Surface X-ray scattering

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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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Scattering density profile model of POPG bilayers as determined by molecular dynamics simulations and small-angle neutron and x-ray scattering experiments

Scattering density profile model of POPG bilayers as determined by molecular dynamics simulations and small-angle neutron and x-ray scattering experiments

Area per lipid is often used as the key parameter when assessing the validity of MD simulations. However, similar to the disparate experimentally obtained results for lipid areas, pub- lished MD simulations have also reported a wide range of values. For example, CHARMM (Chemistry at HARvard Mo- lecular Mechanics) force field based simulations show a dramatic lateral condensation and overly ordered lipid acyl chains, 9 which in the case of DPPC (1,2-dipalmitoyl-sn-glycero-3-phos- phatidylcholine) bilayers do not resemble the experimentally observed fluid phase structure. 10 This simulation pitfall can, however, be avoided by applying an appropriate positive surface tension, 11,12 which requires the use of precise areas per lipid. Another attempt to enhance the predictive power of MD simulations assigns new partial charges to the lipid’s headgroup and upper acyl chains, the so-called CMAP correction. 13 Although focused on DPPC, even this approach underestimates the fluid phase area per DPPC molecule by about 4 Å 2 . In contrast, OPLS (Optimized Potential for Liquid Simulations) based force fields do not seem to require this additional tweaking. 14 The same level of lateral condensation is not observed in DOPC (1,2-dioleoyl-sn- glycero-3-phosphatidylcholine) bilayers, possibly due to the dif- ferent melting temperatures inherent to the two bilayer systems (i.e., DPPC and DOPC). 15 It is also known, both from experi- ment and from simulation, that the number of double bonds and their positions within the lipid’s acyl chains have a pronounced effect on area per lipid. 16 Finally, there is another layer of com- plexity in determining areas per lipid in bilayers with a net charge (e.g., such as the PG bilayers studied here), that of additional electrostatic interactions.
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Coupling high throughput microfluidics and small-angle x-ray scattering to study protein crystallization from solution

Coupling high throughput microfluidics and small-angle x-ray scattering to study protein crystallization from solution

■ MATERIALS AND METHODS Micro fluidic Setup. Microfluidic Chip Fabrication. Micro- fluidic droplet generation platforms, with rectangular channels with a cross section of 200 × 200 μm 2 , were fabricated using standard soft lithography and cast molding techniques. An inexpensive multilevel negative tone photoresist dry film (WBR2000 series, DuPont, France) was laminated on a glass substrate (Thermo Scienti fic Menzel-Glaser, Germany) follow- ing the procedure described in Figure S1 and Table S1 of the Supporting Information . The desired micro fluidic configuration was patterned by UV exposure (UV-KUB2, Kloe, France) through a low cost emulsion mask, and structures were subsequently developed using sodium carbonate (Na 2 CO 3 ) 1% and rinsed by an aqueous solution of magnesium sulfate (MgSO 4 ) 0.5%. In addition, the dry film structures were silanized to gain hydrophobic surface properties before a
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Structural analyses by advanced X-ray scattering on GaP layers epitaxially grown on silicon for integrated photonic applications

Structural analyses by advanced X-ray scattering on GaP layers epitaxially grown on silicon for integrated photonic applications

au-dessus de 500°C qui confirme ce qui a été reporté dans la litérature 7,8 Un scénario de formation des micro-macles est proposé via la formation de lacunes ainsi qu’une énergie d’activation mise en jeu pour éviter ce phénomène. Cependant, la croissance à haute température génère une surface très rugueuse qui ne peut être utilisée ensuite pour la réalisation de dispositifs. Une procédure de croissance dite « MEE » (Migration Enhanced Epitaxy qui consiste à déposer de manière alternée Ga et P) a été développée et optimisée par caractérisation DRX et AFM. Les échantillons « MEE » présentent après optimisation et pour une même épaisseur déposée, un volume maclé beaucoup plus faible et une surface beaucoup plus lisse que les meilleurs échantillons réalisés par MBE classique à même température de croissance. Enfin, la structure de la couche GaP/Si a été optimisée par une séquence de croissance de deux étapes: une première croissance de 40 monocouches de GaP à 350 °C (basse température) par la MEE suivie d’une deuxième croissance de 40 nm de GaP à 500 °C (haute température) par la MBE. La figure 2 a) représente la figure de pôle de cet échantillon (S1330), où l’intensité de micro-macles est très faible. La faction volumique de micro-macles est évalué à inférieur à 1% (la limite de résolution de ces méthodes par diffraction des rayons X à base résolution). La rugosité surfacique de cet échantillon est mesurée à 0.3 nm (la limite de sensibilité de cette technique d’AFM est de l’ordre de 0.15 nm) par l’image d’AFM comme présenté dans la figure 2 b).
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Applications of Neutron and X-ray Scattering to the Study of Biologically Relevant Model Membranes

