We explore the different local symmetries in colloidal glasses beyond the standard pair correlation analysis. Using our newly developed X-ray cross correlation analysis (XCCA) concept together with brilliant coherent X-ray sources, we have been able to access and classify the otherwise hidden local order within disorder. The emerging local symmetries are coupled to distinct momentum transfer (Q) values, which do not coincide with the maxima of the amorphous structure factor. Four-, 6-, 10-and, most prevalently, 5-fold symmetries are observed. The observation of dynamical evolution of these symmetries forms a connection to dynamical heterogeneities in glasses, which is far beyond conventional diffraction analysis. The XCCA concept opens up a fascinating view into the world of disorder and will definitely allow, with the advent of free electron X-ray lasers, an accurate and systematic experimental characterization of the structure of the liquid and glass states.coherent X-ray diffraction ͉ higher-order correlations ͉ structure D isordered matter, such as glasses and liquids, does not exhibit translational symmetry and in turn is able to accommodate different local symmetries in the same system, among them the icosahedral local order, which belongs to the forbidden motifs in periodic structures. This mysterious and so far experimentally inaccessible localized order within disorder has been fascinating scientists for many decades (1-5), because it is held responsible for the undercooling of liquids and the existence of the glass state. Similarly, nonperiodic materials have always attracted the attention of materials scientists, because they do carry-through these structural degrees of freedom-a unique potential to display novel smart functions (6-8).The microscopic understanding of the structure and properties of crystals has advanced rapidly during the last decades. The translational invariance of the crystalline state allowed the introduction of the Brillouin Zone concept, thus enabling an elegant and powerful theoretical description of the thermal, electronic and magnetic properties. At the same time, crystal diffraction has continuously been developed to such a fine art that even complex biological structures can be solved today with atomic resolution (when forced to form a crystal). In severe contrast to this, the local microscopic structure of disordered matter has remained a challenge and a mystery (1-3). Our lack of knowledge on the local order within disorder constrains the development of a better understanding of the properties of liquids and glasses (9). In turn, the open question of how the structure of the liquid and amorphous states can be accessed experimentally has become one of the holy grails in condensed matter science (10).The fundamental limits of conventional (X-ray, neutron, electron) diffraction from disordered materials are accountable for this situation, because such techniques only allow to extract the pair distribution function g(r) ϭ n 0 Ϫ2 ͗(0)(r)͘ of the single particle density (r) ϭ ͚...

The nanoscale structuring during evaporation of a droplet consisting of an aqueous colloidal solution of 2 nm gold nanoparticles in water on a silicon substrate is followed in real time. The authors investigated the transfer of lateral order and vertical layering as a function of time at the three-phase contact line air-solution substrate combining a nanometer-sized x-ray beam with a grazing incidence geometry. A pronounced retardation of vertical ordering is observed with respect to lateral ordering. While individual layers are deposited during evaporation of the solvent, the growth parallel to the substrate shows a strongly nondiffusive behavior. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2776850͔Large-scale arrays of ordered nanoparticles are fascinating materials for science and technology, e.g., data storage 1 or DNA sensoring, 2 due to their distinct optical properties. [2][3][4] To deposit the nanoparticle layer on top of the substrate, several methods are available, e.g., vacuum deposition 1,5 and solution casting. Solution casting allows nanostructuring of large-area two-dimensional ͑2D͒ thin films with specific morphology, offering the possibility to design 2D or threedimensional photonic crystals. This method is especially important and applicable in the field of colloidal particles, as colloidal particles are often suspended in aqueous solutions.Nanostructuring, however, is a very complex process involving several mechanisms. 6 The solvent evaporates and increases the concentration of the colloidal particles. The increased evaporation near the contact line drives a convective flow within the drop that transports material toward the periphery. 7 Additionally, an increased solute concentration and a decreased temperature near the three-phase contact line ͑TPCL͒ may trigger solutal 8 and thermocapillary 9 Marangoni flows. Furthermore, the interaction with the substrate 10 and transversal contact line instabilities 11 have to be taken into account. Finally, capillary forces come into play as soon as the solution film has a comparable thickness as the colloidal particles' diameter. 12 Previous studies addressed the ordering of nanoparticles at the liquid-air interface. 13 However, for technical applications it is of great importance to transfer this order to a solid substrate. 14 The interaction with the substrate allows for tuning the arrangement of the nanoparticles and thus the layers' optical properties. Hence, it is only natural to investigate in situ the evolution of ordering at the TPCL liquid-air substrate.Grazing incidence small angle x-ray scattering 5,6 ͑GISAXS͒ has proven to be a well suited technique for realtime studies. Here, the x-ray beam impinges under a small angle ␣ i Ͻ 1°on to the sample surface. 6 We combined a nanobeam small angle x-ray scattering ͑nano-SAXS͒ geometry of ID13 /ESRF with a grazing incidence setup, allowing for nanobeam-grazing incidence small angle x-ray scattering ͑nano-GISAXS͒ experiments. We used the extremely brilliant 300 nm size beam ͑full width at h...

