) as a function of angle of incidence 0 (= 20-80 ) (after Yarmoshenko et al., 1983 reproduced with the publisher s permission).

The calculation of the x-ray emission spectra are now not a difficult target for the DV-Xa method. The development of experimental method using the synchrotron radiation now provides circularly and linearly polarized x-ray spectra, spin-selective x-ray spectra, and resonance x-ray spectra. These x-ray spectra will be calculated by the present DV-Xa method without any revision of the FORTRAN code. When the agreement between the experiment and the calculation is not satisfactory in the x-ray spectra, the only thing we must do is to check the experiment or to check the cluster model we used in the calculation. 

The surface provides an asymmetrical field. Two kinds of coordination bonds of the ion at the surface are possible, one in parallel with surface and the other perpendicular to it. Each will have different structures. The present technique using the horizontally polarized X-ray radiation fi om synchrotron is sensitive to the coordinating atoms sitting on the horizontal plane of the X-ray absorbing atom. The N value for Br from an LiBr solution is less than six, while the value from the STAB solution is very large, more than nine. These results indicate that for normal Br the possibility of finding the coordinating water molecules at horizontal positions is less at the surface than in the bulk., while when the STA cation at the surface attracts Br anions, the anions are surrounded by water molecules horizontally as illustrated in Fig. 7. 

Templeton, D. H., and Templeton, L. K. Polarized X-ray absorption and double refraction in vanadyl bisacetylacetonate. Acta Cryst. A36, 237-241 (1980). 

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