The relationship between growth kinetic and photocatalysis of SrTiO 3 nanoparticles is investigated by close correlation of their growth behaviors under the different stages. The detailed structural characterizations show that SrTiO 3 crystal growth does not follow the classic route. A new growth mechanism, including the first formation of SrTiO 3 mesoporous sphere followed by the single crystal growth via oriented attachment, size shrinking, and Ostwald ripening, is proposed. The photocatalytic ability of the as-grown SrTiO 3 products at different growth stages, checked by the degradation of methyl orange, shows different properties. The results indicate that the size, morphology, and defects of the resultant SrTiO 3 products, tailored during the different growth stages, were highly responsible for the photocatalytic activity. Especially, the semicrystalline SrTiO 3 mesoporous spheres produced by oriented attachment at the initial stage show the highest photocatalytic ability.

Recently, the issue of ferromagnetism enhancement in two-dimensional (2D) van der Waals (vdW) layered magnetic systems has been highly concerned. It is believed that ion intercalation in vdW layered ferromagnets, targeting either enhanced interlayer spin exchanges or intralayer ones, can be an efficient scheme. In this work, by means of the first-principles calculations, we investigate the Li-ion intercalation between the two monolayers of the ferromagnetic (FM) vdW Fe3GeTe2 (FGT) bilayer and its impact on the ferromagnetism. It is revealed that the Li-ion intercalation provides hopping carriers between the two interfacial Te sublayers, beneficial for the enhancement of the interlayer FM coupling at a relatively low intercalation level. On the other hand, the Li-ion intercalation lifted Fermi level promotes the electron transfer from the minority spin channel to the majority one for the Fe-3d bands, favoring the stronger intralayer FM coupling. However, the over-intercalation generated carriers may fill up the majority spin channel, reversely leading to the reduced interlayer FM coupling. Consequently, an optimized intercalation level is expected in terms of ferromagnetism enhancement. This work not only helps to explain the recent experimental finding on the gate-controlled Li-ion intercalation in vdW FGT few-layers but also suggests a general scheme for ferromagnetism enhancement in 2D vdW layered ferromagnets using the ion intercalation approach.

Two-dimensional (2D) ferroelectrics refer to those ferroelectrics with layered structure and weak interlayer interactions (e.g., van de Waals interlayer coupling). A number of basic physical issues in the framework of ferroelectricity deserve clarifications, and one of them is the size effect regarding the dependence of ferroelectricity on material thickness. In this work, we investigate the ferroelectric domain structures of 2D ferroelectric CuInP2S6 nanoflakes attached on heavily doped Si wafers and polarization switching using the piezoresponse force microscopy. While the domain structure shows highly irregular morphology and 180° domain walls, the statistics on domain size (diameter) W and nanoflake thickness d demonstrates the remarkable thickness dependence of domain size, illustrated by the shrinking domain size from 630 nm to 75 nm with decreasing thickness d from ∼130 nm to ∼11 nm. This dependence fits the Landau-Lifshitz-Kittel (LLK) scaling law with the scaling exponent of ∼0.65, slightly larger than 0.5 for 3D ferroelectrics. It is suggested that the size effect in terms of the LLK scaling law does not show an essential difference between the 2D and 3D ferroelectric systems.

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Recently, two-dimensional van der Waals ferroelectrics have been receiving much interest with continuous exploration of the underlying physics and device applications. While α-In2Se3 in an atomically thin crystal form is believed to have nonzero out-of-plane polarization, its ferroelectric (FE) instability in competition with the antiferroelectric (AFE) ground state is highly concerned. Along this line, a bilayer α-In2Se3 structure should be a good object for clarifying this issue since it is the simplest 2D lattice accommodating an AFE state, possibly allowing the AFE–FE competition. In this work, we employ the first-principles calculation to investigate the lattice and electronic structures of bilayer α-In2Se3, and special attention is paid to the FE instability in competition with the AFE ground state. It is found that the energy difference between the AFE ground state and FE state is small, thereby allowing an electric field modulation of the AFE–FE inter-conversion. More importantly, the Hyed–Scuseria–Ernzerhof algorithm predicts that the FE state is indeed semiconducting rather than metallic, removing the inconsistency between experimental observation and theoretical prediction. The spin–orbital coupling effect can further enlarge the bandgap and drive the indirect-to-direct bandgap transition, and thus appears to be an important ingredient of the underlying physics.