Tribology is an interdisciplinary field related to the science and technology of friction, wear, and lubrication, and is expected to contribute to the realization of a carbon-neutral society. Recent advances in tribology are largely due to dramatic advances in nanotechnology and surface science. Recent topics are introduced along with the history of tribology.

Faceted macrostep formed at equilibrium is demonstrated based on numerical calculations using the tensor network method and the Monte Carlo method. The adopted model is a lattice model where the surface roughness excitations and the step-step attractive energy (ε_int) are taken into consideration. We calculated ε_int–T and p–T faceting diagrams for faceted macrosteps where T is the temperature, and p is the surface slope for an inclined surface. Applying the faceting diagrams to Si(113)＋(114) surfaces, the step-step attractive energy is approximately 123 meV. We also discuss elementary step attachment/detachment processes to/from the faceted macrostep near equilibrium.

In this article, we discuss applications of topology to materials science. We explain how topology is used to express the structure and shape of materials. The structure of a multicyclic polymer is described by applying graph theory and the 3-dimensional shape is described by applying knot theory. Polycontinuous patterns of microphase separation of a block copolymer melt can be analyzed by applying the 3-dimensional topology. We also discuss the topological structures of interlocking molecules composed of metal-peptide rings using the concept of polyhedral links.

Organometal halide perovskites have captured wide interest as a promising material for light-weight and high-efficiency solar cells. Through recent studies of the organometal halide perovskite solar cells (PSCs), the composition of organometal halide perovskites is recognized as one of the key factors in the improvement of the PCE. In this study, we investigated mixed cation perovskite absorber. Additionally, we successfully constructed monolithic PSC mini-module without I-V hysteresis. In the case of MA-free PSCs, the 24.9% PCE (0.187 cm²) and 21.6% PCE (2.76 cm² monolithic PSC mini-module) were obtained, respectively. We also developed semitransparent perovskite top cells with higher durability and transmittance for tandem solar cells. The PCEs of 19.5% (certified 19.3%) and 26.2% were achieved for a 1 cm² semi-transparent perovskite top cell and four-terminal PSC/CIGS tandem solar cells, respectively.

It has been reported that the introduction of ferromagnetism by various ways into topological insulators (TIs) can induce concerted effects, resulting in various novel magnetic phenomena such as quantum anomalous Hall effect and skyrmions. In addition, recently, efforts to increase the observation temperature of quantum phenomena by enhancing the crystal quality and improving electronic coherence have been pursued with great enthusiasm. Self-assembled regular alloy crystals such as Mn(Bi,Sb)₂Se(Te)₄ are called “intrinsic” ferromagnetic TIs that have recently attracted much attention, and we have observed skyrmions in sandwich structures based on these crystals. Furthermore, we have newly observed the ferromagnetic proximity effect even at room temperature at the heterojunction interface between Fe and topological crystalline insulator SnTe by polarized neutron reflectometry. As an extension of these efforts, it is hoped that the unique properties of TIs will be utilized to develop next-generation robust devices for such as spintronics and quantum computing.