X-ray reflectivity from curved liquid interfaces.

X-ray reflectivity studies of the structure of liquid-vapour and liquid-liquid interfaces at modern sources, such as free-electron lasers, are currently impeded by the lack of dedicated liquid surface diffractometers. It is shown that this obstacle can be overcome by an alternative experimental approach that uses the natural curvature of a liquid drop for variation of the angle of incidence. Two modes of operation are shown: (i) sequential reflectivity measurements by a nanometre beam and (ii) parallel acquisition of large ranges of a reflectivity curve by micrometre beams. The feasibility of the two methods is demonstrated by studies of the Hg/vapour, H2O/vapour and Hg/0.1 M NaF interface. The obtained reflectivity curves match the data obtained by conventional techniques up to 5αc in micro-beam mode and up to 35αc in nano-beam mode, allowing observation of the Hg layering peak.

Hierarchical Surface Patterns upon Evaporation of a ZnO Nanofluid Droplet: Effect of Particle Morphology.

Surface structures with tailored morphologies can be readily delivered by the evaporation-induced self-assembly process. It has been recently demonstrated that ZnO nanorods could undergo rapid chemical and morphological transformation into 3D complex structures of Zn(OH)2 nanofibers as a droplet of ZnO nanofluid dries on the substrate via a mechanism very different from that observed in the coffee ring effect. Here, we have investigated how the crystallinity and morphology of ZnO nanoparticles would affect the ultimate pattern formation. Three ZnO particles differing in size and shape were used, and their crystal structures were characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). Their dispersions were prepared by sonication in a mixture of isobutylamine and cyclohexane. Residual surface patterns were created by drop casting a droplet of the nanofluid on a silicon substrate. The residual surface patterns were analyzed by scanning electron microscopy (SEM) and microfocus grazing incidence X-ray diffraction (µGIXRD). Nanofluid droplets of the in-house synthesized ZnO nanoparticles resulted in residual surface patterns consisting of Zn(OH)2 nanofibers. However, when commercially acquired ZnO powders composed of crystals with various shapes and sizes were used as the starting material, Zn(OH)2 fibers were found covered by ZnO crystal residues that did not fully undergo the dissolution and recrystallization process during evaporation. The difference in the solubility of ZnO nanoparticles was linked to the difference in their crystallinity, as assessed using the Scherrer equation analysis of their XRD Bragg peaks. Our results show that the morphology of the ultimate residual pattern from evaporation of ZnO nanofluids can be controlled by varying the crystallinity of the starting ZnO nanoparticles which affects the nanoparticle dissolution process during evaporation.

SiO_{2} Glass Density to Lower-Mantle Pressures.

The convection or settling of matter in the deep Earth's interior is mostly constrained by density variations between the different reservoirs. Knowledge of the density contrast between solid and molten silicates is thus of prime importance to understand and model the dynamic behavior of the past and present Earth. SiO_{2} is the main constituent of Earth's mantle and is the reference model system for the behavior of silicate melts at high pressure. Here, we apply our recently developed x-ray absorption technique to the density of SiO_{2} glass up to 110 GPa, doubling the pressure range for such measurements. Our density data validate recent molecular dynamics simulations and are in good agreement with previous experimental studies conducted at lower pressure. Silica glass rapidly densifies up to 40 GPa, but the density trend then flattens to become asymptotic to the density of SiO_{2} minerals above 60 GPa. The density data present two discontinuities at ∼17 and ∼60 GPa that can be related to a silicon coordination increase from 4 to a mixed 5/6 coordination and from 5/6 to sixfold, respectively. SiO_{2} glass becomes denser than MgSiO_{3} glass at ∼40 GPa, and its density becomes identical to that of MgSiO_{3} glass above 80 GPa. Our results on SiO_{2} glass may suggest that a variation of SiO_{2} content in a basaltic or pyrolitic melt with pressure has at most a minor effect on the final melt density, and iron partitioning between the melts and residual solids is the predominant factor that controls melt buoyancy in the lowermost mantle.

Erratum: Uniform electroactive fibre-like micelle nanowires for organic electronics.

This corrects the article DOI: 10.1038/ncomms15909.

Tunable Strain in Magnetoelectric ZnO Microrod Composite Interfaces.