We present a new method to extract the intermediate scattering function from series of coherent diffraction patterns taken with 2D detectors. Our approach is based on analyzing speckle patterns in terms of photon statistics. We show that the information obtained is equivalent to the conventional technique of calculating the intensity autocorrelation function. Our approach represents a route for correlation spectroscopy on ultrafast timescales at X-ray free-electron laser sources.

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We report on an x-ray photon correlation spectroscopy experiment investigating the surface structure and dynamics of colloidal particles suspended in a supercooled viscous liquid. The static structure factor in the direction parallel and perpendicular to the surface reveals a more disordered structure at the surface as compared to the bulk. The particles display heterogeneous ballistic dynamics parallel to the surface. The particle dynamics in the direction perpendicular to the surface is much slower and does not show the hallmarks of ballistic motion.

We determine the absolute electron density of a lithographically grown nanostructure with 25 nm resolution by combining hard x-ray Fourier transform holography with iterative phase retrieval methods. While holography immediately reveals an unambiguous image of the object, we deploy in addition iterative phase retrieval algorithms for pushing the resolution close to the diffraction limit. The use of hard (8 keV) x rays eliminates practically all constraints on sample environment and enables a destruction-free investigation of relatively thick or buried samples, making holographic diffraction imaging a very attractive tool for materials science. We note that the technique is ideally suited for subpicosecond imaging that will become possible with the emerging hard x-ray free-electron lasers.

A combinatorial high-throughput approach is used to investigate a solution cast gradient consisting of colloidal gold nanoparticles on top of a silicon substrate by means of a X-ray nanobeam. Classification algorithms are used to reveal and visualize structural transitions from a frozen colloidal solution to a well-defined nanostructure. Prominent length scales on the order of 100 nm are observed. A periodic change in the nanostructure along the gradient is explained by a simplified stick-slip model.The fundamental understanding of wetting and flow behavior of nanoparticle and (bio)polymeric solutions and blends on solid substrates is crucial for their application in many technological fields, for example, proteomics, optical coatings, or data storage applications.1-6 Typical deposition methods are spin-coating, Langmuir-Blodgett/Langmuir-Schaefer 8 techniques, or solution casting.9,10 The latter is widely applied in producing designed colloidal, polymeric, and biopolymeric thin films. 4,11,12 It allows for realizing dedicated morphologies and morphological gradients in order to perform combinatorial investigations of thin films 4,9 for different applications, for example, to produce two-and threedimensional photonic crystals. 13,14 Combinatorial methods 15,16 are routinely used for material testing and optimization. By testing a large physical parameter space in short time, one is able to determine the structure-function relationship desired from the application. Solution casting of individual droplets allows one to study structures and morphologies present after deposition on solid wetting substrates. This offers a deeper understanding of the structures induced by the solvent evaporation and its implications for coating, which is of great interest for inkjet printing. 17 In an individual droplet, a multitude of structures is formed, depending on the wetting behavior of the substrate, for example, the rim and a wetting region. The wetting region might extend far from the droplet rim and could be used for installing large scale arrays of ordered colloidal and nanoparticles with respect to high-throughput applications such as surface enhanced Raman scattering (SERS), 18 colorimetric detection of biopolymers, 19 or sensing. 20,21Nanostructuring during colloidal solution casting is a complex, nonequilibrium process. The self-assembly involves the interplay of several flow and time-dependent mechanisms. It involves rheology, phase changes, and nonequilibrium thermodynamics. 22,23 In detail, the nanostructuring takes places at the triple phase contact line air-colloidal solution-substrate.11 The process can be described as follows: During solvent evaporation, the droplet cools at the interface and the concentration of the colloidal particles increases. The evaporation rate is nonuniform and increased near the contact line. This leads to a convective flow and material transport toward the contact line 24 or in the inverse direction, depending on the ratio of the surface tensions of solute and solvent.

The dynamic behavior of charge-stabilized colloidal particles in suspension was studied by photon correlation spectroscopy with coherent X-rays (XPCS). The short-time diffusion coefficient, D(Q) , was measured for volume concentrations phi < or = 0.18 and compared to the free particle diffusion constant D(0) and the static structure factor S(Q) . The data show that indirect, hydrodynamic interactions are relevant for the system and hydrodynamic functions were derived. The results are in striking contrast to the predictions of the PA (pairwise-additive approximation) model, but show features typical for a hard-sphere system. The observed mobility is however considerably smaller than the one of a respective hard-sphere system. The hydrodynamic functions can be modelled quantitatively if one allows for an increased effective viscosity relative to the hard-sphere case.