Half-Metallic Properties of the Mn<Subscript>2</Subscript>Te Telluride by a First-Principles Study

The electronic band structure, magnetic properties, and half-metallic properties of the Mn₂Te compound in the C1_b-type, CaF₂-type, and Ni₂In-type structures have been studied by using the full-potential linearized augmented plane wave (FPLAPW) method within the generalized gradient approximation (GGA). The ferrimagnetic ground state of the Mn₂Te compound is the most stable with the C1_b-type structure. The value of total magnetic moment, 2 μ _B/f.u. at the equilibrium lattice constant a ₀= 5.92 Å, agrees with the Slater–Pauling rule for the C1_b-type Mn₂Te compound. The Mn₂Te compound with the C1_b-type structure is found to be a half-metallic ferrimagnet with a half-metallic band gap of 1.19 eV. Half metallicity is kept for a broad range of lattice constants below 6.13 Å. The Curie temperature for the C1_b-type structure is calculated to be 1231 K in the mean field approximation (MFA).     

1989 Polycyclic Aromatic Hydrocarbon Research Award

Organic electroluminescent devices recently have been focus of attention. Since the first demonstrations in this field, rapid developments have occurred in the usage of organic polyaromatic compounds and their derivatives for the purpose of multi-layer structures, multi-color, and full-color organic light-emitting diode displays. In the part-1 of the present short review, recent technical developments in the preparation and structure of organic light emitting diodes with special attention to organic emitters involving polyaromatic kernels have been considered.     

ELECTROLUMINESCENT PROPERTIES OF CERTAIN POLYAROMATIC COMPOUNDS: PART 2–ORGANIC EMITTERS

This review is based on the electroluminescent and optical properties of certain polyaromatics in OLEDs with special attention to their specific function in the emitting layer, performance and emissive color. DAD and TDAD dopants depending on their concentration in the emitting layer exhibit good efficiencies and color purity for blue emission. When copolyethers with diphenylanthracene emitting segments are used in a single layer diode, visible pure blue light (440 nm maximum) around 15-20V can be achieved. J-Aggregates including anthracene moieties contribute to the efficient IR electroluminescence. Blue, white, yellow and orange electroluminescent devices can be obtained by ADN- or ADN-doped with rubrene at ultra low concentrations. Pyrene derivatives (P1, P2) linked to fluorene exhibit high thermal stability, bright blue emission and improved hole injection ability. Aminobenzanthrone derivatives as host emitters emit orange-to-red light with high brightness (25000 cd.m^?2), current efficiency (3.52 cd.A^?1) and power efficiency. Due to its bipolar transport property, when doped in Alq₃ or NPB, tetraphenylnaphtacene shows excellent yellow electroluminescence. Multiple quantum well (MQW) structures including rubrene are helpful in narrower and tunable spectral emission, as well as higher emission efficiency. Perylene derivatives such as copolymer+PVK blend show sharp red emission peaks, photochemical and thermal stability. Pentacene derivatives, DPP, 1-DNP and 2-DNP can be used to obtain highly pure purple color. An increase in the doping concentration of DPP enhances photoluminescent peak intensity. New blue-green emitting dopants like coronene, decacylene and conjugated ladder systems based on phthalocyanines are centers of attraction for electroluminescence in recent years.     

MOLECULAR ORBITAL TREATMENT OF SOME ENDOHEDRALLY DOPED C60 SYSTEMS

The present review article is a collection of the theoretical studies about some endohedrally doped C ₆₀ systems, based on density functional theory and ab initio calculations. The energies of the composite system, as well as molecular orbital energies depend on the type of dopant, symmetry of the system and the spin state. In the case of C@C ₆₀ , the dopant interacts with the cage depending on the symmetry and spin state, whereas in Be@C ₆₀ , Be is found to be unbound. In certain cases (as Ca, Sc and Y) the interaction results in electron transfer from the dopant to the cage.     

