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X-ray reflectivity data of polymer bilayer systems have been analyzed using a Fourier method which takes into account different limits of integration in q-space. It is demonstrated that the interfacial parameters can be determined with high accuracy although the difference in the electron density (the contrast) of the two polymers is extremely small. This method is not restricted to soft-matter thin films. It can be applied to any reflectivity data from low-contrast layer systems.

The sputter deposition of thin magnetic NiMnSb films on MgO(001) and Si(001) is investigated by in situ x-ray scattering. It is shown that the roughness of the layers as a function of the film thickness increases according to power laws with unusually large growth exponents. The optimum growth conditions are found on the substrate MgO(001) at temperatures of 250 °C during the deposition.

We report on the formation of tetrahydrofuran clathrate hydrate studied by x-ray Raman scattering measurements at the oxygen K edge. A comparison of x-ray Raman spectra measured from water-tetrahydrofuran mixtures and tetrahydrofuran hydrate at different temperatures supports stochastic hydrate formation models rather than models assuming hydrate precursors. This is confirmed by molecular dynamics simulations and density functional theory calculations of x-ray Raman spectra. In addition, changes in the spectra of tetrahydrofuran hydrate with temperatures close to the hydrate's dissociation temperature were observed and may be connected to changes in hydrate's local structure due to the formation of hydrogen bonds between guest and water molecules. We report on the formation of tetrahydrofuran clathrate hydrate studied by x-ray Raman scattering measurements at the oxygen K edge. A comparison of x-ray Raman spectra measured from water-tetrahydrofuran mixtures and tetrahydrofuran hydrate at different temperatures supports stochastic hydrate formation models rather than models assuming hydrate precursors. This is confirmed by molecular dynamics simulations and density functional theory calculations of x-ray Raman spectra. In addition, changes in the spectra of tetrahydrofuran hydrate with temperatures close to the hydrate's dissociation temperature were observed and may be connected to changes in hydrate's local structure due to the formation of hydrogen bonds between guest and water molecules. We report on the formation of tetrahydrofuran clathrate hydrate studied by x-ray Raman scattering measurements at the oxygen K edge. A comparison of x-ray Raman spectra measured from water-tetrahydrofuran mixtures and tetrahydrofuran hydrate at different temperatures supports stochastic hydrate formation models rather than models assuming hydrate precursors. This is confirmed by molecular dynamics simulations and density functional theory calculations of x-ray Raman spectra. In addition, changes in the spectra of tetrahydrofuran hydrate with temperatures close to the hydrate's dissociation temperature were observed and may be connected to changes in hydrate's local structure due to the formation of hydrogen bonds between guest and water molecules.

The islet amyloid polypeptide (IAPP) or amylin is a pancreatic hormone and crucially involved in the pathogenesis of type-II diabetes mellitus (T2DM). Aggregation and amyloid formation of IAPP is considered as the primary culprit for pancreatic beta-cell loss in T2DM patients. In this study, first X-ray reflectivity (XRR) measurements on IAPP at lipid interfaces have been carried out, providing a molecular level characterization of the first steps of the lipid-induced fibrillation process of IAPP, which is initiated by lipid-induced nucleation, oligomerization, followed by detachment of larger IAPP aggregate structures from the lipid membrane, and terminated by the formation of mature fibrils in the bulk solution. The adsorption process of IAPP at lipid interfaces in the absence and presence of negatively charged lipid has also been studied by complementary ATR-FTIR spectroscopic measurements. The morphological properties were followed by atomic force microscopy (AFM). Moreover, we show that the polyphenolic red wine compound resveratrol is able to inhibit IAPP aggregation also in the presence of aggregation-fostering negatively charged lipid interfaces, revealing its potential as a drug candidate for T2DM.