The intrinsic strain at coupled components in magnetoelectric composites plays an important role for the properties and function of these materials. In this in situ X-ray nanodiffraction experiment, the coating-induced as well as the magnetic-field-induced strain at the coupled interface of complex magnetoelectric microcomposites were investigated. These consist of piezoelectric ZnO microrods coated with an amorphous layer of magnetostrictive (Fe90Co10)78Si12B10. While the intrinsic strain is in the range of 10-4, the magnetic-field-induced strain is within 10-5, one order of magnitude smaller. Additionally, the strain relaxation distance of around 5 µm for both kinds of strain superposes indicating a correlation. The value of both intrinsic and magnetic-field-induced strain can be manipulated by the diameter of the rodlike composite. The intrinsic interface strain within the ZnO increases exponentially by decreasing the rod diameter while the magnetic-field-induced strain increases linearly within the given range. This study shows that miniaturizing has a huge impact on magnetoelectric composite properties, resulting in a strongly enhanced strain field and magnetic response.

Uniform electroactive fibre-like micelle nanowires for organic electronics.

Micelles formed by the self-assembly of block copolymers in selective solvents have attracted widespread attention and have uses in a wide variety of fields, whereas applications based on their electronic properties are virtually unexplored. Herein we describe studies of solution-processable, low-dispersity, electroactive fibre-like micelles of controlled length from π-conjugated diblock copolymers containing a crystalline regioregular poly(3-hexylthiophene) core and a solubilizing, amorphous regiosymmetric poly(3-hexylthiophene) or polystyrene corona. Tunnelling atomic force microscopy measurements demonstrate that the individual fibres exhibit appreciable conductivity. The fibres were subsequently incorporated as the active layer in field-effect transistors. The resulting charge carrier mobility strongly depends on both the degree of polymerization of the core-forming block and the fibre length, and is independent of corona composition. The use of uniform, colloidally stable electroactive fibre-like micelles based on common π-conjugated block copolymers highlights their significant potential to provide fundamental insight into charge carrier processes in devices, and to enable future electronic applications.

Spectroscopic Ellipsometry of Nanocrystalline Diamond Film Growth.

With the retention of many of the unrivaled properties of bulk diamond but in thin-film form, nanocrystalline diamond (NCD) has applications ranging from micro-/nano-electromechanical systems to tribological coatings. However, with Young's modulus, transparency, and thermal conductivity of films all dependent on the grain size and nondiamond content, compositional and structural analysis of the initial stages of diamond growth is required to optimize growth. Spectroscopic ellipsometry (SE) has therefore been applied to the characterization of 25-75 nm thick NCD samples atop nanodiamond-seeded silicon with a clear distinction between the nucleation and bulk growth regimes discernable. The resulting presence of an interfacial carbide and peak in nondiamond carbon content upon coalescence is correlated with Raman spectroscopy, whereas the surface roughness and microstructure are in accordance with values provided by atomic force microscopy. As such, SE is demonstrated to be a powerful technique for the characterization of the initial stages of growth and hence the optimization of seeding and nucleation within films to yield high-quality NCD.

Nanoscale Structural Features in Major Ampullate Spider Silk.

Spider major ampullate silk is often schematically represented as a two-phase material composed of crystalline nanodomains in an amorphous matrix. Here we are interested in revealing its more complex nanoscale organization by probing Argiope bruennichi dragline-type fibers using scanning X-ray nanodiffraction. This allows resolving transversal structural features such as an about 1 µm skin layer composed of around 100 nm diameter nanofibrils serving presumably as an elastic sheath. The core consists of a composite of several nm size crystalline nanodomains with poly(l-alanine) microstructure, embedded in a polypeptide network with short-range order. Stacks of nanodomains separated by less ordered nanosegments form nanofibrils with a periodic axial density modulation which is particularly sensitive to radiation damage. The precipitation of larger ß-type nanocrystallites in the outer core-shell is attributed to MaSp1 protein molecules.

Influence of solvent polarity on the structure of drop-cast electroactive tetra(aniline)-surfactant thin films.