Applications of Neutron and X-ray Scattering to the Study of Biologically Relevant Model Membranes

Pabst et al. (2007a) , and inset shows the crystallographic structure of alamethicin ( Fox and Richards, 1982 ). Alamethicin is a 20 amino acid fungal peptide from Trichoderma viride and is known to form pores in membranes ( Bezrukov and Vodyanoy, 1997 ). This pore formation ability is promoted by its amphiphatic ␣-helical structure, where the peptide’s hydropho- bic side faces the membrane’s interior and its hydrophilic side forms the aqueous surface of the pore. At very low peptide-to-lipid molar ratios, alamethicin, like many other amphiphatic peptides, adsorbs to the membrane with its helical axis parallel to the mem- brane surface, leading to a local deformation ( He et al., 1996; Heller et al., 1997 ). As the peptide concentration is increased, the pep- tides accumulate on the membrane surface – possibly aggregating – and above a certain threshold concentration insert transver- sally into the membrane forming a pore ( Huang, 2006 ). Using the OS technique in combination with X-ray scattering, it was shown by Pabst et al. (2007a) ( Fig. 13 ) and later on by Pan et al. (2009) that the pore formation process “softens” DOPC bilay- ers by ∼50%. This result is consistent with the other studies that recorded a drop in membrane bending rigidity in the presence of amphiphatic peptides ( Vitkova et al., 2006; Tristram-Nagle and Nagle, 2007 ).
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Structural analyses by advanced X-ray scattering on GaP layers epitaxially grown on silicon for integrated photonic applications

Structural analyses by advanced X-ray scattering on GaP layers epitaxially grown on silicon for integrated photonic applications

au-dessus de 500°C qui confirme ce qui a été reporté dans la litérature 7,8 Un scénario de formation des micro-macles est proposé via la formation de lacunes ainsi qu’une énergie d’activation mise en jeu pour éviter ce phénomène. Cependant, la croissance à haute température génère une surface très rugueuse qui ne peut être utilisée ensuite pour la réalisation de dispositifs. Une procédure de croissance dite « MEE » (Migration Enhanced Epitaxy qui consiste à déposer de manière alternée Ga et P) a été développée et optimisée par caractérisation DRX et AFM. Les échantillons « MEE » présentent après optimisation et pour une même épaisseur déposée, un volume maclé beaucoup plus faible et une surface beaucoup plus lisse que les meilleurs échantillons réalisés par MBE classique à même température de croissance. Enfin, la structure de la couche GaP/Si a été optimisée par une séquence de croissance de deux étapes: une première croissance de 40 monocouches de GaP à 350 °C (basse température) par la MEE suivie d’une deuxième croissance de 40 nm de GaP à 500 °C (haute température) par la MBE. La figure 2 a) représente la figure de pôle de cet échantillon (S1330), où l’intensité de micro-macles est très faible. La faction volumique de micro-macles est évalué à inférieur à 1% (la limite de résolution de ces méthodes par diffraction des rayons X à base résolution). La rugosité surfacique de cet échantillon est mesurée à 0.3 nm (la limite de sensibilité de cette technique d’AFM est de l’ordre de 0.15 nm) par l’image d’AFM comme présenté dans la figure 2 b).
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Synchrotron x-ray scattering study of charge-density-wave order in HgBa2CuO4+δ