We present a new sample cell for measuring nonresonant inelastic x-ray scattering spectra of a tetrahydrofuran (THF)-water liquid mixture and THF hydrate. The hydrate is formed inside the cell after nucleation seeds have been offered by a special magnetic stirring mechanism. Hydrate formation was verified by wide angle x-ray scattering and nonresonant x-ray Raman scattering spectra at the oxygen K-edge. A broad range of scattering angles can be studied with this cell which is necessary for momentum transfer dependent inelastic x-ray scattering. This cell is ideal to examine other liquid hydrate formers or other liquid samples, which have to be mixed in situ during the measurements.

10th International Conference on Surface X-Ray and Neutron Scattering, SXNS10, Paris, France, 2 Jul 2008 - 5 Jul 2008; European physical journal special topics 167(1), 133-136 (2009). doi:10.1140/epjst/e2009-00948-1, The adsorption of $\gamma\hbox{-}{\rm Fe}_2{\rm O}_3$ (maghemite) nanoparticles at the aqueous solution/gas interface was investigated by x-ray reflectivity. Two different concentrations (0.07 g/L and 0.7 g/L) were probed. The x-ray reflectivities indicate the adsorption of nanoparticles at the liquid surface for the highly concentrated solution, while no nanoparticle adsorption could be detected at the surface of the low concentrated solution within several hours. The vertical electron density profile of the high concentration solution/gas interface indicates the formation of a low ordered monolayer of nanoparticles occupying only 6% of the interfacial region., Published by Springer, Berlin

The x-ray scattering cross section from capillary waves at large values of the momentum transfer parallel to the surface is discussed. In contrast to the conventional approach where only the height-height correlation of the surface is taken into account the full-wave-motion-induced static correlations are embedded in the calculation. This leads to an increase in scattering intensity especially at large wave vector parallel to the sample's surface which has been interpreted as evidence for a wave-vector-dependent surface tension previously. We are discussing under which conditions surface-sensitive x-ray scattering experiments can be used to derive the surface Hamiltonian of capillary waves.

Herein, we explore the effect of different types of osmolytes on the high-pressure stability and tertiary structure of a well-characterized monomeric protein, staphylococcal nuclease (SNase). Changes in the denaturation pressure and the radius of gyration are obtained in the presence of different concentrations of trimethylamine N-oxide (TMAO), glycerol and urea. To reveal structural changes in the protein upon compression at various osmolyte conditions, small-angle X-ray scattering (SAXS) experiments were carried out. To this end, a new high-pressure cell suitable for high-precision SAXS studies at synchrotron sources was built, which allows one to carry out scattering experiments up to maximum pressures of about 7 kbar. Our data clearly indicate that the osmolytes that stabilize proteins against temperature-induced unfolding drastically increase their pressure stability and that the elliptically shaped curve of the pressure-temperature-stability diagram of proteins is shifted to higher temperatures and pressures with increasing osmolyte concentration. A drastic stabilization is observed for the osmolyte TMAO, which exhibits not only a significant stabilization against temperature-induced unfolding, but also a particularly strong stabilization of the protein against pressure. In fact, such findings are in accordance with in vivo studies (for example P. J. Yancey, J. Exp. Biol. 2005, 208, 2819-2830), where unusually high TMAO concentrations in some deep-sea animals were found. Conversely, chaotropic agents such as urea have a strong destabilizing effect on both the temperature and pressure stability of the protein. Our data also indicate that sufficiently high TMAO concentrations might be able to largely offset the destabilizing effect of urea. The different scenarios observed are discussed in the context of recent experimental and theoretical studies.

We present a rigorous description of the effects of partial coherence and detector resolution on intensity autocorrelation functions as they can be measured by x-ray photon correlation spectroscopy (XPCS). Based on the Huygens-Fresnel propagation law and on the first Born approximation, we derive a general expression for the normalized intensity autocorrelation function. We calculate how the mutual coherence function of the x-ray beam propagates from an aperture to the sample and how it propagates after the scattering process to the detector area and consequently influences the intensity autocorrelation function. We illustrate our calculation with examples of XPCS intensity autocorrelation functions of liquid surfaces calculated for grazing incidence geometry.

