The development of synthetic processes for oxide nanomaterials is an issue of considerable topical interest. While a number of chemical methods are available and are extensively used, the collaborations are often energy intensive and employ toxic chemicals. On the other hand, the synthesis of inorganic materials by biological systems is characterized by processes that occur at close to ambient temperatures and pressures, and at neutral pH (examples include magnetotactic bacteria, diatoms, and S-layer bacteria). Here we show that nanoparticulate magnetite may be produced at room temperature extracellularly by challenging the fungi, Fusarium oxysporum and Verticillium sp., with mixtures of ferric and ferrous salts. Extracellular hydrolysis of the anionic iron complexes by cationic proteins secreted by the fungi results in the room-temperature synthesis of crystalline magnetite particles that exhibit a signature of a ferrimagnetic transition with a negligible amount of spontaneous magnetization at low temperature.

A new undulator beamline (P22) for hard X-ray photoelectron spectroscopy (HAXPES) was built at PETRA III (DESY, Hamburg) to meet the increasing demand for HAXPES-based techniques. It provides four special instruments for high-resolution studies of the electronic and chemical structure of functional nano-materials and catalytic interfaces, with a focus on measurements under operando and/or ambient conditions: (i) a versatile solid-state spectroscopy setup with optional wide-angle lens and in-situ electrical characterization, (ii) a HAXPEEM instrument for sub-µm spectro-microscopy applications, (iii) an ambient pressure system (> 1 bar) for operando studies of catalytic reactions and (iv) a time-of-flight spectrometer as a full-field k-microscope for measurements of the 4D spectral function ρ(E B ,k). The X-ray optics were designed to deliver high brightness photon flux within the HAXPES energy range 2.4-15 keV. An LN 2-cooled double-crystal monochromator with interchangeable pairs of Si(111) and (311) crystals is optionally combined with a double channel-cut post-monochromator to generate X-rays with variable energy bandpass adapted to the needs of the experiment. Additionally, the beam polarization can be varied using a diamond phase plate integrated into the beamline. Adaptive beam focusing is realized by Be compound refractive lenses and/or horizontally deflecting mirrors down to a spot size of ~20x17 µm 2 with a flux of up to 1.1x10 13 ph/s (for Si(111) at 6 keV).

All-inorganic cesium lead halide (CsPbX3; X = Cl, Br, and I) perovskite nanocubes (NCs) exhibit fascinating optical and optoelectronic properties. Postsynthesis anion exchange by mixing NCs with reactive anion species has emerged as a unique strategy to control their composition and band gap. For example, we started with CsPbBr3 NCs with intense green emission, and then anion exchange with iodide ions yields CsPb­(Br/I)3 mixed halides and CsPbI3 with emission color systematically varying in the green-red region. However, the internal structure of the anion-exchanged perovskite NCs is not probed. It is believed that the NCs possess a homogeneous alloyed composition, but X-ray diffraction pattern could not give evidence for such alloy formation, because the crystal structure also varies with anion composition. Here, we elucidate the internal heterostructure of anion-exchanged NCs using variable energy hard X-ray photoelectron spectroscopy. The results show that, in contrast to a homogeneous alloy, there is a significant inhomogeneity in the composition across the radius of NCs. The surface of CsPb­(Br/I)3 NCs is rich with exchanged iodide ions, whereas the core is rich with native bromide ions. Even CsPbI3 NCs obtained after assumed complete anion exchange show a small amount of bromide ions in the core. This finding of gradient internal heterostructure inside the anion-exchanged NCs will be important for future understanding of electronic properties and stability-related issues of CsPbX3 NCs.

Peptide 1 with an Aβ42 amyloid nucleating core demonstrates step-wise self-assembly in water. Variation of temperature or solvent composition arrests the self-assembly to give metastable nanoparticles, which undergo self-assembly on gradual increase in temperature and eventually produce kinetically controlled nanofibers and thermodynamically stable twisted helical bundles. Mechanical agitation of the fibers provided access to short seeds with narrow polydispersity index, which by mediation of seeded supramolecular polymerization establishes perfect control over the length of the nanofibers. Such pathway dependence and the length control of the supramolecular peptide nanofibers is exploited to tune the mechanical strength of the resulting hydrogel materials.

We report intrinsic memory effect in magnetization and dielectricity for the spin-chain compound Sm 2 BaNiO 5 , pointing the cooperative glassy response below ∼8 K. Signature of anomaly around 8 K is verified by the magnetization, heat capacity, dielectric permittivity, magnetostriction, and structural parameters as obtained from the synchrotron diffraction studies. Intriguingly, the memory effect is observed well below the magnetic and ferroelectric ordering temperatures, pointing to a reentrant frozen state. Ferroelectricity emerges above antiferromagnetic Néel temperature at 45 K. For 4.5 kV/cm poling field the spontaneous electric polarization attains the value of 1300 μC/m 2 , that is the highest value in the R 2 BaNiO 5 series. Synchrotron diffraction studies confirm that ferroelectricity emerges due to structural transition from the centrosymmetric I mmm to a noncentrosymmetric I mm2 space group. Magnetoelectric coupling is significant and scales linearly to the squared magnetization as described by the Ginzburg-Landau theory.