Synchrotron x-ray scattering study of charge-density-wave order in HgBa2CuO4+δ

its connection with charge transport in the cuprates. The structural simplicity of Hg1201 enabled us to establish a direct link between properties of the CDW order and the Fermi-surface-reconstructed state. The consideration of our results along with available quantum-oscillation data allowed us to simulate the size of the Fermi pocket in Hg1201 and its evolution with doping. Although the observed doping and temperature dependences of the charge correlations in Hg1201 are similar to YBCO, the CDW order is more robust in the latter compound. The characteristic charge-order temperature and correlation length universally increase with increasing carrier con- centration. In YBCO, the correlation length reaches a maximum of about 20 lattice units and CDW order is observed up to about optimal doping. In contrast, in Hg1201 the maximum is only about 8 lattice units and CDW order disappears well before optimal doping is reached, once the correlation length is comparable to the CDW modulation period. For Hg1201, the charac- teristic onset temperature of the CDW phenomenon as determined with X-rays coincides with the characteris- tic temperature identified in prior transient reflectivity work. Consideration of the disorder induced by the in- terstitial oxygen atoms led us to propose that the CDW correlation length in Hg1201 is limited by pairs of such dopants within the same unit cell. Finally, our analy- sis of CDW satellite peaks observed via X-ray diffraction indicates that the dominant atomic displacements asso-
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X-ray reflectivity, diffraction and grazing incidence small angle X-ray scattering as complementary methods in the microstructural study of sol–gel zirconia thin films

X-ray reflectivity, diffraction and grazing incidence small angle X-ray scattering as complementary methods in the microstructural study of sol–gel zirconia thin films

zirconia phase and the SAXS signal in the transmission mode is recovered and exhibits a well defined scattered intensity peak at a non zero scattering vector. During the dipping, the liquid film runs out on the substrate, adheres to its surface and the evaporation of solvents leads to its rapid solidification. The as prepared layer could be considered as a xerogel obtained by a concentration effect. As for the bulk xerogel, we do not observe GISAXS signal for this raw layer even by using the synchrotron radiation facilities of LURE. At the beginning of the annealing, the correlation length corresponding to the appearing zirconia nanocrystals, about 4 nm at 300 -C, is in good agreement with the zirconium rich primary particle size present in the sol. During the temperature increase, the layer microstructure evolves by normal grain growth of the zirconia nanocrystals in agreement with the theoretical approach developed by Thompson [27] . For a given low temperature thermal treatment and whatever the substrate, the thin film GISAXS as well as the bulk xerogel SAXS patterns display quite similar feature in spite of very different experimental data recording ( Fig. 7 ). At this stage, the layer evolves as bulk xerogel and the film-substrate interface does not seem to influence its microstructural evolution. These results are in good agreement with the observations carried out on similar systems [28] .
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Neutron and X-ray Scattering for Biophysics and Biotechnology: Examples of Self-Assembled Lipid Systems

Neutron and X-ray Scattering for Biophysics and Biotechnology: Examples of Self-Assembled Lipid Systems

spreading monolayers at the air–water interface is the ability to also control in situ the lateral packing pressure of the lipids. A simple example of reflectometry data is shown in Fig. 4. 74 It is commonly found that artificial hard surfaces present a location for protein aggregation in vivo or in test equipment exposed to biological fluids. It is hoped that custom designed surface coat- ings that are made from more biologically compatible materials will prevent this ‘‘biofouling’’. Such thin films may only be nanometres thick, and measuring their structural dimensions to see if the method of manufacture results in the desired surface with the preferred properties, is difficult. Ellipsometry data is often inconclusive without knowledge of the dielectric constant of the material. Furthermore, while attenuated total reflection infrared spectroscopy may be very sensitive to changes in surface structures, determination of a static surface structure requires interpretation of the FTIR (Fourier transform infrared spec- troscopy) absorption bands.
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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

To find the surface structure, we need to determine the structure factors from intensities measured along diffraction rods (Robinson & Tweet, 1992; Feidenhans’l, 1989). Normally, such integrated intensities depend on the detector acceptance. The range in l direction, l, measured by a detector is not a constant and varies with the component of the scattering vector perpendicular to the surface ( Q ? ) and the  angle in the angular space of a detector. This is taken into account with the cos  rod interception factor in equation (3). However, if the integration is done directly in reciprocal space, l can be chosen to be the same for each l value given that the reciprocal space map has enough data points. Assuming that l is small enough so that ðd=dÞðQÞ is constant within l we can write
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Anomalous Antiferromagnetism in Metallic RuO₂ Determined by Resonant X-ray Scattering