In situ x-ray reflectivity measurements are used to determine the cooling rate dependent freezing of capillary waves on the oligomer poly(propylene glycol). Only above the glass transition temperature ${T}_{\mathrm{G}}$ can the surface roughness $\ensuremath{\sigma}$ be described by the capillary wave model for simple liquids, whereas the surface fluctuations are frozen-in at temperatures below ${T}_{\mathrm{G}}$. As the state of a glass forming liquid strongly depends on its thermal history, this effect occurs for fast cooling rates already at a higher temperature than for slow cooling. For the fastest cooling rates a very large shift of ${T}_{\mathrm{G}}$ up to $240\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ compared to the bulk value of $196\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ was observed.

High-resolution Compton profiles of the clathrates ${\mathrm{Na}}_{8}{\mathrm{Si}}_{46}$, ${\mathrm{K}}_{7.6}{\mathrm{Si}}_{46}$, and ${\mathrm{Si}}_{136}$ were measured to study the charge transfer of the alkali-metal guest atoms to the clathrates silicon host lattice. The experiment was accomplished utilizing the Compton spectrometer at beamline ID15B of the European Synchrotron Radiation Facility with an incident energy of $56.7\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ and a momentum space resolution of $0.16\phantom{\rule{0.3em}{0ex}}\mathrm{a.u.}$ The valence electron contribution to the total Compton profile of the sodium and potassium guest atoms was extracted and is compared with calculations employing density-functional theory using Becke exchange and Perdew-Wang correlation. Good overall agreement between experiment and theory is found and proves the quality of the underlying wave functions used for the theoretical predictions. On this basis, the charge transfer in these systems is estimated by a Mulliken population analysis and discussed for the different guest atoms.

Using a novel layer-by-layer approach we have deposited metal−organic open frameworks (MOFs) based on benzenetricarboxylic acid ligands and Cu(II)-ions on a COOH-terminated organic surface. The deposited layers were characterized using a number of surface analysis techniques. XRD measurements show that the MOFs deposited using this method have the same bulk structure of HKUST-1.

An X-ray reflectivity set-up to study buried interfaces at beamline BL9 of the electron storage ring DELTA is presented. The structure of solid–gas and solid–liquid interfaces can be investigated using X-rays with incident energies of about 27 keV. A detailed description of the set-up is given and its performance is demonstrated by a discussion of selected applications, i.e. protein adsorption at the solid–liquid interface and gas adsorption at the solid–gas interface at elevated pressures.

Experimentally derived static structure factors obtained for the aggregation-prone protein insulin were analyzed with a statistical mechanical model based on the Derjaguin-Landau-Verwey-Overbeek potential. The data reveal that the protein self-assembles into equilibrium clusters already at low concentrations. Furthermore, striking differences regarding interaction forces between aggregation-prone proteins such as insulin in the preaggregated regime and natively stable globular proteins are found.

The giant dipole resonance of Ba embedded into the complex Si host lattice structure of ${\mathrm{Ba}}_{8}{\mathrm{Si}}_{46}$ has been observed under ambient and high-pressure conditions. The measurements have been accomplished using nonresonant inelastic x-ray scattering for different momentum transfers. The resonance appears as a broad feature between 100- and $150\text{\ensuremath{-}}\mathrm{eV}$ energy loss for low momentum transfer but vanishes for high momentum transfer. Calculations within the time-dependent local-density approximation have been performed by means of a real-space multiple-scattering Green's-function approach. The results reproduce the shape and the width of the observed resonance. Modulations of the giant resonance spectra are predicted by computations ranging from ambient pressure up to $20\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ which can be used to study the local environment of the Ba guest. A corresponding experimental setup for high-pressure studies is presented, potential applications to study the phase transitions of Ba clathrates are discussed, and first experimental results are shown.

