Diamond-rich crystalline nanosheets seeded with a Langmuir monolayer of arachidic acid on water.

The enigmatic self-assembling ability of nanodiamond (ND) particles has been discovered herein. Diamond-rich crystalline nanosheets with thickness of approximately ∼25 nm were grown from a Langmuir monolayer of arachidic acid (AA) at the interface between air and a dilute aqueous ND solution. Their fine rectangular shapes with uniform uniaxial birefringence indicate appreciable crystallinity, thus supporting that they are hydrated colloidal crystals of homogeneous ND particles.

Two-Dimensional Layered Organic-Inorganic Hybrid Perovskite Thin-Film Fabrication by Langmuir-Blodgett and Intercalation Techniques.

We demonstrate the formation of a well-organized thin film of two-dimensional (2D) layered (C18H37NH3)2PbI4 hybrid perovskite by immersing octadecyl amine (ODA) Langmuir-Blodgett (LB) films in an aqueous solution of PbI2/HI. The immersed films exhibit a sharp absorption band at 486 nm (2.55 eV), which is assigned to the excitonic absorption. The film exhibits a bright green emission under ultraviolet light at room temperature. The photoluminescence spectrum has a distinct peak at 497 nm (2.49 eV) and is a mirror image of the absorption spectrum. X-ray diffraction (XRD) analyses reveal that the film has a bilayer-like structure with a d-spacing of 6.4 nm, which is equal to that of a (C18H37NH3)2PbI4 perovskite single crystal with a quantum well (QW) structure. Only intense peaks of the (0 0 l) (l = 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24) reflections are observed in the out-of-plane XRD pattern, indicating that the c axis is vertically oriented with respect to the substrate surface, and the orientational order is remarkably high. Fourier transform infrared spectroscopy reveals that the ODA molecules are protonated in the PbI2/HI solution. These results suggest that the nitrogen atoms of the ODA molecules in the film are protonated in the PbI2/HI solution, and then, inorganic layers of the PbI6 octahedra are intercalated in the alkyl ammonium film to neutralize the positive charge and form a QW structure. Fluorescence microscopy observation reveals that the 2D layered (C18H37NH3)2PbI4 film has a relatively uniform surface, reflecting the well-organized layered structure of the base material (ODA LB film). Because the intercalation process can be applied to various metal cations and halogen anions, we believe that the proposed technique will aid in the development of highly efficient 2D layered organic-inorganic hybrid perovskite materials.

Spherulitic Crystallization in Langmuir-Blodgett Films of the Ditetradecyldimethylammonium-Au(dmit)2 Salt.

Spherulitic crystallization in Langmuir-Blodgett (LB) films of the ditetradecyldimethylammonium-Au(dmit)2 [2C14N+Me2-Au(dmit)2] salt has been characterized by polarized light microscopy, Fourier-transform infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD) analyses. Analyses by differential scanning calorimetry (DSC) for the bulk crystals indicate that annealing in the temperature range of 58-100 °C may be appropriate to improve the order in the LB film. The polarized light microscopy measurement further revealed that a spherulite structure was formed after the film was annealed at 80 °C for 60 min. FT-IR spectroscopy measurements demonstrated that the order of the principal hydrocarbon chains was improved and that the rotation of CH3 groups was hindered by the annealing. Out-of-plane XRD analyses revealed that the d-spacing of the 2C14N+Me2-Au(dmit)2 LB film changed from 3.1 to 2.5 nm upon annealing. We hypothesize that a layered structure with interdigitated hydrocarbon chains, which is equivalent to or close to that of the corresponding bulk crystal, has been realized in the LB film by annealing. We consider that two different kinds of one-dimensional (1D) interactions along the a-axis are the driving forces to realize the spherulite structure in the LB system; one is an extended 1D contact due to the pronounced interdigitation of the alkyl chains of the ammonium ion, which plays a role similar to that of the folding of chains in the lamellar structures of polymers, and the other is a 1D extended sulfur-sulfur contact between Au(dmit)2 dimer pairs. So far, spherulite formation in LB films has been reported almost exclusively for polymerized materials. Here, we demonstrate that a spherulite texture can also be formed in LB films based on nonpolymerized materials via the interdigitation of hydrocarbon chains, leading to a new well-ordered state.