surface X-ray diffraction

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New reactor dedicated to in operando studies of model catalysts by means of surface x-ray diffraction and grazing incidence small angle x-ray scattering

New reactor dedicated to in operando studies of model catalysts by means of surface x-ray diffraction and grazing incidence small angle x-ray scattering

A new experimental setup has been developed to enable in situ studies of catalyst surfaces during chemical reactions by means of surface x-ray diffraction 共SXRD兲 and grazing incidence small angle x-ray scattering. The x-ray reactor chamber was designed for both ultrahigh-vacuum 共UHV兲 and reactive gas environments. A laser beam heating of the sample was implemented; the sample temperature reaches 1100 K in UHV and 600 K in the presence of reactive gases. The reactor equipment allows dynamical observations of the surface with various, perfectly mixed gases at controlled partial pressures. It can run in two modes: as a bath reactor in the pressure range of 1 – 1000 mbars and as a continuous flow cell for pressure lower than 10 −3 mbar. The reactor is connected to an UHV preparation chamber also equipped with low energy electron diffraction and Auger spectroscopy. This setup is thus perfectly well suited to extend in situ studies to more complex surfaces, such as epitaxial films or supported nanoparticles. It offers the possibility to follow the chemically induced changes of the morphology, the structure, the composition, and growth processes of the model catalyst surface during exposure to reactive gases. As an example the Pd 8 Ni 92 共110兲 surface structure was followed by SXRD under a few millibars of hydrogen and during butadiene hydrogenation while the reaction was monitored by quadrupole mass spectrometry. This experiment evidenced the great sensitivity of the diffracted intensity to the subtle interaction between the surface atoms and the gas molecules. © 2007 American Institute of Physics.
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Structure of the Al13Co4(100) surface: Combination of surface x-ray diffraction and ab initio calculations

Structure of the Al13Co4(100) surface: Combination of surface x-ray diffraction and ab initio calculations

So far, experimental studies of complex intermetallic compounds have mainly used conventional surface-science methods. STM images the electronic density of states and pro- vides only indirect information of the surface structure. Elastic and inelastic processes experienced by low-energy electrons (30–300 eV) ensure that the detected diffracted beam intensi- ties are derived entirely from the outermost few atomic layers. However, LEED is dominated by multiple scattering, which implies a demanding data analysis based on a large number of approximations, including nonstructural parameters: spherical atomic potentials, constant inner potential, neglect of the po- tential barrier at the surface, uniform absorption, and isotropic temperature factors [ 27 , 28 ]. The alternative diffraction method is surface x-ray diffraction (SXRD) [ 29 – 31 ]. In this case, one can generally ignore multiple scattering, which makes data analysis easier. However, the weak interaction between x rays and matter implies some experimental complexity. The latter is performed at synchrotron facilities, under con- ditions that minimize the scattering contributions from the underlying bulk to ensure surface sensitivity. This technique has already been applied successfully to get insight into the structure of a fivefold quasicrystalline surface (icosahedral Al 70.4 Pd 21.4 Mn 8.2 ) [ 32 ]. Only the specular crystal truncation
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Integration techniques for surface X-ray diffraction data obtained with a two-dimensional detector

Integration techniques for surface X-ray diffraction data obtained with a two-dimensional detector

1. Introduction Surface X-ray diffraction (SXRD) is an established powerful technique for in situ surface and interface structure determi- nation (Feidenhans’l, 1989; Robinson & Tweet, 1992). SXRD experiments are mostly performed at synchrotron light sources with high brilliance, owing to the weak X-ray scat- tering cross section and small number of surface scatterers. The surface signal is about one million times weaker than the bulk signal. Historically, point detectors have been used for data acquisition, but these are gradually being replaced by the next generation two-dimensional (or area) detectors, which come with much higher resolution, lower noise, better dynamic range and faster acquisition. However, the lack of knowledge of suitable data acquisition techniques or the absence of appropriate ex post data analysis methods not only means that the full advantages of using two-dimensional detectors may not be realized, but might also lead to misin- terpretation of the experimental data.
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Topography of the graphene/Ir(111) moiré studied by surface x-ray diffraction