Calculations of the nonresonant inelastic x-ray spectra for $L$ edges of Si, Mg, and Na have been performed using a Bethe-Salpeter equation approach and an implementation of a real-space multiple-scattering Green's function approach. The computational results are compared with each other and with the measured spectra. It is shown to what extent both methods reproduce the general shape of the edges, their fine structure, and the dependence on the momentum transfer and thus on the weight of dipole and multipole transitions. Characteristics of the calculations concerning screening and the calculation of the density of states are also discussed in detail. The comparison between the multiple-scattering approach, the more sophisticated calculations using the Bethe-Salpeter approach, and experiment on these simple systems is essential for applications of real-space multiple-scattering calculations on more complex systems, which are not accessible by other computational methods.

Physical review letters 98, 47801 (2007). doi:10.1103/PhysRevLett.98.047801, Published by APS, College Park, Md.

Physical review letters 99, 96104 (2007). doi:10.1103/PhysRevLett.99.096104, Published by APS, College Park, Md.

Since 1999, the Dortmund 1.5 GeV electron storage ring DELTA was continuously extended. The facility serves universities and industries as a source of synchrotron radiation on a regional level. By now, DELTA, operated for 3000 hours per year, has reached a reliability comparable to other facilities in the world. Improvements have been achieved in the installation of the beamlines. At present, two undulator beamlines and several dipole beamlines are in operation. The 5.3 T superconducting asymmetric multipole wiggler (SAW) serves three beamlines in the hard X-ray regime with circular polarized radiation. Also the accelerator physics research program has been promoted. The vacuum system was revised during the last year to provide extra space for test sections and additional diagnostics. Substantial progress was achieved by SVD based orbit correction as well as detailed coupled bunch mode (CBM) studies. Future developments for machine improvements, such as a DSP-based fast local orbit feedback and a frequent injection mode are in preparation.

High-resolution Compton scattering spectra of methane, methane hydrate, and ice were measured using incident photon energy of $56.4\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ at beamline ID15B of the European Synchrotron Radiation Facility. The experimental Compton profiles are compared to calculations employing density-functional theory using model atomic clusters. The hydrate has a cagelike structure built up from water molecules and the related Compton profile is observed to change apparently when compared to hexagonal ice. Furthermore, the influence of the guest-host interactions between the methane molecules and the water molecules of the cages on the Compton profile is discussed.

The influence of high hydrostatic pressure on the structure and protein-protein interaction potential of highly concentrated lysozyme solutions up to about 370 mg ml(-1) was studied and analyzed using small-angle X-ray scattering in combination with a liquid-state theoretical approach. In the concentration region below 200 mg ml(-1), the interaction parameters of lysozyme solutions are affected by pressure in a nonlinear way, which is probably due to significant changes in the structural properties of bulk water, i.e., due to a solvent-mediated effect. Conversely, for higher concentrated protein solutions, where hydration layers below ∼4 water molecules are reached, the interaction potential turns rather insensitive to compression. The onset of transient (dynamic) clustering is envisaged in this concentration range. Our results also show that pressure suppresses protein nucleation, aggregation and finally crystallization in supersaturated condensed protein solutions. These findings are of importance for controlling and fine-tuning protein crystallization. Moreover, these results are also important for understanding the high stability of highly concentrated protein solutions (as they occur intracellularly) in organisms thriving under hydrostatic pressure conditions such as in the deep sea, where pressures up to the kbar-level are reached.

We studied the adsorption behavior of the gas octafluoropropane at the water/gas interface as a function of different pressures. In a custom-made measurement cell, the gas pressure was varied in a range between 1 bar and close to the condensation pressure of octafluoropropane. The electron density profiles of the adsorption layers show that the layer thickness increases with pressure. The evolution of the layer electron density indicates that the bulk electron density is reached if a layer consisting of more than one monolayer of octafluoropropane is adsorbed on the water surface.

