Layered structures and exfoliated nanosheets have attracted much interest as 2D materials in recent years. In previous studies, layered materials were used as host for the intercalation of guests and precursor for the exfoliation into the nanosheets. Our group has focused on the structural flexibility of layered materials for their functionalization. Layered composites of inorganic hosts and organic guests are used for preparation of the surface-modified nanosheets through the exfoliation in organic dispersion media. Stimuli-responsive color-change properties of layered conjugated polymers are tuned by the intercalation of guest ions and molecules. Moreover, amorphous conjugated polymer networks as amorphous graphene analogues are synthesized by the random copolymerization of conjugated monomers. These flexible layered materials have potentials for extraction of dynamic functions. This account focuses on such layered materials with the structural flexibility and their functions.

  Inorganic nanosheets obtained by exfoliating layered ionic crystals have emerged as versatile platforms for electronics and energy conversion due to their diverse compositions and excellent physicochemical properties. In contrast to the extensive studies on single-anion nanosheets such as oxides, hydroxides, and chalcogenides, the synthesis and characterization of mixed-anion nanosheets remain challenging. In this report, we summarize our recent progress on mixed-anion nanosheets. First, the electronic structures of titanium oxide and nitrogen-doped titanium oxide nanosheets are described. To elucidate the effect of nitrogen incorporation, we developed a new synthetic route to produce nitrogen-doped titanium oxide nanosheets with a high nitrogen content. Next, two kinds of single-crystalline oxyfluoride nanosheets were synthesized by exfoliating layered bismuth oxyfluorides intercalated with nitrate ions. A second harmonic generation measurement revealed that one of the nanosheets possesses a noncentrosymmetric structure. These findings highlight the potential of mixed-anion nanosheets as a promising platform for future materials innovation.

  Chalcogenide materials containing Group 16 elements are promising candidates for next-generation electronic devices. In this article, the growth of chalcogenide thin films by sputtering is introduced. In particular, an amorphous-to-crystalline transformation technique is presented as an effective approach for the growth of two-dimensional layered materials. Sb₂Te₃ is found to serve as a favorable contact electrode material for monolayer MoS₂ channels. Moreover, a metastable GeTe₂ phase is identified as a novel layered material that can be obtained exclusively through amorphous crystallization. This technique is demonstrated to be a versatile and powerful method for creating a variety of highly oriented two-dimensional layered thin films, thereby enabling performance enhancement in future electronic devices.

  High-quality single crystals of van der Waals transition-metal dichalcogenides provide a versatile platform for exploring quantum phenomena that emerge from layered structures, strong spin–orbit coupling, electron correlations, and polymorphism. Recent advances in crystal growth have enabled precise characterization of topological surface states in PdTe₂ and PtSe₂, extremely large magnetoresistance and quantum oscillations in WTe₂, and polymorph-dependent CDW/superconductivity in TaSe₂, and metastable Cr(S,Se)₂ realized by topochemical routes. These examples highlight the key role of crystal development in opening a broad landscape for engineered quantum materials.

  Layered dichalcogenide superconducting single crystals were grown by the flux method using alkali metal chloride flux. Particularly, cesium chloride (CsCl) is a powerful flux for the growth of chalcogenide materials single crystals. In this paper, the focus was on the superconductors of BiS₂-based and misfit layered compounds single crystals. Those grown single crystals were plate-like in shape, with a size of 1-2 mm and a thickness of 10-100 μm. Additionally, the single-crystal growth method using a reduction agent was introduced for the alkali metal intercalated layered dichalcogenide. The alkali metal intercalated into the layered dichalcogenide single crystals was obtained from the flux using Cd metal, which was the reduction agent.

  Layered mixed-anion compounds possess a natural superlattice structure, where layers with significantly different properties are alternately stacked, exhibiting physical properties and functions not found in single anion compounds. On the other hand, the difficulty in synthesizing single crystals has hindered fundamental property evaluations and applications. Single crystals of such structurally complex compounds have been conventionally synthesized using methods like the flux or CVT method, where crystal size, quality, and yield were not always satisfactory. Recently, we discovered that some layered mixed-anion compounds undergo congruent melting though issues of volatilization and multinuclear growth remain. This indicates the potential for high-yield single crystal growth even in multi-component layered compounds. We therefore report on the development of these congruent melting compounds and the growth of single crystals by melt solidification. These compounds enable the growth of large single crystals while possessing low-dimensionality, expected to lead to a fields of “low-dimensional bulk single crystals”.