arXiv subjects

Takuro Nagai

Publications and source records attributed to Takuro Nagai.

3 recordsLinked to original sources

arXiv2025

Scalable alloy-based sputtering of high-conductivity PdCoO$_2$ for advanced interconnects

As integrated circuits continue to scale down, the search for new metals is becoming increasingly important due to the rising resistivity of traditional copper-based interconnects. A layered oxide PdCoO$_2$ is one of the candidate materials for interconnects, having bulk ab-plane conductivity exceeding that of elemental Al. Despite its potential, wafer-scale vacuum deposition of PdCoO$_2$, crucial for interconnect applications, has not yet been reported. In this study, we succeeded in the scalable growth of c-axis oriented PdCoO$_2$ thin films via reactive sputtering from Pd-Co alloy targets. Our method paves the way to harness the unique properties of PdCoO$_2$ in semiconductor devices.

cond-mat.mtrl-sci↗

arXiv2025

Atomic-Scale Observation of Moire potential in Twisted Hexagonal Boron Nitride Layers by Electron Microscopy

Moire superlattices (MSLs) are an emerging class of two-dimensional functional materials whose electronic states can be tuned by the twist angle between two van der Waals layers and/or the relative placement of the layers. The intriguing properties of MSLs are closely correlated to the moiré potential, which is the electrostatic potential induced by interlayer coupling. Intensive efforts have been made to understand the nature and distribution of the moire potential by using various experimental and theoretical techniques. However, the experimental observation of the moiré potential is still challenging because of the possible presence of the surface and/or interlayer contaminants. In this work, we develop a method to obtain hexagonal boron nitride (hBN) nanolayers (with or without twist) using a specially designed chemical exfoliation technique. The resulting hBN nanolayers are atomically clean and strain free, hence providing ideal MSLs for the investigation of their moiré potential. Aberration-corrected high resolution transmission electron microscopy measurements on the twisted hBN nanolayers allow us to observe moiré diffraction spots in Fourier space. Then, the moire potential is reconstructed by the inverse fast Fourier transform of the moire diffraction spots. It has been revealed that the local interlayer atomic overlap plays a decisive role in determining the periodicity and distribution of the moiré potential, as supported by density functional theory calculations. This work not only provides a general strategy to observe the moire potential in MSLs, but it also expands the application of electron microscopy to the further study of MSLs with atomic resolution.

cond-mat.mtrl-sci↗

arXiv2021

Tunable Néel-Bloch magnetic twists in Fe3GeTe2 with van der Waals structure

The advent of ferromagnetism in two-dimensional (2D) van der Waals (vdW) magnets has stimulated high interest in exploring topological magnetic textures, such as skyrmions for use in future skyrmion-based spintronic devices. To engineer skyrmions in vdW magnets by transforming Bloch-type magnetic bubbles into Néel-type skyrmions, the heterostructure of heavy metal/vdW magnetic thin film has been made to induce interfacial Dzyaloshinskii-Moriya interaction (DMI). However, the unambiguous identification of the magnetic textures inherent to vdW magnets, e.g., whether the magnetic twists (skyrmions/domain walls) are Néel- or Bloch-type, is unclear. Here we demonstrate that the Néel- or Bloch-type magnetic twists can be tuned in the vdW magnet Fe3GeTe2 (FGT) with/without interfacial DMI. We use an in-plane magnetic field to align the modulation wavevector q of the magnetizations in order to distinguish the Néel- or Bloch-type magnetic twists. We observe that q is perpendicular to the in-plane field in the heterostructure (Pt/oxidized-FGT/FGT/oxidized-FGT), while q aligns at a rotated angle with respect to the field direction in the thin plate by thinning bulk FGT. We find that the aligned domain wall twists hold fan-like modulations, coinciding qualitatively with our computational results.

cond-mat.mtrl-sci↗