The scattering image produced by coherent X-rays appears grainy and is denoted a speckle pattern. An analysis of the static and time-dependent properties of a speckle pattern generated by scattering of a partially coherent synchrotron beam from a liquid surface is given here. Unique surface sensitivity is achieved by applying the X-rays under a grazing angle of incidence. The observed contrast of the speckle pattern depends on the momentum transfer parallel to the surface, unlike the case of transmission small-angle X-ray scattering (SAXS), where essentially no q-dependence of the contrast has been observed. The appearance of the speckles and the contrast of the image can be understood qualitatively by use of geometrical arguments and by the fact that liquid surfaces are extremely flat.

We present an x-ray reflectivity study of molecularly thin films of liquid isobutane adsorbed on liquid glycerol. The glycerol-isobutane interface serves as a model system to investigate the influence of the substrate adsorbate interactions on both adsorption isotherms and capillary wave fluctuations. The measured surface roughness is smaller than expected from the harmonic approximation of the interaction potential. Expressions for the surface roughness in slightly anharmonic potentials are given and compared to the experimental data. A good agreement between data and theory is achieved.

We have performed x-ray specular and diffuse scattering on liquid polymer films and analyzed the spectra as a function of film thickness and molecular weight. The results show that films whose molecular weight is close to the entanglement length behave as simple liquids except that the shortest wavelength is determined by the radius of gyration (${R}_{g}$) rather than the monomer-monomer distance. When the molecular weight is higher than the entanglement length, the strong deviations from liquidlike behavior are observed. We find that the long wavelength cutoff vector, ${q}_{l,c}$, scales with film thickness, $d$ as ${d}^{\ensuremath{-}1.1\ifmmode\pm\else\textpm\fi{}0.1}$ rather than the usual ${d}^{\ensuremath{-}2}$ expected for simple liquids. If we assume that these deviations are due to surface pinning of the polymer chains, then our results are consistent with the formalism developed by Fredrickson et al. to explain the capillary wave spectrum that can propagate in a polymer brush.

X‐ray diffraction measurements in the region of small incidence and exit angles on thin amorphous silicon/germanium films on laterally structured surfaces are performed. From fits of the data we obtain directly how the Fourier components of the substrates propagate through the evaporated films without being influenced by the intrinsic statistical roughness of the interfaces. The results show that a replication factor extracted from a given model can be quantitatively tested with our measurements.

We present X-ray reflectivity investigations of the concentration distribution in binary liquid thin films on silicon substrates. The liquid-vapor coexistence of the binary mixture investigated, hexane and perfluorohexane, is far from criticality. Therefore, a sharp interface separates the liquid film from the vapor. The data reveal a separation of the film in layers parallel to the substrate. A phase diagram is constructed as a projection to the (composition difference, temperature) space, covering a temperature range corresponding to the one-phase and the two-phase regime of the bulk liquid. Although the composition data indicate a mixing gap similar to that of the bulk system, there are two major differences: i) only the near-surface phase changes its composition significantly, and ii) a composition gradient in the film exists also at higher temperatures where in the bulk system the one-phase regime exists.

We report on in situ x-ray reflectivity measurements of the surface roughness of supercooled glass forming polymers in a temperature range from 190 to 330 K. The experimentally determined rms roughness has been found to obey the capillary wave model of a single liquid/vapor interface over the entire temperature range. An expression for the surface roughness below the bulk glass transition (T(G) approximately equal to 200 K) is deduced from the viscoelastic theory of surface fluctuations; however, no indication of a frozen-in surface roughness has been observed in the experiment. Additionally, it is shown that precise values of the surface tension of highly viscous liquids in the supercooled state can be determined by x-ray reflectivity.