Topography of the graphene/Ir(111) moiré studied by surface x-ray diffraction

European Synchrotron Radiation Facility, Boˆıte Postale 220, F-38043 Grenoble Cedex 9, France (Dated: June 24, 2015) The structure of a graphene monolayer on Ir(111) has been investigated in situ in the growth chamber by surface x-ray diffraction including the specular rod, which allows disentangling the effect of the sample roughness from that of the nanorippling of graphene and iridium along the moir-like pattern between graphene and Ir(111). Accordingly we are able to provide precise esti- mates of the undulation associated with this nanorippling, which is small in this weakly interacting graphene/metal system and thus proved difficult to assess in the past. The nanoripplings of graphene and iridium are found in phase, i.e. the in-plane position of their height maxima coincide, but the amplitude of the height modulation is much larger for graphene (0.379 ± 0.044 ˚ A) than, e.g., for the topmost Ir layer (0.017 ± 0.002 ˚ A). The average graphene-Ir distance is found to be 3.38 ± 0.04 ˚ A.
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Characterization of polycrystalline materials using synchrotron X-ray imaging and diffraction techniques

Characterization of polycrystalline materials using synchrotron X-ray imaging and diffraction techniques

propagation in the grain highlighted in Figure 3e. Here the crack is observed to accelerate as soon as it changes its growth plane to a well defined crystallographic (101) plane. However, for the alloy system and the spatial resolution employed in this study (~ 2 µm full width at half maximum of the detector point spread function), one can not observe a global prevalence of orientations corresponding to reported slip planes in body centered cubic metals ({110}, {112}, {123} 28 ). The same experiment, carried out in a different beta Ti alloy system shows almost exclusive propagation in single slip mode 29 . One may therefore speculate, if the absence of crystallographic signature indicates a lack of resolution to resolve microscopic facets caused by alternating slip on two simultaneously activated slip systems 30 . This point will be addressed in future work which will include 3D inspection of the fracture surface at higher spatial resolution, as provided by X-ray zoom tomography 31 .
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Structure of nanocrystalline calcium silicate hydrates: insights from X-ray diffraction, synchrotron X-ray absorption and nuclear magnetic resonance

Structure of nanocrystalline calcium silicate hydrates: insights from X-ray diffraction, synchrotron X-ray absorption and nuclear magnetic resonance

structurally bound (Chen et al., 2010). These characteristics, together with the use of several different methods of analysis by different research groups, have led to the development of numerous structural models, with two of them being domi- nant. In the first model, the evolution of the C–S–H structure as a function of its Ca/Si ratio is described by the existence of two phases having crystal structures close either to tober- morite or to jennite (Richardson, 2008; Taylor, 1986), depending on the Ca/Si ratio. The former is assumed to be analogous to C–S–H for Ca/Si ratios lower than 1.3 and the latter is assumed to be analogous to C–S–H for higher Ca/Si ratios. These two minerals are layered structures built of Ca polyhedra (in sevenfold coordination in tobermorite, sixfold in jennite) with ribbons of wollastonite-like Si chains running at the surface. In both cases, the layers are separated by a hydrated interlayer space that may contain cations. In the alternative model, the whole range of Ca/Si is described using tobermorite and a varying amount of calcium hydroxide (CH), which may be structurally bound to the tobermorite layers (Richardson, 2008, 2014). C–S–H and CH form a nano- composite (i.e. intimate mix of the two phases), with CH filling the micropores in the C–S–H structure, possibly through interstratification of C–S–H and CH layers (Gira˜o et al., 2010; Grangeon, Claret, Linard & Chiaberge, 2013; Richardson, 2014), when the Ca/Si ratio approaches 1.5. At higher Ca/Si, C–S–H and CH form a microcomposite, with CH precipitating outside C–S–H micropores (Chen et al., 2010), as supported by the frequent observation of a discrete CH phase (portlandite) in X-ray diffraction patterns of C–S–H having a Ca/Si ratio higher than 1.5 (Garbev, Beuchle et al., 2008; Renaudin et al., 2009). The tobermorite-like model explains electrophoretic measurements made on C–S–H suspensions (Churakov et al., 2014) and aluminium uptake by C–S–H (e.g. Andersen et al., 2003; Myers et al., 2013, 2015; Pardal et al., 2012; Pegado et al., 2014). It is also in agreement with recent developments made in thermodynamic modelling (e.g. Myers et al., 2014; Richardson, 2008; Walker et al., 2007). A sketch of the C–S–H structure under the tobermorite-like assumption is shown in Fig. 1.
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Multireflection grazing-incidence X-ray diffraction: A new approach to experimental data analysis

Multireflection grazing-incidence X-ray diffraction: A new approach to experimental data analysis

the values of  11 ,  22 and d 0 hkl can be found. This is the prin- ciple of the simplest methodology for stress measurement, which is widely used in the community and fully supported by the available commercial software. However, many specific methodologies for stress measurement have been proposed, and they require simple and clear interpretations. One such method is multireflection grazing-incidence X-ray diffraction (MGIXD), developed by Marciszko et al. (2013, 2016) and used for the determination of stress variation under the sample surface. In this work a new simple method for inter- pretation of MGIXD measurements is proposed and tested. The main advantage of this method is its simplicity and the possibility of clear results presentation.
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Synchrotron X-ray diffraction experiments with a prototype hybrid pixel detector

