Azimuthal scan

Azimuthal scans obtained for tliree surface phases of Ni l 10] are shown in figure B 1.23.9 [38]. The minima observed for the clean and hydrogen-covered surfaces are due only to Ni atoms shadowing neighbouring Ni atoms, whereas for the oxygen-covered surface minima are observed due to both O and Ni atoms shadowing... 

Figure 2 Experimental data from an early stage of CO adsorbed on Fe (001) known as the GC3 state polar scans (a) of the C 1s-0 Is Intansity ratio taken in two Fe (001) azimuthal planes, the (100) and the (ITO) (the C Is and O Is electron kinetic energies are 1202 aV and 955 aV, respectively) C Is azimuthal scan (b) taken at the polar angle of maximum intensity in (a) and geometry (c) deduced from the data.

The ability of XPD and AED to measure the short-range order of materials on a very short time scale opens the door for surface order—disorder transition studies, such as the surface solid-to- liquid transition temperature, as has already been done for Pb and Ge. In the caseofbulkGe, a melting temperature of 1210 K was found. While monitoring core-level XPD photoelectron azimuthal scans as a function of increasing temperature, the surface was found to show an order—disorder temperature 160° below that of the bulk. 

Figure 9.6. Fanning-out of an equatorial streak in a fiber pattern caused from misorienta-tion. Dashed arcs indicate azimuthal scans that are performed in practical measurements. The recorded scattering curves are used to separate the effects of misorientation and extension of the structural entities... 

Figure 4. Example of an azimuthal scan. The microdensitometer readings Ds are plotted against an azimuthal coordinate (0-360°). Two symmetry-related equatorial...

The position and boundary of each spot are determined interactively from contour maps, using contour heights selected by taking radial and azimuthal scans through the approximate centre as described in section2. 

Careful work is necessary to remove all preferred orientation from powder samples. Figure 1 shows results obtained with polyethylene terephthalate (PET) fibers. Curve is a typical azimuthal scan of the 010 peak (20 = 17,5°) for a bundle of parallel fibers placed perpendicularly to the x-ray beam. Curve b is the same scan carried out on a "powder" sample, showing that all preferred orientation is removed in our conditions of moulding (350 kg/ m2). For each kind of fiber, it is necessary to do preliminary trials to find the best experimental conditions. For PET fibers, we show on Figure 2 the relative crystallinity index and the residual orientation plotted against the cut-lengh. (5). 

In principle, rotations around three axis (one of them 6) would be sufficient to bring any lattice plane into an orientation satislying the Bragg condition (see above) and to intercept the resulting diffracted beam with the detector. However, the fourth degree of freedom makes possible an azimuthal scan of a reftection, during which the plane remains in a reftecting position but the crystal rotates around the normal to this plane (so-called ir axis). 

Fig. 3 Shallow take-off angle (0 - relative to the surface) XPD 01s azimuthal scans for epitaxial a-Fe203(0001) on a-AbOsCOOOl) grown by OPA-MBE. The surface was prepared two different ways to maximize the likelihood of achieving an O termination (a), and an Fe termination (b). Also shown are single scattering simulations for the two terminations. Qualitatively, agreement is superior for the Fe termination for both methods of preparation.

Fig. 12 Experimental (dots) and calculated (lines) Fe 2p3/2 XPD azimuthal scans for (V2xV2)R45°- Fe304(001) on MgO(OOl) grown by OPA-MBE. The letters adjacent to the theory curves correspond to the structural models shown in Fig. 13.

Lorentz and polarization effects [14,15], No correction for crystal decomposition was necessary. Inspection of the azimuthal scan data [16] showed a variation which was not symmetric around 180° in phi, probably due to a mis-centering of the crystal. For this reason an empirical correction was made to the data based on the combined differences of Fobs and Fcic following refinement of all atoms with isotropic thermal parameters (Tmax = 1.16, Tmin = 0.87, no theta dependence) [17]. Inspection of the systematic absences indicated uniquely space group Ia3. Removal of systematically absent data and averaging of redundant data yielded the unique data in the final sets, which were 149 for 20°C and 241 for -127°C For the former, R(I) = 5.1% for observed data and 5.4% for all data, and for the latter R(I) = 3.9% for the observed data and 4.3% for all data. 

A total of 1463 raw intensity data were collected. Inspection of the azimuthal scan data showed a variation of /mia//max = 0.82 for the average curve. An empirical correction based on the observed variation was applied to the data as a first approximation. The structure was solved by Patterson methods in space group P. Refinement and elucidation of additional atoms proceeded via standard least-squares and Fourier techniques. Examination of the triclinic model demonstrated the correct monoclinic space group, P2Jc (the apparent absence of hOl, l 2n has been found), and refinement continued in (hat group... 

Azimuthal scan A scan of diffraction data measured as the crystal rotates about the diffraction vector. This is used to make an empirical absorption correction and to remove possible errors due to double reflections. 

Figure 41 shows radial (a), azimuthal (b), and CTR (c) scans in the (lOO)s direction for a Ag(411) electrode in contact with a sodium acetate solution. From the radial and azimuthal scans (Fig. 3.41a, b respectively), it is clear that the silver surface is of high quality. 

Figure 42. The (10) reflection for lead un-derpotentially deposited on a Ag(l 11) electrode, (a) azimuthal scan, (b) radial scan, (c) radial scan at an applied potential of 0.0 V vs. Ag/AgCl where no monolayer is present. (From Samant, M. G., Toney, M. F. et al., J. Phys. Chem. 92,220 (1988), with permission.)...

Having characterized the substrate, they then investigated the structure of a monolayer of lead underpotentially deposited on the silver(l 11) electrode surface. Figures 42a and b, respectively, show radial and azimuthal scans from a lead monolayer underpotentially deposited on a Ag(lll) electrode surface at a potential of —0.40 V vs. Ag/AgCl. That the diffraction arises from the lead monolayer was conclusively demonstrated by the fact that at an applied potential of 0.0 V vs. Ag/AgCl, where the monolayer is stripped, no diffraction peaks were observed (Fig. 42c). For the deposited monolayer, diffraction peaks spaced at 60° intervals were observed, consistent with the anticipated hexagonal lead overlayer. From these measurements, it was concluded that the electrodeposited lead forms a hexagonal monolayer that is incommensurate with the silver substrate and that at this potential, the Pb-Pb distance is 3.45 A. 

D GIXRD patterns of 1 1 RR-P3HT PCBM films (spin-coated at lOOOrpm) fabricated with different ty (a) 30s and (b) 80s. ID out-of-plane (c) X-ray and (d) azimuthal scan (at ij(lOO)) profiles extracted from (a) and (b). (Reused from li, G. et al., Adv. Funct. Mater., 17, 1636, 2007. With permission.)... 

Figure 12.23 Azimuthal scan for SP15 PAN precursor fiber carried out at a position corresponding to the major peak determined in the equitoriai scan range 0-500° in steps of 0.335° at 5 s per step using Cu K i radiation. Source Graph prepared by Courtaulds Ltd.

PTT waxd crystal orientation function/ o can be measured from the azimuthal scan of 010 reflection. The Herman orientation function equation using this reflection has been given by (38), and is based on Wilchinsky s treatment of uniaxial orientation ... 

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