The influence of processing conditions on the thin film microstructure is a fundamental question that must be understood to improve the performance of solution-processed organic electronic materials. Using grazing-incidence X-ray diffraction, we have studied the structure of thin films of a tetra(aniline)-surfactant complex prepared by drop-casting from five solvents (hexane, chloroform, tetrahydrofuran, dichloromethane and ethanol), selected to cover a range of polarities. We found that the structure, level of order and degree of orientation relative to the substrate were extremely sensitive to the solvent used. We have attempted to correlate such solvent sensitivity with a variety of solvent physical parameters. Of particular significance is the observation of a sharp structural transition in the thin films cast from more polar solvents; such films presented significantly greater crystallinity as measured by the coherence length and paracrystalline disorder parameter. We attribute this higher structural order to enhanced dissociation of the acid surfactant in the more polar solvents, which in turn promotes complex formation. Furthermore, the more polar solvents provide more effective screening of (i) the attractive ionic interaction between oppositely charged molecules, providing greater opportunity for dynamic reorganisation of the supramolecular aggregates into more perfect structures; and (ii) the repulsive interaction between the positively charged blocks permitting a solvophobic-driven aggregation of the aromatic surfaces during solvent evaporation.

Fate of MgSiO3 melts at core-mantle boundary conditions.

One key for understanding the stratification in the deep mantle lies in the determination of the density and structure of matter at high pressures, as well as the density contrast between solid and liquid silicate phases. Indeed, the density contrast is the main control on the entrainment or settlement of matter and is of fundamental importance for understanding the past and present dynamic behavior of the deepest part of the Earth's mantle. Here, we adapted the X-ray absorption method to the small dimensions of the diamond anvil cell, enabling density measurements of amorphous materials to unprecedented conditions of pressure. Our density data for MgSiO3 glass up to 127 GPa are considerably higher than those previously derived from Brillouin spectroscopy but validate recent ab initio molecular dynamics simulations. A fourth-order Birch-Murnaghan equation of state reproduces our experimental data over the entire pressure regime of the mantle. At the core-mantle boundary (CMB) pressure, the density of MgSiO3 glass is 5.48 ± 0.18 g/cm(3), which is only 1.6% lower than that of MgSiO3 bridgmanite at 5.57 g/cm(3), i.e., they are the same within the uncertainty. Taking into account the partitioning of iron into the melt, we conclude that melts are denser than the surrounding solid phases in the lowermost mantle and that melts will be trapped above the CMB.

Directed Growth of Virus Nanofilaments on a Superhydrophobic Surface.

The evaporation of single droplets of colloidal tobacco mosaic virus (TMV) nanoparticles on a superhydrophobic surface with a hexagonal pillar-pattern results in the formation of coffee-ring type residues. We imaged surface features by optical, scanning electron, and atomic force microscopies. Bulk features were probed by raster-scan X-ray nanodiffraction. At ∼100 pg/µL nanoparticle concentration, the rim of the residue connects to neighboring pillars via fibrous extensions containing flow-aligned crystalline domains. At ∼1 pg/µL nanoparticle concentration, nanofilaments of ≥80 nm diameter and ∼20 µm length are formed, extending normal to the residue-rim across a range of pillars. X-ray scattering is dominated by the nanofilament form-factor but some evidence for crystallinity has been obtained. The observation of sheets composed of stacks of self-assembled nanoparticles deposited on pillars suggests that the nanofilaments are drawn from a structured droplet interface.

A superhydrophobic chip based on SU-8 photoresist pillars suspended on a silicon nitride membrane.

We developed a new generation of superhydrophobic chips optimized for probing ultrasmall sample quantities by X-ray scattering and fluorescence techniques. The chips are based on thin Si3N4 membranes with a tailored pattern of SU-8 photoresist pillars. Indeed, aqueous solution droplets can be evaporated and concentrated at predefined positions using a non-periodic pillar pattern. We demonstrated quantitatively the deposition and aggregation of gold glyconanoparticles from the evaporation of a nanomolar droplet in a small spot by raster X-ray nanofluorescence. Further, raster nanocrystallography of biological objects such as rod-like tobacco mosaic virus nanoparticles reveals crystalline macro-domain formation composed of highly oriented nanorods.

Room temperature palladium catalysed coupling of acyl chlorides with terminal alkynes.

Conditions are reported for the facile, high-yielding coupling of acyl chlorides with terminal alkynes in a reaction involving palladium and copper iodide; the reaction is tolerant of a wide variety of acyl chlorides and terminal alkynes and provides a convenient one-pot route to acetylenic ketones.