arXiv subjects

Yoshikazu Ito

Publications and source records attributed to Yoshikazu Ito.

6 recordsLinked to original sources

arXiv2026

A depth resolved investigation of hydrogen uptake in carbon based nanostructures by soft-to-hard photoemission spectroscopy

Hydrogen chemisorption on graphitic carbon modifies the carbon orbital hybridization from sp2 to sp3, altering both structural and electronic properties. Understanding not only the lateral extent but also the depth distribution of hydrogen uptake in three-dimensional carbon architectures is essential for both fundamental studies and storage applications. To this end, we investigate here the evolution of the C 1s core-level lineshape in nanoporous graphene (NPG) and vertically aligned carbon nanotubes (CNTs) upon hydrogenation, exploiting soft-to-hard X-ray photoemission spectroscopy to achieve a depth-resolved analysis. Decomposition of the C 1s spectra reveals the formation of an sp3 rich overlayer, indicating hydrogen chemisorption limited to the outermost accessible surfaces in both systems. These results clarify the depth distribution of hydrogen in curved and porous graphitic networks and provide quantitative constraints on its chemisorption for carbon-based hydrogen storage applications.

cond-mat.mtrl-sci↗

arXiv2026

Insulating Electronic States Near the Dirac Point Arising from Twisted Stacking and Curvature in 3D Nanoporous Graphene

Twist-stacked graphene with a twist angle $θ$ of $\sim 5^\circ$--$30^\circ$ retains two-dimensional monolayer graphene-like Dirac states near the Dirac point. In three-dimensional nanoporous graphene (3D-NPG), curvature inherently produces twist-stacking and topological defects required to form a porous network. When regions with $θ\ge 5^\circ$ dominate, Dirac states in individual layers are expected to persist, allowing the Dirac-electron behavior to be tuned through coupling to the 3D curved geometry. However, predicted band gap formation or localized states have remained unobserved. Here we report that 3D-NPG maintains monolayer-like Dirac electronic states while simultaneously exhibiting insulating behavior near the Dirac point. Raman G-band softening confirms these monolayer-like states, and an Arrhenius-type temperature-resistance trend coexisting with weak localization near the Dirac point indicates partially insulating states induced by topological defects. These findings demonstrate that 3D-NPG hosts distinctive Dirac electronic states coupled to 3D curvature, providing a platform for developing new functionalities in 3D graphene-based electronics and energy devices.

cond-mat.mes-hall↗

arXiv2020

Dirac Fermion kinetics in three-dimensionally curved graphene

Three dimensionally curved graphene with a wide range of curvature radii from 25 nm to 1000 nm demonstrates that nano-scale curvature is a new degree of freedom to tune the transport properties of graphene by manipulating 2D electron kinetics on 3D curved surfaces.

cond-mat.mes-hall↗

arXiv2020

Topological effects of three-dimensional porous graphene on Dirac quasiparticles

This paper reports on the topological effects of three-dimensional (3D) porous graphene with tunable pore sizes and a preserved 2D graphene system of Dirac quasiparticles on its electrical properties. This 3D architecture is characterized by the intrinsic curvature of smoothly interconcnected graphene sheets without edges, the structures and properties of which can be controlled with its pore sizes. The impact of pore size on the electrical transport properties was investigated through magnetoresistance measurements. We observed that 3D graphene with small pores exhibits transitioning to weak localization with decreasing temperature. The comparison with the theory based on the quantum correction clarified that an increase in the intrinsic curvature significantly induces the intervalley scattering event, which breaks the chirality. This increase in the intervalley scattering rate originates from the unique topological effects of 3D graphene, i.e., the topological defects required to form the high curvature and the resulting chirality mixing. We also discuss the scattering processes due to microscopic chemical bonding states as found by high spatial-resolved X-ray photoemission spectral imaging, to support the validity of our finding.

cond-mat.mtrl-sci↗

arXiv2017

Three-dimensional porous graphene networks expand graphene-based electronic device applications

Graphene with excellent 2D characters has been required to expand their potentials for meeting applicational demands in recent years. As one avenue, several approaches for fablicating 3D porous graphene network structures have been developed to realize multi-functional graphene materials with 2D graphene. Here we overview characteristics of 3D porous graphene for future electronic device applications along with physical insights into "2D to 3D graphene", where the characters of 2D graphene such as massless Dirac fermions are well preserved. The present review thus summarizes recent 3D porous graphene studies with a perspective for providing new and board graphene electronic device applications.

cond-mat.mtrl-sci↗

arXiv2016

Electric Properties of Dirac Fermions Captured into 3D Nanoporous Graphene Networks

Graphene, as a promising material of post-silicon electronics, opens a new paradigm for the novel electronic properties and device applications. On the other hand, the 2D feature of graphene makes it technically challenging to be integrated into 3D transistors with a sufficient processor capacity. Although there are many attempts to assemble 2D graphene into 3D structures, the characteristics of massless Dirac fermions cannot be well preserved in these materials for transistor applications. Here we report a high-performance graphene transistor by utilizing 3D nanoporous graphene which is comprised of an interconnected single graphene sheet and a commodious open porosity to infuse an ionic liquid for a tunable electronic state by applying electric fields. The 3D nanoporous graphene transistor, with high carrier mobility of 5000-7500 cm$^2$V$^{-1}$s$^{-1}$, exhibits two to three orders of magnitude higher electric conductance and capacitance than those of 2D graphene devices, along with preserved ambipolor electronic nature of Dirac cones. Moreover, the 3D graphene networks with Dirac fermions turn out to exhibit a unique nonlinear Hall resistance in a wide range of the gate voltages. The high quality 3D nanoporous graphene EDLT may open a new field for utilizing Dirac fermions in 3D network structures for various fundamental and practical applications.

cond-mat.mtrl-sci↗