Engineering topics

Ishigami, Masahiro

Publications and source records attributed to Ishigami, Masahiro.

4 records

DOE OSTI2023

Electronic structure in a transition metal dipnictide TaAs 2

Abstract The family of transition-metal dipnictides has been of theoretical and experimental interest because this family hosts topological states and extremely large magnetoresistance (MR). Recently, T a A s 2 , a member of this family, has been predicted to support a topological crystalline insulating state. Here, by using high-resolution angle-resolved photoemission spectroscopy (ARPES), we reveal both closed and open pockets in the metallic Fermi surface (FS) and linearly dispersive bands on the ( 2 ‾ 01 ) surface, along with the presence of extreme MR observed from magneto-transport measurements. A comparison of the ARPES results with first-principles computations shows that the linearly dispersive bands on the measured surface of T a A s 2 are trivial bulk bands. The absence of symmetry-protected surface state on the ( 2 ‾ 01 ) surface indicates its topologically dark nature. The presence of open FS features suggests that the open-orbit fermiology could contribute to the extremely large MR of T a A s 2 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Autonomous scanning probe microscopy investigations over WS2 and Au{111}

Abstract Individual atomic defects in 2D materials impact their macroscopic functionality. Correlating the interplay is challenging, however, intelligent hyperspectral scanning tunneling spectroscopy (STS) mapping provides a feasible solution to this technically difficult and time consuming problem. Here, dense spectroscopic volume is collected autonomously via Gaussian process regression, where convolutional neural networks are used in tandem for spectral identification. Acquired data enable defect segmentation, and a workflow is provided for machine-driven decision making during experimentation with capability for user customization. We provide a means towards autonomous experimentation for the benefit of both enhanced reproducibility and user-accessibility. Hyperspectral investigations on WS 2 sulfur vacancy sites are explored, which is combined with local density of states confirmation on the Au{111} herringbone reconstruction. Chalcogen vacancies, pristine WS 2 , Au face-centered cubic, and Au hexagonal close-packed regions are examined and detected by machine learning methods to demonstrate the potential of artificial intelligence for hyperspectral STS mapping.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Scanning tunneling microscopy and spectroscopy of NiTe 2

Nickel ditelluride is an unusual member of the transition metal dichalcogenide family which has garnered interest due to potential valley spin-polarized surface states near the Fermi level and the presence of Dirac nodes in its electronic band structure. In this work, exfoliation of bulk nickel ditelluride is performed under ultra-high vacuum in order to generate a clean surface for scanning tunneling microscopy and spectroscopy at 4.8 K. Multiple features in the observed electronic density of states are observed in the vicinity of the Fermi level and compared to calculated band structures to elucidate their origins. Finally, our results are consistent with the presence of the spin-polarized surface states, yet indicate trivial states, which are close to the Fermi level, can interfere with their potential utility in spintronic applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Metallicity of 2H-MoS 2 induced by Au hybridization

Recent studies have shown that MoS 2 can undergo a structural phase transition from the 2H to 1T' phase on Au substrates at moderate temperatures. In this study, we use ultraviolet and x-ray photoelectron spectroscopy, Raman and photoluminescence spectroscopy, and scanning tunneling microscopy/spectroscopy to probe the impact of annealing exfoliated, monolayer MoS 2 on Au. Our results across multiple length scales indicate that 2H-MoS 2 becomes hybridized with Au upon thermal annealing without inducing the 1T' structural phase and the bandgap can be modulated to zero width depending on the degree of hybridization. These results can be used to control the resistance of metal-MoS 2 contacts at the atomic scale without introduction of defects or structural phase transitions and are important for devices such as memristors.

36 MATERIALS SCIENCE↗