Laser excited Raman spectra of Gr. VI semiconducting compounds

Raman spectra of hexagonal layer compounds MoS₂, MoSe₂ and MoTe₂ were excited by a HeNe laser (6328Å). All the Raman active long-wave-length phonon frequencies were determined. These are A_1g, E¹_2g, E_1g and E²_g. The frequencies decrease as we pass from sulphur to tellurium and the quasiacoustical mode E²_2g has the lowest frequency. A comparison of the results with infrared spectra shows that the i.r. active mode for E ⊥ C is degenerate with one of the Raman active modes in the basal plane for all the compounds.     

Influence of Catalyst on the Formation of 5(10)-Ene Ketals From Estra-4-en-3-ones

The effect of catalyst on formation of isomeric ketals from 19-nortestosterone and 19-nor-ethisterone is reported. Regioselectivity has been achieved with metal hydrides as catalyst, reported for the first time, to give 5(10)-ene ketals.

     

Symmetric units and group identities

In this paper we study rings R with an involution whose symmetric units satisfy a group identity. An important example is given by FG, the group algebra of a group G over a field F; in fact FG has a natural involution induced by setting g?g ⁻¹ for all group elements g∈G. In case of group algebras if F is infinite, charF≠ 2 and G is a torsion group we give a characterization by proving the following: the symmetric units satisfy a group identity if and only if either the group of units satisfies a group identity (and a characterization is known in this case) or char F=p >0 and 1) FG satisfies a polynomial identity, 2) the p-elements of G form a (normal) subgroup P of G and G/P is a Hamiltonian 2-group; 3) G is of bounded exponent 4p ^s for some s≥ 0. Received: 8 August 1997     

Energy spectra and energy correlations in the decayH→ZZ→μ+μ−μ+μ−

It is shown that in the sequential decay $H \to ZZ \to (f_1 \bar f_1 ) + (f_2 \bar f_2 )$ , the energy distribution of the final state particles provides a simple and powerful test of theHZZ vertex. For a standard Higgs boson, the energy spectrum of any final fermion, in the rest frame ofH, is predicted to be dΓ/dx～1+β⁴?2(x?1)², with $\beta = \sqrt {1 - 4m_Z^2 /m_H^2 } $ and 1?β≤x=4E/m _H ≤1+β. By contrast, the spectrum for a pseudoscalar Higgs is dΓ/dx～β²+(x?1)². There are characteristic energy correlations betweenf ₁ andf ₂ and betweenf ₁ andf ₂. These considerations are applied to the “gold-plated” reactionH→ZZ→μ⁺μ^?μ⁺μ^?, including possible effects ofCP-violation in theHZZ coupling. Our formalism also yields the energy spectra and correlations of leptons in the decay $H \to W^ + W^ - \to l^ + v_l l^ - \bar v_l $ .     

Self assembled nanoparticle Pb1−xFexSe/single crystal Si heterojunctions

Nanoparticle Pb_1−xFe_xSe (0.00  x  0.16) thin films have been deposited on quartz, glass and silicon substrates by chemical bath deposition technique. Structural and optical properties of the films with iron concentration 0.00  x  0.16 indicate that the films grow as single-phase Pb_1−xFe_xSe ternary alloys with rocksalt structure and with direct optical band gaps (E_g) that increase with decrease in grain size and have values larger than 0.28 eV of the bulk PbSe. Average grain size in films grown at fixed bath temperature T_b of 85 °C is observed to decrease from 72 to 22 nm whereas lattice parameter is observed to increase from 6.12 to 6.14 Å with increase in Fe concentration from x = 0.00 to x = 0.16. The observed blue shift in film materials originates from quantum confinement in the nanograins. Nanoparticle Pb_1−xFe_xSe/single crystal Si heterojunctions show rectifying behavior. On illumination of heterojunctions with visible light current is observed to increase in forward and reverse bias. This increase in current in the presence of visible light is considered to be due to carrier multiplication by Auger electron emission.     

Sol-Gel derived CeO2:TiO2 coatings for electrochromic devices

Thin films of mixed CeO₂-TiO₂ with different Ce/Ti mole ratios were prepared following an alcohol based sol-gel route via the spin coating technique using mixed inorganic-organic [CeCl₃.7H₂O and Ti(OPr)₄] precursors. Ion storage capacity for films obtained from aged sols was observed to be high. Enhanced titanium oxide content improved the insertion capacity of the corresponding films as was evident from inserted charge determined by multiple step chronoamperometric measurements. Electrochemical, optical, structural and thermal performances showed the suitability of the films in an all solid state electrochromic (transmissive) device with tungsten trioxide (WO₃) as electrochromic material and a conductive polymeric electrolyte based on lithium. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Structural,morphological and photoluminescence characteristics of sol-gel derived nano phase CeO<Subscript>2</Subscript> films deposited using citric acid

Homogenous nano structured CeO₂ films have been prepared by a sol-gel process using different mole ratios of citric acid as additive. XPS studies clearly illustrate an increase in Ce³⁺ proportion upon the use of higher citric acid content for the deposition of films. The crystallite sizes in the films lie in the nanorange. Photoluminescence emission in the films is attributed to various defects resulting from crystallization. Lowest transparency, high Ce³⁺ content and optimum sized crystallites in CeO₂ (1:1.5) films have led to its highest PL characteristics. Ce³⁺ chemical state is the major contributor to the PL activity of these films. The SEM micrographs show a reduced level of CeO₂ agglomeration in the films deposited using higher citric acid contents. A comparison of different properties of CeO₂ films deposited using citric acid and CeO₂–TiO₂ films has also been made.