Masaki Nakano

We report on a high performance visible-blind Schottky ultraviolet photodiode composed of a ZnO (0001) bulk single crystal and a transparent conducting polymer, poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate), fabricated with a simple spin-coating process at room temperature in air. The quantum efficiency as high as unity in ultraviolet region and a visible rejection ratio of about 103 were achieved in the spectral response of the photodiode under zero-bias condition. The normalized dete

Molecular beam epitaxy (MBE) provides a simple but powerful way to synthesize large-area high-quality thin films and heterostructures of a wide variety of materials including accomplished group III-V and II-VI semiconductors as well as newly developing oxides and chalcogenides, leading to major discoveries in condensed-matter physics. For two-dimensional (2D) materials, however, main fabrication routes have been mechanical exfoliation and chemical vapor deposition by making good use of weak van

High quality Schottky junctions were fabricated on a ZnO (0001) bulk single crystal by spin coating a commercial conducting polymer, poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS), as the metal electrodes. The junctions exhibited excellent rectifying behavior with a typical ideality factor of 1.2. Such parameters as Schottky barrier height (ϕb) and built-in potential (Vbi) show negligible variation among junctions. The electron affinity of ZnO derived from ϕb and qVbi value

The field-effect transistor (FET) provides an electrical switching function of current flowing through a channel surface by external voltage. Here, we report on a field-effect device that enables electrical switching of optical transmittance as well as conventional electrical current. We investigated optical properties of vanadium dioxide (VO2) thin film under the presence of electric field generated at the interface between VO2 and ionic liquid in a FET geometry, and found that the device exhib

The discoveries of intrinsic ferromagnetism in atomically thin van der Waals crystals have opened a new research field enabling fundamental studies on magnetism at two-dimensional (2D) limit as well as development of magnetic van der Waals heterostructures. Currently, a variety of 2D ferromagnetism has been explored mainly by mechanically exfoliating "originally ferromagnetic (FM)" van der Waals crystals, while a bottom-up approach by thin-film growth technique has demonstrated emergent 2D ferro

A defect-free and electronically abrupt polymer/oxide interface can be achieved by spin-coating of PEDOT:PSS on ZnO-based heterostructures. The interface yielding Schottky contact leads to the successful modulation of quantum 2D transport in MgZnO/ZnO interfaces via the electric-field effect, which indicates that the polymer/oxide interface enables a high-mobility field-effect transistor. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents

In a conventional magnetic material, a long-range magnetic order develops in three dimensions, and reducing a layer number weakens its magnetism. Here we demonstrate anomalous layer-number-independent ferromagnetism down to the two-dimensional (2D) limit in a metastable phase of Cr₃Te₄. We fabricated Cr₃Te₄ thin films by molecular-beam epitaxy and found that Cr₃Te₄ could host two distinct ferromagnetic phases characterized with di

Electrolyte gating on correlated VO 2 thin films enables electrical control of the “bulk” electronic and structural phases over the electrostatic screening length. Although this unique functionality potentially provides novel electronic and optoelectronic device applications, there are intense discussions on the mechanism of the device operation both from electrostatic and electrochemical viewpoints. Here it is shown that the reversibility of the device operation strongly depends on substrates,

Spectral response of Schottky photodiodes consisting of a MgxZn1-xO (x≤0.43) thin film and a transparent conducting polymer, poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate), was characterized under a zero-bias condition at room temperature. The cut-off wavelength in each photodiode was systematically tuned by Mg content (x), while its high quantum efficiency was kept near unity. The steepness in the photo-response around the cut-off wavelength was maintained for higher x samples, implyin

Molecular-beam epitaxy (MBE) enables the stabilization of a nonequilibrium material phase, providing a powerful approach to the exploration of emergent phenomena in condensed-matter research. Here we demonstrate that one of the metallic two-dimensional (2D) materials, TaSe₂, grown by MBE crystallizes into the pure 3<i>R</i> phase with the self-intercalated Ta atoms, 3<i>R</i>-Ta_1+<i>x</i>Se₂, which is thermodynamically metastable and does not exist in nature as a

Magnetocrystalline anisotropy, a key ingredient for establishing long-range order in a magnetic material down to the two-dimensional (2D) limit, is generally associated with spin-orbit interaction (SOI) involving a finite orbital angular momentum. Here we report strong out-of-plane magnetic anisotropy without orbital angular momentum, emerging at the interface between two different van der Waals (vdW) materials, an archetypal metallic vdW material NbSe₂ possessing Zeeman-type SOI and

A ZnO/Mg0.2Zn0.8O heterostructure was characterized at T=2 K through capacitance measurements with using a conducting polymer, poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), as a Schottky contact. The Nyquist diagram, which is the trajectory curve of the complex impedance vector, appeared to be an excellent semicircular shape, implying that the PEDOT:PSS/ZnO/Mg0.2Zn0.8O junction can be described with an equivalent single RC parallel circuit. Capacitance-voltage characterist

Abstract Emergent properties of 2D materials attract considerable interest in condensed matter physics and materials science due to their distinguished features that are missing in their bulk counterparts. A mainstream in this research field is to broaden the scope of material to expand the horizons of the research area, while developing functional interfaces between different 2D materials is another indispensable research direction. Here, the emergence of electrical conduction at the interface

Magnetic semimetals form an attractive class of materials because of the nontrivial contributions of itinerant electrons to magnetism. Because of their relatively low-carrier-density nature, a doping level of those materials could be largely tuned by a gating technique. Here, we demonstrate gate-tunable ferromagnetism in an emergent van der Waals magnetic semimetal Cr₃Te₄ based on an ion-gating technique. Upon doping electrons into the system, the Curie temperature (<i>T</i