The radical-cation salt (DOEO)4[HgBr4] · TCE: Synthesis, structure and conductivity

Crystals of a new radical-cation salt (DOEO)₄[HgBr₄] · TCE (I) (DOEO = (1,4-dioxanediyl-2,3-dithio)ethylenedioxotetrathiafulvalene, TCE = 1,1,2-trichloroethane) were synthesized by electrocrystallization method at constant current (i=5×10^?6 A/cm²). Crystal structure was studied at room (293 K) and low (30 K) temperatures and was found to consist of the radical-cation layers alternating along the z-axis with tetrahedral HgBr ₄ ^2? anions and TCE molecules. The anion is disordered over three positions at room and over two positions at low temperatures with occupancy factors 87, 11, 2 and 98, 2%, respectively. The poorly occupied positions of the anion are overlapped with positions of the TCE molecule disordered over two equally occupied positions. The DOEO ethylene groups disordered at 293 K were found ordered at 30 K. The conductivity of I exhibits the following peculiarity: in a temperature interval of 120–140 K, the temperature dependence of resistivity has a pronounced maximum.     

Anomalously strong relaxation of the polarization of muons in the magnetically ordered and paramagnetic states of the TbMnO<Subscript>3</Subscript> multiferroic

An anomalously strong relaxation of the muon polarization in a magnetically ordered state in the TbMnO₃ multiferroic has been revealed by the method below the μSR Néel temperature (42 K). Such a relaxation is due to the muon channel of relaxation of the polarization and the interaction of the magnetic moment of the muon with inhomogeneities of the internal magnetic field of an ordered state in the form of a cycloid. Above the Néel temperature, beginning with temperatures depending on the applied magnetic field, a two-phase state has been revealed where one phase has an anomalously strong relaxation of the muon polarization for a paramagnetic state. These features of the paramagnetic state are due to short-range magnetic order domains that appear in strongly frustrated TbMnO₃. A true paramagnetic state has been observed only at T ≥ 150 K.     

Gallium vacancy ordering in Ga<Subscript>2</Subscript>Se<Subscript>3</Subscript> thin layers on Si(100), Si(111), and Si(123) substrates

Thin Ga₂Se₃ layers deposited on silicon substrates with the (100), (111), and (123) orientations are studied by transmission electron microscopy and X-ray microanalysis. Some features and regularities of the stoichiometric gallium vacancy ordering at different substrate orientations are discussed. The Ga₃Se₄(100)с(2 × 2) and Ga₂Se₃(111)(√3 × √3)-R30° ordered structures are formed on the Si(100) and Si(111) surfaces, respectively.     

The Modern Problems of Ultrafast Magnetoacoustics (Review)

Acoustical Physics - A review of modern lines of research in the field of ultrafast magnetoacoustics is presented. Effects of interaction of ultrashort (picosecond) acoustic pulses with a magnetic...     

Regiospecific plasmonic assemblies for in situ Raman spectroscopy in live cells

Multiple properties of plasmonic assemblies are determined by their geometrical organization. While high degree of complexity was achieved for plasmonic superstructures based on nanoparticles (NPs), little is known about the stable and structurally reproducible plasmonic assemblies made up from geometrically diverse plasmonic building blocks. Among other possibilities, they open the door for the preparation of regiospecific isomers of nanoscale assemblies significant both from a fundamental point of view and optical applications. Here, we present a synthetic method for complex assemblies from NPs and nanorods (NRs) based on selective modification of NRs with DNA oligomers. Three types of assemblies denoted as End, Side, and Satellite isomers that display distinct elements of regiospecificity were prepared with the yield exceeding 85%. Multiple experimental methods independently verify various structural features, uniformity, and stability of the prepared assemblies. The presence of interparticle gaps with finely controlled geometrical parameters and inherently small size comparable with those of cellular organelles fomented their study as intracellular probes. Against initial expectations, SERS intensity for End, Side, and Satellite isomers was found to be dependent primarily on the number of the NPs in the superstructures rationalized with the help of electrical field simulations. Incubation of the label-free NP-NR assemblies with HeLa cells indicated sufficient field enhancement to detect structural lipids of mitochondria and potentially small metabolites. This provided the first proof-of-concept data for the possibility of real-time probing of the local organelle environment in live cells. Further studies should include structural optimization of the assemblies for multitarget monitoring of metabolic activity and further increase in complexity for applications in transformative optics.     