Anomalous Antiferromagnetism in Metallic RuO₂ Determined by Resonant X-ray Scattering

DOI: 10.1103/PhysRevLett.122.017202 In electronic systems with localized d electrons and an insulating ground state, ordered magnetism arises from strong exchange interactions that are often described within the framework of the Heisenberg model. However, in metals with partly itinerant d electrons, it is often more appropriate to interpret magnetic phenomena on the basis of correlation effects between bandlike states. A basic understanding of magnetism in ferromagnetic metals has been obtained at a level of mean field approximation and beyond, in the framework of the Hubbard model [1] . However, a general description of spin order in antiferro- magnetic metals remains challenging. The best known example is probably that of Cr metal, whose incommen- surate spin density wave (SDW) is characterized by a wave vector determined by the nesting properties of its Fermi surface [2] . Some perovskite chromates, such as CaCrO 3 and SrCrO 3 , have been recently established as antiferro- magnetic metals (AFMs) as well, but the roots of the AFM order have remained elusive [3 –9] .
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TiC-carbide derived carbon electrolyte adsorption study by ways of X-ray scattering analysis

TiC-carbide derived carbon electrolyte adsorption study by ways of X-ray scattering analysis

Barbara Daffos 1,2 • Pierre-Louis Taberna 1,2 • Patrice Simon 1,2 Abstract Understanding ion adsorption in nanoporous carbon electrodes is of great importance for designing the next-generation of high energy density electrical double- layer capacitors. In this work, X-ray scattering is used for investigating the impregnation of nanoporous carbons with electrolytes in the absence of applied potential. We are able to show that interactions between the carbon surface and electrolytes allow adsorption to take place in sub-nano- pores, thus confirming experimentally for the first time the results predicted by molecular dynamic simulations.
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Mapping the unoccupied state dispersions in ${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$ with resonant inelastic x-ray scattering

Mapping the unoccupied state dispersions in ${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$ with resonant inelastic x-ray scattering

x-ray emission spectrometer (SAXES) [ 24 ]. A scattering an- gle of 130 ◦ was used, and all the spectra presented here were measured with linearly σ -polarized incident light [perpendic- ular to the scattering plane; see Fig. 1(a) ]. The combined energy resolution was 150 meV at the Ni L 3 edge (∼850 eV). Ta 2 NiSe 5 single crystals were cleaved in situ [with a surface in the (001) direction] at a pressure of about 1 × 10 −8 mbar. Ta 2 NiSe 5 single-crystalline samples were prepared by reacting the elemental nickel, tantalum, and selenium with a small amount of iodine in a evacuated quartz tube. The tube was slowly heated and kept with a temperature gradient from 950 ◦ C to 850 ◦ C for 7 days, followed by slow cooling. Single- crystalline samples with a typical size of 0 .04 × 1 × 10 mm 3 were obtained in the cooler end. Density functional theory and the projector augmented wave method implemented in VASP [ 25 – 30 ] were used for band structure calculations in the monoclinic phase with experimentally determined structural parameters [ 31 ]. The kinetic energy cutoff of the plane-wave basis was 500 eV, and the Brillouin zone integration was performed using a 11 × 11 × 5 k-point grid. The exchange- correlation effects were included within the strongly con- strained and appropriately normed [ 32 ] metageneralized gra- dient approximation.
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Characterizing plasma conditions in radiatively heated solid-density samples with x-ray Thomson scattering

Characterizing plasma conditions in radiatively heated solid-density samples with x-ray Thomson scattering

