Background : Alterations in homeostasis after various cellular stresses, which prevent protein folding and cause an accumulation of misfolding or malfolding proteins in the endoplasmic reticulum (ER), have the potential to induce cellular damage, and are therefore a type of 'ER stress.' To understand the molecular events or cascades underlying the ER stress response regulated by gene transcription and mediated by stress transducers, it is crucial to identify the molecules induced during ER stress and to analyse the roles of these genes.
Angle-resolved photoemission spectroscopy using a micro-focused beam spot [micro-angle-resolved photoemission spectroscopy (ARPES)] is becoming a powerful tool to elucidate key electronic states of exotic quantum materials. We have developed a versatile micro-ARPES system based on the synchrotron radiation beam focused with a Kirkpatrick–Baez mirror optics. The mirrors are monolithically installed on a stage, which is driven with five-axis motion, and are vibrationally separated from the ARPES measurement system. Spatial mapping of the Au photolithography pattern on Si signifies the beam spot size of 10 µm (horizontal) × 12 µm (vertical) at the sample position, which is well suited to resolve the fine structure in local electronic states. Utilization of the micro-beam and the high precision sample motion system enables the accurate spatially resolved band-structure mapping, as demonstrated by the observation of a small band anomaly associated with tiny sample bending near the edge of a cleaved topological insulator single crystal.
Boron-based two-dimensional (2D) materials are an excellent
platform
for nanoelectronics applications. Rhombohedral boron monosulfide (r-BS)
is attracting particular attention because of its unique layered crystal
structure suitable for exploring various functional properties originating
in the 2D nature. However, studies to elucidate its fundamental electronic
states have been largely limited because only tiny powdered crystals
were available, hindering a precise investigation by spectroscopy
such as angle-resolved photoemission spectroscopy (ARPES). Here we
report the direct mapping of the band structure with a tiny (∼20
× 20 μm2) r-BS powder crystal by utilizing microfocused
ARPES. We found that r-BS is a p-type semiconductor with a band gap
of >0.5 eV characterized by the anisotropic in-plane effective
mass.
The present results demonstrate the high applicability of micro-ARPES
to tiny powder crystals and widen an opportunity to access the yet-unexplored
electronic states of various novel materials.
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