Synchrotron X-ray diffraction experiments with a prototype hybrid pixel detector

2. Experimental setup 2.1. XPAD3.1 prototype detector The XPAD3.1 detector comprises eight modules of seven hybrid integrated circuits (chips) on a single silicon sensor (Medjoubi et al., 2010). A schematic description of the detector is given in Fig. 1. The silicon diode sensor has its rear face pixelized and each pixel is coupled via ‘bump-bonding’ to an electronic counting device in a dedicated circuit. Hybrid pixel detectors work in a single-photon-counting pixel mode. A single chip contains 120  80 pixels, each of them measuring 130  130 mm, except for the first and last columns of the chip, which have a nearly 2.5 times larger size in the horizontal direction. For the prototype version, the total size of the detection surface is 12  7:5 cm. Modules are assem- bled in tiles, which are inclined with an angle  of 7.5  with respect to the vertical direction of the detector plane, with some superposition zones in order to minimize dead areas. Even in this case, some shadowed areas still exist (horizontal lines of a few pixels width), the width of the dead zones depending on the mounting accuracy of the modules and the geometry of the experiment. Dead lines between the modules should be taken into account to correct raw data images. According to the detector geometry, reliable image correc- tions can be carried out to obtain the correct diffraction angle corresponding to each pixel, as will be discussed in detail in the following sections.
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In Situ X-ray Diffraction Study of GaN Nucleation on Transferred Graphene

In Situ X-ray Diffraction Study of GaN Nucleation on Transferred Graphene

6 Figure 1. Schematic of the in situ Nanostructures and Surface (INS) set up at the ESRF/BM32 beamline, which couples UHV-chamber with a diffractometer. The in-plane lattice parameters, associated to the crystallographic planes perpendicular to the sample surface, were measured by scanning the detector along the δ angle. The signal was integrated over 5° out-of-plane to increase the counting statistics. These radial scans allowed us to investigate in situ the in-plane deformation of the two materials at the early stage of the growth. The GaN out-of-plane lattice parameter was measured by scanning the detector along the β angle. This second configuration was used to characterize the system after growth by performing a wide out-of-plane reciprocal space mapping (RSM). Finally, the presence of GaN nanocrystals grown on graphene was confirmed by ex situ scanning electron microscopy (SEM) using a ZEISS-Ultra 55 instrument.
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Phase transformation and amorphization upon alloys magnesiation: combining operando X-Ray diffraction and X-Ray Absorption Spectroscopy

Phase transformation and amorphization upon alloys magnesiation: combining operando X-Ray diffraction and X-Ray Absorption Spectroscopy

e-mail: magali.gauthier@cea.fr Magnesium appears as a great alternative to lithium due to its high capacity, low cost, abundance and largely smaller reactivity compared to lithium [1]. Magnesium metal has however a tendency to react with conventional electrolytes to form a barrier on its surface [1], impeding cations exchange, and thus dramatically limiting reversible stripping/deposition of Mg. An interesting alternative is to replace Mg metal with negative electrode materials based on p-block elements (In, Sn, Sb, Bi…) as they electrochemically alloy with Mg and possess adequate stability in standard electrolytes [2]. These substitute electrodes can thus prove a promising solution to overcome the problem of compatibility with electrolytes, even if the reaction mechanisms behind their operation in conventional electrolytes remain partly unsolved.
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Synchrotron X-ray diffraction experiments with a prototype hybrid pixel detector

Synchrotron X-ray diffraction experiments with a prototype hybrid pixel detector

2. Experimental setup 2.1. XPAD3.1 prototype detector The XPAD3.1 detector comprises eight modules of seven hybrid integrated circuits (chips) on a single silicon sensor (Medjoubi et al., 2010). A schematic description of the detector is given in Fig. 1. The silicon diode sensor has its rear face pixelized and each pixel is coupled via ‘bump-bonding’ to an electronic counting device in a dedicated circuit. Hybrid pixel detectors work in a single-photon-counting pixel mode. A single chip contains 120  80 pixels, each of them measuring 130  130 mm, except for the first and last columns of the chip, which have a nearly 2.5 times larger size in the horizontal direction. For the prototype version, the total size of the detection surface is 12  7:5 cm. Modules are assem- bled in tiles, which are inclined with an angle  of 7.5  with respect to the vertical direction of the detector plane, with some superposition zones in order to minimize dead areas. Even in this case, some shadowed areas still exist (horizontal lines of a few pixels width), the width of the dead zones depending on the mounting accuracy of the modules and the geometry of the experiment. Dead lines between the modules should be taken into account to correct raw data images. According to the detector geometry, reliable image correc- tions can be carried out to obtain the correct diffraction angle corresponding to each pixel, as will be discussed in detail in the following sections.
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Spontaneous soft x-ray fluorescence from a superlattice under Kossel diffraction conditions

