Kazuki Nagashima 교수

A multistate nonvolatile memory operated at sublithographic scale has been strongly desired since other nonvolatile memories have confronted the fundamental size limits owing to their working principles. Resistive switching (RS) in metal-oxide-metal junctions, so-called ReRAM, is promising for next generation high-density nonvolatile memory. Self-assembled oxide nanowire-based RS offers an attractive solution not only to reduce the device size beyond the limitation of current lithographic length

A stress relaxation effect on the transport properties of strained vanadium dioxide epitaxial thin films grown on $\mathrm{Ti}{\mathrm{O}}_{2}$ (001) single crystal was investigated. When varying the film thickness ranging from $10\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}30\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, there were no significant changes on the crystal structures identified by x-ray diffraction, i.e., no observable stress relaxation effects. On the other hand, incr

On the development of flexible electronics, a highly flexible nonvolatile memory, which is an important circuit component for the portability, is necessary. However, the flexibility of existing nonvolatile memory has been limited, e.g. the smallest radius into which can be bent has been millimeters range, due to the difficulty in maintaining memory properties while bending. Here we propose the ultra flexible resistive nonvolatile memory using Ag-decorated cellulose nanofiber paper (CNP). The Ag-

Resistive switching (RS) memory effect in metal-oxide-metal junctions is a fascinating phenomenon toward next-generation universal nonvolatile memories. However the lack of understanding the electrical nature of RS has held back the applications. Here we demonstrate the electrical nature of bipolar RS in cobalt oxides, such as the conduction mechanism and the switching location, by utilizing a planar single oxide nanowire device. Experiments utilizing field effect devices and multiprobe measurem

The resistive switching characteristics of room temperature grown SnO2 films were investigated by fabricating the metal-oxide-metal sandwich structures. The unipolar operation was found in all devices. Experiments, including the size and material dependencies of the top electrodes and the three terminal device structures, demonstrated the rupture and formation of conducting filaments near the anode. The Ohmic behavior was observed in both on- and off-states when using Au and Ti top electrodes, w

The interface effects on the metal-insulator transition (MIT) of strained VO2 ultrathin films grown epitaxially on TiO2 (001) single crystal substrate were investigated. Varying the surface conditions of TiO2 substrate, such as the roughness and the surface reconstructions, produced the remarkable changes in the MIT events of VO2 thin films, including the transition temperature and the abruptness. The presence of the surface reconstructions was found to be detrimental for applying effectively st

Single-use disposable nonvolatile memory devices hold promise for novel applications in internet of everything (IoE) technology by storing the health status of individual humans in daily life. However, conventional memory devices are not disposable because they are mostly composed of non-renewable, non-biodegradable and sometimes toxic materials, causing serious damage to ecological systems when they are released to the environment. Here, we demonstrate an environment-friendly, disposable nonvol

We fabricated single-crystalline MgO nanowires epitaxially grown on MgO single crystal substrate using the Au catalyst-assisted pulsed laser deposition (PLD). Controlling appropriately the amount of Au catalyst and the substrate temperature was found to be crucial for the MgO nanowire growth using the catalyst-assisted PLD. In addition, (100) oriented MgO nanowires were epitaxially grown on (100), (110), and (111) oriented substrates, allowing the limited growth directions. The possible growth m

The effect of ambient atmosphere on metal-to-insulator transition (MIT) in strained vanadium dioxide (VO2) ultrathin films (7–8nm) grown epitaxially on TiO2 (001) single crystal substrate by pulsed laser deposition was investigated by varying the ambient oxygen pressure and substrate temperature with the intention being to control arbitrarily the MIT events of strained VO2 ultrathin films, including the MIT temperature and the resistivity change. When reducing the ambient oxygen pressure, the MI

Heterostructured transition metal oxide nanowires are potential candidates to incorporate rich functionalities into nanowire-based devices. Although the oxide heterointerface plays a crucial role in determining the physical properties, the effects of the heterointerface on the oxide nanowire's properties have not been clarified. Here we investigate for the first time the significant role of the heterointerface in determining the transport properties of well-defined MgO/titanate heterostructured

Oxide nanowires formed via the vapor-liquid-solid (VLS) mechanism are attractive building blocks toward nanowire-based electronic devices due to their fascinating physical properties. Although well-defined oxide nanowires are strongly required for the applications, tapering during oxide nanowire VLS growth has been detrimental and uncontrollable. Here we demonstrate the mechanism to control the tapering during oxide VLS growth. Suppressing simultaneously both the oxidization of adatoms at the si

We demonstrate the facile, rational synthesis of monodispersedly sized zinc oxide (ZnO) nanowires from randomly sized seeds by hydrothermal growth. Uniformly shaped nanowire tips constructed in ammonia-dominated alkaline conditions serve as a foundation for the subsequent formation of the monodisperse nanowires. By precisely controlling the sharp tip formation and the nucleation, our method substantially narrows the distribution of ZnO nanowire diameters from σ = 13.5 nm down to σ = 1.3 nm and c

Although controlling morphologies of oxide nanowires formed using vapor-liquid-solid (VLS) mechanism is desired in developing functional oxide-nanowire applications, a comprehensive understanding of the key factors affecting oxide-nanowire VLS growth is still lacking. Here, the authors demonstrate the controllability of magnesium oxide nanowire morphologies by varying the ambient temperature and discuss the underlying mechanism. Decreasing the ambient temperature resulted in shorter, tapered, an

This study demonstrates the effect of surroundings on a memristive switching at nanoscale by utilizing an open top planar-type device. NiO(x) and CoO(x) planar-type devices have exhibited a memristive behavior under atmospheric pressure, whereas TiO(2-x) planar-type devices did not show a memristive switching even under the same surroundings. A memristive behavior of TiO(2-x) planar-type devices has emerged when reducing an ambient pressure and/or employing a SiO(2) passivation layer. These resu