This special issue highlights the activities of the Division of Young Researchers of the Japan Society of Vacuum and Surface Science. The division now actively promotes interdisciplinary exchange through annual workshops and publications. Recent efforts include an online school and a joint symposium with the Kanto Branch. This issue features contributions from emerging researchers and personal accounts on topics such as research transitions and international experience.

We demonstrate that single- and double-bilayer antimony honeycomb lattices (antimonene) form moiré superlattices on a Bi(111) substrate due to lattice mismatch. Scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES), combined with density functional theory (DFT) calculations, reveal that the surface band structure features saddle points near the Fermi level, leading to van Hove singularities. Furthermore, spin-resolved ARPES measurements show that the observed surface states are Rashba-type spin-polarized, similar to those in Bi(111). These properties offer fascinating implications for the possible coexistence of strong electron correlations and topologically protected electronic states.

Photocatalysis enables redox reactions to proceed non-thermally under ambient conditions, offering a low-energy alternative to conventional thermocatalytic processes. Traditionally, it has been assumed that oxidation occurs exclusively at the semiconductor surface via photogenerated holes, while reduction takes place on metal cocatalysts that capture photogenerated electrons. However, the absence of microscopic insights into the detailed reaction mechanism has hindered rational design of catalysts. To address this, we employed kinetic analysis and operando infrared spectroscopy to directly monitor reactive species under reaction conditions. Our investigations reveal that metal cocatalysts also play a crucial role in oxidation by interacting with photogenerated holes, contrary to traditional understanding. Moreover, the reactive electrons are not located within the metal cocatalysts but are shallowly trapped in in-gap states of the semiconductor surface at their periphery. These findings redefine the concept of catalytic active sites and provide a basis for designing more efficient photocatalytic systems.

Metal surfaces provide unique reaction fields where molecules can exhibit behaviors unattainable in isolation. To elucidate such behaviors, we have proposed a localized theoretical framework that treats adsorbed molecules as open quantum subsystems. Within this framework, we have constructed an effective Hamiltonian incorporating resonance lifetimes via complex energy eigenvalues, which is realized through our open-boundary cluster model (OCM). This model captures surface photodynamics by eliminating artificial level repulsions present in isolated conventional cluster models. We demonstrate that OCM-derived excited-state potential energy surfaces naturally describe ultrafast electron transfer and wavepacket dynamics following photoexcitation. Furthermore, we investigate plasmon–molecule strong coupling on metal nanoparticles, showing that even in the absence of light, localized surface plasmons can reshape molecular potential energy surfaces and reduce the photon energy required for photodissociation. Through these studies, we aim to illuminate the complex and surprising behavior of molecules at metal interfaces.

Lightwave-driven scanning tunneling microscopy (STM) that controls tunneling current by electric field of light has attracted much attention to study ultrafast surface phenomena. We generated broadband mid-infrared pulses and combined them to STM. We achieved fastest temporal resolution of 29 fs in lightwave-driven STM. This technique is expected to be a new way to reveal non-equilibrium electronic states in atomic scale.

The origin of the characteristic overpotentials for electrochemical deposition of metals in ionic liquids are discussed with the viewpoint of the role of the interfacial structure of ionic liquids on electrodes. For this purpose, we developed a novel method for deriving interfacial information by using surface-enhanced infrared absorption spectroscopy (SEIRAS) even under electrochemical deposition that modifies the substrate structure. In-situ interfacial measurement by using this method revealed that onset potential of Co electrodeposition is identical to that for the anion-cation replacement in the first ionic layer on the electrode. This can be explained by including interfacial charge-ordered structure into Marcus theory.