Spontaneous soft x-ray fluorescence from a superlattice under Kossel diffraction conditions

Regarding the second factor, we note that the primary radiation is s-polarized and the secondary fluorescence radiation undergoing Bragg diffraction can be decomposed into two linear components of s- and p-type in an appropriate reference frame. From the theoretical point of view this decomposition is not a simple task. This complicated operation should be similar to the one employed by Maradudin and Mills for modelling of the scattering by surface roughness[24]. However, we did not perform it in our simulations. In the framework of our model we have calculated the scattering cross-sections of the s-polarisation of the primary radiation towards the s- and p-polarisation of the secondary fluorescence radiation. We found that they are practically the same. Since the factors depending on the geometry affecting these two channels (primary s -> secondary s and primary s -> secondary p) are different and unknown, there remains in our simulations an element source of uncertainty.
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Super-Resolution for Line Parallel Imaging in Energy Dispersive X-Ray Diffraction

Super-Resolution for Line Parallel Imaging in Energy Dispersive X-Ray Diffraction

2 Direct Model The EDXRD setup is composed of a collimated poly-chromatic X-ray source and a collimated spectroscopic detector D placed at angle θ from the beam axis. The studied object O is placed at the center of the diffractometer defined as the intersection of the scatter collimator axis and the source collimator axis. To define our direct model, we consider an elementary surface of one detector dd, an elementary surface of the source ds and an elementary volume of the object do. This triplet define the scattering angle θ. In the case the studied sample is a crystal, the average number of photons m(λ) arriving at each energy, on the detector dd is given by crystallographic theory (see [2, 4]):
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Operando investigation of the lithium/sulfur battery system by coupled X-ray absorption tomography and X-ray diffraction computed tomography

Operando investigation of the lithium/sulfur battery system by coupled X-ray absorption tomography and X-ray diffraction computed tomography

In this cross-section, the red outer shape indicates the glass tube. In the electrode, the higher absorption (red) corresponds to sulfur particles, which are distributed randomly in the electrode (with a less dense region on the right side probably due to electrode damage during cell assembly). Even if a small off-centering of the electrode can be noticed, the coverage between the positive and the negative electrodes was at least 95%. No impact of such off-centering on the electrochemical performances was noticed in coin-cell configuration. It is also possible to see the Viledon® fibers in blue, which are in contact with the S@CBD surface. In figure 2.b, the sulfur particles were segmented using ImageJ. This image shows only sulfur particles (white) and the carbon binder domain (black). The sulfur particle sizes are randomly distributed around a mean of tens of micrometers, as expected for bare (non-cycled micron-sized) elemental sulfur particles 12 used. By comparing different 2D tomographic slices along the height of the electrode, the sulfur particles seem to be randomly distributed around a mean value of tens of micrometers, as expected for bare (non-cycled micron sized) elemental sulfur particles.
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X-ray powder diffraction in reflection geometry on multi-beam kJ-type laser facilities

X-ray powder diffraction in reflection geometry on multi-beam kJ-type laser facilities

For this measurement, we used the same VISAR sensitivities as those used in the previous experiment. Given the low free surface velocities, the large error bars do not allow us to observe significant transverse inhomogeneities in these measurements. Indeed, the expansion velocities measured both in the center (in blue) and at the edge (in orange) of the probed zone are largely included in the error bars of the one measured in the intermediate zone (in green). We can then back-propagate the equations of motion to accurately determine the pressure history within the sample layer, using the characteristics method, as described in [60, 61], or using hydrodynamic simulations. We used this second option, having taken care upstream to calibrate the laser deposition in our simulations using specific shots, where the same laser pulse shape was applied on simple Al-coated diamond membranes, as well as on simple iron sheets. The agreement between the measurement and the simulated release of the diamond window shown in the same figure (dotted red line) allows us to give confidence to the simulation. We also note thanks to these simulations that a 25% reduction of the laser intensity (dotted brown line) has a limited influence on the compression dynamics and that the expected free surface velocities remain very close to those measured at the edge of the focal spot (orange line) despite the large error bars. As presented in the previous section, the simulated density map of this example is shown in Figure 10.c. and allows evaluating the hydrodynamic conditions probed between 14.2 and 15.2 ns, i.e. during the probed time, with the same Heα X-ray source.
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Insights on the Electrochemical Magnesiation of InSb from Combined Operando X-ray Diffraction and X-ray Absorption Spectroscopy