COMPUTATIONAL STUDIES ON NOVEL ENERGETIC MATERIALS: TETRANITRO-[2,2]PARACYCLOPHANES

Computational studies on tetranitro derivatives of [2,2]paracyclophane are carried out at B3LYP/6-31G(d,p) level of theory. Optimized geometries, electronic structures and some thermodynamic properties have been obtained in their ground states. Also, detonation performances were evaluated by the Kamlet-Jacobs equations, based on the quantum-chemical calculated densities and heat of formation values. Aromaticities were investigated by performing NICS (nucleus independent chemical shift) calculations using the gauge invariant atomic orbital (GIAO) approach at the same theoretical level. The results show that these kinds of compounds possess some properties of energetic materials and if these stable tetra-nitro substituted [2,2]paracyclophanes can be synthesized, they may be potential candidates for powerful energetic materials.     

Guiding of emulsion droplets in microfluidic chips along shallow tracks defined by laser ablation

We demonstrate controlled guiding of nanoliter emulsion droplets of polar liquids suspended in oil along shallow hydrophilic tracks fabricated at the base of microchannels located within microfluidic chips. The tracks for droplet guiding are generated by exposing the glass surface of polydimethylsiloxane (PDMS)-coated microscope slides via femtosecond laser ablation. The difference in wettability of glass and PDMS surfaces together with the shallow step-like transverse topographical profile of the ablated tracks allows polar droplets wetting preferentially the glass surface to follow the track. In this study, we investigate guiding of droplets of two different polar liquids (water/ethylene glycol) with and without surfactant suspended in an oil medium along surface tracks of different depths of 1, 1.5, and 2 \(\upmu\)m. The results of experiments are also verified with computational fluid dynamics simulations. Guiding of droplets along the tracks as a function of the droplet composition and size and the surface profile depth is evaluated by analyzing the trajectories of moving droplets with respect to the track central axis, and conditions for stable guiding are identified. The experiments and numerical simulations indicate that while the track topography plays a role in droplet guiding using 1.5- and 2-\(\upmu\)m deep tracks, for the case of the smallest track depth of 1 \(\upmu\)m, droplet guiding is mainly caused by surface energy modification along the track rather than the presence of a topographical step on the surface. Our results can be exploited to sort passively different microdroplets mixed in the same microfluidic chip, based on their inherent wetting properties, and they can also pave the way for guiding of droplets along reconfigurable tracks defined by surface energy modifications obtained using other external control mechanisms such as electric field or light.     

The effect of radiation-induced cross-linking on the wear rate of polyvinylidene fluoride during friction in a liquid

Results are shown of the exploration of the radiation-induced cross-linking effect on the wear rate of polyvinylidene fluoride during friction in a liquid (running water and water containing abrasive particles). It is shown that the wear rate has an extreme pattern with the minimum being within the range of the absorbed gamma radiation: 100–300 kGy. It is established that the radiation wear enables considerably increasing the wear resistance of the polymer during friction in the liquid.     

Friction machine for testing materials under boundary lubrication

The design of a pin-on-disk friction machine intended for the testing materials under boundary lubrication has been considered. Engineering solutions involved in the development of the machine that are used to provide the precision of the adjustment of friction surfaces of specimens with regard to the counterface and to retain stable thermal conditions in the zone of contact at any duration of the test have been described. The machine is intended for carrying out wear tests of materials and coatings under various conditions, including conditions that correspond to the operation of shut-off valves of oil pipelines.     

Thermal Expansion of Ni<Subscript>3</Subscript>S<Subscript>2</Subscript> in Ni<Subscript>3</Subscript>S<Subscript>2</Subscript>-Ni Alloys

The thermal expansion of nickel sulfide in Ni₃S₂-Ni alloys (a sample synthesized in this work and a commercial Ni₃S₂-Ni-Cu₉S₅ converter matte) is measured using high-temperature x-ray diffraction. The best fit equations are derived for the temperature-dependent (≤980 K) parameters of the rhombohedral (hexagonal) and cubic cells of nickel sulfide, and the thermal expansion coefficients of Ni₃S₂ are determined. The results demonstrate that the thermal expansion of Ni₃S₂ is influenced by impurity phases: Ni metal and Cu₉S₅. The chemical strain arising from the dissolution of the copper sulfide in Ni₃S₂ cancels out the shear strain near the polymorphic transformation.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 8, 2005, pp. 1005–1010.Original Russian Text Copyright ¢ 2005 by Vershinin, Selivanov, Gulyaeva, Sel’menskikh.