We report on the electronic properties of straight, 1.6 nm wide, silicene nanoribbons on Ag(110), arranged in a one-dimensional grating with a pitch of 2 nm, whose high-resolution scanning tunneling microscopy images reveal a honeycomb geometry. Angle-resolved photoemission shows quantum confined electronic states of one-dimensional character. The silicon band dispersion along the direction of the nanoribbons suggests a behavior analogous to the Dirac cones of graphene on different substrates.

Topological nodal line semimetals, a novel quantum state of materials, possess topologically nontrivial valence and conduction bands that touch at a line near the Fermi level. The exotic band structure can lead to various novel properties, such as long-range Coulomb interaction and flat Landau levels. Recently, topological nodal lines have been observed in several bulk materials, such as PtSn₄, ZrSiS, TlTaSe₂ and PbTaSe₂. However, in two-dimensional materials, experimental research on nodal line fermions is still lacking. Here, we report the discovery of two-dimensional Dirac nodal line fermions in monolayer Cu₂Si based on combined theoretical calculations and angle-resolved photoemission spectroscopy measurements. The Dirac nodal lines in Cu₂Si form two concentric loops centred around the Γ point and are protected by mirror reflection symmetry. Our results establish Cu₂Si as a platform to study the novel physical properties in two-dimensional Dirac materials and provide opportunities to realize high-speed low-dissipation devices.

We present a new method to engineer the charge carrier mobility and its directional asymmetry in epitaxial graphene by using metal cluster superlattices self-assembled onto the moir\'e pattern formed by graphene on Ir(111). Angle-resolved photoemission spectroscopy reveals threefold symmetry in the band structure associated with strong renormalization of the electron group velocity close to the Dirac point giving rise to highly anisotropic Dirac cones. We further find that the cluster superlattice also affects the spectral-weight distribution of the carbon bands as well as the electronic gaps between graphene states.

Nanostructured TiO₂ is one of the best materials for photocatalysis, thanks to its high surface area and surface reactivity, but its large energy bandgap (3.2 eV) hinders the use of the entire solar spectrum. Here, it is proposed that defect‐engineered nanostructured TiO₂ photocatalysts are obtained by hydrogenation strategy to extend its light absorption up to the near‐infrared region. It is demonstrated that hydrogenated or colored TiO₂ hollow spheres (THS) composed of hierarchically assembled nanoparticles result in much broader exploitation of the solar spectrum (up to 1200 nm) and the engineered surface enhances the photogeneration of charges for photocatalytic processes. In turn, when applied for photodegradation of a targeted drug (Ciprofloxacin) this results in 82% degradation after 6 h under simulated sunlight. Valence band analysis by photoelectron spectroscopy revealed the presence of oxygen vacancies, whose surface density increases with the hydrogenation rate. Thus, a tight correlation between degree of hydrogenation and photocatalytic activity is directly established. Further insight comes from electron paramagnetic resonance, which evidences bulk Ti³⁺ centers only in hydrogenated THS. The results are anticipated to disclose a new path toward highly efficient photocatalytic titania in a series of applications targeting water remediation and solar fuel production.

The authors perform a systematic ARPES and first-principles study of the origin of silicene/Ag(111) electronic states and find that the first layer has sigma bands but no $$\pi${}$ bands.