Insights on the Electrochemical Magnesiation of InSb from Combined Operando X-ray Diffraction and X-ray Absorption Spectroscopy

The continued acceleration of the lithium demand combined with its relatively low abundance and uneven concentration on the Earth’s crust might dramatically increase its price in a near future. Mg-batteries are promising candidates to replace Li-ion batteries thanks to Mg abundance, theoretical capacity (2.2Ah/g - 3.8Ah/cm 3 ), low cost and safety. However, metallic Mg reacts with standard electrolytes to form a blocking layer on its surface, preventing cation exchange, and thus dramatically limiting reversible stripping/deposition. An interesting alternative is to substitute Mg metal with another negative electrode made of p-block elements as they electrochemically alloy with Mg and possess adequate stability in standard electrolytes [1].
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Insights on the electrochemical magnesiation of InSb from combined $operando$ X- Ray diffraction and X-Ray Absorption Spectroscopy

Insights on the electrochemical magnesiation of InSb from combined $operando$ X- Ray diffraction and X-Ray Absorption Spectroscopy

e-mail: lucie.blondeau@cea.fr The continued acceleration of the lithium demand combined with its relatively low abundance and uneven concentration on the Earth’s crust might dramatically increase its price in a near future. Mg-batteries are promising candidates to replace Li-ion batteries thanks to Mg abundance, theoretical capacity (2.2Ah/g - 3.8Ah/cm 3 ), low cost and safety. However, metallic Mg reacts with standard electrolytes to form a blocking layer on its surface, preventing cation exchange, and thus dramatically limiting reversible stripping/deposition. An interesting alternative is to substitute Mg metal with another negative electrode made of p-block elements as they electrochemically alloy with Mg and possess adequate stability in standard electrolytes [1].
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X-ray diffraction analysis of nanoparticles: recent developments, potential problems and some solutions

X-ray diffraction analysis of nanoparticles: recent developments, potential problems and some solutions

Keywords: X-ray diffraction; oxides. 1. Introduction Powder diffraction techniques have a wide variety of applications in compositional, structural, microstructural and many other areas. The ease in data collection makes its application to the microstructure of nanomaterials an obvious choice. In the study of nanomaterials, the crystallite size is usually the sole factor of interest. The broadening of reflections in a powder diffraction pattern contains much infor- mation, such as crystallite strain, shape and stacking faults, which are often not considered. Nanomaterials even have their own unique problems, such as multiply twinned particle phenomena in metal nanoparticles. The extensive peak broadening and possible overlap exhibited by nanomaterials can even make determining phase purity a nontrivial process, and mis-identification of a two-phase system as being single-phase could lead to some very misleading results. Visual inspection is often insufficient where closely related phases can co-exist, e.g., in solid solution series.
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In situ powder x-ray diffraction, synthesis, and magnetic properties of the defect zircon structure ScVO4−x

In situ powder x-ray diffraction, synthesis, and magnetic properties of the defect zircon structure ScVO4−x

oxidation we decided to investigate this process further using in situ diffraction and thermal analytical methods. In situ techniques are particularly suitable for the detailed under- standing of solid state reaction pathways. Frequently ex situ investigations cannot provide equivalent information and are prone to missing significant intermediates. Using in situ methods we can prove the occurrence of intermediates which are subsequently prepared as bulk samples after optimization of the preparative methods. Only very few defect zircon structures such as RE 0.9 CrO 3.85 (RE = Gd, Yb, Y) 16 have
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High pressure and high temperature in situ X-ray diffraction studies in the Paris-Edinburgh cell using a laboratory X-ray source

High pressure and high temperature in situ X-ray diffraction studies in the Paris-Edinburgh cell using a laboratory X-ray source

Figure 7. In-situ XRD HP-HT study of MgB 2 and C-diamond syntheses. high temperature, due to the overlapping of those potential peaks with the ones of the sample environment (BN, graphite furnace, NaCl). After quenching, we observe Bragg spots which could be assigned to diamond in the XRD image acquired at a slightly smaller pressure of 4.5 GPa (see fig. 7(b)). However due to the partial overlapping with Bragg peaks/diffraction rings of recrystallized NaCl and Ni ((220) NaCl and (111) Ni reflections with the (111) C-diamond one for example) further characterizations of the recovered sample (Raman spectroscopy for example) are necessary.
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