Hexagonal phase

About: Hexagonal phase is a research topic. Over the lifetime, 3847 publications have been published within this topic receiving 101779 citations.

An inverted hexagonal phase of cationic liposome-DNA complexes related to DNA release and delivery

Abstract: A two-dimensional columnar phase in mixtures of DNA complexed with cationic liposomes has been found in the lipid composition regime known to be significantly more efficient at transfecting mammalian cells in culture compared to the lamellar (LalphaC) structure of cationic liposome-DNA complexes. The structure, derived from synchrotron x-ray diffraction, consists of DNA coated by cationic lipid monolayers and arranged on a two-dimensional hexagonal lattice (HIIC). Two membrane-altering pathways induce the LalphaC --> HIIC transition: one where the spontaneous curvature of the lipid monolayer is driven negative, and another where the membrane bending rigidity is lowered with a new class of helper-lipids. Optical microscopy revealed that the LalphaC complexes bind stably to anionic vesicles (models of cellular membranes), whereas the more transfectant HIIC complexes are unstable and rapidly fuse and release DNA upon adhering to anionic vesicles.

Hexagonal Sodium Yttrium Fluoride Based Green and Blue Emitting Upconversion Phosphors

Abstract: Hexagonal sodium yttrium fluoride, NaYF4, is the most efficient host material to date for green (Yb3+/Er3+ doped) and blue (Yb3+/Tm3+ doped) upconversion (UC) phosphors, i.e., phosphors which emit visible light upon infrared (IR) excitation. The structure of the hexagonal phase gives rise to controversy about the cation sites and distribution. The X-ray diffraction patterns of our phosphors do not fit well with the crystal structure reported for NaNdF4 (space group P6, Z = 1.5). The Na:M ratio (M = Y, Nd, Er, Tm, Yb) of the hexagonal phase deviates significantly from 1:1, and it depends on M and the preparation temperature. It is proposed that the hexagonal phase is isostructural to the chlorides Na3xM2-xCl6 with M = La−Sm. This structure (space group P63/m, Z = 1) contains only one M3+ site which is partially occupied by Na+, and the formula Na3xM2-xF6 (x ≈ 0.45) accounts for the nonstoichiometry. The model was derived from powder X-ray diffraction on the green and blue phosphor materials as well as the...

Estimation of lattice strain in zno nanoparticles: x-ray peak profile analysis

Abstract: ZnO nanoparticles were synthesized from chitosan and zinc chloride by a precipitation method. The synthesized ZnO nanoparticles were characterized by Fourier transform infrared spectroscopy, X-ray diffraction peak profile analysis, Scanning electron microscopy, Transmission electron microscopy and Photoluminescence. The X-ray diffraction results revealed that the sample was crystalline with a hexagonal wurtzite phase. We have investigated the crystallite development in ZnO nanoparticles by X-ray peak profile analysis. The Williamson–Hall analysis and size–strain plot were used to study the individual contributions of crystallite sizes and lattice strain ϵ on the peak broadening of ZnO nanoparticles. The parameters including strain, stress and energy density value were calculated for all the reflection peaks of X-ray diffraction corresponding to wurtzite hexagonal phase of ZnO lying in the range 20°–80° using the modified form of Williamson–Hall plots and size–strain plot. The results showed that the crystallite size estimated from Scherrer’s formula, Williamson–Hall plots and size–strain plot, and the particle size estimated from Transmission electron microscopy analysis are very much inter-correlated. Both methods, the X-ray diffraction and Transmission electron microscopy, provide less deviation between crystallite size and particle size in the present case.

Bandgap opening in few-layered monoclinic MoTe 2

Abstract: Monoclinic transition metal dichalcogenides offer the possibility of topological quantum devices, but they are difficult to realize. One route may be through switching from the common hexagonal phase, for which a method is now shown. Layered transition metal dichalcogenides (TMDs) have attracted renewed interest owing to their potential use as two-dimensional components in next-generation devices1,2. Although group 6 TMDs, such as MX2 with M = (Mo, W) and X = (S, Se, Te), can exist in several polymorphs3, most studies have been conducted with the semiconducting hexagonal (2H) phase as other polymorphs often exhibit inhomogeneous formation1,4,5,6. Here, we report a reversible structural phase transition between the hexagonal and stable monoclinic (distorted octahedral or 1T′) phases in bulk single-crystalline MoTe2. Furthermore, an electronic phase transition from semimetallic to semiconducting is shown as 1T′-MoTe2 crystals go from bulk to few-layered. Bulk 1T′-MoTe2 crystals exhibit a maximum carrier mobility of 4,000 cm2 V−1 s−1 and a giant magnetoresistance of 16,000% in a magnetic field of 14 T at 1.8 K. In the few-layered form, 1T′-MoTe2 exhibits a bandgap opening of up to 60 meV, which our density functional theory calculations identify as arising from strong interband spin–orbit coupling. We further clarify that the Peierls distortion is a key mechanism to stabilize the monoclinic structure. This class of semiconducting MoTe2 unlocks the possibility of topological quantum devices based on non-trivial Z2-band-topology quantum spin Hall insulators in monoclinic TMDs (ref. 7).