Articles in 2015

Applying in situ TEM techniques to GST-based vertical PCRAM cells, we directly observed the DC set switching process of real devices for the first time. The results show that the microstructure of crystalline GST matrix is an important structural parameter determining the local temperature distribution. In the case of highly crystallized GST matrix, the device failure occurred via two-step void formation due to the polarity-dependent electromigration.

3D Networked NiCo₂S₄ nanosheet array/carbon cloth composites are synthesized by a facile hydrothermal reaction and subsequent sulfurization process, and the rational material composition and structure design lead to their outstanding overall performance as an anode material in lithium-ion batteries.

The transparent C₃N₂H₅ClO₄ ferroelectric film on ITO coated PET substrate can be bent to 3.1 mm radius without affecting its ferroelectric properties. Furthermore, its local piezoelectric response is comparable to that of Pb(Zr_0.2Ti_0.8)O₃ film.

Nanoporous metals made by dealloying can take the form of macroscopic bodies that exhibit a uniform and highly interconnected network of nanoscale ‘ligaments’. Our study used this material as the reinforcement phase in novel interpenetrating-phase nanocomposites. Tensile tests on our cm-sized composite samples for the first time demonstrate tensile ductility in a nanoporous-metal-based material. Whereas the strength, σ, of pure nanoporous metal scales with the phase faction, ϕ, as σ ∝ ϕ^3/2, the composite has a linear scaling relation σ ∝ ϕ that favors strengthening at small solid fraction. We find this strengthening also in quantitative agreement with the data behind the well-known ‘smaller is stronger’ of metal nanostructures. Thus, our material’s design strategy exploits the high strength of individual metal nano-objects such as nanowires for making a strong and ductile material from which macroscopic things can be formed.

We fabricated compact helical antenna operating in the industry-scientific-medical radio band. With a total length of only 5.5 mm, it is about five times smaller compared with the conventional dipole antenna. The transmission and receiving signals between helical antennas and the communication between a helical antenna and a smartphone is reported. Owing to the shape and dimensions, we successfully demonstrate the possibility to address the antenna, when embedded in a tooth, as well as to implant the antenna using standard medical syringes. These demonstrations highlight the potential of helical antennas for medical applications as components of smart system implants.

Novel high-κ dielectric materials are identified by automated ab initio calculations on ~1800 oxides. The cubic BeO is found to possess an unprecedented material property of 10 eV for band gap and 275 for dielectric constant. Candidate high-κ oxides are suggested for microelectronic devices such as CPU, DRAM and flash memory.

Ultra-small Ni(OH)₂ nanoparticles with different average sizes are prepared in large scale, and the best electrochemical performance is obtained at the critical size rather than the smallest size, which provides a new insight on nanosize effect on electrode materials in energy storage.

A nanosheet structure on a glass plate can transfer naked DNA into difficult-to-transfect cells (for example, stem cells) in limited time after contact (‘transfection window’) without any vector. The transfected cells express the specific proteins a week later. The gene uptake and expression are associated with the cytoskeleton arrangement on the silica nanosheets by activating the cell-membrane integrin receptor.

The development of scalable chemistries for the production and processing of graphene is essential if its potential in structures and devices is to be realized. This review is a chemist’s perspective on the methods developed for the production of processable graphene and graphene precursors dispersion, their integration into polymers and fabrication into a variety of structures.

A novel confinement-free synthesis of CP-HMNSFs possessing straight channels at fiber center surrounded by concentric short-pitch helical channels is discovered. The chloropropyl groups are found mainly located at central cylindrical part of the nanofibers. Helical PtCo nanowires with small and narrowly distributed radii of gyration are also fabricated, showing distinct ferromagnetic properties as compared with the straight counterparts.

The rational all-oxide TiC_1-xO_x@TiO_y-TiO₂ heterostructures with the significantly enhanced thermoelectric properties had been designed, and a high dimensionless figure of merit (ZT) value of up to 0.84 at 973 K was achieved in all-oxide TiC_0.1O_0.9@TiO_y-TiO₂ heterostructures.

Novel Cr³⁺-doped non-gallate near-infrared phosphorescent phosphor, Zn₂SnO₄: Cr, with the special optical characteristics of broad emission band (650–1200 nm, peaking at 800 nm) and long afterglow duration (>35 h) was presented, which successfully avoid the existing ubiquitous reliance on gallates as hosts in Cr³⁺-doped phosphorescent phosphors. This research also deals with the method of finely tailoring the local crystal field around the activator center, Cr³⁺, along with essential redeployment of trap distributions by adding Al. Indeed, such redeployment permits band gap adjustment and the dynamic variation of the annihilation and formation of defects.

The most recent developments in the synthesis and structure engineering of CeO₂-encapsulated noble metal hybrids for catalytic applications are critically discussed.

The low cost, significant reduction potential and relative safety of the zinc electrode is a common hope for a reductant in secondary batteries, but it is limited mainly to primary implementation due to shape change. In this work, we exploit such shape change for the benefit of static electrodes through the electrodeposition of hyper-dendritic nanoporous zinc foam. Electrodeposition of zinc foam resulted in nanoparticles formed on secondary dendrites in a three-dimensional network with a particle size distribution of 54.1–96.0 nm. The nanoporous zinc foam contributed to highly oriented crystals, high surface area and more rapid kinetics in contrast to conventional zinc in alkaline mediums. The anode material presented had a utilization of ~88% at full depth-of-discharge (DOD) at various rates indicating a superb rate capability. The rechargeability of Zn⁰/Zn²⁺ showed significant capacity retention over 100 cycles at a 40% DOD to ensure that the dendritic core structure was imperforated. The dendritic architecture was densified upon charge–discharge cycling and presented superior performance compared with bulk zinc electrodes.

In the growing field of nanotechnology, there is an interest in developing hybrid organic–inorganic devices that have controllable electrical or magnetic properties.¹ Because of the nanoscale involved, the surface-to-volume ratio in these devices is large; hence, the devices can be controlled by varying their surface properties. Exerting control by using light is particularly attractive because making conventional hard electric contacts may be difficult due to size and material properties. The work of Suda et al.² presents a device in which superconductivity is controlled by light through the excitation of a gate made from spiropyran.³ Figure 1 schematically presents the device and its mode of operation (right panel) relative to that of a common field effect transistor (left panel). Spiropyran serves as the gate and is reversibly photoisomerized from a nonionic to a zwitterionic form. In its neutral form, no field is applied to the thin single crystal of κ-(BEDT-TTF)₂Cu[N(CN)₂]Br (κ-Br) (BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene). Upon photoexcitation with UV light, zwitterions are formed in the spiropyran film, and as a result, holes are injected into the κ-Br, converting it to a superconductor at low temperatures. Irradiation with visible light returns the film to its neutral state.

Schematic synthesis of the robust superhydrophobic coating from strawberry-like Janus hemispherical particles: (a) the dispersion of aqueous particles is sprayed onto the E-51 layer on the substrate; (b) the Janus particles self-orientate to form a layer; and (c) after the epoxy resin is cured by cationic catalysis, the robust superhydrophobic coating is fabricated.

The thermotropic ionic liquid crystal with the wide temperature range of the liquid crystal phase is reported using polyhedral oligomeric silsesquioxane. We found the liquid crystal phase of the POSS-tethered ion salts can be maintained until the pyrolysis occurs.