Self-assembly of chiral nanoparticle pyramids with strong r/s optical activity

Chirality at the nanometer scale represents one of the most rapidly developing areas of research. Self-assembly of DNA-nanoparticle (NP) hybrids enables geometrically precise assembly of chiral isomers. The concept of a discrete chiral nanostructure of tetrahedral shape and topology fabricated from four different NPs located in the corners of the pyramid is fundamental to the field. While the first observations of optical activity of mixed pyramidal assemblies were made in 2009 ( Chen , W. ; Nano Lett. 2009 , 9 , 2153 - 2159 ), further studies are difficult without finely resolved optical data for precisely organized NP pyramidal enantiomers. Here we describe the preparation of a family of self-assembled chiral pyramids made from multiple metal and/or semiconductor NPs with a yield as high as 80%. Purposefully made R- and S-enantiomers of chiral pyramids with four different NPs from three different materials displayed strong chiroptical activity, with anisotropy g-factors as high as 1.9 × 10(-2) in the visible spectral range. Importantly, all NP constituents contribute to the chiroptical activity of the R/S pyramids. We were able to observe three different circular dichroism signals in the range of 350-550 nm simultaneously. They correspond to the plasmonic oscillations of gold, silver, and bandgap transitions of quantum dots. Tunability of chiroptical bands related to these transitions is essential from fundamental and practical points of view. The predictability of optical properties of pyramids, the simplicity of their self-assembly in comparison with lithography, and the possibility for polymerase chain reaction-based automation of their synthesis are expected to facilitate their future applications.     

Relationships between the magnetic structure parity of an easy-axis antiferromagnet and the refraction mode of electromagnetic waves of the TM and TE types

The role of antisymmetry in the refraction processes of electromagnetic waves of the TM and TE type that recede from nonmagnetic media at an arbitrary angle on the surface of a compensated antiferromagnet for a longitudinal magnetooptical configuration is examined.     

Two types of charge carrier localization centers in (DOEO)4[HgBr4] · TCE single crystals

Using ESR spectroscopy, it has been found that the additional paramagnetic centers appear in the (DOEO)₄[HgBr₄] · TCE crystals at temperatures of 5?C70 K. The symmetry of their crystal field differs from that observed for charge carriers in a temperature range of 70?C300 K. The comparison of the temperature dependences of resistivity with parameters of the ESR spectra makes it possible to assume that the carriers localize at two types of sites differing by the crystalline surrounding at 70 K.     

Rheological properties and the mechanism of a viscous flow of aqueous pectin solutions

The rheological properties and mechanisms of a viscous flow of diluted apple pectin solutions are investigated. It is found that the rise in solution viscosity upon an increase in concentration and a drop in temperature is, along with the corresponding degree to which the interaction between pectin molecules and solvent is reduced, associated with the processes of structuring. The entropy of a viscous flow of pectin solutions is found to be positive: it grows with a rise in concentration is virtually temperature independent. It is established that the entropy factor makes the main contribution to the free energy value of a viscous flow.     

Influence of Packing of Radical Cations on the Conductivity of the New Molecular Semiconductor (Doet)2ReO4

A new molecular semiconductor, (Doet)₂ReO₄(Doet is (1,4-dioxanediyl-2,3-dithio)ethylenedithiotetrathiafulvalene), is synthesized and examined by X-ray diffraction analysis. The crystal structure of (Doet)₂ReO₄is formed by [Doet]^+1/2layers with isle [ReO₄]^–anions located between them. The Doet radical cations from the adjacent layers are linked by intermolecular hydrogen interactions of the O···H type.