Research Highlights

Studying materials with small or powdered crystals has long been a challenge in materials science.

One such example is the layered rhombohedral boron monosulfide (r-BS), whose two-dimensional BS single layers are predicted to exhibit properties such as high hydrogen storage, efficient photocatalysis, and high-T_c superconductivity. However, current fabrication methods can only produce r-BS in the powder single crystal form, making spectroscopic investigations difficult—even for advanced techniques such as microfocused angle-resolved photo-emission spectroscopy (µ-ARPES).

“Technically, the small size of the r-BS grains (< 30 µm) is not a problem for µ-ARPES measurements,” says Katsuaki Sugawara, a member of an ARPES research team at AIMR. “The challenge lies in how to reliably select and expose the ideal grain sample to the microfocused beam.”

In a 2023 article¹, the AIMR team achieved just this by first dispersing r-BS powder onto a Au substrate before cleaving the sample in the ultrahigh-vacuum instrument chamber. The team then used optical microscopy and scanning µ-PES to locate and select the ideal r-BS powder crystals for local ARPES measurements, respectively.

“Our sample-preparation methodology enabled us to make the first high-quality ARPES observation of the r-BS electronic structure; our results show that r-BS may be a semiconductor with a substantial bandgap (> 0.5 eV) and a valence-electron effective mass larger than that of h-BN,” highlights Sugawara.

“As we move on, we will expand this methodology to investigate the band structure and fermiology of a wide variety of powder crystals that have yet to be experimentally probed.”

(Author: Patrick Han)