International audience; Nitride quantum dots (QD’s) grown in the wurtzite phase present a strong vertical ordering along the (0001) direction when they are stacked in multilayers. This alignment results from a minimum of the elastic energy density at the surface of the AlN capping layer induced by the buried GaN dot underneath. The aim of this work is to investigate the strain distribution in a quantum dot multilayer using high-resolution transmission electron microscopy and anomalous grazing incidence x-ray diffraction. This x-ray method is based on the strong sensitivity of the elastic scattering cross section to the Ga compounds for energies in the vicinity of the Ga absorption edge. It is observed that uncapped GaN dots are almost completely relaxed, while embedded quantum dots are compressively strained. In addition, a modulation of the in-plane lattice parameter in the AlN spacer layer is clearly identified, induced by the QD’s on the surrounding matrix which causes the vertical alignment.

We measure the dispersion relation of capillary waves on a liquid surface by heterodyne x-ray photon correlation spectroscopy near the transition from propagating to overdamped dynamic behavior. A strong deviation of the propagation frequency from the small-damping result ${\ensuremath{\omega}}_{p}\ensuremath{\propto}{k}^{3/2}$ is observed long before the actual transition where $(\ensuremath{\partial}{\ensuremath{\omega}}_{p}/\ensuremath{\partial}k)l0$ and ${\ensuremath{\omega}}_{p}$ tends to zero. This behavior is successfully described by expressions derived within linear response theory.

A dedicated setup comprising an efficient cryogenic device for the in situ preparation of large surface areas of prototypical organic glass formers in a wide temperature range (170–340 K) is presented. This setup provides the necessary temperature and vibrational stability for surface x-ray and neutron scattering experiments, including the extremely sensitive technique of x-ray photon correlation spectroscopy (XPCS). XPCS is an emerging method which is made possible by the high coherent photon flux produced by third-generation synchrotrons. We demonstrate that microscopic motion at the surface can be studied in a direct way in the liquid and supercooled state using XPCS. In addition, we have used a charge-coupled-device detector to record two-dimensional images of static speckle patterns forming on surfaces in the glassy state.

We report measurements of propagating capillary waves on a liquid water surface at $T=5\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ with x-ray photon correlation spectroscopy. The experiment has been performed under grazing incidence conditions with an incoming x-ray beam below the critical angle of total external reflection. In the $\mathbf{q}$ region investigated the measured intensity-intensity autocorrelation functions of the liquid water surface were found to be heterodyne signals, i.e., a combination of first- and second-order correlation functions ${g}_{1}(\ensuremath{\tau})$ and ${g}_{2}(\ensuremath{\tau})$.

Inelastic x-ray scattering spectra have been measured for energy losses around the Be K-edge in order to perform a systematic study of the dependence of the corresponding dynamic structure factor on both the absolute value and the direction of the momentum transfer. The measured x-ray Raman spectra show clear differences between spectra of different momentum transfer which are related to deviations from the dipole approximation of the x-ray Raman scattering cross section with increasing momentum transfer. In particular, the directional differences between x-ray Raman spectra for momentum transfer parallel and perpendicular to the c axis of single-crystal Be vanish completely at high momentum transfer. These results are attributed to monopole transitions of the excited electrons to s-type final states according to the results of a first-principles calculation which takes the particle-hole interaction into account. This theoretical approach is a valuable tool for modeling x-ray Raman spectra.

International audience; The layer-to-layer vertical alignment of GaN quantum dots in AlN multilayers is quantified as a function of the spacer layer thickness and the number of bilayers, using grazing-incidence X-ray scattering. Although the density of dots is comparable to the density of (0001) threading dislocations, we observe that the strong vertical ordering is strain induced by the buried dots. Elasticity theory calculations confirm this experimental result and explain the observation of the exceptionally strong vertical alignment in nitride compared to other classical systems.

