Structural and chemical analysis of gadolinium halides encapsulated within WS2 nanotubes

Picoperovskites: The Smallest Conceivable Isolated Halide Perovskite Structures Formed within Carbon Nanotubes

Halide perovskite structures are revolutionizing the design of optoelectronic materials, including solar cells, light-emitting diodes, and photovoltaics when formed at the quantum scale. Four isolated sub-nanometer, or picoscale, halide perovskite structures formed inside ≈1.2-1.6 nm single-walled carbon nanotubes (SWCNTs) by melt insertion from CsPbBr₃ and lead-free CsSnI₃ are reported. Three directly relate to the ABX₃ perovskite archetype while a fourth is a perovskite-like lamellar structure with alternating Cs₄ and polyhedral Sn₄ I_x layers. In ≈1.4 nm-diameter SWCNTs, CsPbBr₃ forms Cs₃ Pb^II Br₅ nanowires, one ABX₃ unit cell in cross section with the Pb²⁺ oxidation state maintained by ordered Cs⁺ vacancies. Within ≈1.2 nm-diameter SWCNTs, CsPbBr₃ and CsSnI₃ form inorganic-polymer-like bilayer structures, one-fourth of an ABX₃ unit cell in cross section with systematically reproduced ABX₃ stoichiometry. Producing these smallest halide perovskite structures at their absolute synthetic cross-sectional limit enables quantum confinement effects with first-principles calculations demonstrating bandgap widening compared to corresponding bulk structural forms.

Synthesis and characterization of quaternary La(Sr)S-TaS2 misfit-layered nanotubes

Misfit-layered compounds (MLCs) are formed by the combination of different lattices and exhibit intriguing structural and morphological characteristics. MLC Sr x La1- x S-TaS2 nanotubes with varying Sr composition (10, 20, 40, and 60 Sr atom %, corresponding to x = 0.1, 0.2, 0.4 and 0.6, respectively) were prepared in the present study and systematically investigated using a combination of high-resolution electron microscopy and spectroscopy. These studies enable detailed insight into the structural aspects of these phases to be gained at the atomic scale. The addition of Sr had a significant impact on the formation of the nanotubes with higher Sr content, leading to a decrease in the yield of the nanotubes. This trend can be attributed to the reduced charge transfer between the rare earth/S unit (La x Sr1- x S) and the TaS2 layer in the MLC which destabilizes the MLC lattice. The influence of varying the Sr content in the nanotubes was systematically studied using Raman spectroscopy. Density functional theory calculations were carried out to support the experimental observations.

Metal fluoride nanotubes featuring square-planar building blocks in a high-pressure polymorph of AgF2

At a pressure of ca. 15 GPa, AgF₂ transforms to an unprecedented orthorhombic polymorph featuring an array of tubular subunits which are built of corner sharing [AgF₄] squares. This seems to be the first type of a metal fluoride nanowire and also the only one showing rigid square planar rather than common hexagonal or octahedral moieties.