Creating vertically aligned 2D nanostructures is a promising approach to achieving advanced electronic and optoelectronic materials. In this study, Mg2Si nanosheet bundles were synthesized by Ca atom extraction from CaSi2 microwalls grown on Si substrates via thermal annealing in a MgCl2/Mg mixed vapor. The nanosheet bundle structure was modified to compound nanosheet bundles from previously reported Si nanosheet bundles. The observed Mg2Si nanosheets consist of thin Mg2Si layers, and well-defined fine-scale Mg2Si superlattice-like structures were achieved in the nanosheet bundles. In addition, the Raman scattering and photoluminescence properties were examined, and structural and electronic modifications of the nanosheet bundle compared with the bulk crystals were suggested. To obtain tailored properties and functionalities of the nanosheet bundles, structural modification of layered crystals is a useful technique.

Mg-based silicate nanosheet bundles were synthesized by thermal annealing using CaSi 2 crystal powders and MgCl 2 with the appropriate O 2 and/ or H 2 O content in the atmosphere. The silicate compound nanosheet bundle formation was caused by the nanosheet bundle synthesis by Ca-atom extraction from the CaSi 2 crystal powders followed by Mg incorporation along with the oxidation and/or hydroxidation by employing the topological synthesis technique. The morphological and structural properties of the Mg 2 SiO 4 nanosheet bundles were clarified and the growth mechanism of the silicate nanosheets was discussed. The growth feature of the Mg-silicates and related materials, such as Mg 2 Si, MgO, SiO 2 and magnesium silicate hydroxides, is discussed from thermodynamic points of view. The possible formation of magnesium silicate hydroxides as a flake-like structure is also mentioned.

Si-based nanowire/nanosheet bundle complexes were synthesized from CaSi 2 crystal powders by thermal annealing under MnCl 2 /NH 4 Cl vapors. The formation of the complexes is a result of two processes that simultaneously occurred. One is the nanosheet bundle synthesis by Ca-atom extraction from the CaSi 2 crystals. Another is the growth of the Si nanowires by thermal annealing using MnCl 2 . The mixing of these materials resulted in the successful synthesis of the nanowire/nanosheet bundle complexes. In addition to the formation of the complex, nanotubes were also synthesized by bottom-up nanostructure synthesis technique, which resulted by the thermal annealing of the catalytic Mn-related materials under a higher vapor pressure using NH 4 Cl. The growth mechanism of the nanotubes is discussed based on the inhomogeneous Mn-related catalyst deposition and the surface diffusion of Si atoms.

CaF2 nanostructures were synthesized from Ca-silicide powders by a diluted aqueous HF treatment. Commercially-available CaSi2 crystal powders and calcium silicide powders prepared by mechanical alloying were used as the source materials, and CaF2 nanosheet bundles and nanobunches of the CaF2 nanoparticles were obtained, respectively. The morphological property of the resulting CaF2 nanostructures was characterized by electron microscopy. It was found that the morphology of the resulting products depended on the starting materials. In addition, the growth mechanism of the CaF2 nanostructures was discussed from a topological synthesis point of view.

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