Single‐crystalline nanowires of Fe3O4 hydrothermally synthesized under a magnetic field are reported. The square and hexagonal crystals formed in zero applied field are shown to give way to nanowires as the magnetic field is increased. The Figure shows the situation for a 0.25 T field. The structure and magnetic properties are characterized by transmission electron microscopy, X‐ray and electron diffraction, and magnetometry.

Selective extraction of metal ions from a complex aqueous mixture into an organic phase is used to separate toxic or radioactive metals from polluted environments and nuclear waste, as well as to produce industrially relevant metals, such as rare earth ions. Selectivity arises from the choice of an extractant amphiphile, dissolved in the organic phase, which interacts preferentially with the target metal ion. The extractant-mediated process of ion transport from an aqueous to an organic phase takes place at the aqueous-organic interface; nevertheless, little is known about the molecular mechanism of this process despite its importance. Although state-of-the-art X-ray scattering is uniquely capable of probing molecular ordering at a liquid-liquid interface with subnanometer spatial resolution, utilizing this capability to investigate interfacial dynamical processes of short temporal duration remains a challenge. We show that a temperature-driven adsorption transition can be used to turn the extraction on and off by controlling adsorption and desorption of extractants at the oil-water interface. Lowering the temperature through this transition immobilizes a supramolecular ion-extractant complex at the interface during the extraction of rare earth erbium ions. Under the conditions of these experiments, the ion-extractant complexes condense into a two-dimensional inverted bilayer, which is characterized on the molecular scale with synchrotron X-ray reflectivity and fluorescence measurements. Raising the temperature above the transition leads to Er ion extraction as a result of desorption of ion-extractant complexes from the interface into the bulk organic phase. XAFS measurements of the ion-extractant complexes in the bulk organic phase demonstrate that they are similar to the interfacial complexes.

Ion distributions play a central role in various settings-from biology, where they mediate the electrostatic interactions between charged biomolecules in solution, to energy storage devices, where they influence the charging properties of supercapacitors. These distributions are determined by interactions dictated by the chemical properties of the ions and their environment as well as the long-range nature of the electrostatic force. Recent theoretical and computational studies have explored the role of correlations between ions, which have been suggested to underlie a number of counterintuitive results, such as like-charge attraction. However, the interdependency between ion correlations and other interactions that ions experience in solution complicates the connection between physical models of ion correlations and the experimental investigation of ion distributions. We exploit the properties of the liquid/liquid interface to vary the coupling strength Γ of ion-ion correlations from weak to strong while monitoring their influence on ion distributions at the nanometer scale with X-ray reflectivity and the macroscopic scale with interfacial tension measurements. These data are in agreement with the predictions of a parameterfree density functional theory that includes ion-ion correlations and ion-solvent interactions over the entire range of experimentally tunable correlation coupling strengths (from 0.8 to 3.7). This study provides evidence for a sharply defined electrical double layer for large coupling strengths in contrast to the diffuse distributions predicted by mean field theory, thereby confirming a common prediction of many ion correlation models. The reported findings represent a significant advance in elucidating the nature and role of ion correlations in charged soft matter.liquid surface scattering | ion density profile | surface excess charge | Poisson-Boltzmann | Debye-Hückel hole T he works by Gouy (1) and Chapman (2) introduced the Poisson-Boltzmann (PB) equation to describe the distribution of ions and the accompanying variation of electric potential at the interface between a charged planar electrode and an electrolyte solution (1, 2). This seminal theory considered point-like ions interacting through their mean electric field in a continuum solvent but neglected both chemically specific ion-solvent interactions and correlations between ions. Specific ion interactions are exemplified by the well-known Hofmeister series (3). The study of ion correlations has been motivated by observations of the reentrant condensation of DNA (4) and proteins (5) in solution, in which like-charged biomolecules aggregate in the presence of multivalent ions, and reports of charge reversal in colloidal suspensions, in which the sign of the screened charge on a colloid can be changed by varying the surrounding electrolyte solution (6, 7).Correlations between ions that are caused by their electrostatic interactions are expected to be important when the average electrostatic interaction energy between neighboring ions...

Due to fundamental interest and potential applications in quantum computation, tremendous efforts have been invested to study topological superconductivity. However, bulk topological superconductivity seems to be difficult to realize and its mechanism is still elusive. Several possible routes to induce topological superconductivity have been proposed, including proximity efforts, doping or pressurizing a topological insulator or semimetal. Among them, the pressurizing is considered to be a "clean" way to tune the electronic structures. Here we report the discovery of a pressure-induced topological and superconducting phase of SnSe, a material which is highly focused recently due to its superior thermoelectric properties. In situ highpressure electrical transport and synchrotron X-ray diffraction measurements show that the superconductivity emerges along with the formation of a CsCl-type structural symmetry of SnSe above around 27 GPa, with a maximum critical temperature of 3.2 K at 39 GPa. Based on ab initio calculations, this CsCl-type SnSe is predicted to be a Dirac line nodes (DLN) semimetal in the absence of spin-orbit coupling, whose DLN states are protected by the coexistence of timereversal and inversion symmetries. These results make CsCl-type SnSe an interesting model platform with simple crystal symmetry to study the interplay of topological physics and superconductivity.