Twenty-four to 26 laser beams heat the x-ray converter foil wrapped around the sample, each providing 500 J at 351 nm in a 1-ns square pulse, as seen in the upper left-hand corner of Fig. 1 (indicated as “heater” beams). The beams were set to best focus without phase plates and were arranged evenly over the surface of the cylinder. Chromium is used as the converter foil material for the boron samples and converts the laser energy to chromium K-shell line emission, which ranges between 5.4 and 5.9 keV in energy. Silver is used to heat the beryllium sample and heats the samples through silver L-shell emission, ranging from 3.6–4.2 keV. Six to 10 laser beams heat the Zn foils, beginning at 1.2 ns, around the time the inner-cylinder is expected to reach its maximum temperature (indicated as “probe” beams in the upper left of Fig. 1 ). The 9 keV Zn He-α x-rays that scatter from the sample are collected by the spectrometer, ZSPEC. ZSPEC is a Bragg crystal spectrometer that consists of a 50 × 25 mm highly ori- ented pyrolytic graphite (HOPG) crystal placed equidistantly from a four-strip microchannel plate (MCP). Each strip is time gated and integrates over 180 ps. The axis of the sample cylinder is aligned with the ZSPEC’s line-of-sight. The 400-
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Improving sensitivity of a small angle x-ray scattering camera with pinhole collimation using separated optical elements

Improving sensitivity of a small angle x-ray scattering camera with pinhole collimation using separated optical elements

The monochromator is first optically adjusted using the procedure described by Spencer. 12 A specially designed mir- ror bender 共ACTAL, Canberra兲 imposes asymmetric couples on both ends of the thin rectangular Ge plate. Optimal thick- ness was found to be 0.25 mm: finer plates are too difficult to machine and thicker plates break when bent. To improve sensitivity of the camera, lateral ‘‘tails’’ observed near the edge of the beam stop have to be reduced. This strong para- sitic scattering is observed when monochromators are used with the surface state after cut and flattening. The origin of this strong ‘‘tail’’ close to the beam stop is the residual sur- face roughness and defects introduced during cutting. At least 1 order of magnitude of reduction can be obtained by chemical etching, which has the advantage of removing the perturbed layer without introducing strain. Optimization of the etching procedure has to be performed. It has been found 13,14 that a few minutes of etching in warm acid mix- ture removes 40 ␮ m of surface and reduces the observed limiting factor in the horizontal plane by a factor of 10. The
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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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The X-ray universe

The X-ray universe

Cosmic X-rays are interesting because they need a lot of energy to produce them. They require temperatures of millions of degrees, or particles accelerated to very high speeds. The outer atmosphere of the Sun – its corona - has million- degree temperatures and produces X-rays. However they are not strong by cosmic standards and we can only observe and map them because the Sun lies very close to us. To be visible at a distance of millions of light years requires energy of a different order entirely. Some of those dots could be distant galaxies containing lots of

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X-ray Surveyor Discussion Session Results from the X-ray Vision Workshop

X-ray Surveyor Discussion Session Results from the X-ray Vision Workshop

3.3 What precursor observations and/or theoretical calculations can be made, at any wavelength, that would either help define the parameters of the X-ray Surveyor or provide inputs for its observing programs? All of the questions could benefit from precursor observations to better define the samples for X-ray Surveyor studies, as shown in Table A2. The observations mentioned in the discussion cover the entire wavelength range, from radio to X-rays, and involve a suite of existing and planned observatories across the full electromagnetic spectrum. SKA, ALMA, JWST, Chandra, ASTRO-H, eROSITA were all cited.
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Comparison of resonant inelastic x-ray scattering spectra and dielectric loss functions in copper oxides

Comparison of resonant inelastic x-ray scattering spectra and dielectric loss functions in copper oxides

T. Gog and D. Casa XOR, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA 共Received 27 December 2008; revised manuscript received 4 February 2009; published 30 March 2009 兲 We report empirical comparisons of Cu K-edge indirect resonant inelastic x-ray scattering 共RIXS兲 spectra, taken at the Brillouin-zone center, with optical dielectric loss functions measured in a number of copper oxides. The RIXS data are obtained for Bi 2 CuO 4 , CuGeO 3 , Sr 2 Cu 3 O 4 Cl 2 , La 2 CuO 4 , and Sr 2 CuO 2 Cl 2 , and analyzed by considering both incident and scattered-photon resonances. An incident-energy-independent response function is then extracted. The dielectric loss functions, measured with spectroscopic ellipsometry, agree well with this RIXS response, especially in Bi 2 CuO 4 and CuGeO 3 .
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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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