The division of Young Researchers was established in 2018. This division organizes interdisciplinary workshops in a format that facilitates learning for students and young researchers. In this special issue, the recent research achievements have been introduced by young researchers and lecturers at the previous workshop. The presented topics cover angle-resolved photoemission spectroscopy, water molecule networks on solid surfaces, simulation of laser processing of semiconductors, and in situ observation of electrode surfaces by high-speed atomic force electron microscopy. This special issue also contains an article on how to write a scientific paper.

Quasi-one-dimensional materials offer an ideal playground to investigate weak topological insulators (WTIs) and higher-order topological insulators (HOTIs), since their characteristic boundary states emerge in the naturally cleaved surfaces. Utilizing laser-based angle-resolved photoemission spectroscopy (ARPES) and synchrotron-based nano-ARPES, we show evidence of a WTI phase in β-Bi₄I₄ and a HOTI phase in Bi₄Br₄.

Environmentally sustainable and selective conversion of methane to valuable chemicals under ambient conditions is pivotal for the development of next-generation photocatalytic technology. However, the lack of microscopic knowledge on its reaction mechanism prevents the development of engineering strategies for methane photocatalysis. Here we introduce key molecular-level insights into the photocatalytic green utilization of methane. Activation of the robust C–H bond of methane is hardly induced by the direct interaction with photogenerated holes trapped at the surface of photocatalyst ; instead, the C–H activation is significantly promoted by the photoactivated interfacial water species. The interfacial water hydrates and properly stabilizes hydrocarbon radical intermediates, thereby suppressing their overstabilization. Owing to these water-assisted effects, the photocatalytic conversion rates of methane under wet conditions are dramatically improved by typically more than 30 times at ambient temperatures (～300 K) and pressures (～1 atm) in comparison to those under dry conditions.

Recent developments in the simulations of processing of semiconductors and metals by femto- (10^－15) second pulse laser, especially silicon and aluminum, are presented. Laser processing is a complex process involving nonlinear phenomena. We have developed microscopic first-principles calculations that describe the light-electron interaction, the semiclassical Vlasov equation that can also include relaxation in metal, and a novel temperature model that allows us to study the entire initial processing process. Each method allows us to analyze the entire process from the moment of laser irradiation to the stage of energy transfer to the lattice. This paper describes the details of the methods and the findings obtained from the results.

Dynamic behavior of electrochemical interfacial phenomena is key issue for material science. Scanning probe microscope can observe the surface on the nanoscale, however, it is difficult to discuss the reaction process due to poor temporal resolution. High-speed atomic force microscopy (HS-AFM) is one of powerful in-situ observation tools. Here, we would like to introduce the HS-AFM applications for electrochemistry, such as Cu electrodeposition, polyethylene glycol (PEG) adsorption, and nanobubble electrolytic evolution by HS-AFM.

An attempt is made to visualize hydrogen permeation through vanadium membranes using operando hydrogen microscopy. Prior to visualization, experimental conditions are determined. The vanadium sample surface for hydrogen introduction is coated with Pd-25 mol%Ag alloy. Also, the optimal temperature of the vanadium sample for hydrogen visualization is determined. By optimizing the experimental conditions, some correlation was found between the distribution of permeated hydrogen and the morphology of vanadium particles observed in secondary electron image of scanning electron microscopy.