Physical review / B 65(18), 184207 (2002). doi:10.1103/PhysRevB.65.184207, Published by Inst., Woodbury, NY

The shape of the Ba 4d?4f giant dipole resonance is studied for Ba atoms embedded inside complex Si networks covering structures consisting of Si nanocages and nanotubes, i.e. the clathrate Ba8Si46, the complex compound BaSi6, and the semiconducting BaSi2. Here, non-resonant x-ray Raman scattering is used to investigate confinement effects on the shape of the giant resonance in the vicinity of the Ba NIV, V-edge. The distinct momentum transfer dependence of the spectra is analyzed and discussed. The measurements are compared to calculations of the giant resonance within time-dependent local density approximation in the dipole limit. No modulation of the giant resonance?s shape for Ba atoms confined in different local environments was observed, in contrast to the calculations. The absence of such shape modulation for complex Ba/Si compounds is discussed providing important implications for further studies of giant resonance phenomena utilizing both theory and experiment.

We present a study on ion specific effects on the intermolecular interaction potential V(r) of dense protein solutions under high hydrostatic pressure conditions. Small-angle X-ray scattering in combination with a liquid-state theoretical approach was used to determine the effect of structure breaking/making salt anions (Cl(-), SO4(2-), PO4(3-)) on the intermolecular interaction of lysozyme molecules. It was found that besides the Debye-Hückel charge screening effect, reducing the repulsiveness of the interaction potential V(r) at low salt concentrations, a specific ion effect is observed at high salt concentrations for the multivalent kosmotropic anions, which modulates also the pressure dependence of the protein-protein interaction potential. Whereas sulfate and phosphate strongly influence the pressure dependence of V(r), chloride anions do not. The strong structure-making effect of the multivalent anions, dominating for the triply charged PO4(3-), renders the solution structure less bulk-water-like at high salt concentrations, which leads to an altered behavior of the pressure dependence of V(r). Hence, the particular structural properties of the salt solutions are able to influence the spatial organization and the intermolecular interactions of the proteins, in particular upon compression. These results are of interest for exploring the combined effects of ionic strength, temperature and pressure on the phase behavior of protein solutions, but may also be of relevance for understanding pressure effects on the hydration behavior of biological matter under extreme environmental conditions.

The surfaces of polystyrene (PS) films decorated with gold nanoclusters were investigated by x-ray reflectivity measurements. The thicknesses of the films are much larger than the radii of gyration of the different PS samples. By annealing the films above the glass transition temperature ${T}_{g}$ an embedding process of the clusters into the polymer is detected which is accompanied by a substantial increase in the cluster layer thickness due to Brownian motion. These processes start at a sufficiently low viscosity and may be regarded as a probe of the glass transition in the near surface region of the PS films. Simultaneously the thermal expansion of the entire film and hence its approximate bulk behavior were monitored. Two samples of different molecular weight do not show a significant difference between the surface and bulk ${T}_{g}$ values.

International audience

Physical review / B 62(15), 10377 - 10382 (2000). doi:10.1103/PhysRevB.62.10377, Published by Inst., Woodbury, NY

Physical review letters 83(17), 3470 - 3473 (1999). doi:10.1103/PhysRevLett.83.3470, The surfaces of liquid thin perfluorohexane, cyclohexane, decane, and ethanol films adsorbed on silicon wafers have been investigated by means of x-ray reflectivity, diffuse scattering, and grazing incidence diffraction. The measurements prove that the surface structure of the wetting films can be described by a universal height-height correlation function derived from a capillary wave model with the surface tension and particular cutoffs as parameters. The data favor a reduced capillary wave surface tension as predicted by exact theories, over an enhanced capillary wave surface tension, as suggested by simple mode-coupling models., Published by APS, College Park, Md.

Physical review letters 83(3), 564 - 567 (1999). doi:10.1103/PhysRevLett.83.564, The surfaces of thermally annealed thin polystyrene films on silicon were investigated by specular and diffuse x-ray scattering. The data cannot be interpreted satisfactorily with capillary wave calculations assuming attractive van der Waals substrate film interactions. The analysis shows that polystyrene films coated on silicon substrates are in a strongly confined state even for film thicknesses much larger than the radius of gyration, possibly due to strong confinement that arises from the interaction at the polymer/substrate interface and the viscoelastic behavior of the thin films., Published by APS, College Park, Md.