Continual development and improvement in information technology has been achieved through unrelenting miniaturisation of the single memory bit in integrated ferromagnetic, ferroelectric, optical, and related circuits. However, as miniaturisation is approaching its theoretical limit of 1–10 terabits per square inch1,2), alternative memory materials are being sought as replacements. While the discovery of hysteretic magnetism from a singlemolecule magnet (SMM) is promising in this regard3), its low operating temperature hinders its practical use. Here, we report a unique material exhibiting single-molecule electric polarisation switching that can be operated above room temperature4). The switching occurs in a Preyssler-type polyoxometalate (POM) cluster we refer to as a single-molecule electret (SME), which exhibits the characteristics of ferroelectricity but without long-range dipole ordering. The SME affords bi-stability due to the two potential positions of localisation of a terbium ion (Tb3+), which results in extremely slow relaxation of the polarization and electric hysteresis with very high spontaneous polarisation and coercive electric fields. Our findings demonstrate that SMEs can be applied to ultrahigh-density memory operating above room temperature5,6). They may also be applicable to other molecular-level electronic devices, such as piezoelectric nano-generators, sensors, and actuators7,8).
Ligand-protected metal clusters, composed of less than 100 metal atoms, show novel and size-specific properties due to unique electronic and geometric structures. The geometric structure is key information for understanding the origin of the specific and novel properties and for rational design of their functions. X-ray absorption spectroscopy (XAS) is a powerful tool for determining the local structure and electronic state of a specific element within the clusters regardless of their environment. This article summarizes the results of our XAS studies on the atomic packing of metal clusters, location of dopant in the clusters, interfacial structures between the clusters and the surroundings, and bond stiffness of the clusters.
Inorganic nanosheets obtained by exfoliation of inorganic layered crystals are two-dimensional crystalline nanoparticles with the thickness around 1 nm and the lateral length up to several micrometers. Some inorganic nanosheets form colloidal liquid crystals, which is called inorganic nanosheet liquid crystals. We have fabricated hierarchical assemblies of liquid crystalline inorganic nanosheets with the aid of external forces such as electric field and laser radiation pressure. Colloidal nanosheets are aligned upon laser beam irradiation into the direction of the incident laser beam. At the focal point, the nanosheet orientation depends on the electric field of the polarized laser beam. When liquid crystalline nanosheets are irradiated, giant tree-ring-like nanosheet textures of more than 100 μm are organized at the periphery of the focal point. Combination of an external force such as laser radiation pressure and a cooperative effect of liquid crystalline nanosheets is important for the formation of such hierarchical structures.
Methane exists abundantly around Japan as methane hydrate. For the effective use of such a methane, the conversion of methane into methanol has recently attracted much attention. Photocatalytic reaction is one of the methods which convert methane into methanol without using much energy. However, it is indispensable to improve the photocatalytic activity for their practical use. In this work, we have attempted to improve the activity of mesoporous WO3 and TiO2 (m-WO3 and m-TiO2) photocatalysts, which convert methane into methanol, by loading the fine metal clusters as cocatalyst on the photocatalysts. As a result, we have succeeded in loading ultrafine metal-cluster cocatalysts onto m-WO3 and m-TiO2, and thereby improving their photocatalytic activity. This study also demonstrated that the kind of metal element suitable for each photocatalyst depends on the kind of the photocatalysts and thereby it is important to select the metal clusters suitable to each photocatalyst for improving its photocatalytic activity.
Cu1-xZnxFe2O4 (x = 0, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.9) nanoparticles encapsulated with amorphous SiO2 were prepared by our original wet chemical method and magnetization measurements were performed. x = 0.5 sample showed highest maximum magnetization (MS) and magnetic resonance relaxation rate R2. Cu0.5Zn0.5Fe2O4 sample of 20 nm showed the biggest heat dissipation and the temperature rise of the sample was about 19 K. By these measurements, Cu0.5Zn0.5Fe2O4 nanoparticle of 20 nm could be expected as the heating agent of magnetic hyperthermia and contrast agent for MRI.